CHAPTER 5

DISCUSSION

5.1. G e n e r a l

O f t h e 3 0 0 0 s p e c i e s of p l a n t s u s e d by man f o r

f o o d and o t h e r p u r p o s e s on ly 1 5 0 s p e c i e s h a v e been

c o m n e r c i a l l y e x p l o i t e d f o r t h e d a y t o d a y

r e q u i r e m e n t s . Now t h e s e l i m i t e d numbers a r e f u r t h e r

s h o r t e n e d t o o n l y 2 0 c r o p s p e c i e s (Randhawa. 1988).

These h i g h y i e l d i n g v a r i e t i e s a r e now b e i n g t h r e a t e n e d

by v a r i o u s v i r u l a n t d i s e a s e p a t h o g e n s and t h e man-made

g r e e n h o u s e e f f e c t s . T h i s c r i t i c a l s i t u a t i o n w a r r a n t s

s u i t a b l e " L i f e Suppor t S p e c i e s " f o r t h e c o n t i n u o u s

s u p p l y of p r o d u c t s . I n s p i t e of o u r r i c h f l o r a t h a t

o f f e r s g r e a t p r o m i s e , we a r e s t i l l r e l y i n g o n l y upon a

v e r y smal l f r a c t i o n of t h e p l a n t w e a l t h . The n e e d f o r

p r o d u c i n g more a g r i c u l t u r a l p r o d u c t s f o r r a p i d l y

i n c r e a s i n g human and l i v e s t o c k p o p u l a t i o n i n t h e

second h a l f of t h e c u r r e n t c e n t u r y n e c e s s i t a t e d

b r i n g i n g u n d e r t h e p lough of more and more ' m a r g i n a l

l a n d s ' . I t a l s o n e c e s s i t a t e d t h e a c c e l e r a t i o n of

d e g r a d e d s o i l s en r ichment and f e r t i l i t y t h r o u g h

a f f o r e s t a t i o n . T h i s h a s r a i s e d a s e r i o u s t h o u g h t t o

t h e concept o f ' a d o p t i n g p l a n t s s u i t e d t o t h e

environment ' . A g r i c u l t u r a l s c i e n t i s t s a r e now a c t i v e

t o c o l l e c t , i n t r o d u c e and e v a l u a t e t h e v a s t a r r a y o f

u n d e r u t i l i s e d p l a n t s p e c i e s and a l s o t o b r e e d f o r

v a r i e t i e s which can w e l l a d a p t t h e m s e l v e s t o t h e h a r s h

e n v i r o n m e n t a l and d e g r a d e d s o i l c o n d i t i o n s . T h e i r

a t t enp t s resulted i n the screening and ident i f ica t ion of a

large n d e r of food plants , fodder and energy plants and

i n d u s t r i a l and h y d r o c a r b o n p l a n t s b e l o n g i n g t o

v a r i o u s a g r o - e c o l o g i c a l h a b i t a t s .

A g r e a t d e a l of i n t e r e s t and s p e c u l a t i o n h a s

r i s e n c o n c e r n i n g t h e u s e o f p l a n t l a t e x a s a

s u b s t i t u t e f o r p e t r o l e u m ( N e i l s o n g . , 1977;

C a l v i n , 1979a . 1983 ; Dehgan and Wang, 1979 ; Maug,

1979 1 . Among t h e o t h e r hydrocarbon p l a n t s ,

e s p e c i a l l y f o r N R , c e r t a i n p r o m i s i n g g e n o t y p e s o f

g u a y u l e r u b b e r , such a s Ar izona 2 and HG 8 were found

t o b e of g r e a t p o t e n t i a l i t i e s . Moreover , t h e e n e r g y

r e q u i r e m e n t and c o s t of t h e p r o d u c t i o n of s y n t h e t i c

r u b b e r i s a b o u t 12 t i m e s more t h a n t h a t o f NR

( S p e d d i n g . 1 9 8 1 ) i n a d d i t i o n t o t h e p o l l u t i o n

h a z a r d s . A t r e e which can p r o v i d e r u b b e r , w i t h o u t

p o l l u t i o n b u t p r o t e c t i n g t h e sub-marg ina l l a n d s w i l l

be more p r e f e r a b l e . C a l v i n ( 1 9 7 7 ; 1979; 1 9 8 0 ) .

Buchanan G. ( 1 9 7 8 a . 1978b. 1 9 7 9 ) . Wang and

Huffman ( 1 9 8 1 ) . Roth - - e t a l . (1984) ; Maxwell et g .

( 1 9 8 5 ) ; Mechesney and Adams ( 1 9 8 5 ) ; C a r r et g .

( 1 9 8 6 ) ; C a r r and Bagby ( 1 9 8 7 ) . Marimuthu s l . ( 1 9 8 9 ) and s e v e r a l o t h e r i n v e s t i g a t o r s have s c r e e n e d

a l a r g e number of s p e c i e s f o r f u e l s , h y d r o c a r b o n s ,

i n d u s t r i a l o i l s and o t h e r e n e r g y s o u r c e s . The most

i m p o r t a n t s o u r c e of NR i s H. b r a s i l i e n s i s for k i c h a

s u i t a b l e s u c c e s s o r o r a l t e r n a t i v e s p e c i e s h a s n o t y e t

been i d e n t i f i e d t o t a k e o v e r c h a r g e i n t h e even t of a

c a t a s t r o p h e . An i n t e n s i v e s e a r c h i n t h i s l i n e

r e s u l t e d i n t h e i d e n t i f i c a t i o n o f a h i t h e r t o n o t c a r e d

s p e c i e s which can t h r i v e u n d e r h o s t i l e e n v i r o n m e n t s .

Thus Manihot g l a z i o v i i h a s been i n v e s t i g a t e d t o b r i n g

ou t i t s h i d d e n q u a l i t i e s f o r e n l i s t i n g i t a s a

p r o s p e c t i v e a l t e r n a t i v e s o u r c e o f N R and i t s m e r i t s

and r e c t i f i a b l e d e m e r i t s a r e d i s c u s s e d .

5 .2 . Morphology, p r o p a g a t i o n and d i s e a s e s

G e n e r a l g rowth and morphology of - M . G a z i o v i i

v a r i e s w i t h a g r o c l i m a t i c c o n d i t i o n s and p r o p a g a t i o n

m e t h o d s . When p r o p a g a t e d t h r o u g h c u t t i n g s , t h e t r e e s

t a k e s i t s n a t u r a l c o u r s e of g rowth l e a d i n g t o s l i g h t l y

crooked s t em. T h i s i s due t o t h e e a r l y b r a n c h i n g

h a b i t of t h e v e g e t a t i v e c u t t i n g s , which d u r i n g

subsequen t g rowth u n d e r g o s e l f p r u n i n g s e a s o n a l l y

l e a v i n g a s i n g l e l e a d i n g s t e m . I n such p l a n t s

g i r t h i n g of t h e s t e m was found t o b e more t h a n i n t h e

s e e d l i n g s of t h e same a g e . Dijkman (1951) h a s

r e p o r t e d t h e same phenomena i n Hevea, where t h e r a t e

of g i r t h i n g i s more a f t e r t h e f o r m a t i o n of b r a n c h e s

and development o f crown. However, f o r t h e e a s e o f

t a p p i n g low b r a n c h i n g i s n o t a d v i s a b l e and a l l

b r a n c h e s s h o u l d b e pruned u p t o a h e i g h t of abou t 2 . 5 m

l e a v i n g a h e a l t h y and c l e a n t r u n k ( R a d h a k r i s h n a

127

P i l l a i , 1 9 8 0 ) . The b o l e of such p o p u l a t i o n i n t h e

n a t u r a l h a b i t a t a r e m o s t l y h a v i n g s t o u t and s t r a i g h t

s t e m . Here t h e w i l d t r e e s a r e h a v i n g t h e l i g h t s p r e a d

canopy, which i s m o s t l y r e s t r i c t e d t o t h e t o p . The

l e a v e s a r e p a l m a t e l y l o b e d , u s u a l l y w i t h 3-5 l o b e s .

However i n L o c a t i o n I 1 where t h e t r e e h a s t o f a c e a

h o s t i l e t h e r m a l s t r e s s , showed a f u r t h e r l o b i n g f rom

2-7 i n c e r t a i n o b s e r v e d c a s e s . T h i s a p p e a r s t o b e a

x e r o t h e r m i c a d a p t a t i o n of t h e s p e c i e s t o r e d u c e t h e

l e a f a r e a a s i n t h e c a s e of o t h e r s p e c i e s g rowing i n

t h e a r i d r e g i o n s .

Another p e c u l i a r h a b i t o f _M. g l a z i o v i i i s t h e

s h e d d i n g o f s h o o t and b u d s . One of t h e most i m p o r t a n t

d r o u g h t r e s i s t a n c e mechanisms of p l a n t s i n v o l v e s

r e d u c t i o n i n t r a n s p i r i n g s u r f a c e . Thus n a t u r a l

s h e d d i n g of l e a v e s and o t h e r p l a n t p a r t s r e d u c e s t h e

t r a n s p i r i n g s u r f a c e a r e a d u r i n g a p e r i o d of s o i l

d r y i n g and p r e v e n t s d e h y d r a t i o n of p l a n t s t o l e t h a l

l e v e l s . S e e d l i n g s of 1 - 2 y e a r s g rowth show symptoms

of l e a f s h e d d i n g by t h e o n s e t of sumner . I t t a k e s

abou t a month t o shed t h e l e a v e s and d u r i n g t h a t

p e r i o d t h e growth w i l l b e a r r e s t e d . A f t e r c o m p l e t e

s h e d d i n g of l e a v e s . t h e s t e m remains g r e e n f o r a n o t h e r

p e r i o d , of abou t a month . Then i t s t a r t s s l o w d r y i n g

f rom t h e t i p t o downwards. Along w i t h t h i s t h e

a x i l l a r y b u d s a l s o w i l l b e s h e d . The s low d r y i n g

p r o c e e d s downwards f r o m i n t e r n o d e t o i n t e r n o d e . The

p r o c e s s i s s o s low t h a t a b o u t 5-10 cm l e n g t h o f t h e

shoo t g e t d r i e d i n a month . When t h e s e a s o n becomes

f a v o u r a b l e one of t h e dormant buds w i l l s p r o u t g i v i n g

r i s e t o a new s h o o t .

T h i s n a t u r a l a d a p t a t i o n o f t h e t r e e i s a

c o n t i n u o u s p r o c e s s t h r o u g h o u t t h e l i f e s p a n . Mature

t r e e s i n b o t h t h e l o c a t i o n s a l s o showed t h i s

c h a r a c t e r . The b r a n c h l e t s g e t s l o w l y d r i e d , a f t e r

w i n t e r i n g . By s e l f p r u n i n g t h e d r i e d b r a n c h l e t s w i l l

b e d e t a c h e d f rom t h e t r e e . The s h e d d i n g of b r a n c h e s

of p l a n t s of a r i d r e g i o n s i s a comnon d r o u g h t

r e s i s t a n c e a d a p t a t i o n ( O r s h a n , 1963. 1 9 7 2 ) . The t r e e

i s h a v i n g a r a m i f i e d canopy due t o i t s r e p e a t e d

t r i c h o t o m o u s k a n c h i n g . But t h r o u g h t h i s s e l f p r u n i n g

mechanism, i t i s c a p a b l e of m a i n t a i n i n g a n optimum

canopy . Canopy c o n t r o l t o a n optimum l e v e l i s a

d e s i r a b l e c h a r a c t e r f o r a s p e c i e s exposed t o h o s t i l e

e n v i r o n m e n t s . Moreover t h e b i o m a s s d e p o s i t s h e l p t o

i n c r e a s e t h e f e r t i l i t y o f t h e p o o r s o i l .

T h i s i s one o f t h e c h a r a c t e r s which q u a l i f i e s 2.

g l a z i o v i i a s a s u i t a b l e s p e c i e s f o r t h e d r y r e g i o n s .

E a r l y f l o w e r i n g i s c o n s i d e r e d t o b e a d e s i r a b l e

c h a r a c t e r i n c r o p s which a r e meant f o r i t s s e e d s .

Most o f t h e t r e e s p e c i e s p r o d u c e f l o w e r s a f t e r 3-5

y e a r s . From t h e b r e e d e r s ' s i d e t h i s i s a v e r y l o n g

t i m e , s o t h a t v a r i o u s f l o w e r i n d u c t i o n t e c h n i q u e s h a s

t o b e a t t e m p t e d . I n - Hevea, d u r i n g t h e c o u r s e o f t h e

c r o p improvement programmes d i f f e r e n t t e c h n i q u e s l i k e

r i n g - b a r k i n g and chemica l s p r a y i n g s were t r i e d t o

i n d u c e e a r l y and o f f season f I o w e r i n g (Camacho and

J i m e n e z , 1963 ; Cannel . 1971; Saraswathyamna, 1975 ;

Premakumari and N a i r , 1 9 7 6 ) . But t h e most a t t r a c t i v e

h a b i t n o t e d i n - M . g l a z i o v i i i s i t s e a r l y n a t u r a l

f l o w e r i n g h a b i t . U s u a l l y March-Apri l i s t h e f l o w r i n g

season and f r u i t s a r e formed by May-June. T h i s

f u r t h e r e n a b l e s t h e c o l l e c t i o n of f r e s h s e e d s f o r

p r o p a g a t i o n d u r i n g t h e p r e c e e d i n g p l a n t i n g s e a s o n .

Crop improvement t h r o u g h b r e e d i n g can b e a c h i e v e d

w i t h o u t w a i t i n g f o r a l o n g p e r i o d .

Leaves o f most o f t h e d e c i d u o u s t r e e s o f t h e

t e m p e r a t e zone a r e shed i n t h e b e g i n n i n g of sumner .

Deciduous t r e e l i k e - H . b r a s i l i e n s i s s h e d s i t s l e a v e s

by J a n u a r y - F e b r u a r y and r e f o l i a t i o n t a k e s p l a c e i n a

s h o r t p e r i o d (George - e t - a l . , 1 9 6 7 ) even b e f o r e t h e

sumner months a r e o v e r . But i n M. g l a z i o v i i ,

d e f o l i a t i o n s t a r t 5 o n l y by J a n u a r y - F e b r u a r y and t h e

t r e e s remain l e a f l e s s u n t i l t h e sumner s e a s o n i s o v e r .

However e a r l y r e f o l i a t i o n may o c c u r i f t h e p l a n t

r e c e i v e s s u f f i c i e n t pre-monsoon s h o w e r s . T h e r e i s

c o n s i d e r a b l e v a r i a t i o n i n a n n u a l l e a f s h e d d i n g i n

t r o p i c a l c l i m a t e s b e c a u s e o f v a r i a t i o n s i n h u m i d i t y

and s e a s o n a l d i s t r i b u t i o n of r a i n f a l l (Kozlowski ,

1 9 7 3 ) . One of t h e most i m p o r t a n t d r o u g h t r e s i s t a n c e

mechanism of p l a n t s i n v o l v e s r e d u c t i o n i n t r a n s p i r i n g

s u r f a c e , d u r i n g t h e p e r i o d of s o i l d r y i n g . I n B r a z i l ,

where C e a r a r u b b e r i s a n a t i v e , t h e l e a v e s of

p r a c t i c a l l y a l l d e c i d u o u s t r e e s a b s c i s e w i t h t h e o n s e t

of a d r o u g h t and a r e r e p l a c e d when t h e d r o u g h t e n d s

(Alv im, 1 9 6 4 ) . Leaf s h e d d i n g i s an a d a p t a t i o n of t h e

d e c i d u o u s t r o p i c a l p e r e n n i a l s t o overcome t h e t h e r m a l

s t r e s s (Longman and J e n i k , 1 9 7 4 ) . The c o n s i d e r a b l e

t i m e gap between d e f o l i a t i o n and r e f o l i a t i o n e x h i b i t e d

by M. g l a z i o v i i i s an a d a p t a t i o n of t h e p l a n t t o

overcome d r o u g h t s t r e s s .

I n g. g l a z i o v i i t h e number of s t o m a t a p e r 1 mn 2

r a n g e s f r o m 510-660 and t h e a v e r a g e number o b s e r v e d

i s 593 . The s p e c i e s shows a h i g h e r f r e q u e n c y of

s t o m a t a compared t o 411 .69 i n - H . b e n t h a m i a n a , 447.76

i n g . s p c e a n a n a and 465 .17 i n a c l o n e of - H .

b r a s i l i e n s i s (Senanayake , 1969 I . S i m i l a r l y t h e number

of e p i d e r m a l c e l l s p e r 1 mn2 a l s o shows a h i g h e r

a v e r a g e v a l u e of 3052 .

The number of s t o m a t a p e r u n i t a r e a v a r i e s n o t

on ly between s p e c i e s , b u t a l s o w i t h i n any one s p e c i e s

d u e t o t h e i n f l u e n c e of t h e e n v i r o n m e n t a l f a c t o r s . I t

was r e p o r t e d t h a t more c e l l s p e r u n i t a r e a and more

s t o m a t a p e r u n i t a r e a a r e s e e n i n l e a v e s of p l a n t s

growing i n d r y s o i l and low h u m i d i t y compared w i t h

t h o s e growing i n mois t s o i l and h i g h h u m i d i t y (Meidner

and Mansf i e l d , 1968).

Stomata1 movements a r e c l o s e l y a f f e c t e d by w a t e r

s u p p l y t o t h e p l a n t . S t a l f e l t ( 1 9 5 5 ) h a s r e p o r t e d

t h a t s t o m a t a 1 open ing i s c l o s e l y dependen t upon t h e

h y d r o s t a t i c p r e s s u r e w i t h i n t h e epidermiurn. Dur ing

w a t e r d e f i c i t s t o m a t a g e t s c l o s e d d u e t o h y d r o a c t i v e

c l o s u r e . Hea th and M a n s f i e l d ( 1 9 6 2 ) h a v e found t h a t

t h e s t o m a t a l s e n s i t i v i t y t o Co2 i n c r e a s e d enormously

i n l e a v e s w i t h a h i g h w a t e r d e f i c i t . A s t h e w a t e r

d e f i c i t i n c r e a s e d , t h e s t o m a t a became more c l o s e d and

t h e C 0 2 s e n s i t i v i t y i n c r e a s e d p r o g r e s s i v e l y r e s u l t i n g

i n s t o m a t a l c l o s u r e . T h i s h e l p s t h e p l a n t t o c u t t i n g

down the t r a n s p i r a t i o n a l w a t e r l o s s . I n t h e c a s e of g.

g l a z i o v i i a t t h e peak of w a t e r s t r e s s , t h e e n t i r e

f o l i a g e i s shed and t h e r o l e of s t o m a t a seems t o b e o f '

n o t much i m p o r t a n c e d u r i n g t h e d r y months . However,

t h e h i g h number o f s t o m a t a p r e s e n t i n t h e l e a v e s o f

t h e r e f o l i a t e d t r e e , when s u f f i c i e n t w a t e r s u p p l y i s

r e g a i n e d , h e l p t h e t r e e t o s t a r t p h o t o s y n t h e s i s a t a

r a p i d r a t e , t h e r e b y t o r e s t o r e t h e c a r b o h y d r a t e

r e s e r v e s e x h a u s t e d d u r i n g t h e i n a c t i v e sumner s e a s o n .

132

P r o p a g a t i o n by s e e d i s a n i m p o r t a n t t e c h n i q u e

f o r r a i s i n g a g r i c u l t u r a l c r o p s wor ldwide . T h i s method

i s of ex t reme i m p o r t a n c e t o t h e p r o p a g a t i o n o f woody

p l a n t s . whe ther f o r f o r e s t r y o r p l a n t a t i o n u s e . Seed

i s g e n e r a l l y a low c o s t method of p r o p a g a t i o n ,

compared t o v e g e t a t i v e p r o p a g a t i o n . Moreover , r a t e of

g rowth and a b i l i t y t o e s t a b l i s h f 011 owing

t r a n s p l a n t i n g i s v e r y o f t e n f a s t e r due t o s e e d l i n g

v i g o r . But t h e r e a r e c e r t a i n l i m i t a t i o n s t o

p r o p a g a t i o n by s e e d . G e n e t i c v a r i a t i o n w i l l b e s o

h i g h t h a t u n i f o r m i t y i n y i e l d w i l l b e d i f f i c u l t .

T h e r e w i l l b e d i f f i c u l t i e s i n g e r m i n a t i o n d u e t o s e e d

dormancy and h a r d s e e d c o a t . I n s u c h s e e d s i t i s

n e c e s s a r y t o c a r r y out p re - sowing t r e a t m e n t s t o remove

t h e h a r d o r waxy s e e d c o a t f o r s u c c e s s f u l g e r m i n a t i o n

(Macdonald , 19'86).

The s e e d s of M . - q l a z i o v i i a l s o n e e d

p r e - t r e a t m e n t f o r e f f i c i e n t g e r m i n a t i o n t o remove a

p o r t i o n o f t h e h a r d seed c o a t . O f t h e v a r i o u s

t e c h n i q u e s t r i e d , g r i n d i n g a p o r t i o n of t h e seed c o a t

was found t o b e t h e most r e l i a b l e method g i v i n g 72%

g e r m i n a t i o n . Acid t r e a t m e n t i s a u s u a l method t o

s o f t e n t h e seed c o a t of s i m i l a r t y p e s e e d s . But t h e

s h e l l i s h a v i n g a t h i c k n e s s of a b o u t 1 t o 1 . 5 mn ( F i g .

7 C ) . Due t o t h i s t h i c k n e s s , t h e comnon a b r a s i o n

t e c h n i q u e s a l s o was found t o b e of no u s e . Among s e e d

t r e a t m e n t t e c h n i q u e s , l i g h t b u r n i n g of t h e s e e d s was

found t o g a i n 11% g e r m i n a t i o n . I n t h i s t e c h n i q u e ,

though t h e method can a c c e l e r a t e g e r m i n a t i o n , i t was

obse rved t h a t abou t 10% of t h e s e e d s were k i l l e d d u e

t o o v e r h e a t .

The o b s e r v a t i o n s r e v e a l e d t h a t when t h e

endosperm i s g i v e n t h e o p p o r t u n i t y t o imbibe w a t e r ,

t h e seed g e r m i n a t e s . The maximum g e r m i n a t i o n

p e r c e n t a g e o b t a i n e d i n t h e g r i n d i n g t e c h n i q u e can b e

a t t r i b u t e d t o t h i s f a c t o r . Whi le i n a l l t h e o t h e r

c a s e s i t was o b s e r v e d t h a t t h e s h e l l g e t s

d i s i n t e g r a t e d s l o w l y a f t e r t h e t r e a t m e n t , a l l o w i n g

w a t e r a b s o r p t i o n . But s i n c e t h e s e t r e a t m e n t s h a v e no

u n i f o r m a c t i o n on t h e seed c o a t , g e r m i n a t i o n t i m e a l s o

showed much d i f f e r e n c e .

S i n c e t h e s e e d i s v e r y small i n s i z e ( F i g . 7 A )

and weigh on ly 0 . 5 0 - 0 . 6 0 g , i t i s v e r y e a s y f o r

s t o r a g e and t r a n s p o r t a t i o n . One k i l o g r a m s e e d s

c o n t a i n abou t 1750 numbers .

The s e e d s o f _M. g l a z i o v i i remain v i a b l e f o r a

v e r y l o n g p e r i o d .

M. g l a z i o v i i c a n b e s u c c e s s f u l l y p r o p a g a t e d -

t h r o u g h v e g e t a t i v e c u t t i n g s a l s o . T h i s i s a g r e a t

a d v a n t a g e o v e r t h e t e d i o u s b u d g r a f t i n g method a d o p t e d

i n t h e p r o p a g a t i o n of Hevea. J o s e p h and Saraswathy

(1992) ; Ooi - e t - a 1 ., (1976) : RRIM (1964); and Webster

(19891, h a v e e x p l a i n e d t h e v a r i o u s v e g e t a t i v e

p r o p a g a t i o n t e c h n i q u e s such a s brown b u d d i n g , g r e e n

b u d d i n g , b e n c h g r a f t i n g , e t c i n - H . b r a s i l i e n s i s . T h e s e

t e c h n i q u e s h a v e g o t many d i s a d v a n t a g e s l i k e

st o c k - s c i o n i n t e r a c t i o n (Abbas and G i n t i n g , 1981 poor

budd ing s u c c e s s , h i g h m a i n t e n a n c e c o s t , i n i t i a l g rowth

r e t a r d a t i o n , e t c . I n _M. g l a z i o v i i , a f t e r t h e

s e l e c t i o n o f a d e s i r a b l e g e n o t y p e , c l o n i n g can b e done

q u i c k l y , w i t h o u t t h e i n t e r m e d i a t e s t o c k p l a n t . From

t h e exper iment i t was found t h a t brown wood c u t t i n g s

t a k e n f rom t h e m a t u r e t r e e s a r e t h e b e s t m a t e r i a l f o r

v e g e t a t i v e p r o p a g a t i o n . Though 20 cm l o g c u t t i n g s

p roduced a b o u t 50% s p r o u t s compared t o 40 cm, most o f

them a r e s h o t l i v e d . T h i s may b e d u e t o t h e

i n s u f f i c i e n c y of n u t r i t i o n f o r t h e f a s t growing s h o o t .

T h e r e i s n o t much d i f f e r e n c e be tween t h e s p r o u t i n g of

brown and m a t u r e c u t t i n g s . However t h e on ly

d i s a d v a n t a g e o b s e r v e d i n t h e e x p e r i m e n t a l f i e l d i s t h e

e a r l y b r a n c h i n g , which was d i s c u s s e d e a r l i e r .

C u t t i n g s d e v e l o p t r i c h o t o m o u s b r a n c h e s a t an average

h e i g h t of a b o u t 150 cm. But t h i s can b e r e c t i f i e d by

c o r r e c t i v e p r u n i n g . Bes t r e s u l t was o b t a i n e d when

c u t t i n g s a r e p l a n t e d i n punched p o l y b a g s of 30 cm x 25

cm s i z e . The s p r o u t e d ( r o o t e d ) c u t t i n g s can t h u s b e

t r a n s p l a n t e d i n t h e f i e l d w i t h o u t a f f e c t i n g t h e

g r o w t h . T h i s c h e a p e r method of p r o p a g a t i o n i s a n added

a d v a n t a g e of 3. g l a z i o v i i .

I n t h i s c o n t e x t i t i s w o r t h n o t i n g t h a t t h e c o s t

of r a i s i n g a one y e a r o l d p o l y b a g p l a n t o f H.

b r a s i l i e n s i s w i l l b e a b o u t f i v e t i m e s more t h a n t h a t

of - M . g l a z i o v i i .

V a r i o u s f u n g a l d i s e a s e s and p e s t s a r e r e p o r t e d

t o a t t a c k 3. g l a z i o v i i i n t h e w i l d s t a n d a s w e l l a s i n

t h e c u l t i v a t e d f i e l d s , c a u s i n g s e v e r e d e f o l i a t i o n , d r y

s h o o t s and b a r k damage ( G o l a t o and M e o s s i , 1971 ; T e r i ,

1980; T e r i and Keswani , 1981 ; B a s t o s and M a g a l h a e s ,

1981 ; B a s t o s e c., 1981 ; B a s t o s e and F l e c h t m a n n ,

1985 ; S e r i e r . 1 9 8 8 ) . But none of t h e s e d i s e a s e s and

p e s t s a r e r e p o r t e d s o f a r i n I n d i a .

Secondary l e a f f a l l (SLF) i s comnon i n t h e r u b b e r

p l a n t a t i o n s (Hevea b r a s i l i e n s i s ) t h r o u g h o u t Sou th

I n d i a d u r i n g t h e months of A p r i l , May, September and

O c t o b e r . Damp e n v i r o n m e n t s and h i g h h u m i d i t y a r e t h e

p r e - r e q u i s i t e s f o r t h e s p r e a d of t h e d i s e a s e

(Ramakri shnan and R a d h a k r i shna P i l l a i . 1961;

R a d h a k r i s h n a P i l l a i e t a 1 ., 1 9 8 0 ) . T h i s i s t h e f i r s t

r e p o r t t h a t M. - g l a z i o v i i a s a n a l t e r n a t e h o s t p l a n t

f o r t h e f u n g u s Gloeospor ium s p .

The symptoms o f t h e d i s e a s e was f i r s t o b s e r v e d

i n t h e m a t u r e t r e e s i n L o c a t i o n I . But t h e s e c o n d a r y

l e a f f a l l was n o t s o s e r i o u s t o w a r r a n t any p l a n t

p r o t e c t i o n o p e r a t i o n . The d i s e a s e i s n o t o b s e r v e d i n

C e a r a r u b b e r t r e e s o r i t s s a m p l i n g s g rowing i n

L o c a t i o n I 1 ( M e t t u r H i l l s ) . T h i s might b e due t o t h e

d r y a t m o s p h e r e and s c a n t y r a i n f a l l of l o c a l i t y . Such

environment i s u n f a v o u r a b l e f o r t h e g rowth of t h e

f u n g u s . However, i t i s o b s e r v e d t h a t t h e germplasm

b r o u g h t from L o c a t i o n 1 1 , which a r e b e i n g grown i n

L o c a t i o n I , a r e found a f f e c t e d by t h e d i s e a s e . I n

Locat i o n I , t h e s p o r e s 'of t h e p a t h o g e n a r e p l e n t y d u e

t o t h e e x t e n s i v e a r e a p l a n t e d w i t h Hevea b r a s i l i e n s i s .

T h i s c l e a r l y shows t h a t M. g l a z i o v i i can b e grown i n

t h e d r y r e g i o n s w i t h o u t b e i n g a f f e c t e d by SLF c a u s e d

by Gloeospor ium.

The g e n e r a l h a b i t and m o r p h o l o g i c a l f e a t u r e s of

t h e s p e c i e s a r e of a s p e c i a l n a t u r e , e s p e c i a l l y s u i t e d

t o t h e h o s t i l e e n v i r o n m e n t . The m o r p h o l o g i c a l

f e a t u r e s o f t h e b o l e g i v e a n a p p e a r e n c e of a v e r y

rough b a r k , b e c a u s e of t h e f l a k y r h y t i d o m e . But t h i s

p r o t e c t i v e mechanism h e l p s t h e t r e e a l o t t o e s c a p e

from s e v e r e s u n s c o r c h . Most t r e e c r o p s p e c i e s need

p r o t e c t i v e s h a d i n g , w h i t e washing of t h e s t e m , t h i c k

mulching (Watson, 1 9 8 9 ) and f o l i a r s p r a y s e t c t o

overcome t h e sumner s e a s o n . But _M. g l a z i o v i i n e v e r

r e q u i r e s a n y p r o t e c t i o n a g a i n s t s u n s c o r c h

The s e a s o n a l d e f o l i a t i o n of t h e t r e e h e l p s i t t o

r e d u c e e x c e s s i v e l o s s of w a t e r d u r i n g sumner . Such

t r e e s a r e g rouped u n d e r ' sumner d e c i d u o u s ' p l a n t s ,

where i t s a b s c i s s i o n i s c o r r e l a t e d w i t h m o i s t u r e

s t r e s s ( A d d i c o t t and Lyon, 1 9 7 3 ) . However, t h e l o n g

t i m e gap between d e f o l i a t i o n and r e f o l i a t i o n may

a f f e c t t h e p h o t o s y n t h e t i c a c t i v i t y of t h e t r e e .

The d r o u g h t s u r v i v a l a d a p t a t i o n of t h e s e e d l i n g s

a l s o shows i t s s e l f d e f e n s i v e a b i l i t y . When t h e

s e e d l i n g n u r s e r i e s of o t h e r i m p o r t a n t c r o p p l a n t s need

c a r e f u l s h a d i n g , mulching and w a t e r i n g , i n M. g l a z i o v i i

t h e s e e d l i n g s t a k e s a f a s t growth d u r i n g t h e

f a v o u r a b l e s e a s o n and p r e p a r e i t s e l f t o f a c e t h e

s t r e s s by s h e d d i n g a p o r t i o n o f t h e s h o o t . Romberger

( 1 9 6 3 ) h a s r e p o r t e d t h a t a number of woody s p e c i e s

t e r m i n a t e a f l u s h of s h o o t g rowth by a b o r t i o n and

a b s c i s s i o n of s h o o t t i p s r a t h e r t h a n by f o r m a t i o n of a

t e r m i n a l bud e n c l o s e d i n bud s c a l e s . Thus i t i s

e v i d e n t t h a t t h e c o s t o f c u l t i v a t i o n and m a i n t e n a n c e

of - M. g l a z i o v i i t r e e s w i l l b e c o n s i d e r a b l y low, when

compared t o t h e e x p e n s e s t o b e i n c u r r e d f o r o t h e r c r o p

s p e c i e s .

E a r l y f l o w e r i n g h a b i t , coup led w i t h s i m p l e

v e g e t a t i v e p r o p a g a t i o n f a c i l i t i e s o f f e r g r e a t c h a n c e s

t o improve t h e p r o d u c t i v i t y o f t h e c r o p .

5.3. Bark s t r u c t u r e

Bark a n a t omical i n v e s t i g a t i o n s o f a l a t e x

b e a r i n g t r e e i s of much i m p o r t a n c e a s t h e

p r o d u c t i v i t y i s ma in ly b a s e d on t h e l a t i c i f e r o u s

s y s t e m p r e s e n t i n t h e b a r k . ' B a r k ' i s a

n o n - t e c h n i c a l t e r m t h a t d e s c r i b e s a l l t i s s u e s

e x t e r i o r t o t h e v a s c u l a r cambium ( E s a u , 1965 ;

S r i v a s t a v a , 1 9 6 4 ) . c o m p r i s i n g of e p i d e r m i s , c o r t e x ,

p r i m a r y phloem and t h e complex s e c o n d a r y phloem

t i s s u e ( K o z l o w s k i , 1 9 7 1 ) . The o u t e r b a r k i n a m a t u r e

t r e e i s an a g g r e g a t i o n o f d e a d t i s s u e s c u t o f f by t h e

p e r i d e r m o r rhy t idome (Eames and Mc D a n i e l s , 1947 ;

E s a u , 1 9 6 5 ) . The r e m a i n i n g l i v i n g t i s s u e s of t h e

b a r k , phloem and t h e p h e l l o g e n and p h e l l o d e r m , a r e

c o l l e c t i v e l y termed a s i n n e r b a r k (Eames and Mc

D a n i e l s , 1947; Whitmore, 1 9 6 3 ) . The f u n c t i o n a l

l a t i c i f e r o u s t i s s u e of a l a t e x b e a r i n g t r e e i s

c o n c e n t r a t e d i n t h e i n n e r l i v i n g b a r k t i s s u e i n

a s s o c i a t i o n w i t h o t h e r s e c o n d a r y phloem e l e m e n t s .

Bark can b e c l a s s i f i e d i n t o smooth b a r k ,

furrowed b a r k , s c a l e b a r k , r i n g b a r k and winged b a r k

b a s e d on t h e i r a p p e a r a n c e , t e x t u r e and e x t e r n a l

morphology ( B o r g e r . 1 9 7 3 ) . M. g l a z i o v g i s a smooth

b a r k e d t r e e c h a r a c t e r i s e d by a s u p e r f i c i a l p e r i d e r m

l a y e r w i t h f l a c k y r h y t i d o m e and h o r i z o n t a l l y

e l o n g a t e d l e n t i c e l s . The h a r d and waxy a n a l o g u e of

t h e p e e l a b l e p e r i d e r m / r h y t i d o m e i s a n a d d i t i o n a l

f e a t u r e of Manihot b a r k which i n t u r n p r o t e c t s t h e

t r e e a g a i n s t i n t e n s e e v a p o r a t i o n and t h e r e b y h e l p s t o

r e t a i n m o i s t u r e c o n t e n t i n t h e b a r k (George , 1 9 9 3 ) .

The h i g h m o i s t u r e c o n t e n t of Manihot b a r k r e p o r t e d

e l s e w h e r e c o n f i r m s t h i s , i n d i c a t i n g t h e d r o u g h t

r e s i s t a n t a d a p t a t i o n of t h i s t r e e s p e c i e s .

I t h a s a l r e a d y been p roved t h a t m a j o r i t y of t h e

s p e c i e s f o r m i n g p e r i d e r m a l s o f orm l e n t i c e l s (De

B a r y , 1984 ; E s a u , 1965 ; Eames and Mc D a n i e l s , 1 9 4 7 ) .

L e n t i c e l s of Manihot b a r k a r e m u l t i - l a y e r e d and made

up of l o o s e l y a r r a n g e d complementary c e l l s w i t h

i n t e r c e l l u l a r s p a c e s . Such numerous a i r f i l l e d

i n t e r c e l l u l a r s p a c e s a s s o c i a t e d w i t h t h e l e n t i c e l s i n

Manihot b a r k may p r o v i d e t h e r m a l i n s u l a t i o n and

p r o t e c t t h e cambial zone f rom r a p i d t e r m p e r a t u r e

c h a n g e s a s s u g g e s t e d by Cooke ( 1 9 4 8 ) . Hare ( 1 9 6 5 ) .

M a r t i n ( 1 9 6 3 ) and S t i c k e l (1941) i n v a r i o u s smooth

ba rked a n g i o s p e r m s p e c i e s . T h i s t y p e of b a r k

c h a r a c t e r i s t i c s of Manihot g l a z i o v i i can a l s o b e

c o n s i d e r e d a s a n a d a p t a b i l i t y o f t h i s t r e e s p e c i e s t o

d r o u g h t and o t h e r h o s t i l e e n v i r o n m e n t s .

The i n t e r n a l s t r u c t u r e of Manihot b a r k i s more

o r l e s s s i m i l a r t o t h a t o f Hevea b a r k . However.

s t r u c t u r a l v a r i a t i o n h a s been n o t i c e d w i t h r e s p e c t t o

c e r t a i n c h a r a c t e r i s t i c s .

The h a r d n e s s o f b a r k d e p e n d s on t h e q u a n t i t y o f

s c l e r i f i e d s t o n e c e l l s p r e s e n t i n t h e o u t e r b a r k zone

and t h e n a t u r e and development of s t o n e c e l l s h a v e

been r e c e i v e d much a t t e n t i o n i n r e l a t i o n t o t a p p i n g

( B o b i l i o f f , 1919; Gomez, 1982 ). The l e s s f r e q u e n t

s t o n e c e l l s i n t h e o u t e r b a r k zone of Manihot when

compared t o t h a t of 3 b a r k r e v e a l s t h a t t h e

f o r m e r i s s o f t e r t h a n t h e l a t t e r whereby t a p p i n g can

b e done s m o o t h l y . Moreover , t h e a l i g n m e n t of s t o n e

c e l l s , i n t h e o u t e r zone of Manihot b a r k i s more o r

l e s s i n l i n e s a l t e r n a t i n g w i t h l a t i c i f e r s w i t h o u t

d i s t u r b i n g t h e c o n t i n u i t y of most of t h e l a t i c i f e r s

u n l i k e i n Hevea b a r k where t h e s t o n e c e l l s a r e

d i s t r i b u t e d randomly making t h e l a t i c i f e r s p r e s e n t i n

t h e o u t e r zone of t h e b a r k d i s c o n t i n u o u s . Because o f

t h i s f e a t u r e more l a t i c i f e r s i n Manihot g l a z i o v i i a r e

f u n c t i o n a l i n n a t u r e .

The q u a n t i t y of l a t i c i f e r o u s t i s s u e p roduced

by a t r e e d e p e n d s not on ly on t h e number of l a t i c i f e r

rows b u t on t h e number ( d e n s i t y ) of l a t e x v e s s e l s

w i t h i n a row a l s o (Gomez, 1982). Mendonca and Maria

S i l v i a d e (1992) have r e p o r t e d t h a t t h e d i s t r i b u t i o n

of l a t i c i f e r o u s v e s s e l s and t h e i r d e n s i t y a r e g r e a t e r

i n t h e l i v e r b a r k ( s o f t b a r k ) of M. glaziovii. The -

p r e s e n t s t u d y a l s o showed t h e maximum d i s t r i b u t i o n o f

l a t i c i f e r s i n t h e s o f t b a r k z o n e . I n t h i s s t u d y t h e

t o t a l number of l a t i c i f e r rows of Manihot b a r k i s

c o n s i d e r a b l y lower t h a n t h a t of Hevea b a r k and t h e

d i f f e r e n c e between them i s more t h a n 50%. S i m i l a r l y

t h e d e n s i t y of l a t e x v e s s e l s p e r row p e r 1 nnn

c i r c u m f e r e n c e of t h e t r e e i s a l s o found t o b e lower

( 2 8 . 5 ) i n Manihot b a r k i n compar ison w i t h t h a t o f

Hevea b a r k ( 3 3 . 7 2 ) . The low mean v a l u e s of t h e s e two

c h a r a c t e r s i n Manihot g l a z i o v i i may b e some of t h e

r e a s o n s f o r t h e low y i e l d of t h i s s p e c i e s . The lower

mean v a l u e s of t h e t h i c k n e s s o f b a r k i n Manihot a l s o

may b e a f a c t o r which l i m i t s t h e number and d e n s i t y

o f l a t i c i f e r t i s s u e i n t h e s p e c i e s .

The d i a m e t e r o f l a t e x v e s s e l s p l a y s a

s i g n i f i c a n t r o l e on t h e r a t e of f l o w of l a t e x d u r i n g

t a p p i n g ( F r e y - W y s s l i n g , 1 9 3 0 ; R i c h e s and Gooding,

1 9 5 2 ) . Ashp lan t ( 1 9 2 7 , 1928) o b s e r v e d a good

c o r r e l a t i o n between d i a m e t e r of l a t e x v e s s e l s and

y i e l d i n Hevea b r a s i l i e n s i s . The mean d i a m e t e r o f

l a t e x v e s s e l s of Manihot g l a z i o v i i i n t h e p r e s e n t '

s t u d y , i s 14 .15pl i n d i c a t i n g t h a t t h e l a t e x v e s s e l s

a r e n a r r o w e r i n t h e fo rmer which i n t u r n a l s o r e s u l t s

i n low l a t e x y i e l d . However, t h e i n t e r a c t i o n o f t h e

p h y s i o l o g y o f l a t e x f l o w , l e n g t h of t a p p i n g c u t , t h e

r a t e of l a t e f l o w e t c . a r e c o n s i d e r e d t o b e t h e major

f a c t o r s d i r e c t l y o r i n d i r e c t l y r e l a t e d t o t h e l a t e x

y i e l d s u g g e s t e d by De Jonge ( 1 9 6 9 a . b ) , Sou thorn and

Gomez ( 1 9 7 0 ) i n Hevea b r a s i l i e n s i s . I n t h i s c o n t e x t ,

t h e r e s u l t s of t h e e a r l i e r s t u d i e s conduc ted by Gomez

e t a l . ( 1 9 7 2 ) . Narayanan e t a l . ( 1 9 7 3 , 1 9 7 4 ) ; and Ho -- -- e t a l . ( 1 9 7 3 ) i n Hevea b r a s i l i e n s i s a l s o d e s e r v e s - -

much a t t e n t i o n and c o n s i d e r a t i o n . The b a r k

a n a t o m i c a l t r a i t s which a r e c o n t r i b u t i n g y i e l d and

p r o d u c t i v i t y o f - M. q l a z i o v i i can b e improved t h r o u g h

c r o p improvement and b r e e d i n g p r o g r a m n e s . However,

t h e r e l a t i o n between t h e a n a t o m i c a l p a r a m e t e r s and

l a t e x f l o w and t h e r e b y l a t e x y i e l d n e e d s f u r t h e r

d e t a i l e d i n v e s t i g a t i o n s .

C o n s i d e r i n g t h e e f f e c i e n c y of t a p p i n g t h e

d i s t a n c e between cambial zone and t h e inner row o f

s e c o n d a r y l a t i c i f e r s p l a y a major r o l e . The t a p p i n g

i s done i n such a way t h a t t h e t a p p i n g c u t s h o u l d no t

wound t h e cambial c e l l s . U s u a l l y t h e t a p p e r i s

a d v i s e d t o e x p l o i t t h e b a r k up t o a d e p t h l e a v i n g

abou t 1 mn r e s i d u a l b a r k c l o s e t o t h e cambium. I n

Hevea b r a s i l i e n s i s t h e r e s i d u a 1 b a r k l e f t u n t a p p e d

d u r i n g e x p l o i t a t i o n l e a v e s a b o u t 40% o f t h e

l a t i c i f e r s l e f t uncut. The e f f i c i e n c y o f t a p p i n g

and t h e d e s i r a b l e d e p t h o f t a p p i n g cu t w i t h o u t

wounding t h e cambium and t h e p e r c e n t a g e o f

l a t i c i f e r o u s t i s s u e t o b e l e f t u n c u t e t c . , h a v e n o t

been a s c e r t a i n e d i n M . g l a z i o v i i s o f a r . However,

t h e s e a r e v i t a l a s p e c t s t o b e c o n s i d e r e d f o r

comnerc ia l e x p l o i t a t i o n of t h e s p e c i e s . The p r e s e n t

s t u d y on t h e s t r u c t u r e of b a r k of t h i s s p e c i e s

r e v e a l s t h a t t h e t h i c k n e s s of l a t e x v e s s e l f r e e zone

c o n t i n u o u s t o cambium i n _M. q l a z i o v i i i s abou t 4.2%

of t h e t o t a l t h i c k n e s s of b a r k w h e r e a s i t i s o n l y

abou t 3.06% i n Hevea b r a s i l i e n s i s . T h i s c l e a r l y

i n d i c a t e s t h a t t h e p e r c e n t a g e of l a t i c i f e r s l e f t

u n c u t d u r i n g t a p p i n g i s minimal i n - M . g l a z i o v i i

t h e r e b y maximum e x p l o i t a t i o n of l a t e x i s p o s s i b l e

w i t h o u t wounding cambial l a y e r . I t h a s a l r e a d y been

r e p o r t e d by De Jonge ( 1 9 6 9 a , b t h a t deep t a p p i n g s o

a s t o s e v e r e maximum number of l a t i c i f e r s w i l l b e

more e f f e c t i v e f o r i n c r e a s i n g y i e l d i n Hevea. I n

Manihot however , t h e s i t u a t i o n n e e d n o t h e l d t r u e a s

t h e r e s i d u a l b a r k w i l l not c o n t a i n many l a t i c i f e r s .

The s t u d y on t h e a v e r a g e of t h e d i s t a n c e

between l a t i c i f e r rows i n Y . g l a z i o v i i (0.327 mn) and

t h a t of - H . b r a s i l i e n s i s (0.187 rrm: i n d i c a t e d t h a t t h e

l a t i c i f e r rows a r e l e s s c l o s e r i n t h e f o r m e r . I t h a s

a l r e a d y been e s t a b l i s h e d t h a t t h e f o r m a t i o n o f

l a t i c i f e r s i s a r h y t h m i c p r o c e s s and a r e

d i f f e r e n t i a t e d f r o m t h e f u s i f o r m i n i t i a l s o f t h e

v a s c u l a r cambium ( P a n i k k a r , 1 9 7 4 1 . The l a t i c i f e r

i n i t i a l s p roduced by t h e f u s i f o r m i n i t i a l s l e a d t o

l a t i c i f e r f o r m a t i o n , w h e r e a s o t h e r c e l l s

d i f f e r e n t i a t e d f rom f u s i f orm i n i t i a l s l e a d t o t h e

format i o n of s i e v e e l e m e n t s and o t h e r p h l o i c t i s s u e s .

Hence t h e i n c r e a s e i n t h e d i s t a n c e between l a t i c i f e r

rows i n - M . g l a z i o v i i may b e d u e t o t h e d e c r e a s e i n

t h e r a t e of l a t i c i f e r i n i t i a l d i f f e r e n t i a t i o n . The

r e d u c t i o n i n t h e number of l a t i c i f e r rows i n - M .

g a z i o v i i a l s o h e l p s t o c o n f i r m t h i s r e s u l t .

In d r o u g h t a f f e c t e d r e g i o n s many s p e c i e s shed

t h e i r l e a v e s when s t r e s s e d f o r m o i s t u r e a s a n

a d a p t a t i o n t o p r e v e n t w a t e r l o s s t h r o u g h

t r a n s p i r a t i o n .

M . g l a z i o v i i i s a d e c i d u o u s s p e c i e s , which -

shows a p r o l o n g e d l e a f l e s s p e r i o d . The p l a n t grows

i n t h e d r y rocky a r e a s where m o i s t u r e s t r e s s w i l l b e

v e r y s e v e r e . Under such c i r c u m s t a n c e , t h e t r e e

r e t a i n s c e r t a i n amount of w a t e r by means of m o i s t u r e

c o n s e r v a t i o n i n t h e b a r k .

M . G a z i o v i i l a t e x c o n t a i n s an a v e r a g e of 30% -

t o t a l s o l i d s . The remain ing p o r t i o n i s m a i n l y w a t e r .

Dur ing t a p p i n g , a l o n g w i t h each m l of l a t e x 7 0 % w a t e r

i s l i k e l y t o d r a i n f rom t h e t r e e s . Whi le i n H . -

b r a s i l i e n s i s t h e l a t e x c o n t a i n s a b o u t 60% of w a t e r .

The sumner y i e l d of l a t e x i n M . g l a z i o v i i i s -

c o m p a r a t i v e l y more and t h e d r a i n a g e was found no t

a f f e c t i n g t h e t r e e d u r i n g t h e p e r i o d of t h e

e x p e r i m e n t . T h i s a g a i n g i v e s a p o i n t f o r f u r t h e r

i n v e s t i g a t i o n on t h e a d a p t a t i o n of t h e s p e c i e s

a g a i n s t s t r e s s c o n d i t i o n s . But a f t e r removing t h e

p e r i d e r m , t h e exposed b a r k d r i e s q u i c k l y . Hence f o r

t a p p i n g a c a r e f u l removal o f t h e p e r i d e r m i s needed

( f o r which a s p e c i a l k n i f e i s r e q u i r e d f o r t h e e a s y

o p e r a t i o n and i t was d e s i g n e d and d e v e l o p e d d u r i n g

t h e c o u r s e o f t h e i n v e s t i g a t i o n ( ~ i ~ . 3 ~ ) .

The s p e c i e s - M . g l a z i o v i i i s h i g h l y t o l e r a n t t o

p r o l o n g e d d r o u g h t and t h r i v e s we11 a t h i g h

e l e v a t i o n s . C e r t a i n d r o u g h t r e s i s t a n t a d a p t a t i o n s of

t h e t r e e h a v e been d i s c u s s e d e a r l i e r . The s o f t b a r k

b e n e a t h t h e p e r i d e r m c o n s e r v e s c o n s i d e r a b l e

p e r c e n t a g e of m o i s t u r e . Another p e c u l i a r i t y o b s e r v e d

i s t h e p r e s e n c e of c h l o r o p h y l l i n t h e b a r k .

P r e d o m i n a n t l y g r e e n and y e l l o w i s h w h i t e a r e t h e two

t y p e s o f b a r k o b s e r v e d i n _M. g l a z i o v i i . I n t h i s

s t u d y a 2 0 0 p e r c e n t h i g h e r l e v e l o f c h l o r o p h y l l

c o n t e n t was o b s e r v e d i n t h e g r e e n b a r k of M . -

g l a z i o v i i ( T a b l e 7 ) compared t o Hevea b a r k . The

g r e e n b a r k i s u s u a l l y s e e n on t h e s i d e of t h e s t e m

f a c i n g s u n l i g h t . A p p r e c i a b l e p h o t o s y n t h e s i s o f

b r a n c h e s a n d b a r k o f t e n o c c u r s i n d r o u g h t d e c i d u o u s

p l a n t s of a r i d r e g i o n s ( J a e z e r , 1 9 5 5 ; P e a r s o n a n d

L o w r e n c e . 1 9 5 8 ) .

T h e p i o n e e r i n g work on t h e r o l e of b a r k on

p h o t o s y n t h a t e p r o d u c t i o n was d o n e i n Aspen ( P o p u l u s

s p . ) i n t h e l a t e 1 9 5 0 ' s ( J a e j e r . 1 9 5 5 ; P e a r s o n a n d

L o w r e n c e . 1 9 5 8 a n d E d l i n , 1 9 7 5 ) . They o b s e r v e d t h a t

t h e c h l o r o p h y l l c o n t e n t i n t h e b a r k s t a r t i n c r e a s i n g

a t t h e o n s e t of w i n t e r i n g . They a l s o e s t a b l i s h e d t h e

a c c u m u l a t i o n o f p h o t o s y n t h a t e r e s u l t a n t o f t h e

a c t i v i t y of b a r k c h l o r o p l a s t . Some p o p u l a t i o n o f

a s p e n h a v e b a r k of y e l l o w - g r e e n c o l o u r i n c o n t e n t

w i t h t h e more f a m i l i a r powdery w h i t e b a r k . C o t t a m

( 1 9 5 4 ) h a s o b s e r v e d t h a t t h e Aspen t r e e w i t h g r e e n i s h

b a r k a r e f o u n d a t h i g h e l e v a t i o n s a n d w e l l a d a p t e d t o

t h e s t r e s s d u e t o c o l d a n d summer.

T h e r o l e of h i g h p e r c e n t a g e of c h l o r o p h y l l i n

t h e b a r k n e e d s f u r t h e r i n v e s t i g a t i o n s .

5.4. Yield in f luenc ing f a c t o r s and yield

N a t u r a l r u b b e r i s t h e most i m p o r t a n t e c o n o m i c

p r o d u c t o f t h e r u b b e r y i e l d i n g s p e c i e s . I n s p e c i e s

l i k e P a r a t h e n i u m a r g e n t a t u r n , t h e method f o l l o w e d f o r

e x t r a c t i o n and r e c o v e r y o f r u b b e r i s

mechano-chemical . T h i s method w i l l h a v e t o b e

c o n s i d e r e d f o r e x t r a c t i o n of r u b b e r i n l a t i c i f e r o u s

h e r b s a l s o i f and when such s p e c i e s a r e c o n s i d e r e d a s

p o t e n t i a l a l t e r n a t i v e s o u r c e s . I n t r e e s p e c i e s ,

however , t h e l a t e x i s c o n t a i n e d i n t h e s p e c i a l i s e d

t i s s u e s y s t e m m o s t l y c o n f i n e d t o t h e b a r k . Both i n

H . b r a s i l i e n s i s and i n M , g l a z i o v i i where t h e r u b b e r - -

c o n t a i n i n g l a t e x i s s y n t h e s i s e d i n t h e s p e c i a l i s e d

a r t i c u l a t e d a n a s t omosing l a t i c i f e r s . L a t e x can b e

c o l l e c t e d b y d i f f e r e n t t y p e s o f c u t s and p r i c k s . The

w i d e l y a d o p t e d method of t a p p i n g i n g . b r a s i l i e n s i s ,

c o n s i s t s of c o n t r o l l e d wounding a t s p e c i f i e d

i n t e r v a l s s o a s t o open t h e l a t e x v e s s e l s . T h i s

method i s e q u a l l y a p p l i c a b l e i n t h e c a s e of M.

g l a z i o v i i .

D u r a t i o n of l a t e x f l o w and t o t a l y i e l d o f l a t e x

c o l l e c t e d on each t a p p i n g a r e i n f l u e n c e d by v a r i o u s

p h y s i o l o g i c a l and b i o c h e m i c a l f a c t o r s . I n H.

b r a s i l i e n s i s l a t e x v e s s e l t u r g o r (PLV and l a t e x

v e s s e l p l u g g i n g (PI) a r e t h e two major f a c t o r s

r e p o r t e d t o i n f l u e n c e y i e l d ( S e t h u r a j , 1981:.

O t h e r f a c t o r s l i k e number and d i a m e t e r of l a t e x

v e s s e l r i n g s ' a r e a1 s o i n f l u e n c i n g t h e y i e l d . S i n c e

t h e a n a t o m i c a l f e a t u r e s of t h e b a r k of M. g l a z i o v i i

a r e more o r l e s s s i m i l a r t o t h o s e of H. b r a s i l i e n s i s

t h e a b o v e f a c t o r s may b e of much r e l e v a n c e .

T u r g o r p r e s s u r e o f t h e l a t i c i f e r s i s a n

i m p o r t a n t f a c t o r i n f l u e n c i n g t h e f l o w of l a t e x . The

l a t i c i f e r s a r e q u i t e t u r g i d i n v i v o , b u t k e e p i n g a n

e q u i l i b r i u m w i t h t h e a d j a c e n t t i s s u e s . Opening of

t h e l a t i c i f e r s r e s u l t s i n t h e r e l e a s e of t u r g o r

p r e s s u r e . Thus l a t e x e x u d a t i o n i s a p r e s s u r e f l o w

phenomenon. G r a d u a l l y t h e f l o w s t o p s b e c a u s e of t h e

g r a d u a l r e d u c t i o n i n p r e s s u r e a s w e l l a s f l o c c u l a t i o n

and s e a l i n g of t h e c u t e n d s o f t h e l a t i c i f e r s .

Boatman ( 1 9 6 6 ) and S o u t h o r n ( 1 9 6 9 ) h a v e f u r t h e r

e x p l a i n e d t h e r e a s o n s f o r t h e c e s s a t i o n of l a t e x f l o w

i n Hevea. When a c u t i s made on t h e b a r k of t h e

l a t i c i f e r o u s t r e e , l a t e x f l o w s out q u i t e r a p i d l y ,

b e c a u s e of t h e v e r y h i g h t u r g o r p r e s s u r e i n t h e

l a t i c i f e r s ( B u t t e r y and Boatman, 1964 ; Raghavendra - e t

a l . , - 1 9 8 4 ) . The r a p i d i n i t i a l f l o w i s a l s o d u e t o

t h e e l a s t i c c o n t r a c t i o n of t h e w a l l s , a s t h e f l u i d

c e l l s a p of t h e l a t i c i f e r s i s e x p e l l e d a f t e r a sudden

r e l e a s e i n t h e i r t u r g o r (Boatman, 1970; B u t t e r y and

Boatman, 1976 ; Gomez, 1983 ; S o u t h o r n , 1969!. A s t h e

t u r g o r p r e s s u r e f a l l s t o low l e v e l s , f u r t h e r f l o w of

l a t e x w i l l b e s l o w l y l i m i t e d . The t u r g o r p r e s s u r e o f

v a r i o u s l a t i c i f e r o u s p l a n t s were s t u d i e d by d i f f e r e n t

i n v e s t i g a t o r s ( T a b l e 1 0 ) . The PLV i s v e r y h i g h ( 1 . 5

MPa) i n H . b r a s i l i e n s i s and low ( 0 . 6 MPa) i n Nerium -

o l e a n d e r . _M. g l a z i o v i i r e c o r d e d a mean PLV o f 1 MPa

which i s l e s s t h a n t h a t i n H . b r a s i l i e n s i s where t h e -

maximum PLi r e p o r t e d i s 1 . 5 MPa. T u r g o r p r e s s u r e i s

a n i m p o r t a n t f a c t o r which i s e a s i l y i n f l u e n c e d by t h e

w a t e r r e l a t i o n s o f t h e p l a n t ( B u t t e r y and Boatman,

1964; Gomez, 1983; P a k i a n a t h a n e t a l . , 1 9 8 9 ) . Though -- t h e i n i t i a l f l o w r a t e i s h i g h i n M . g l a z i o v i i i t - d e c r e a s e s r a p i d l y and t h e f l o w c e a s e s i n a b o u t 10 t o

20 m i n u t e s . Whi le i n H. b r a s i l i e n s i s t h e f l o w i s

p r o l o n g e d t o a b o u t 2 - 2 . 5 h o u r s g i v i n g a h i g h t o t a l

volume. I t i s e v i d e n t t h a t t h e l a t e x v e s s e l t u r g o r

p r e s s u r e i s a c t i v e o n l y f o r a few m i n u t e s i n M . - g l a z i o v i i . B u t t e r y and Boatman ( 1 9 6 7 ) found t h a t

t u r g o r p r e s s u r e i s a c l o n a l c h a r a c t e r and v a r i e s f rom

c l o n e t o c l o n e . I n t h e w i l d s e e d l i n g t r e e s of - M .

g l a z i o v i i t h i s v a r i a t i o n h a s been o b s e r v e d . h e n c e

t h e r e i s s c o p e f o r improv ing t h e d u r a t i o n of l a t e x

f l o w t h r o u g h b r e e d i n g and c l o n a l s e l e c t i o n .

A g e n e r a l concep t on l a t e x f l o w was p roposed by

A r i z (19281 , F r e y - W y s s l i n g ( 1 9 3 2 ) and Gooding (1952

a and b ) on t h e b a s i s of t h e i r s t u d i e s conduc ted i n

Hevea. I t was f u r t h e r m o d i f i e d w i t h t h e e v i d e n c e --

t h a t l a t e x f l o w i s b l o c k e d by p l u g g i n g o f l a t e x

v e s s e l s a f t e r t a p p i n g (Boatman, 1966 ; B u t t e r y and

Boatman, 1 9 6 7 ) . A p h y s i c a l p l u g f o r m s n e a r t h e c u t

end o f t h e l a t e x v e s s e l and b l o c k s f u r t h e r f l o w of

l a t e x and f i n a l l y t h e e x u d a t i o n c o m p l e t e l y s t o p s

(Boatman, 1966 ; S o u t h o r n , 1 9 6 9 ) . The t o t a l y i e l d o f

a l a t e x y i e l d i n g t r e e i s t h u s d e t e r m i n e d by t h e

i n i t i a l r a t e o f f l o w a n d t h e r a t e of p l u g g i n g . The

P I may b e changed by e n v i r o n m e n t a l s t r e s s e s ,

e s p e c i a l l y w a t e r s t r e s s a n d e x p l o i t a t i o n t e c h n i q u e s

( R a g h a v e n d r a , 1 9 9 1 ) . I n - M. g l a z i o v i i a h i g h p l u g g i n g

i n d e x i s r e c o r d e d i n t h e l o c a t i o n where s o i l m o i s t u r e

was more d u e t o d i s t r i b u t e d a n n u a l r a i n f a l l . I d e a l

s o i l and good r a i n f a l l a r e t o t a l l y u n s u i ' t a b l e t o

c e a r a r u b b e r (Wickham, 1 9 0 8 ) . Whereas Hevea p e r f o r m s

w e l l o n l y i n s u c h c o n d i t i o n s . P r o l o n g e d s e v e r e s o i l

m o i s t u r e s t r e s s and h i g h summer t e m p e r a t u r e a r e t h e

m a j o r e n v i r o n m e n t a l c o n s t r a i n t s f o r g r o w t h and

p r o d u c t i v i t y o f p a r a r u b b e r . E f f e c t s o f t h e s e

a d v e r s e c o n d i t i o n s on g r o w t h of Hevea ( S e t h u r a j - e t

a1 ., 1989; B h a s k a r e t a1 ., 1 9 9 0 ) and e f f e c t s o f - - -

e x t r e m e s t r e s s c o n d i t i o n s on y i e l d and y i e l d

components e t c . a r e w e l l s t u d i e d ( G u r u r a j a Rao $-

a 1 . , - 1988; Devakumar & e., 1988; Vi jayakumar - e t

a l . , 1988). Though the i n i t i a l flow ra te i s sa t i s fac tory

for the f i r s t f ive minutes i n _M. glaziovii , it contributes

l i t t l e to the to ta l volume of l a t e x . I n M . glaziovii -

u n l i k e i n Hevea t h e f l o w s t o p s w i t h i n 10 t o 2 0

m i n u t e s and s p o n t a n e o u s c o a g u l a t i o n t a k e s p l a c e

b l o c k i n g t h e l a t e x v e s s e l s . T h i s f l o w r e s t r i c t i o n

mechanism i s d u e t o c e r t a i n p a r t i c l e s c o n t a i n e d i n

t h e l a t e x , which i n t u r n i n f l u e n c e p l u g g i n g .

D e t a i l e d i n v e s t i g a t i o n s on t h e p h y s i o l o g y of l a t e x

f l o w i n M . g l a z i o v i i a r e needed t o f i n d out t h e -

components r e s p o n s i b l e f o r h i g h l a t e x v e s s e l p l u g g i n g

and s p o n t a n e o u s c o a g u l a t i o n .

The p h y s i o l o g i c a l b a s i s of y i e I d p o t e n t i a l o f

h i g h y i e l d i n g and low y i e l d i n g c l o n e s of Hevea had - been s t u d i e d by S e t h u r a j -- e t a l . (1973). I t was found

t h a t t h e i n i t i a l f l o w r a t e was p o s i t i v e l y c o r r e l a t e d

w i t h y i e l d and t h e p l u g g i n g i n d e x was n e g a t i v e l y

c o r r e l a t e d . With t h i s v i e w p o i n t t h e h i g h P I and low

y i e l d of _M. g l a z i o v i i can b e i n t e r p r e t e d i n a n o t h e r

way. When t a p p i n g i s d o n e , t h e f l o w of l a t e x i s

r a p i d , b u t t h e l a t e x on c o n t a c t w i t h t h e humid a i r ,

s t a r t s fo rming a f i l m of c o a g u l a t e d l a t e x . T h i s f i l m

format i o n c o n t i n u e s r e s u l t i n g i n t o t a l c o a g u l a t i o n of

t h e n a t u r a l l y t h i c k l a t e x . T h i s p e c u l i a r i t y was

o b s e r v e d i n t h e l a t e x c o l l e c t e d . That t h e l a t e x i n

M . - g l a z i o v i i c o a g u l a t e s on a d d i n g w a t e r s t r o n g l y

i n d i c a t e s t h a t w a t e r o r h u m i d i t y p l a y major r o l e i n

t h e s p o n t a n e o u s c o a g u l a t i o n . T h i s i s i n s h a r p

c o n t r a s t t o t h e n a t u r e o f l a t e x i n g . b r a s i l i e n s i s

where c o a g u l a t i o n t a k e s p l a c e o n l y w i t h t h e h e l p of a

c o a g u l a t i n g a g e n t , t h e comnonly u s e d o n e s i n

c o m n e r c i a l p r a c t i c e b e i n g d i l u t e f o r m i c a c i d o r

a c e t i c a c i d .

The l a t e x v e s s e l rows a l s o i n f l u e n c e y i e l d . I n

Hevea, t h e c o r r e l a t i o n a n a l y s i s between t h e rows o f

l a t e x v e s s e l s and y i e l d and between t h e rows of l a t e x

v e s s e l s and i n i t i a l f l o w r a t e , showed t h a t t h e number

and rows of l a t e x v e s s e l s were p o s i t i v e l y c o r r e l a t e d

w i t h b o t h y i e l d and t h e i n i t i a l f l o w r a t e . I n M.

g l a z i o v i i however t h e l a t e x v e s s e l s a p p a r e n t l y a r e

no t i n f l u e n c i n g P I , b u t c o n t r i b u t e s t o w a r d s i n i t i a l

f l o w r a t e .

B e a u f i l s (1957) and d ' Auzac ( 1 9 6 0 ) h a v e

i n v e s t i g a t e d t h e r e a s o n s f o r p r e m a t u r e c o a g u l a t i o n of

l a t e x a t t h e t a p p i n g p a n e l and r e p o r t e d t h a t i t i s

a s s o c i a t e d w i t h h i g h magnesium c o n t e n t and Mg/P

r a t i o . I t h a s been o b s e r v e d t h a t Hevea c l o n e s w i t h

low P/Mg r a t i o s i n l a t e x h a v e a t e n d e n c y f o r h i g h e r

p l u g g i n g i n d e x (Yip and Gomez, 1 9 8 0 ) . Magnesium

c o n t e n t of 2280 ppm e s t i m a t e d i n t h e f r e s h l a t e x o f

M . - g l a z i o v i i may b e one o f t h e A a j o r r e a s o n s f o r t h e

s p o n t a n e o u s c o a g u l a t i o n and low y i e l d .

Y i e l d

The d r y r u b b e r r e c o v e r e d f rom t h e l a t e x exud ing

out on t a p p i n g i s t h e t r u e measure of t h e

p r o d u c t i v i t y . I n t h e c e a r a r u b b e r t r e e , p r o d u c t i v i t y

i s dependen t on many f a c t o r s . O f t h e s e v e r a l f a c t o r s

i n f l u e n c i n g t h e t o t a l q u a n t i t y of d r y r u b b e r , volume

of l a t e x o b t a i n e d on t a p p i n g , t h e d r y r u b b e r c o n t e n t

of t h e l a t e x , g i r t h and b a r k t h i c k n e s s of t h e t r e e

and t h e e n v i r o n m e n t a l c o n d i t i o n t o which t h e t r e e i s

exposed t o a r e i m p o r t a n t . Above a l l , t h e g e n e t i c

c o n s t i t u t i o n of each i n d i v i d u a l g e n o t y p e i s a l l t h e

more i m p o r t a n t . The e x t e n t and n a t u r e of t h e

l a t i c i f e r o u s t i s s u e , e s p e c i a l l y of t h e b a r k , a r e a l s o

f a c t o r s which govern p r o d u c t i v i t y .

The d a t a g e n e r a t e d from t h e p r e s e n t s t u d y b e a r

ample t e s t i m o n y t o t h e p o t e n t i a l i t i e s of M. q l a z i o v i i -

a s a n a l t e r n a t i v e s o u r c e of NR and a l s o p o i n t out t o

t h e v a s t s c o p e f o r p r o d u c t i v i t y improvement t h r o u g h

c o n v e n t i o n a l g e n e t i c r ecombina t i o n and s e l e c t i o n . I t

h a s t o b e remembered i n t h i s c o n t e x t t h a t a l m o s t

e x c l u s i v e l y N R of commerce i s o b t a i n e d f r o m a s i n g l e

s p e c i e s , H. b r a s i l i e n s i s a n d a l s o t h a t l i t t l e

a t t e n t i o n h a s been g i v e n t o M . g l a z i o v i i e i t h e r i n

I n d i a o r a b r o a d . A s s u c h t h e s t a g e which M. -

g l a z i o v i i now h a s can b e compared w i t h t h e

p r e - c o m n e r c i a l i s a t i o n s t a t u s which - H . b r a s i l i e n s i s

had d u r i n g t h e l a t t e r h a l f of t h e 1 9 t h C e n t u r y .

That v e g e t a t i v e means a s can b e assumed, i s a n

e f f e c t i v e method o f p r o p a g a t i o n and e s t a b l i s h m e n t o f

a more o r l e s s u n i f o r m p o p u l a t i o n of M. g l a z i o G ,

h a s imnense s i g n i f i c a n c e and p o t e n t i a l i t i e s . The

mean monthly y i e l d of t h e t r e e s , i n L o c a t i o n I , which

a r e r e s u l t a n t o f p r o p a g a t i o n t h r o u g h c u t t i n g s

e x h i b i t e d o n l y a n a r r o w r a n g e f rom 4 . 1 9 t o 5 . 5 9 g p e r

t r e e p e r t a p . The coef f i c i e n t of v a r i a t i o n i n y i e l d

between p l a n t s i s low ( 7 . 8 t o 1 6 . 4 p e r c e n t ) which

i n d i c a t e s t h a t t h e t r e e t o t r e e v a r i a t i o n i n y i e l d i s

n e g l i g i b l e . Monthly v a r i a t i o n i n y i e l d a l s o f o l l o w e d

t h e same t r e n d . The mean y i e l d ranged from 2 . 5 8 g

r e c o r d e d d u r i n g t h e month of J u l y t o 5 . 7 6 g p e r t r e e

p e r t a p o b t a i n e d d u r i n g March. The q u a r t e r June t o

August showed t h e p e r i o d of lowes t p r o d u c t i o n , t h e

y i e l d o f r u b b e r p e r t r e e p e r t a p b e i n g on ly 3 . 4 7 g .

The p e r i o d December t o March was t h e h i g h y i e l d i n g

s e a s o n , t h e mean y i e l d p e r t r e e b e i n g 5 . 4 9 g p e r t a p

( T a b l e 1 4 ) . The q u a r t e r June t o A u g u s t , which

r e c o r d e d c o n s i d e r a b l y low y i e l d , e n j o y e d maximum

p r e c i p i t a t i o n . The t o t a l r a i n f a l l o b t a i n e d d u r i n g

t h i s p e r i o d was 2563 mn, d i s t r i b u t e d i n 82 r a i n i n g

d a y s . The r e l a t i v e h u m i d i t y was a l s o h i g h d u r i n g

t h i s p e r i o d .

In t h e c a s e of _M. g l a z i o v i i o n l y J u l y , J u n e ,

August and May r e c o r d e d i n o r d e r ; a p r o d u c t i o n l e s s

t h a n t h a t of t h e mean month ly p r o d u c t i o n d u r i n g t h e

y e a r . T h i s i s i n s h a r p c o n t r a s t t o t h e s i t u a t i o n i n

t h e p a r a r u b b e r t r e e g. b r a s i l i e n s i s , where a l l t h e

months f rom F e b r u a r y t o August r e c o r d e d a p r o d u c t i o n

l e s s t h a n t h a t o f t h e month ly a v e r a g e (Rubber B o a r d .

1 9 9 3 ) . The p r o d u c t i o n was minimum d u r i n g F e b r u a r y

f o l l o w e d by March, J u n e , J u l y , A p r i l , August and May

i n o r d e r . The monthly c o n t r i b u t i o n t r e n d s t o w a r d s

a n n u a l d r y r u b b e r y i e l d i n - M . g l a z i o v i i and 5 .

b r a s i l i e n s i s a r e p r e s e n t e d i n F i g . 14 and F i g . 2 4

r e s p e c t i v e l y . NR b e i n g a v i t a l l y s t r a t e g i c

i n d u s t r i a l raw m a t e r i a l , s t e a d y a s s u r e d s u p p l y round

t h e y e a r i s a l w a y s welcome. I n a s i t u a t i o n where

p r o p e r package of p r a c t i c e s f o r g. g l a z i o v i i i s

d e v e l o p e d and t h e s p e c i e s c u l t i v a t e d on a c o m n e r c i a l

s c a l e , t h e low p r o d u c t i o n f rom one d u r i n g a

p a r t i c u l a r p a r t of t h e y e a r can b e compensated by t h e

c o m p a r a t i v e l y h i g h p r o d u c t i o n f rom t h e o t h e r on a

complementary b a s i s

Compared t o t h e more o r l e s s u n i f o r m p o p u l a t i o n

i n L o c a t i o n I , t h e s t a n d i n g t r e e s i n L o c a t i o n I1 w e r e

h i g h l y v a r i a b l e i n n a t u r e . 3 . g l a z i o v i i i s a c r o s s

f e r t i l i s e d s p e c i e s , w i t h a l o n g l i f e c y c l e . The

s p e c i e s i s t h u s h i g h l y h e t e r o z y g o u s b e c a u s e o f t h e

b r e e d i n g b e h a v i o u r and s e e d p r o p a g a t i o n u n d e r n a t u r a l

Jan Feb Mar Apr May June Jul Aug Sept Oct Nov Dec

Fig. 24. Monthly contribution (%I towards annual dry rubber yield in g . brasiliensis

c o n d i t i o n . While t h e mean DRC o f t h e l a t e x f rom t h e

t r e e s o f Locat ion I and I1 d i d n o t d i f f e r much, b e i n g

23 .6% i n t h e f o r m e r and 23.44% i n t h e l a t t e r t r e e t o

t h e v a r i a t i o n was v e r y v i d e i n L o c a t i o n 11. V a r i a t i o n

i n DRC ranged f rom 2 1 . 7 t o 2 5 . 7 i n t h e f i r s t L o c a t i o n .

Compared t o t h i s v a r i a t i o n i n t h e o t h e r l o c a t i o n was

f rom 15.0% t o 33.1% w i t h 60% of t h e t r e e s h a v i n g a DRC

l e s s t h a n t h e mean of t h e p o p u l a t i o n . Dry r u b b e r

y i e l d and volume y i e l d of l a t e x a l s o showed t h e same

t r e o d . These o b s e r v a t i o n s c l e a r l y show t h a t t h e

p o p u l a t i o n of M . - g l a z i o v i i i n L o c a t i o n I1 a r e h a v i n g

h i g h g e n e t i c v a r i a t i o n . Compared t o t h e l i m i t e d

germplasm r e s o u r c e s a v a i l a b l e i n - H . b r a s i l i e n s i s i n

t h e e a r l y p a r t of g e n e t i c improvement p rogramnes

( S c h u l t z , 1977 ; Swaminathan, 1977 ; P a n i k k a r e.. 1980 and Annamna, 1 9 9 2 ) . t h e germplasm r e s o u r c e s of M.

g l a z i o v i i a v a i l a b l e w i t h i n t h e c o u n t r y a t p r e s e n t i s

v e r y r i c h . Volume of l a t e x and t h e d r y r u b b e r i t

c o n t a i n s a r e i m p o r t a n t f a c t o r s g o v e r n i n g d r y r u b b e r

y i e l d ( S e t h u r a j , 1968, 1977, 1992 ; S e t h u r a j and Usha,

1 9 8 0 ) . I n L o c a t i o n 11. 2% of t h e p o p u l a t i o n

c o n t r i b u t e d t o 27.8% of t h e t o t a l r u b b e r y i e l d of t h e

p o p u l a t i o n . S e r i e r ( 1 9 8 8 ) h a s r e p o r t e d t h a t 1% of t h e

t r e e s i n a p o p u l a t i o n of M f i a z i o v i i was o u t s t a n d i n g .

These o b s e r v a t i o n s open out t h e imnense s c o p e f o r

g e n e t i c improvement i n M. g l a z i o v i i by j u d i c i o u s

p l a n n i n g of p a r e n t a l c o m b i n a t i o n s and v e g e t a t i v e

p r o p a g a t i o n of t h e h i g h 1 y promi s i n g r e c o m b i n a n t s .

The a v e r a g e p r o d u c t i v i t y o f t h e - M . g l a z i o v i i

p o p u l a t i o n i n L o c a t i o n I was e s t i m a t e d t o be 701.19 g

p e r t r e e p e r y e a r ( T a b l e 1 5 ) . C o n s i d e r i n g a s t a n d of

450 t r e e s p e r h e c t a r e , t h i s works out t o an e s t i m a t e d

p r o d u c t i v i t y of 315 kg d r y r u b b e r p e r h e c t a r e .

G e n e t i c improvement of t h e s p e c i e s and a d o p t i o n of

s c i e n t i f i c methods of c u l t i v a t i o n can improve

p r o d u c t i v i t y s u b s t a n t i a l l y h a s been c l e a r l y

e s t a b l i s h e d i n t h e c a s e of - H . b r a s i l i e n s i s . The

p r o d u c t i v i t y was on ly 284 kg p e r h e c t a r e p e r y e a r i n

1950-51 , which improved t o 1154 kg d u r i n g 1992-93

(Rubber Board , 1 9 9 4 ) d u r i n g a s p a n o f l e s s t h a n 50

y e a r s . C a r e f u l l y p l a n n e d t r e e improvement p rogramne ,

i f implemented s c i e n t i f i c a l l y , can be e x p e c t e d t o

r e s u l t i n t h e i d e n t i f i c a t i o n of s u p e r i o r g e n o t y p e s i n

M . g l a z i o v i i a s w e l l i n a r e a s o n a b l e s p a n of t i m e . -

The u n c a r e d s e e d l i n g g e n o t y p e s of M. g l a z i o v i i

i n L o c a t i o n I 1 amounts t o a r o u n d 2000 s e e d l i n g t r e e s .

Even t h e o b s e r v a t i o n s o f a few randomly s e l e c t e d

s e e d l i n g t r e e s have i n d i c a t e d an y i e l d v a r i a t i o n f rom

4 . 2 1 g p e r t r e e p e r t a p t o 1 0 . 5 5 g t r e e p e r t a p . I n

t h e c a s e o f volume y i e l d t h e r a n g e h a s been f rom a

l o w e s t o f 1 5 m l p e r t a p t o 4 7 m l . I n t h e c a s e o f d r c

t h e minimum r e c o r d e d was 1 5 . 0 % . t h e maximum b e i n g 3 5 . 5

p e r c e n t . S y s t e m a t i c o b s e r v a t i o n s of t h e p o p u l a t i o n .

b a s e d on f a c t o r s l i k e t o t a l v o l u m e , d r y r u b b e r

c o n t e n t . t r e e g i r t h , e t c , w h i c h d i r e c t l y i n f l u e n c e

y i e l d c a n b e t h o u g h t of a s a m e a n s of i d e n t i f y i n g

s u p e r i o r g e n o t y p e s i n t h i s w i d e r a n g e o f g e n e t i c a l l y

d i f f e r e n t t r e e p o p u l a t i o n . T h a t p r o p a g a t i o n b y

c u t t i n g s c a n e a s i l y b e a d o p t e d , t h e t i m e i n v o l v e d i n

b r i n g i n g o u t p o t e n t i a l l y p r o m i s i n g s e l e c t i o n s c a n b e

d r a s t i c a l l y b r o u g h t dovrn. D u r i n g t h e e a r l y p h a s e of

t h e c u l t i v a t i o n of t h e p a r a r u b b e r t r e e ,

i d e n t i f i c a t i o n of e l i t e t r e e s f o r m among g e n e t i c a l l y

d i v e r g e n t s e e d l i n g p o p u l a t i o n s a n d e s t a b l i s h m e n t of

p r i m a r y c l o n e s h a d p a i d r i c h d i v i d e n t s ( D i j k m a n ,

1 9 5 1 ) . I n f a c t t h i s method of o r t e t s e l e c t i o n i s e v e n

now a d o p t e d f o r e s t a b l i s h m e n t of l o c a t i o n s p e c i f i c

c u l t i v a r s i n K. b r a s i l i e n s i s i n a l m o s t a l l NR r e s e a r c h

i n s t i t u t i o n s .

5.5. C h a r a c t e r i s a t i o n of l a t e x a n d r u b b e r

P r o p e r t i e s of l a t e x

L i k e most c o l l o i d s l a t e x f r o m g a z i o v i i i s w h i t e

i n c o l o u r a n d i t s g e n e r a l a p p e a r a n c e i s s i m i l a r t o

t h a t o f Hevea l a t e x . At l e a s t i n t h e l a t e x s t a g e t h e

n o n - r u b b e r c o n s t i t u e n t s i n g a n i h o t l a t e x a r e n o t f o u n d

i n f l u e n c i n g i t s c o l o u r . No s i g n i f i c a n t v a r i a t i o n i n

c o l o u r was o b s e r v e d among t h e i n d i v i d u a l t r e e s .

The v i s c o s i t y o f a l i q u i d i s a measure o f i t s

r e s i s t a n c e t o f l o w . Manihot l a t e x i s h a v i n g a

v i s c o s i t y i n t h e same r a n g e a s t h a t o f -- Hevea l a t e x .

G e n e r a l l y v i s c o s i t y of a r u b b e r l a t e x i n c r e a s e s w i t h

i t s r u b b e r c o n t e n t ( B l a c k l e y . 1966). However, i n t h e

p r e s e n t c a s e Manihot l a t e x i s found h a v i n g a s l i g h t l y

h i g h e r v i s c o s i t y i n s p i t e of a lower r u b b e r c o n t e n t .

I t i s b e l i e v e d t h a t t h e c o m p a r a t i v e l y h i g h e r v i s c o s i t y

o f Manihot l a t e x i s c o n t r i b u t e d m o s t l y by i t s h i g h e r

non- rubber c o n t e n t .

S p e c i f i c g r a v i t y of Manihot l a t e x i s v e r y n e a r l y

u n i t y . However, compared t o Hevea l a t e x t h i s i s --

s l i g h t l y h i g h e r , i n s p i t e of t h e f a c t t h a t t h e

s p e c i f i c g r a v i t y of d r y s h e e t r u b b e r p r e p a r e d f rom

Manihot l a t e x i s v e r y c l o s e t o t h a t of Hevea r u b b e r . - I t may a l s o b e n o t e d t h a t t h e d r c of Manihot l a t e x i s

l o w e r . I t i s t h e r e f o r e i n f e r r e d t h a t t h e h i g h e r

s p e c i f i c g r a v i t y of Manihot l a t e x i s c o n t r i b u t e d by ---

t h e p r e s e n c e of n o n - r u b b e r c o n s t i t u e n t s .

Both t o t a l s o l i d s c o n t e n t and d r y r u b b e r c o n t e n t

a r e found t o be lower i n t h e c a s e of Manihot l a t e x .

However, i t may be n o t e d t h a t t h e Manihot t r e e s were

t a p p e d a lmost d a i l y d u r i n g 1993 f o r t h e s e

i n v e s t i g a t i o n s , w h i l e t h e Hevea t r e e s were t a p p e d on ly

on a l t e r n a t e d a y s . T a p p i n g i n t e n s i t y h a s b e e n

r e p o r t e d t o b e one of t h e i m p o r t a n t f a c t o r s

Hevea l a t e x c o n t r i b u t i n g t o t h e s o l i d s c o n t e n t of -

( J a c o b a., 1 9 8 9 ) . One o f t h e most s i g n i f i c a n t

d i f f e r e n c e s b e t w e e n l a t e x f r o m - Hevea a n d Manihot i s

t h e m a r k e d l y h i g h e r n o n - r u b b e r s o l i d s c o n t e n t i n t h e

l a t t e r . T h i s i s f o u n d t o b e more t h a n d o u b l e t h e

v a l u e o b t a i n e d i n t h e c a s e o f H e v e a . I t must b e

p o i n t e d o u t h e r e t h a t t h e a c t u a l n o n - r u b b e r s o l i d s

c o n t e n t o f t h e l a t e x i s much h i g h e r t h a n t h e v a l u e s

shown i n T a b l e 1 8 , a s t h e d r c f i l m o b t a i n e d f r o m t h e

l a t e x s t i l l c o n t a i n s s u b s t a n t i a l q u a n t i t i e s of

n o n - r u b b e r c o n s t i t u e n t s .

The n o n - r u b b e r s o l i d s c o n t e n t of t h e Man iho t

l a t e x c o m p r i s e s m o s t l y p r o t e i n s , r e s i n s a n d m i n e r a l s .

P r o t e i n s a n d r e s i n s a r e a s s o c i a t e d more w i t h t h e

r u b b e r p a r t i c l e s a s i s i n d i c a t e d b y t h e s u b s t a n t i a l l y

h i g h e r p r o t e i n a n d a c e t o n e e x t r a c t a b l e c o n t e n t of t h e

s h e e t r u b b e r ( T a b l e 2 0 ) . T h e s i z e of r u b b e r p a r t i c l e s

i n Manihot l a t e x h a s b e e n r e p o r t e d t o b e i n t h e r a n g e

of 600 -1800 A a s a g a i n s t 1 0 0 0 - 1 5 0 0 0 A i n t h e c a s e of

Hevea ( S t a v e l y g c., 1 9 6 1 ) . T h e l o w e r a v e r a g e -

p a r t i c l e s i z e c a u s e s a s s o c i a t i o n of a h i g h e r

n o n - r u b b e r c o n t e n t w i t h t h e r u b b e r p h a s e a s t h e

n o n - r u b b e r s o l i d s a r e f o r m i n g a p r o t e c t i v e l a y e r o v e r

t h e p a r t i c l e s u r f a c e .

A l t h o u g h Man iho t l a t e x i s c o a g u l a t e d by f o r m i c

a c i d a n d a c e t i c a c i d . c o a g u l a t i o n i s n o t f o u n d

c o m p l e t e , w i t h t h e s e r u m r e m a i n i n g s l i g h t l y t u r b i d .

I t i s p r o b a b l e t h a t t h e h i g h e r p r o t e i n c o n t e n t of t h e

l a t e x i s r e s p o n s i b l e f o r t h e i n c o m p l e t e c o a g u l a t i o n by

a c i d s . I t i s a l s o p r o b a b l e t h a t t h e i s o e l e c t r i c p o i n t

o f t h e p r o t e i n s i n Man iho t l a t e x i s l o w e r t h a n t h a t

of t h e p r o t e i n s i n Hevea l a t e x . A s t h e l a t e x i s

c o a g u l a t e d b y a c i d s , i t i s i n f e r r e d t h a t t h e p a r t i c l e s

i n Manihot l a t e x a r e n e g a t i v e l y c h a r g e d .

Manihot l a t e x i s f o u n d t o u n d e r g o s p o n t a n e o u s

c o a g u l a t i o n a s i n t h e c a s e o f Hevea l a t e x .

S p o n t a n e o u s c o a g u l a t i o n i s c a u s e d by t h e a c t i o n o f

b a c t e r i a on t h e c a r b o h y d r a t e s i n l a t e x . I t i s f o u n d

t h a t s p o n t a n e o u s c o a g u l a t i o n t a k e s p l a c e i n Man iho t

l a t e x a l m o s t a t t h e same r a t e a s i n Hevea l a t e x .

S p o n t a n e o u s c o a g u l a t i o n o f l a t e x c o u l d b e f o l l o w e d by

c h a n g e s i n v i s c o s i t y . F i g u r e s 1 6 and 1 7 show t h e

c h a n g e s i n v i s c o s i t y d u r i n g s t o r a g e of Man iho t a n d

Hevea l a t i c e s r e s p e c t i v e l y . T h e f i g u r e s i n d i c a t e t h a t

s p o n t a n e o u s c o a g u l a t i o n i s a s l o w p r o c e s s a n d t a k e s

p l a c e o v e r a p e r i o d o f 7-8 h .

A v e r y s i g n i f i c a n t o b s e r v a t i o n i s t h e

c o a g u l a t i o n of + n i h o t l a t e x upon d i l u t i o n w i t h w a t e r .

D i l u t e d l a t e x , upon s t o r a g e , r a p i d l y t h i c k e n s a n d

f i n a l l y f o r m s of a lump of c o a g u l u m . I n t h e c a s e of

Hevea l a t e x a l s o d i l u t i o n w i t h w a t e r c a u s e s a n - i n c r e a s e i n v i s c o s i t y i n i t i a l l y which d i s a p p e a r s on

f u r t h e r d i l u t i o n . I t i s known t h a t when l a t e x i s

d i l u t e d , t h e l u t o i d s b u r s t r e l e a s i n g t h e i r c o n t e n t

(B-Serum) which c o n s i s t s of an a c i d serum e n r i c h e d

+ + + + w i t h d i v a l e n t c a t i o n s (Ca and Mg ) and c a t i o n i c

p r o t e i n s . B-serum i s t h u s c a p a b l e of p r o v o k i n g

f o r m a t i o n of m i c r o f l o c s of r u b b e r p a r t i c l e s ( S o u t h o r n

and Y i p , 1968) c a u s i n g t h e v i s c o s i t y of l a t e x t o

i n c r e a s e . I t i s p r o b a b l e t h a t t h e l u t o i d c o n t e n t of

Manihot l a t e x i s much h i g h e r and t h a t i t s B-serum

c o n t a i n s s u f f i c i e n t c a t i o n i c p r o t e i n s and d i v a l e n t

c a t i o n s t o c a u s e c o m p l e t e c o a g u l a t i o n of l a t e x . The

f a c t t h a t Manihot l a t e x c o n t a i n s a s u b s t a n t i a l l y

h i g h e r magnesium and c a l c i u m s u p p o r t s t h i s . I t i s

a l s o seen f r o m T a b l e 20 t h a t t h e c o n c e n t r a t i o n o f

magnesium and c a l c i u m i n t h e d r y s h e e t r u b b e r f rom

Manihot l a t e x i s v e r y c l o s e t o t h o s e of t h e t o t a l

s o l i d s f i l m . T h i s c l e a r l y i n d i c a t e s t h a t b o t h

magnesium and c a l c i u m a r e g e t t i n g c h e m i c a l l y l i n k e d t o

t h e r u b b e r p a r t i c l e s on c o a g u l a t i o n , f u r t h e r

s u p p o r t i n g t h e c o n c l u s i o n t h a t c o a g u l a t i o n o f Manihot

l a t e x i s r e s u l t i n g f rom t h e a c t i o n of d i v a l e n t m e t a l

i o n s r e l e a s e d i n t o i t by t h e b u r s t i n g of t h e l u t o i d

p a r t i c l e s on d i l u t i o n .

P r o p e r t i e s of t o t a l s o l i d s f i l m f rom l a t e x

The t o t a l s o l i d s f i l m , p r e p a r e d by d r y i n g t h e

l a t e x , i s t h e r i g h t m a t e r i a l f o r s t u d y i n g t h e chemica l

compos i t ion of l a t e x . The f i l m o b t a i n e d f rom Manihot

l a t e x i s found t o b e c o h e r e n t , a s i n t h e c a s e of Hevea

l a t e x . The c o l o u r o f t h e f i l m was , however , found t o

be much d a r k e r i n t h e c a s e o f M a n i h o t . I t was a l s o

found t o b e l e s s t r a n s p a r e n t . Both t h e s e d i f f e r e n c e s

a r e c o n t r i b u t e d by t h e h i g h e r non- rubber c o n t e n t of

Manihot l a t e x .

The chemica l c o m p o s i t i o n of Manihot l a t e x i s

s i g n i f i c a n t l y d i f f e r e n t f rom t h a t o f Hevea l a t e x . The

d i f f e r e n c e i s c l e a r l y o b s e r v e d w i t h r e s p e c t t o t h e

p r o t e i n and r e s i n c o n t e n t s . T h e t o t a l m i n e r a l c o n t e n t

o f Manihot l a t e x a l s o i s h i g h e r t h a n t h a t o f Hevea

l a t e x . The m i n e r a l c o m p o s i t i o n i s a l s o d i f f e r e n t .

One of t h e i m p o r t a n t o b s e r v a t i o n s i s t h a t copper

c o n t e n t i s much lower i n M a n i h o t . T h i s might b e

caused by t h e f a c t t h a t no copper b a s e d f u n g i c i d e was

a p p l i e d f o r Manihot . The most s i g n i f i c a n t d i f f e r e n c e

between t h e two l a t i c e s i s t h e c o n c e n t r a t i o n of

magnesium, which i s a l m o s t f o u r t i m e s i t s

c o n c e n t r a t i o n i n Hevea l a t e x .

P r o p e r t i e s of d r y r u b b e r

T a b l e 2 0 s u m n a r i s e s t h e p r o p e r t i e s o f s h e e t

r u b b e r p r e p a r e d f rom t h e two l a t i c e s . When g r a d e d by

t h e v i s u a l g r a d i n g s y s t e m t h e s h e e t p r e p a r e d f r o m

Manihot l a t e x was f o u n d t o b e l o n g t o RMA 3 w h i l e t h a t

f r o m Hevea l a t e x RMA 2 . T h e d i f f e r e n c e i n t h e g r a d e

was m o s t l y d u e t o i t s d a r k e r c o l o u r a n d l o w e r

t r a n s p a r e n c y . T h u s t h e p r e s e n c e o f h i g h e r n o n - r u b b e r

c o n s t i t u e n t s c a u s e s d o w n g r a d i n g of Manihot r u b b e r ,

u n l e s s a d e q u a t e p r e c a u t i o n s a r e t a k e n t o remove most

o f t h e n o n - r u b b e r c o n s t i t u e n t s w h i l e p r e p a r i n g s h e e t .

D i r t c o n t e n t was f o u n d t o b e s l i g h t l y h i g h e r i n

Man iho t r u b b e r . A s b o t h t h e s h e e t s w e r e p r e p a r e d

u n d e r i d e n t i c a l c o n d i t i o n s o f s i e v i n g a n d

s e d i m e n t a t i o n , t h e h i g h e r d i r t c o n t e n t c o u l d b e

r e s u l t i n g f r o m t h e h i g h e r v i s c o s i t y of t h e l a t e x a f t e r

d i l u t i o n wh ich c a u s e s t h e s e d i m e n t a t i o n p r o c e s s

s l o w e r . I t i s a l s o p o s s i b l e t h a t some of t h e p r o t e i n s

a n d r e s i n s i n t h e r u b b e r g e t p r e c i p i t a t e d a n d f o r m

p a r t o f t h e d i r t c o n t e n t .

T h e a p p e a r a n c e of a n o f f - w h i t e powdery d e p o s i t

on t h e s u r f a c e of s h e e t , s u b j e c t e d t o s t r e t c h i n g , i s

a l s o c a u s e d by t h e n o n - r u b b e r c o n s t i t u e n t s i n t h e

Manihot r u b b e r . T h i s f a c t i s c o n f i r m e d b y t h e f a c t

t h a t t h e i n t e n s i t y of t h e d e p o s i t d e c r e a s e s w i t h

h i g h e r d i l u t i o n of l a t e x b e f o r e c o a g u l a t i o n a n d

t h o r o u g h w a s h i n g of t h e wet s h e e t .

A s u b s t a n t i a l p o r t i o n of t h e p r o t e i n s i n t h e

l a t e x i s a s s o c i a t e d w i t h t h e r u b b e r p a r t i c l e s a n d

h e n c e even a f t e r c o n v e r s i o n of l a t e x i n t o s h e e t

t h r o u g h c o a g u l a t i o n , a b o u t 4 5 p e r c e n t of t h e o r i g i n a l

p r o t e i n c o n t e n t i s found r e t a i n e d i n t h e r u b b e r . T h i s

i s found t o be t o t h e same e x t e n t i n b o t h t h e r u b b e r s .

However, a s t h e o r i g i n a l p r o t e i n c o n t e n t i n Manihot

l a t e x i s much h i g h e r , a p r o p o r t i o n a t e l y h i g h e r p r o t e i n

c o n t e n t i s o b s e r v e d i n t h e s h e e t p r e p a r e d from i t .

Ash c o n t e n t of Manihot r u b b e r i s found t o b e

h i g h e r t h a n t h a t o f H r u b b e r . But i t i s

s u b s t a n t i a l l y lower t h a n t h a t of t h e t o t a l s o l i d s

f i l m . T h i s shows t h a t a major p o r t i o n of t h e m i n e r a l

m a t t e r i s r e m a i n i n g d i s s o l v e d i n t h e serum and a r e

removed d u r i n g p r e p a r a t i o n of s h e e t r u b b e r . A c l o s e r

e x a m i n a t i o n of t h e r e s u l t s i n d i c a t e t h a t t h e

p e r c e n t a g e r e t e n t i o n of a s h i n t h e s h e e t r u b b e r

(compared t o t h a t of t h e t o t a l s o l i d s f i l m ) i s h i g h e r

i n Manihot ( 2 6 p e r c e n t ) t h a n i n Hevea ( 1 2 . 8 p e r c e n t ) .

T h i s i n d i c a t e s t h a t more m i n e r a l c o n s t i t u e n t s a r e

a s s o c i a t e d w i t h t h e coagulum i n t h e fo rmer t h a n i n t h e

l a t t e r .

P R I i s a measure o f t h e r e s i s t a n c e t o o x i d a t i o n

and t h i s i s found t o be s i g n i f i c a n t l y lower i n t h e

c a s e of Manihot r u b b e r . Lower PRI i s u s u a l l y

a t t r i b u t e d t o t h e p r e s e n c e of p r o x i d a n t s l i k e c o p p e r .

manganese and i r o n (Watson , 1969 ) . The lower P R I of

Maniho t r u b b e r i s b e l i e v e d t o b e d u e t o t h e h i g h e r

manganese a n d i r o n c o n t e n t s . I t i s a l s o p o s s i b l e t h a t

t h e n a t u r a l a n t i o x i d a n t s a r e l e s s i n Man iho t r u b b e r o r

t h o s e wh ich a r e p r e s e n t , a r e l e s s e f f e c t i v e .

R e s u l t s f r o m t h e a c c e l e r a t e d s t o r a g e h a r d e n i n g

t e s t i n d i c a t e t h a t Man iho t r u b b e r p o s s e s s e s c o n s t a n t

v i s c o s i t y c h a r a c t e r . When Hevea r u b b e r i s s t o r e d , i t s

v i s c o s i t y i s f o u n d t o b e i n c r e a s i n g . T h i s phenomenon

of s t o r a g e h a r d e n i n g i s known t o i n v o l v e c a r b o n y l

g r o u p s i n r u b b e r , s i n c e h a r d e n i n g i s a l m o s t f u l l y

s u p p r e s s e d by t h e a d d i t i o n of r e a g e n t s t h a t c o u l d

b l o c k c a r b o n y l g r o u p s (Wood, 1 9 5 3 ; S e k h a r . 1962). T h e

f a c t t h a t t h e p l a s t i c i t y of Man iho t r u b b e r d o e s n o t

i n c r e a s e s i g n i f i c a n t l y d u r i n g a c c e l e r a t e d s t o r a g e

s u g g e s t s t h a t c a r b o n y l g r o u p s a r e l e s s i n Man iho t

r u b b e r . T h i s ' i s a s t r i k i n g s u p e r i o r i t y of -- Maniho t

r u b b e r . I n t h e c a s e o f Hevea r u b b e r , i n o r d e r t o

a c h i e v e s t a b l e v i s c o s i t y . i t i s n e c e s s a r y t o a d d

s p e c i a l r e a g e n t s l i k e h y d r o x y l a m i n e s a l t s i n t o l a t e x

b e f o r e c o a g u l a t i o n . T h e r e s u l t s i n d i c a t e t h a t t h i s i s

n o t n e c e s s a r y i n t h e c a s e of Man iho t r u b b e r .

T h e FT-IR s p e c t r a of b o t h t h e r u b b e r s a r e shown

i n F i g u r e s 2 0 a n d 2 1 . T h e s p e c t r a a r e v e r y much

i d e n t i c a l . T h e r e f o r e , i t i s c o n c l u d e d t h a t t h e

c h e m i c a l s t r u c t u r e of Man iho t r u b b e r i s i d e n t i c a l t o

t h a t o f Hevea r u b b e r . The v i s c o s i t y a v e r a g e m o l e c u l a r

we igh t of Manihot r u b b e r i s a l s o found t o b e v e r y

c l o s e t o t h a t of Hevea r u b b e r ,

P r o c e s s i n g p r o p e r t i e s

Mooney v i s c o s i t y v a l u e s of t h e mixes f r o m

Manihot r u b b e r a r e found t o b e s l i g h t l y lower t h a n

t h a t of t h e c o r r e s p o n d i n g mixes f r o m Hevea r u b b e r , i n

s p i t e o f t h e f a c t t h a t t h e f o r m e r had a h i g h e r Mooney

v i s c o s i t y i n t h e raw s t a g e . T h i s s u g g e s t s t h a t t h e

r a t e o f m i l l breakdown i s h i g h e r i n Manihot r u b b e r .

The v u l c a n i z a t i o n b e h a v i o u r , i n c l u d i n g s c o r c h t i m e a n d

optimum c u r e t i m e a r e more o r l e s s i d e n t i c a l i n b o t h

t h e r u b b e r s .

P h y s i c a l p r o p e r t i e s of v u l c a n i z a t es

The gum v u l c a n i z a t e s of Manihot r u b b e r were

found h a v i n g h i g h e r modulus and h a r d n e s s . T h i s i s

b e l i e v e d t o b e d u e t o t h e p r e s e n c e of h i g h e r

concent r a t i o n of non - r u b b e r c o n s t i t u e n t s l i k e

p r o t e i n s .

With t h e a d d i t i o n o f ca rbon b l a c k , t h e

d i f f e r e n c e i n t h e modulus and h a r d n e s s of t h e

v u l c a n i z a t e s was found t o b e d i s a p p e a r i n g . T e n s i l e

s t r e n g t h was found t o b e lower i n t h e c a s e of Manihot

r u b b e r . The a d d i t i o n of b l a c k d i d no t c a u s e any

s i g n i f i c a n t i n c r e a s e i n t e n s i l e s t r e n g t h . The

r e a s o n a b l y h i g h t e n s i l e s t r e n g t h of t h e gum

v u l c a n i z a t e i n d i c a t e s t h a t Manihot r u b b e r a l s o i s

c a p a b l e of u n d e r g o i n g s t r a i n c r y s t a l l i s a t i o n a s i n t h e

c a s e of Hevea r u b b e r .

Manihot r u b b e r h a s been found t o b e s l i g h t l y

i n f e r i o r t o Hevea r u b b e r w i t h r e s p e c t t o t e a r

r e s i s t a n c e , r e s i l i e n c e , h e a t b u i l d - u p and a b r a s i o n

r e s i s t a n c e . The l o w e r r e s i l i e n c e and t h e h i g h e r h e a t

b u i l d up might b e r e s u l t i n g f rom t h e h i g h e r p r o t e i n

c o n t e n t of Manihot r u b b e r . Crack growth r e s i s t a n c e

was found t o b e h i g h e r f o r t h i s r u b b e r . R e s i s t a n c e t o

Ozone and t h e r m o - o x i d a t i v e a g e i n g h a v e been found t o

b e more o r l e s s i d e n t i c a l i n b o t h t h e r u b b e r s .

5 . 6 . C e a r a r u b b e r wood and s e e d oil

The s u r v e y of l i t e r a t u r e r e v e a l s t h a t t h e

i n f o r m a t i o n on t h e s t r u c t u r a l f e a t u r e s and u t i l i z a t i o n

of c e a r a wood i s s t i l l o b s c u r e . Hence t h e p r e s e n t

s t u d y a l s o a i m s a t t h e u n d e r s t a n d i n g of c e r t a i n

p h y s i c a l p r o p e r t i e s . a n a t o m i c a l f e a t u r e s and t h e

c a p a c i t y o f wood f o r chemica l i m p r e g n a t i o n o f w a t e r

b o r n e wood p r e s e r v a t i v e s .

Ceara wood i s d i f f u s e p o r o u s . I t i s a v e r y

l i g h t h a r d wood a c c o r d i n g t o t h e c l a s s i f i c a t i o n

s u g g e s t e d by F i n d l a y ( 1 9 7 5 ) and Bhat ( 1 9 8 5 ) b a s e d on

t h e b a s i c d e n s i t y v a l u e s of wood. I n compar ison t o

Hevea wood, which a l s o i s a l i g h t h a r d wood, t h e b a s i c --

d e n s i t y i s lower i n c e a r a wood. The a t t r a c t i v e w h i t e

y e l l o w i s h c o l o u r , medium c o a r s e t e x t u r e and s t r a i g h t

g r a i n s of c e a r a wood, s i m i l a r t o t h a t of Hevea wood,

i n d i c a t e i t s p o t e n t i a l i t i e s f o r v a r i o u s end u s e s .

The f i b e r s a r e l o n g and b r o a d i n c e a r a wood w i t h

an a v e r a g e v a l u e o f 1577 pm and 30 pm r e s p e c t i v e l y

which a r e h i g h e r t h a n t h a t o f Hevea wood. The f i b e r

l e n g t h o f - H . b r a s i l i e n s i s wood v a r i e s f rom 1 1 8 9 p m t o

1500 p m (Guha and N e g i , 1969 ; S i l v a , 1970; Bhat g

a 1 ., 1984; Reghu e t a 1 ., 1989) w i t h an a v e r a g e w i d t h - - -

o f 27 p m (Reghu & g . , 1 9 8 9 ) . T h i s d i m e n s i o n a l

f e a t u r e o f c e a r a wood m y b e a t t r i b u t e d t o i t s

p o t e n t i a l u s e a s a raw m a t e r i a l f o r p u l p i n d u s t r y .

U n l i k e Hevea wood, t h e wood of M. - g l a z i o v i i i s

c h a r a c t e r i s e d by t h e a b s e n c e o r r a r e occurrence . o f

t y l o s e s i n t h e v e s s e l lumen. T h i s s p e c i a l f e a t u r e o f

c e a r a wood i n d i c a t e s i t s p r e m e a b i l i t y and p e n e t r a t i o n

c a p a c i t y o f wood p r e s e r v a t i v e s d u r i n g chemica l

i m p r e g n a t i o n . I t h a s been r e p o r t e d t h a t t h e p r e s e n c e

of numerous t y l o s e s i n t h e v e s s e l lumen u s u a l l y makes

t h e wood l e s s p e r m e a b l e t o l i q u i d s and p r e s e r v a t i v e s

(Kramer and Koz l o w i s k i . 1 9 6 0 ; Akachuku, 1 9 8 5 ) . The

chemical impregnat i o n of w a t e r b o r n e boron compounds

by vacuum p r e s s u r e method done i n t h e p r e s e n t s t u d y

a l s o j u s t i f i e s t h e h i g h ' t h r o u g h and t h r o u g h '

p e n e t r a t i o n c a p a c i t y of c e a r a wood.

The major d e m e r i t s of c e a r a wood n o t e d f rom t h e

p r e s e n t s t u d y i s i t s s u 5 c e p t i b i l i t y t o f u n g u s and

i n s e c t a t t a c k and t h e o c c u r r e n c e of t e n s i o n wood

s i m i l a r t o t h a t of Hevea wood. The s u s c e p t i b i l i t y t o

f u n g u s and i n s e c t a t t a c k may b e d u e t o t h e p r e s e n c e of

h i g h s o l u b l e s u g a r and s t a r c h c o n t e n t s and a l s o d u e t o

t h e a b s e n c e of h e a r t wood f o r m a t i o n . T h i s d e f e c t can

b e r e c t i f i e d by means of c h e m i c a l i m p r e g n a t i o n of wood

p r e s e r v a t i v e s . T e n s i o n wood f ormat i o n i s a comnon

n a t u r a l d e f e c t of v a r i o u s h a r d wood s p e c i e s which

u l t i m a t e l y a f f e c t s t h e s e a s o n i n g p r o p e r t y of wood

d u r i n g d r y i n g and t h e i n t e n s i t y of t h i s d e f e c t can b e

min imised up t o a c e r t a i n e x t e n t by a d o p t i n g

c o n t r o l l e d s e a s o n i n g s c h e d u l e s d u r i n g t h e c o u r s e of

wood d r y i n g .

I n t h i s c o n t e x t i t may b e r e c a l l e d t h a t d u r i n g

1 9 5 0 ' s Hevea wood h a s been c o n s i d e r e d u n i m p o r t a n t i n

t h e r e p l a n t a t i o n scheme ( S i l v a , 1 9 7 0 ) and were b e i n g

u s e d on ly a s f u e l wood. But i n r e c e n t y e a r s , i t h a s

been we l l p roved t h a t 3 wood c o u l d b e upgraded a s

a s u b s t i t u t e f o r q u a l i t y t i m b e r a f t e r a p p r o p r i a t e

p r e s e r v a t i v e t r e a t m e n t s and s e a s o n i n g ( T e i k , 1 9 8 2 ;

Gnanaharan and George Mathew, 1982 ; Hed ley , 1987 ; Hon

e t a 1 ., 1982; T i s s e v e r a s i n g h e . 1969; S o n t i e t a l . , - - - - 1 9 8 2 ) . Now-a-days, though Hevea wood i s a l i g h t h a r d

wood, i t i s b e i n g u s e d a s a p o t e n t i a l raw m a t e r i a l f o r

v a r i o u s wood b a s e d i n d u s t r i e s such a s match i n d u s t r y ,

p a c k i n g c a s e s , plywood, c o m p o s i t e wood, f u r n i t u r e ,

t e x t i l e a c c e s s o r i e s and even f o r b u i l d i n g

c o n s t r u c t i o n s (Todd, 1970 ; S e k h a r , 19891.

The i n a d e q u a t e a v a i l a b i l i t y of good q u a l i t y

t i m b e r and i t s e v e r i n c r e a s i n g demand w i l l a l w a y s

n e c e s s i t a t e s e a r c h f o r a l t e r n a t i v e s o u r c e of t i m b e r . C e a r a wood may b e a p o t e n t i a l t i m b e r f o r v a r i o u s wood

b a s e d i n d u s t r i e s , i f and when a v a i l a b l e on a l a r g e

s c a l e , a f t e r a d o p t i n g a p p r o p r i a t e p r o p h y l a c t i c and

p r e s e r v a t i v e t r e a t m e n t s .

Seed oil

M . g l a z i o v i i f l o w e r s p r o f u s e l y and s e t s s e e d s . - Manihot s e e d i s a p o t e n t i a l s o u r c e of o i l . I t was

o b s e r v e d t h a t one t r e e g i v e s a b o u t 250 g of s e e d s p e r

annum. Assuming a s t a n d of 4 0 0 t r e e s p e r h e c t a r e

a b o u t 100 kg of s e e d s c o u l d b e e x p e c t e d f rom 1 h e c t a r e

o f M. g l a z i o v i i p l a n t a t i o n .

The a v e r a g e seed we igh t i s 0 . 5 7 g . The k e r n e l

a c c o u n t s f o r a round 20 p e r c e n t o f t h e weight o f s e e d .

T h u s , t h e y i e l d o f k e r n e l i s e s t i m a t e d t o b e i n t h e

r a n g e of 20 kg p e r annum. The o i l c o n t e n t o f t h e

k e r n e l h a s been t e s t e d and found t o b e 4 0 . 8 8 p e r c e n t

by w e i g h t . T h e r e f o r e . 20 k g of k e r n e l may g i v e a n

y i e l d o f a b o u t 8 kg of seed o i l . The a n n u a l y i e l d of

o i l f rom one h e c t a r e of Manihot p l a n t a t i o n i s t h u s

e s t i m a t e d t o b e a p p r o x i m a t e l y 8 k g .

The i m p o r t a n t p h y s i c a l p r o p e r t i e s of t h e s e e d

o i l a r e g i v e n i n T a b l e 2 6 . P r o p e r t i e s of t h e s e e d o i l

f rom Hevea h a v e been r e p o r t e d by Pushpadas g .

( 1 9 8 0 D and a r e r e p r o d u c e d i n t h e same t a b l e f o r

cornpari s o n . I o d i n e v a l u e and s o p a n i f i c a t i o n v a l u e o f

t h e Manihot s e e d o i l a r e found t o b e v e r y c l o s e t o

t h o s e of H s e e d o i l . The h i g h i o d i n e v a l u e

i n d i c a t e s t h a t t h e o i l i s a s e m i d r y i n g one and h e n c e

cou ld f i n d a p p l i c a t i o n s i n p a i n t s and a l s o i n t h e

p l a s t i c s i n d u s t r y . The a c i d v a l u e of t h e o i l i s found

t o b e much lower compared t o t h a t of Hevea seed o i l .

However, i t must b e p o i n t e d out h e r e t h a t t h e Manihot

seed o i l was t e s t e d i m n e d i a t e l y a f t e r e x t r a c t i o n ,

which c o u l d b e one o f t h e r e a s o n s f o r t h e low a c i d

v a l u e o b t a i n e d .

CHAPTER 6

SUMMARY AND FUTURE PROSPECTS