PERCENT SOLIDS AND OTHER CHARACTERISTICS OF

PROGENY RESULTING FROM INTERSPECIFIC

TRISOMIC ONION BACKCROSSES

by

CARLOS A. OROZCO-CASTILLO, B.S.

A THESIS

IN

HORTICULTURE

Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for

the Degree of

MASTER OF SCIENCE

Approved

Accepted

December, 1986

^ -CJ^^ ACKNOWLEDGEMENTS

r ^ I would like to thank Dr. Ellen B. Peffley for her valuable

guidance, support, and time during the course of this study. Special

thanks to Dr. David B. Wester for his help with the statistical

analysis.

Thanks are also due to LASPAU-AID and Universidad de San Carlos de

Guatemala for their economic support to obtain this degree.

n

TABLE OF CONTENTS

ACKNOWLEDGEMENTS ii

ABSTRACT v

OBJECTIVES vii

LIST OF TABLES viii

LIST OF FIGURES x

I. INTRODUCTION 1

II. REVIEW OF LITERATURE 3 Studies on Trisomies 3 Morphological Features of Trisomies 5 Identification of Chromosomes by Giemsa C-banding Technique 7 Cytological Identification of Trisomies 9 Transmission of Extra Chromosomes in Trisomies. . . 10 Preferential Transmission of Alien Chromosomes. . . 12 Studies on Allium Percent Solids 13

III. MATERIALS AND METHODS 16

Germplasm 17 Experimental Design 17 Morphological Characterization of Trisomic Onion Backeross Populations 18 Determination of Percent Solids 20 Cytological Identification of Progency Resulting From Trisomic Onion Baekcrosses 20 Statistical Analyses 23

Analysis of variance 23 Multiple mean comparisons 23 Bartlett's Test for Homogeneous Variances 24 Kruskall-Wallis Test 24 Frequency Distributions 24 Goodness of Fit Test For a Normal Distribution 24

IV. RESULTS AND DISCUSSION 25 Morphological Characterization of Trisomic Onion Backeross Populations 25 Percent Solids of Progenies Resulting From Trisomic Onion Baekcrosses 28 Cytological Identification of Progeny Resulting From Trisomic Onion Baekcrosses 34

m

General Description of Trisomic Plants and Comparison of Morphological Features with Diploids 39 Relationship Between Percent Solids and Trisomies 41

V. CONCLUSIONS 43

VI. SUMMARY 44

LITERATURE CITED 46

APPENDICES 50

IV

ABSTRACT

Segregating populations derived from interspecific trisomic onion

baekcrosses were evaluated. The trisomic parents were DG 11, DG 33, DG

112 and DG 131. _A. cepa ev. 'Temprana' and the interspecific triploid

'Delta Giant' (2n Allium cepa + In Allium fistulosum) from which the

above trisomies were derived were also included in this experiment.

Morphological and cytological studies were conducted. Percent

solids was determined. Data obtained under field conditions failed to

distinguish trisomic from diploid plants. The trisomic backeross

populations had higher mean solids content than ev. 'Temprana' and

lower than 'Delta Giant'. Solids from 5.2 to 17.7 percent were found

in the segregating populations. The distribution of the solids content

of the various populations supports reported research that solids

content is quantitatively inherited, therefore selection should be

effective in increasing solids. Chromosome counts were made and the

extra chromosome was identified in all plants from the backeross

population DG 33 and in a group of plants with high solids from the

other segregating populations. The transmission rate of the extra

chromosome in the backeross population DG 33 was 3.08%. The same extra

chromosome belonging to the £. fistulosum genome was present in the

four segregating populations. All trisomic plants were found to have

high percent solids.

The results suggested that the extra chromosome possesses genes

that confer high solids content, which could be incorporated into A .

cepa. It was demonstrated that alien addition lines can be used to

introgress genes for high percent solids from A . fistulosum to

commercial onion varieties.

VI

OBJECTIVES

1. To characterize morphological features of four segregating

populations from interspecific trisomic individuals baekerossed to

A . cepa.

2. To determine percent solids and how this relates to the occurrence

of trisomic individuals in four segregating populations resulting

from interspecific trisomic onion baekcrosses.

3. To determine transmission rate of the extra chromosome in four

segregating populations derived from interspecific trisomic onion

baekcrosses.

4. To identify the extra chromosome that is transmitted in the

different populations resulting from interspecific trisomic onion

baekcrosses.

v n

LIST OF TABLES

1. Mean Values of Continuous Phenotypic Traits of Segregating Populations Derived From Trisomic Onion Baekcrosses, 1985 26

2. Bartlett's Test For Homogeneous Variances of Continuous Morphological Characters in Four Segregating Populations Derived From Trisomic Onion Baekcrosses, 1985 27

3. Transmission Rate of the Extra Chromosome in the Population DG 33, 1986 57

4. Chromosome Constituency of Plants With High Solids Content Derived From Interspecific Trisomic Backeross Populations, 1986 58

5. Percent Solids of Trisomic Plants in Four Populations of Trisomic Onion Baekcrosses, 1985-1986 59

6. Continuous Data of Trisomic Plants in Four Segregating Populations of Trisomic Onion Baekcrosses, 1985-1986 60

7. Ordinal Data of Trisomic Plants in Four Segregating Populations of Trisomic Onion Baekcrosses, 1985-1986 61

8. Mean Comparisons for Continuous Morphological Characters Between Trisomic and Diploid Plants in The Trisomic Backeross Population DG 33, 1986 62

9. Kruskal-Wallis Test for Comparison of Ordinal Phenotypic Traits Between Trisomic and Diploid Plants in the Trisomic Backeross Population DG 33, 1986. . . . 63

10. Analyses of Variance for the Continuous Character Percent Solids in Four Trisomic Backeross Populations, A . cepa ev. 'Temprana' and Interspecific Triploid 'Delta Giant' (2n A . cepa + In _A. fistulosum), 1985 64

11. Analysis of Variance for the Continuous Character Leaf Length in Four Trisomic Backeross Populations, 1985 65

12. Analysis of Variance for the Continuous Character Leaf Diameter in Four Trisomic Backeross Populations, 1985 . . . . 66

13. Analysis of Variance for the Continuous Character Bulb Diameter in Four Trisomic Backeross Populations, 1985 . . . . 67

• • •

vni

14. Analysis of Variance for the Continuous Character Bulb Height in Four Trisomic Backeross Populations, 1985 68

15. Analysis of Variance for the Continuous Character Leaf Length in Trisomic Plants From Population DG 33, 1986 . . . . 69

16. Analysis of Variance for the Continuous Character Leaf Diameter in Trisomic Plants From Population DG 33, 1986 . . . 70

17. Analysis of Variance for the Continuous Character Bulb Diameter in Trisomic Plants From Population DG 33, 1986 . . . 71

18. Analysis of Variance for the Continuous Character Bulb Height in Trisomic Plants From Population DG 33, 1986 . . . . 72

IX

LIST OF FIGURES

1. Mean percent solids of A . cepa ev. 'Temprana', A. fistulosum and interspecific triploid "^Delta Giant' (2n A . cepa + In A . fistulosum) 29

2. Mean percent solids of four trisomic backeross populations, A . cepa ev. 'Temprana' and interspecific triploid 'Delta Giant' (2n A . cepa + In A . fistulosum). Mean separation by LSD (5%) 31

3. Percent solids and percent progeny in four trisomic backeross populations, A. cepa ev. 'Temprana' and interspecific triploid "^Delta Giant' (2n A . cepa + In A . fistulosum) 32

4. Somatic metaphase chromosomes and karyotype of the trisomic plant DG131T6#20 51

5. Somatic metaphase chromosomes and karyotype of the trisomic plant DG33T10#20 52

6. Somatic metaphase chromosomes and karyotype of the trisomic plant DG112T4#32 53

7. Somatic metaphase ehrosomes and karyotype of the trisomic plant DG11T16#21 54

8. C-banded mitotic metaphase chromosomes of the trisomic plant DG112T9#5 55

9. C-banded mitotic metaphase chromosomes of the trisomic plant DG11T16#21 55

10. C-banded mitotic metaphase chromosomes of the trisomic plant DG33T10#11 56

11. C-banded mitotic metaphase chromosomes of the trisomic plant DG131T11#23 56

CHAPTER I

INTRODUCTION

In the United States, onions rank third in value and seventh in

acreage, among the eleven principal commercial vegetables, with 423.8

million dollars and 129,400 acres respectively in 1984 (50). In Texas

the onion was the number one commercial vegetable with a value of 87.5

million dollars in 1984 (48). Moreover, onions became first in acreage

with 24,600 acres in the same year (48).

Since the bulb onion (Allium cepa L.) is an important

horticultural crop, different sources of genetic variability and

several breeding methods and techniques are being used to improve

desirable commercial characteristics. One source is the use of related

species, e.g. Allium fistulosum as a means to introgress genes for

valuable characters (50). Crosses between ^. cepa and A . fistulosum

have been done, but the progeny has been highly sterile (11, 12). When

hybridization between species results in sterile offspring, the use of

aneuploids, especially their derived trisomies, becomes an important

mechanism to transfer favorable genes from one species to another (38,

44). Alien addition lines (2n = 2x + 1) which are trisomies that

contain an extra chromosome from other related species have been used

successfully in some cultivated plants to introgress genes from wild

species (38, 44). Savitsky (44) used this approach to transfer

nematode resistance from Beta proeumbens to Beta vulgaris. Recently,

alien addition lines were produced in onion, in order to incorporate

the favorable genes for pink root resistance from A . fistulosum to A.

1

cepa (35). These addition lines may also be useful to transfer other

valuable characteristics into commercial onion varieties (35). One

desirable characteristic is a high percentage of solids, which is found

in A . fistulosum (51).

Presently, there is research interest in increasing percent solids

(sucrose, glucose, fructose and oligosaccharides), and decreasing the

proportion of water in the onion. This is particularly important in

those eultivars used for commercial dehydration, since it would

increase the amount of processed product, while the production cost

remains constant. Other benefits of high solids include improved bulb

durability to withstand mechanical harvest, and cold hardiness.

The present study was undertaken to characterize morphological

features, and to determine the percent solid content in four

segregating populations resulting from interspecific trisomic onion

baekcrosses. In addition, transmission rate and identification of the

extra chromosome were determined. The results could be used in future

investigations for breeding and genetic purposes.

CHAPTER II

REVIEW OF LITERATURE

Studies on Trisomies

In plant populations, individuals can be found with chromosome

numbers different from the somatic number typical of the species.

Trisomic (2n + 1) individuals have one extra chromosome in the basic

diploid number (4).

Trisomic series have been used in cytogenetic and breeding

investigations of many crop species, e.g., Lotus peduneulatus (6),

Pennisetum typhoides (16), Solanum sp. (21), Avena strigosa (38),

Lycopersicon esculentum (41), Beta vulgaris (44), and Sorghum vulgare

(45).

Khush (23) and Burnham (4) discussed the following uses of

trisomies: to study the phenotypic effects of individual chromosomes;

to localize genes on specific chromosomes and to identify chromosomes

with their respective linkage groups.

Trisomies can also be important in breeding programs. Khush and

Rick (22) have suggested that the tertiary trisomies of tomatoes can be

used as fertility restorers in hybridization operations utilizing male

sterility. Trisomies that have the two related chromosomes carrying

the recessive male sterility gene and the extra chromosome carrying the

normal gene for fertility can be used as the male parent in crosses

with male sterile plants. All the progeny would be male sterile and

then no roguing is necessary. Rajhathy (38) has considered that the

use of alien addition lines, which contain an extra chromosome from

other related species, offers a controlled and efficient-method for the

transfer of agronomically useful genes from Avena strigosa to Avena

sativa. Savitsky (44) used alien addition lines to transfer nematode

resistance from Beta proeumbens to Beta vulgaris.

Trisomies may appear spontaneously in natural populations. They

also can be produced by using physical and chemical agents (23).

Of those spontaneously occurring, there are different sources of

trisomies among which are: normal disomies, asynaptie and desynaptic

disomies and polyploids (23).

Trisomies occurring spontaneously among the progeny of normal

diploids may be derived from n + 1 gametes produced occasionally as a

result of non-disjunction in the germ line of the somatic tissues or

during meiosis (4). The n + 1 gametes might also result from non-

eongression of a bivalent during metaphase I, so that it goes to only

one pole in telophase I (23).

Trisomies of spontaneous origin in normal diploids have been

isolated in Datura stramonium (3) and Lycopersicon esculentum (41).

In normal diploids, trisomies can also be produced by using

chemical agents such as colchicine and physical agents such as low

temperatures and different kinds of radiation (23). Colchicine was

used to induce trisomies in Collinsia heterophylla (9) and Antirrhinum

majus (43).

In asynapsis, the homologous chromosomes fail to pair during

zygotene, and in desynapsis the homologues pair initially but fall

apart later during meiosis. As a result a variable number of

univalents are present at metaphase I. Those univalents segregating at

random to the two poles produce microspores with extra chromosomes

which produce gametes yielding simple primary trisomies (4). Trisomies

from an asynaptie mutant were obtained in Glycine max (33). Trisomies

derived from desynaptic lines were obtained in Pennisetum americanum

(42) and Avena striqosa (38).

Another source of trisomies is the progeny of polyploids,

especially triploids (23).

During meiosis, each trisomic group of chromosomes in an

autotriploid might form a trivalent or a bivalent plus a univalent (4).

At anaphase I, homologous chromosomes begin to separate, and each of

the chromosomes in excess of the disomie number passes at random to

either pole. Therefore, the triploids produce gametes with different

chromosome numbers varying from n to 2n (23).

Trisomies have been obtained from progenies of triploids in

Lycopersicon esculentum (41), Clarkia unguiculata (51), Antirrhinum

majus (43), Sorghum vulgare (45), Lotus peduneulatus (6), Solanum sp.

(21), Beta vulgaris (44), and Pennisetum typhoides (16).

Morphological Features of Trisomies

For genetic investigations it is helpful if the trisomies are

distinguishable morphologically from the diploids as well as from one

another, because specific chromosomes and genes can be identified and

their effects on morphological characters can be detected.

In some species, trisomic individuals can be distinguished clearly

from the diploid condition by morphological features (3, 6, 16, 41, 42,

43). It is due to the change in genie balance caused by the addition

of the extra chromosome (4, 23).

In some species, such as Lycopersicon esculentum (41), and

Anthirhinum majus (43), trisomies grow more slowly and are usually

different from diploids in morphological characteristics, e.g., leaf

shape, fruit and flower form, leaf color and growth structure of the

plant. In these species (41, 43) the effect of a particular extra

chromosome in one organ was accompanied by a similar change in other

organs, which reflected the same genetic effects of the extra

chromosome on different parts of the plant (41, 43).

In Lotus peduneulatus (6) trisomies differed from diploids in

growth habit, size, shape of leaflets, color of leaves, and size and

shape of flowers. The differences among trisomies and diploids were

considered to be a result of a change in the genie balance, which was

due to the additional chromosome in the genomic complement (6).

In Avena strigosa (38) trisomies were found to be different from

diploids in quantitative characters, e.g., plant height, days to head

and the length of the panicle. A wide range for these characters was

found, some trisomies being higher and others lower in comparison with

diploids. It was considered (38) that loci on several chromosomes,

probably with complementary and epistatic effects determine the

trisomic phenotype.

In certain species, trisomies may not be distinguished from each

other or from disomie sibs (9, 21, 33, 51). In Clarkia unguiculata

(51), no significant effect of the extra chromosome on the mean of

variability of various phenotypic characters was observed. It was

concluded (51) that the environment and genetic background probably

caused variation that could obscure possible specific trisomic

phenotypes. In Glycine max (33) and Collinsia heterophylla (9) no

morphological alteration was found in a set of trisomic plants. It was

suggested (9, 33) that these species can tolerate considerable genetic

imbalance without changing the normal phenotype. In series of

aneuploids in the genus Solanum (21) no morphological differences were

detected in the segregations derived from crosses between trisomies and

diploid plants and in the successive generations after repeated

backcrossing. It was concluded (21) that this was probably due to the

highly heterozygous nature of the material and that the morphological

effects were masked by normal genetic segregations.

Identification of Chromosomes by Giemsa C-Banding Technique

Giemsa C-banding technique has been used for identification of

individual chromosomes and chromosome segments in plants and animals.

This method, which demonstrates constitutive heterochromatin, was first

applied to animal chromosomes and involves denaturation and

reassoeiation of DNA, with highly repetive DNA reassociating faster and

appearing as dark bands (13).

8

Giemsa C-banding technique has been used for identification of

chromosomes in different species, e.g. wheat (13, 46), rye (15) and

onion (10, 19, 53). This identification of chromosomes is done on the

basis of distribution, size, total number and total length of the bands

(13, 14).

Giemsa C-banding technique has been used for identification of

chromosomes of jA. cepa and its allies (10, 19, 20, 53). Results

reported by El-Gadi and Elkington (10) and Vosa (53) indicated that all

chromosomes in A . cepa and A . fistulosum have one band at each

telomere, except the chromosome arms with satellites, in which the band

is proximal to the nuclear constriction, Kalkman (20) reported that A .

fistulosum presents telomeric bands larger than A . cepa and that the

former species has shorter chromosomes than the latter one. Kalkman

(20) also reported the presence of intercalary bands in the chromosomes

2, and 7 of A . cepa.

Researchers have reported nomenclature systems for Al1ium

chromosomes which are based upon chromosome length and centromere

position. Giemsa C-banding technique has been used to assign a number

to the different chromosomes; i.e., El-Gadi and Elkington (10)

classified the smallest chromosome of A . fistulosum as No. 8, Vosa (53)

classified the smallest submetacentric chromosome as No. 6; and Kalkman

(19) classified the smallest submetacentric chromosome of ^. fistulosum

as No. 7.

Cytological Identification of Trisomies

Cytological identification of trisomies has been done (6, 16, 38,

41). After the cytological identification of a trisomic, the extra

chromosome can be related to its phenotypic effects. The extra

chromosome can also be identified in the earlier generations or in the

original parents, either for genetic or breeding purposes.

Identification of the extra chromosome can be done by cytological

observations at the mitotic metaphase stage. Using this procedure,

trisomies were identified in Avena Strigosa (38), Lotus peduneulatus

(6), and Lycopersicon esculentum (41).

The identification of the extra chromosome may also be possible

through cytological observations of meiotie cells at different stages

(pachytene, diakinesis, metaphase I, and anaphase I and II). Pachytene

analyses were used to identify the extra chromosome in trisomies of

Lycopersicon esculentum (41) and Sorghum vulgare (52). Cytological

observations of diakinesis and metaphase I led to the recognition of

the nature of trisomies in Avena strigosa (38) and Lycopersicon

esculentum (41).

Another method of identifying the extra chromosome is the use of

karyotype analysis. By comparing the chromosomes of trisomies with

standard karyotypes of the diploids, the extra chromosome may be

identified and a specific chromosome number can be assigned. This

method was used to identify trisomies in pearl millet (16).

Giemsa C-banding is another method (discussed earlier) used for

identification of trisomies. This technique is based on the

10

distribution, total number, size and length of dark bands of

constitutive heterochromatin. Giemsa C-banding technique was utilized

to identify additional chromosomes in wheat (31) and rye (13, 17).

Transmission of| Extra Chromosomes in Trisomies

Knowing the transmission rate of trisomic chromosomes is important

in understanding the degree of maintenance of trisomies. In

segregations from crosses between trisomic female and diploid male

plants, and the reciprocal crosses, diploid and trisomic individuals

theoretically appear in equal frequency (50%). However, in reality the

ratio of trisomies in the offspring is many times lower than the

expected frequency (3, 7, 25, 41).

The reduced transmission of the extra chromosome in trisomies has

been discussed by Khush (23). In crosses between trisomic females and

diploid males, factors that reduce transmission rate of the extra

chromosome are: elimination of the extra chromosome during meiosis due

to lagging or misdivision, or both; reduced viability of n + 1 spores

and gametophytes, subnormal development of trisomic zygotes, endosperm

and embryos; poor and delayed germination of trisomic seeds, reduced

vigor of trisomic seedlings and the effect of genetic background.

Transmission frequency of the extra chromosome is usually lower through

the male than the female (23) attributed to late maturity of n + 1

pollen tubes, abnormal development of n + 1 pollen tubes and failure of

n + 1 pollen to germinate.

11

On the above basis, researchers generally prefer the use of

trisomic females and diploid males to maintain trisomic lines, even

though low percent transmission is still obtained. Crosses between

trisomic females and diploid males have been done to maintain trisomic

lines and to study transmission rate of the extra chromosome in

different crops, e.g., Lycopersicon esculentum (41), Lotus peduneulatus

(7) and sorghum bicolor (25).

In Lycopersicon esculentum (41) it was observed that the percent

transmission was different according to the extra chromosome present,

lowest rates were 1.1% for chromosome 3 and 0.44% for chromosome 6, and

the highest, 24.7% for chromosome 4. In Lotus peduneulatus (7) the

lowest percent transmission was shown by the trisomic 'Pointed' with

2.91% and the highest by the trisomic 'Narrow' with 26.42%. In Sorghum

bicolor (25), lower transmission rates of trisomies were found, for

instance, the trisomic 'Stiff Branch' had 4.4% and 'Bottle Brush' had

0.5%.

Studies on transmission rate in Lotus peduneulatus (7) indicated

that there was a tendency for the shorter extra chromosome to be

transmitted more frequently than the longer ones. It has been

suggested (7) that the presence of an extra chromosome would cause

genie unbalance, and that this unbalance may cause abortion of some

gametes and zygotes. The longer the extra chromosome, the greater

would be the unbalance, and hence the less chance there would be for

gametes and zygotes to be viable.

12

Preferential Transmission of Alien Chromosomes

The production of alien chromosome addition lines has been used to

study individual chromosomes. Alien addition and substitution lines

are also important for the transfer of useful genetic variation into

economic species (35, 44). Savitsky (44) produced an addition line

with nematode resistance by backcrossing autotriploid hybrids of Beta

proeumbens to Beta vulgaris. By backcrossing this addition line to

Beta vulgaris the disease resistance was transferred into sugarbeet.

Peffley et al. (35), using baekcrosses from the interspecific triploid

variety 'Delta Giant' (2n _A. cepa + In A . fistulosum) to _A. cepa

cultivar 'Temprana', produced addition lines exhibiting putative pink

root resistance. It was suggested (35) that these addition lines could

facilitate the incorporation of disease resistance and other valuable

characters from A . fistulosum into ^. cepa varieties.

Recently unusual preferential transmission of alien chromosomes

has been reported (26, 31). Miller et al. (31) using aneuploids in an

attempt to produce a set of addition lines from Aegilops sharonensis to

the wheat variety 'Chinese Spring', produced only one addition line.

It was found that one chromosome of Ae. sharonensis was transmitted

preferentially. Miller et al. (31) suggested that the alien chromosome

persists in the wheat genome by either meiotie drive or in some way

inducing abortion of gametes that do not have it.

Maan (26) found similar results in Aegilops longissima and Ae.

sharonensis. It was observed that gametes with one Aegilops chromosome

were functional and those without the Aegilops chromosome did not

13

function, suggesting that there was a gametoeidal action of the

sporophyte having an Aegilops chromosome on the gametes lacking this

chromosome.

Studies on Allium Percent Solids

There has been considerable interest in increasing the solids of

onion eultivars used for commercial dehydration. High solids would be

economically important, since the processed product would increase with

the production cost remaining the same. High solid content may also be

important in the improvement of bulb durability of mechanically

harvested onions as well as perhaps indirectly increased cold

hardiness.

The bulb onion (A . cepa) has a relatively low percent solids (30,

50) when compared to Al1ium species. Because of the increase in solids

content related species may be used as sources of improvement. One

useful species, which has higher percent solids than A . cepa, is A .

fistulosum (50). High solids content would be valuable if

incorporated into A . cepa eultivars.

The hand refractometer, which measures percent solids, is

generally used in onion breeding programs to make selection of bulbs

with high solids. This is based on the correlation between percent

soluble solids and dry matter (28). Biryukov (1939), cited by Mann and

Hoyle (28) determined soluble solids in the onion bulb by using the

refractometer. His data showed a high correlation (0.96) between the

refractive index of onion pulp and the oven-percent dry weight; the

14

refractive index is highly related to percent solids content. Mann and

Hoyle (28) determined the percent of solids by measuring the refractive

index of juice expressed from the outer fleshy scales of the bulb in

different varieties of onions. The outer scales can be removed with

little injury to the bulb. They (28) found a high correlation between

refractometer readings and dry weight. This correlation varied between

0.89 and 0.93. Mann and Hoyle (28) concluded that, even though the

outer scales do not constitute a representative dry-weight sample,

their dry weight is sufficiently well correlated with bulb dry weight

to be practical for breeding purposes, since the relative values are

used only for comparisons.

The major portion of soluble solids in the onion bulb is composed

of carbohydrates, which represent 65% of the dry weight (2). The

principal soluble carbohydrates are sucrose, glucose, and fructose,

together with a series of oligosaccharides (1, 34). Sucrose, glucose

and fructose tend to increase from the outer to the inner scale (8),

while the oligosaccharides are absent in the outer scales and compound

more than half the soluble carbohydrates in the inner scales (1).

McCollum (30) determined solids content in the onion variety

'White Sweet Spanish' using a refractometer. An average solid content

of 7.9 percent was reported (30). Van der Meer and van Benekom (50)

compared percent solids in A . cepa and A . fistulosum. Although their

results showed different values on different sampling dates, values of

9.8% and 8.6% for A. cepa and values of 19.6% and 14.6% for ^_.

fistulosum were reported. ^. cepa always had proportionately much

lower solid content than A. fistulosum.

15

Since high solids is a valuable characteristic, there has been

interest in finding out whether it has exploitable genetic variation.

Hence inheritance of percent solids in the onion £. cepa has been

studied (30, 32, 54). Warid (54) determined heritability of percent

solids in crosses between eultivars 'Red Creole' and 'Calred', finding

a heritability from 76% to 81% in field grown populations. Warid (54)

concluded that four to ten gene pairs for solids were involved in the

crosses and that selection would have a positive effect in increasing

percent solids.

Owens (32) studied heritability of percent solids in different

commercial eultivars of onions and from their results, he suggested

that percent solids is due to accumulative gene action of relatively

small number of genes and that selection woud be effective to increase

percent solids. He also indicated that soluble solids is due to the

accumulative action of a small number of genes.

Even though there exists a high degree of variability for percent

solids for _A. cepa and that selection may be effective for high solids,

the use of alien addition lines offer the alternative to obtain gain in

percent solids in a shorter time than by selection. In addition, by

using alien addition lines, only those favourable genes for high solids

may be incorporated into the commercial onion varieties.

CHAPTER III

MATERIALS AND METHODS

The purpose of this research was to characterize morphological

features and to determine percent solids in four interspecific trisomic

onion backeross populations and to identify cytologically trisomic

plants in one backeross population. Plants from the four segregating

trisomic backeross populations which had high solids were also

analyzed cytologically.

Seeds from the four segregating populations were sown in Speedling

flats (*) in the greenhouse on January 16 and 17, 1985, and held until

transplanting (flag stage). Seedlings were transplanted to the field

on March 14 and 15, 1985. The data for morphological characterization

were taken during the mature vegetative stage of the plant. Plants

from the segregating populations were harvested by successive blocks.

The first block was harvested on June 4, 1985; the second block on June

11, 1985; and the last one was harvested on June 17, 1985. Percent

solids were determined by blocks. Bulbs were stored until replanting

in the field. Plants were replanted in the field on October 3 and 4,

1985. All plants of one backeross population and the plants from the

other segregating populations which had high solids were taken from the

field during the spring 1986, and their roots were removed. The stem

plates of the bulbs were placed in contact with water in plastic

The use of trade names in this publication does not imply endorsement by Texas Tech University of the products named.

16

17

containers and new root tips were obtained. Root tips were collected

for mitotic chromosome analyses.

Germplasm

The segregating populations studied were derived from trisomic

individuals baekerossed to diploid A . cepa cultivar 'Temprana'. The

trisomic parents were: DG 11, DG 33, DG 112 and DG 131. The cultivar

'Temprana' (2x) and the shallot variety 'Delta Giant' (3x), from which

the above trisomies were derived were also included in this study.

The generation of the trisomies used in this experiment were

obtained earlier by other researchers (35, 37) as follows: crosses

between A . cepa and A . fistulosum were done, and the genome of the

offpsring was duplicated by colchicine treatment, resulting in

tetraploids (48). Baekcrosses from these tetraploids to A . cepa were

made and as a result triploids were formed. One such triploid was

'Delta Giant' (37). Later crosses between 'Delta Giant' and ^. cepa

ev. 'Temprana' resulted, as was expected, in some trisomic types (35).

These trisomic types were baekerossed again to A . cepa ev. 'Temprana'.

The segregating populations derived from these baekcrosses are the

object of this study.

Experimental Design

The randomized complete block design (RCBD) with three blocks was

used for field evaluation of four backeross populations, _A. cepa ev.

18

'Temprana' and the variety 'Delta Giant'. The four backeross

populations DGll, DG33, DG112 and DG131 had 50 plants in each

replication. The ev. 'Temprana' and the variety 'Delta Giant' had only

18 plants in each replication due to the unavailability of enough

seedlings for transplanting.

Morphological Characterization of Trisomic Onion Backeross PopulationT

Morphological characters were evaluated for each plant under field

conditions. A . cepa and A . fistulosum have specific characters which

distinguish the species, and the expression of these characters in the

offspring, especially those from _A. fistulosum, might be useful for the

identification and recognition of trisomic plants.

The morphological parameters evaluated for each growing plant

under field conditions were:

Leaf length: The length (cm) of one green mature leaf measured from

the basal junction with the leaf sheath to the apex.

Leaf diameter: The diameter (cm) of one green mature leaf measured in

the middle of the leaf.

Leaf veination: Those plants which presented striation were assigned a

value of 1, and those plants without striation were

assigned a value of 2.

Leaf texture: Leaves were arbitrarily classified as to three kinds

of textures: Smooth (1), slightly undulated (2) and

heavily undulated.

19

Leaf shape: An arbitrary classification was determined for this

character as follows: 1 = flat leaf, 2 = triangular

leaf, and 3 = circular leaf.

Plant vigor: An arbitrary visual classification was determined for

this character, with a scale from 1 (poor vigor) to 10

(highly vigorous).

Bulb diameter: The maximum diameter of the bulb was measured (cm).

Bulb height: The height of the bulb (em) from the base to the top.

Bulb size: The size of the bulb was rated according to a scale

from 1 (small bulb) to 10 (large bulb).

Bulb shape: 1 = globe shaped, 3 = oval, and 5 = elongated.

Bulb color: White, yellow, brown, red, pink and purple.

Double bulb: Those plants with a single bulb were assigned a value

of 1, whereas those plants that had divided asexually

into two or more bulbs were assigned a value of 2.

Root vigor: Root vigor was rated from 1 to 10; 1 = poor vigor and

10 = highly vigorous.

For statistical analyses the morphological parameters of leaf

length, leaf diameter, bulb height and bulb diameter were classed as

continuous characters; the morphological characters plant vigor, bulb

size, bulb shape and root vigor were classed as ordinal.

20

Determination of Percent Solids

The refractometer was used to determine percent solids. A sample

of the two outermost fleshy scales of each bulb was removed and

chopped. This sample was placed in a garlic press and crushed. Then a

small amount of juice was squeezed onto the plate of a Zeiss hand sugar

refractometer. The readings were expressed as percentage concentration

of a sucrose solution and corrected according to the temperature

conditions under which they were done.

Cytological Identification of Progeny Resulting From Trisomic Onion Baekcrosses

Mitotic chromosomes of all progeny of the DG 33 population were

counted in order to determine the percent transmission of the extra

chromosome in one population. This information would be used to

correlate morphological characteristics reflected in the absence or

presence of the trisome.

Initially, for the cytological studies, an attempt was made to

select the population exhibiting the most variability for the

morphological parameters leaf length, leaf diameter, bulb height, bulb

diameter and percent solids. The Bartlett's test for homogeneous

variances revealed no significant differences in variability for the

above characters between populations, except for leaf length and bulb

height, in which the population DG 11 exhibited the most variability.

If the characters of leaf length and bulb height could be considered as

determinant factors for selection of the population for cytological

21

studies, this population would have to be DG 11. However, other

factors were also taken into consideration to select the population.

One selection factor was the presence of more live plants with high

percent solids (13-18%), since there could be a chance that plants with

high percent solids might be trisomies. It should be mentioned that

many plants that had high solids content in the four segregating

populations did not survive transplanting and growth through the

winter. The population that had more plants alive with high solids

content was DG 33 (22.3% of the progeny alive had high solids content).

A second selection factor considered was the population that showed the

highest mean percent solids. Analysis of variance and mean comparisons

revealed that of the four populations, DG 33 had the highest mean

percent solids. Under the above criteria, the population DG 33 was

selected for cytological studies.

In order to determine the chromosomal complement of plants with

high percent solids (13-18%) from the other segregating populations,

these were analyzed cytologically as well as high solids trisomic

individuals identified from the segregating populations were further

studied to assign to the extra chromosome a number in the genome.

For the cytological analyses, the root tips were pretreated with

8-hydroxy-quinoline at 4°C for 20 hours, to stop the mitotic process at

metaphase. Root tips were then fixed in 3:1 ethanol-glacial acetic

acid at 4°C for one hour. After fixation, root tips were hydrolyzed in

0.2 N HCl for 10 minutes at 57°C, and then stored in 70% alcohol. Then

root tips were squashed in aceto-carmine. Chromosome number was

22

counted at metaphase stage, using a Zeiss microscope. Only after at

least three definitive counts from more than one root was the number

recorded.

Giemsa C-banding technique was used to identify the extra

chromosome, in at least one trisomic plant from each segregating

population. The procedure for this technique was as follows: 1) root

tips were treated with 8-Hydroxy-quinoline for 20 hours at 4°C; 2)

washed in tap water and fixed for one hour in fresh cold ethanol-

glacial acetic acid 3:1 as above; 3) rehydrated in de-ionized water; 4)

hydrolyzed in 1 N HCl for 15 minutes at 60°C; 5) rinsed in 0.01 M

citric acid-sodium citrate buffer pH 4.5 pH 4.5-4.8 for 20 minutes,

softened in peetinase (1 unit/ml) and cellulase (32 units/ml) in the

same buffer for 45 minutes at 37°C; 6) placed in cold 45% acetic acid

at 4°C for 20 minutes to stop enzymatic action; 7) cheeked for good

spreads under the microscope with phase contrast; 8) squashed in 45%

acetic acid. The cover slips were removed by using the aerosol freezer

Histofreeze (*); 9) the slides were dried and stored overnight; 10)

hydrolyzed in 45% acetic acid at 60°C for 15 minutes; 11) washed gently

in tap water; 12) denatured in 5% Barium Hydroxide at 60 C for 8

minutes; 13) washed in tap water; 14) treated with 2xSSC (0.3 M NaCl

plus 0.03 M trisodium citrate, pH 7.0, at 60°C for 40 minutes;

* The use of trade names in this publication does not imply endorsement by Texas Tech University of the products named.

23

15) washed in tap water; 16) stained in 4% Gurr's R66 Giemsa in

sorensen's phosphate buffer solution at pH 6.8 for 60 minutes; 17)

rinsed in phosphate buffer and then in distilled water; and 18) air

dried and mounted in euparal.

Statistical Analyses

Analysis of variance

Analyses of variance were performed for the following purposes:

1) to determine differences in means for the character percent solids

among the four backeross populations, ev. 'Temprana' and variety 'Delta

Giant'; 2) to determine differences among the means of the four

backeross populations for the continuous characters leaf length, leaf

diameter, bulb diameter, and bulb height; and 3) to determine

differences between trisomies and diploid plants in the DG33 population

for the continuous characters leaf length, leaf diameter, bulb

diameter, bulb height and percent solids. All analyses of variance

appear in the appendix.

Multiple mean comparisons

In those continuous characters in which the analysis of variance

indicated significant difference among populations, means were compared

by using Fisher's Least Significant Difference Test (LSD). The same

test was also used to compare means between trisomic and diploid plants

in the DG 33 population for those continuous characters in which the

analysis of variance indicated significant difference.

24

Bartlett's test for homogeneous variances

The Bartlett's test was used in order to determine the trisomic

backeross population exhibiting the most variability for the characters

leaf length, leaf diameter, bulb diameter, bulb height and percent

solids. The error mean square of analysis of variance within

populations, was used as an estimate of the population variability, and

these estimates were used for the Bartlett's test.

Kruskal-Wallis test

The Kruskal-Wallis test was performed on computed contingency

tables in order to determine differences between trisomic and diploid

plants in the trisomic backeross population DG 33 for the ordinal

characters plant vigor, bulb size, bulb shape and root vigor.

Frequency distributions

Values of percent solids were grouped in different classes ranging

from 4.9% to 23% by increments of 1%. The percentage of plants in each

class of the variable percent solids was found for each population. A

contingency table was used to compute the above data.

Goodness of fit test for a normal distribution

The Kolmogorov-Smirnov goodness of fit for a normal distribution

was conducted to test normal distribution for the continuous character

percent solids in the four backeross populations DGll, DG33, DG112 and

DG131, A . cepa ev. 'Temprana' and variety 'Delta Giant'.

CHAPTER IV

RESULTS AND DISCUSSION

Morphological Characterization of Trisomic Onion Backeross PopulationT

Analysis of variance for the continuous phenotypic traits among

the distinct segregating populations derived from trisomic onion

baekcrosses showed significant differences for leaf diameter and no

significant differences for leaf length, bulb height, and bulb

diameter. T test (LSD) was used in those analyses of variance that

indicated significant differences with results appearing in Table 1.

The leaf diameter of DG 33 was significantly different from DG 11

and DG 131, but was not significantly different from DG 112. The leaf

diameter of DG 112 was significantly different from DG 131 but not

significantly different from DG 11.

The significant difference (P = 0.05) in leaf diameter is probably

due to the effect of the interaction between the environment and the

genotypes, since this character is of quantitative nature.

The Bartlett's test for homogeneous variance (Table 2) showed a

significant difference in variability for the characters leaf length

and bulb height between segregating populations and no significant

difference in variability for the characters leaf diameter, bulb

diameter and percent solids.

DG 11 exhibited the most variability for leaf length and bulb

height. Since leaf length and bulb height are probably controlled by

different genes, the significant difference for these characters in

variability could be due to the effect of cumulative genetic action of

25

26

Table 1. Mean Values for Continuous Phenotypic Traits of Segregating Populations Derived From Trisomic Onion Baekcrosses, 1985.

Populat

DG33

DG112

DGll

DG131

ion Leaf Length

39.42

37.97

37.93

37.50

NS

Leaf Diameter

0.91 a

0.86 ab

0.77 be

0.73 e

*

Bulb Height

5.00

4.74

5.00

4.91

NS

Bulb Diameter

5.65 a

5.39 ab

5.27 ab

4.77 b

NS

* = Significance at P = 0.05

NS = Not significant at P = .05

Means with the same letter are not significantly different (LSD test).

27

Table 2. Bartlett's Test for Homogeneous Variances of Continuous Morphological Characters in Four Segregating Populations Derived From Trisomic Onion Baekcrosses, 1985

.S2.

Population Leaf Leaf Bulb Bulb Percent Length Diameter Height Diameter Solids

DG 11 100.979 a 0.070 a 2.180 a 2.654 a 5.830 a

DG 33 66.745 b 0.058 a 1.258 b 2.069 a 4.789 a

DG 112 68.129 b 0.046 a 1.274 b 1.947 a 5.213 a

DG 131 69.764 b 0.061 a 1.491 b 2.158 a 4.322 a

* = Significance at P = 0.05

NS = Not significant at P = 0.05 2

S Variance for experimental error of analysis of variance of

blocks within populations

Variances with the same letter are not significantly different

28

different genes and the interaction between genotypes and environment.

McCollum (30) has reported heritability from 26% to 76% for bulb height

in onion populations, which reflects the purported additive gene action

on this character.

Percent Solids of Progenies Resulting From Trisomic Onion Baekcrosses

Percent solids of A . cepa ev. 'Temprana', _A. fistulosum and the

interspecific triploid 'Delta Giant' (2n A . cepa + In A , fistulosum)

were determined with results appearing in Figure 1.

The cultivar 'Temprana' (A . cepa) had the lowest percent solids

(6.7%). Van der Meer and van Benekom (50) reported that A . cepa has

low percent solids. The cultivar they assayed had 8.6%. McCollum (30)

reported that ^. cepa cultivar 'White Sweet Spanish' had an average of

7.9% solids.

In contrast, A . fistulosum had higher percent solids (20.1%).

These data are consistent with those of van der Meer and van Benekom

(50), who found a value of 19.2% solids for A . fistulosum. the slight

difference between values found in this study and those obtained by van

der Meer and van Benekom (50) is considered to be due to the different

environment and time under which the data were taken or to the

different eultivars of A . cepa and A . fistulosum used.

The high percent solids for Delta Giant (21.0%) was expected,

since this variety is a triploid derived from crosses between A . cepa

and A. fistulosum and it has been reported that the latter species has

high solids (50).

20

<yf>

16-

12.

29

20.1 21.0

(5

fcc

2a 8 6.8

K^ cgpa Au. fis*:--Jlgs^Jim •Delta Giar.t r - "

Figure 1. Mean percent solids of A. cepa cv. 'Temprana', A. fistulosum and interspecific triploid 'Delta Giant' r2n A. eepa~+" In A. fistulosum).

.30

The analysis of variance for percent solids showed significant

differences among the distinct populations. Figure 2 shows the

difference in means of percent solids between the populations.

DG 33 (11.44%) and DG 131 (11.40%) had lower percent solids than

Delta Giant (21%) but higher than the other populations. DG 11

(10.08%) and DG 112 (10.02%) had higher percent solids than cultivar

Temprana (6.8%) but lower than the others.

The fact that the segregating populations had significantly higher

percent solids than A . cepa ev. 'Temprana' and significantly lower than

'Delta Giant' indicates the putative occurrence of genetic

recombination during meiosis between cv. 'Temprana' and variety 'Delta

Giant' genomes. As a result intermediate values for solids content

were found in the offspring. The significant difference for percent

solids among the trisomic backeross populations also suggests that

recombination of different pairs of genes for solids content occurred

during the meiotie process. This reflects the additive genetic action

of genes for percent solids. Accumulative genetic action of genes for

percent solids in onions has already been reported by McCollum (30),

Owens (32) and Warid (54).

Progenies from each population diagrammed in Figure 3 showed that

'Delta Giant' possessed the highest solids of those plants assayed with

a range from 17% to 23%, whereas cultivar 'Temprana' (A . cepa)

possessed the lowest solids, with a range from 5 to 9%. This major

difference can be attributed to the genetic origin of these varieties.

31

21.0

20—

16—

^ 12-Q

O

10.02 . ,

11.44

8 — 6.8

4 —

Temprana'DGll2 DG11 DG131 DG33 'Delta Gianf a b b c c d-i I

PLANT POPULATIONS.

Figure 2. Hean percent solids of 4 trisomic backeross populations, A. cepa cv. 'Temprana' and interspecific triploid 'Delta Giant' (2n A. cepa + In A. fistulosum).

flean separation by LSD {S%) Ij Means with the same letter are not significantly

different (P>0.05).

32

U 14 II i 2 Tvv.

KU

u 14 1»

f f l n

8C33

S2

i ]i

14 It ft 2 Tu

0CU2 ocm

S2i

41-

22-

11-

14-

10-1

7 9 11 13 iS 17 19 21 23

S2i

44

22

IS

14'

10-

(

; ? 11 13 15 i; 1? n n

HKIW SOIIOS

QUIA ciur

Figure 3. Percent solids and percent progeny in four trisomic backeross populations, A. cepa ev. 'Temprana', and interspecific triploid "^DeHirGiant' (2n A. cepa^ + In A. fistulosum).

33

In the four populations derived from trisomic onion baekcrosses,

percent solids segregated widely with a range from 6.5 to 18% for DG

11, from 5 to 17% for DG 33, from 5 to 16% for DG 112 and from 5 to 18%

for DG 131.

Segregation for percent solids was found within all trisomic

backeross populations. Goodness of fit test for a normal distribution

showed a normal distribution for solids content for all populations,

except for population DGll. The deviation from a normal distribution

in the population DGll could be due to the absence of small values of

percent solids in this population compared with the other populations.

The smallest value in DGll for percent solids was 6.5% whereas the

smallest values in DG33, DG112 and DG131 were 5.6%, 5.15% and 5.2%,

respectively. The general normal distribution probably indicates the

quantitative inheritance of solids percent. This is consistent with

studies on inheritance of solids in some onion varieties (30, 32),

which showed that this character is due to the cumulative action of

different pairs of genes. A proportion of each backeross population

had high solids and since this character is quantitatively inherited,

selection for high solids should be effective. Results reported by

other researchers (30, 54) in some commercial onion eultivars indicated

a high heritability (76-81%) for solids, which means that selection

would be effective to improve this character. Therefore, interspecific

trisomic onion baekcrosses offer a good alternative to exploit genetic

variation for increasing solids content.

34

The high values of percent solids in a proportion of each

segregating population could be due to the random recombination of

different genes for high percent solids; since it has been shown that

percent solids is determined by the additive gene action of different

pairs of genes (32). An alternative explanation is that plants in this

range of high percent solids were trisomies, the extra chromosome

belonging to the A . fistulosum genome, and that high percent solids was

due to the presence of the extra chromosome (supported with cytological

data below). The additional chromosome possibly has genes that confer

higher percent solids.

Cytological Identification of Progeny Resulting From Trisomic Onion Baekcrosses

All plants from the DG 33 population were analyzed cytologically.

Of the 130 plants analyzed, 126 diploid and 4 trisomic plants were

found, with a trisome rate transmission of 3.08% (Table 3 in the

appendix).

The probability of transmission for any given chromosome is 50%;

however, different factors exist that reduce transmission (24). Some

of these factors could be: elimination of the extra chromosome during

meiosis due to lagging or misdivision, or both; reduced viability of n

+ 1 microspores and gametophytes; subnormal development of trisomic

zygotes, endosperms and embryos; poor and delayed germination of

trisomic seedlings, or by the effect of genetic background.

35

In this study, any one or a combination of these factors may have

contributed to the lower transmission rate. An additional

environmental factor, which may have reduced the number of trisomic

plants was plant mortality under field conditions. There is a

possibility that a higher proportion of the plants that did not survive

the harvest, transplanting and growth through the winter, were trisomic

plants and the apparent reduction in transmission reflected these

losses. Researchers agree that most of the trisomic plants of many

species are weaker than normal diploids and more sensitive to stressful

environmental conditions (41, 16).

Since the transmission rate of the trisomies was low in this

experiment, it is necessary to grow a large number of progenies from

trisomic baekcrosses to maintain the trisomic lines.

Chromosome counts of plants in other segregating populations that

had high solids (13-17.5%) were also recorded (Table 4 in the

appendix). Of 15 plants from DG 33 population, five were trisomies; of

10 plants from DG 11 population, two trisomies were found; and of 8

plants in DG 112 population, two were trisomic.

It should be reiterated that all the trisomic plants had high

solids (Table 5 in the appendix) and that these data give additional

support to the hypothesis that the high solids could be due to the

presence of the extra A . fistulosum chromosome; however, normal diploid

plants existed that had high solids. A possible explanation for high

solids could be that recombination for genetic material occurred

between the extra chromosome from A. fistulosum genome carrying genes

36

which code for increased sucrose synthesis and the respective

homoeologous chromosomes from ^. cepa. If trivalents were formed,

allowing for crossing over to occur, and the genes from A . fistulosum

may have been introgressed into jA. cepa, then a diploid plant would be

recovered with ^. fistulosum genes.

With regard to the identification of the extra chromosome,

karyotypie analyses of trisomic individuals from the four segregating

populations revealed that the same extra chromosome was present in all.

This extra chromosome was found to be submetacentric (Figures 4, 5, 6,

and 7 in the appendix).

Assigning a specific number to the extra chromosome transmitted

depends upon previously published classification systems. Chromosomes

of . cepa and _A. fistulosum have been numbered by Kalkman (19), El-

Gadi and Elkington (10), and Vosa (53),-who based their numbering

system upon chromosome length and centromere position. If one follows

Kalkman (19) the extra chromosome would be chromosome 7; if Vosa (53),

it would be chromosome 6; and if El-Gadi and Elkington (10), the extra

chromosome would be chromosome 8.

In this study, the extra chromosome will be assigned with the

number 8 which is compatible with the classification system of El-Gadi

and Elkington (10) who numbered the chromosomes in order of decreasing

length. Additional information of use in assigning this specific

number to the extra chromosome was that reported by Rees and Jones

(40), who indicated that the total chromosome DNA volume in nuclei of

^. cepa was 27% greater than that of -A. fistulosum. In this study the

37

relative length of the extra chromosome from i . fistulosum corresponded

in a similar proportion to the smallest chromosome of A . cepa (i.e., it

was approximately 24% shorter).

The identification of the extra chromosome allows the additional

chromosome and its phenotypic effects to be associated with some degree

of certainty. In this case, the extra chromosome probably has genes

that confer high solids, so that the chromosome could be identified as

a source of this characteristic in earlier generations or in the

original parents for breeding purposes.

Giemsa C-banding technique further confirmed that the same extra

chromosome was transmitted in the different progenies (Figures 8, 9, 10

and 11 in the appendix). All the chromosomes were observed to have

telomeric bands. This is consistent with studies of Giemsa C-bands by

el-Gadi and Elkington (10) who compared the Giemsa C-band karyotypes

and the relationship of jA. cepa and A . fistulosum, finding that both

species are characterized by all chromosomes having one band at each

telomere, except for chromosome arms with satellites, in which the band

is proximal to the nucleolar constriction.

As an observation, it may be pointed out that two of the

chromosome pairs in the A . cepa genome in the population DG 112 showed

intercalary C-bands (Figure 8). One chromosome showed one intercalary

band and the other showed tow intercalary bands. Results found by

Kalkman (20) revealed the presence of one intercalary band in the

chromosome 2, and two intercalary bands in the chromosome 7. In

accordance with Kalkman (20) the same numbers can be assigned to the

38

respective chromosomes with one and two intercalary bands found in this

study.

The extra chromosome from ^. fistulosum presented darker and

relatively larger bands than those of A . cepa and was smaller than the

other chromosomes in the mitotic and C-banded plates. This is in

accordance with Kalkman (20) whose results showed that telometrie bands

of A_. cepa are much smaller than those of A . fistulosum, whereas A .

cepa chromosomes are longer than those of A . fistulosum.

Karyotype analyses and C-banding technique revealed that the same

extra chromosome was transmitted in the four backeross populations.

One explanation for the apparent preferential transmission for the same

alien chromosome in all the populations might be the gametes containing

the alien chromosome transmitted, have competitive advantage over

gametes containing other extra chromosomes. Preferential transmission

of alien chromosomes has also been reported in other species (26, 31).

Miller et al. (31) found preferential,transmission of one

chromosome in production of addition lines from Alegilops sharonensis

to the wheat variety 'Chinese spring'. It was suggested that the alien

chromosome probably ensured its continued presence in the wheat

background by either conferring a competitive advantage to gametes

carrying it, or in some way preventing the functioning of gametes

lacking it. Similar results were reported by Maan (26) using Aegilops

longissima and Ae. sharonensis. It was observed that gametes without

the critical alien chromosome did not function. From his results, Maan

(26) suggested that probably the critical alien chromosome in the

39

sporophyte controlled the exclusive transmission of male and female

gametes carrying that extra chromosome.

The selective segregation of a chromosome in a breeding program

might be of importance, if it carried desirable characters. In the

ease of this study, there exists the possibility that the segregated

extra chromosome may confer a higher level of solids and that the

transfer of these genes to the £. cepa genome may be possible.

The size of the transmitted chromosome relative to the parental

genome may influence the preferential segregation of the extra

chromosome. The extragenetie material, carried on the trisome may have

an effect on the viability of the zygote and seed and the subsequent

establishment of the plant. The smaller the amount of extragenetie

material, the greater the chance for zygote viability and seed and

plant survival (7). In the present study, the same small extra

chromosome was transmitted in the different populations. This could

mean that zygotes, seeds, or plants with less extragenetie material are

more able to resist their genetic unbalance and to grow and survive

normally.

General Description of Trisomic Plants and Comparison of Morphological Features with Diploids

A total of 13 trisomies were found in the different segregating

populations. Continuous data, i.e., percent solids (Table 5), leaf

length, leaf diameter, bulb diameter, bulb height (Table 6) appear in

the appendix. Ordinal data, i.e., plant vigor, bulb size, bulb shape

40

and root vigor are shown in Table 7 (appendix). Additional descriptive

characteristics of the trisomic plants appear in the appendix. It may

be pointed out that all trisomic plants had leaves with striation which

indicates the presence of the A . cepa gene for this character in all

the trisomies found in the backeross populations. For the population

DG 33, an attempt was made to compare trisomies and diploids, even

though only four trisomies were found. Mean comparisons for the

continuous characters leaf length, leaf diameter, bulb diameter, bulb

height and percent solids (Table 8) and a Kruskal-Wallis test for the

ordinal characters plant vigor, bulb size, bulb shape and root vigor

(Table 9) appear in the appendix.

On the basis of the general description of trisomies and the

comparison between trisomies and diploids for the population DG 33,

there seemed to be a tendency for trisomic plants to be smaller than

diploid plants; however, the morphological differences are not \/ery

clear and probably not useful for trisomic identification in this

experiment.

The observations and data taken under field conditions failed to

provide clear morphological features that allowed trisomies to be

distinguished from diploids. Similar results were found in the genus

Solanum (21) and Clarkia unguiculata (51). In the genus Solanum (21)

morphological detection of trisomies was not possible, attributed to

the highly heterozygous nature of the material. In Clarkia unguiculata

(51) it was suggested that variation from environmental causes and

experimental error, as well as genetic background may mask possible

41

specific trisomic phenotypes. In this study, since onions are cross-

pollinated and highly heterozygous the expression of phenotypic

characteristics caused by the presence of the extra chromosome was

probably obscured.

Based upon karyotypie and C-banding studies, the trisome was

determined to be the same small chromosome in the four different

backeross populations. The relatively small amount of additional

genetic material which it carried was probably not enough to cause

severe disequilibrium in the general phenotype of the plant. Similar

effects were observed in Glycine max (33) and in the genus Collinsia

(10). It was suggested that in these species (10, 34) plants can

tolerate some genotypic unbalance and still function normally. The

results obtained in this research could mean that A. cepa can probably

tolerate some genetic unbalance without severe alteration of the normal

phenotype.

Relationship Between Percent Solids and Trisomies

The trisomic plants found in the four backeross populations had

high solids. It has been reported in this experiment that A .

fistulosum has relatively high solids, whereas ^. cepa has relatively

low solids (50). The same extra chromosome, which belongs to the A,.

fistulosum genome, was transmitted in the different populations

(Figures 3, 4, 5, and 6). Results reported in this study (30)

indicates that solids content is affected by the accumulative action of

a small number of genes.

42

On the basis of these results, it appears there is a relationship

between high percent solids and the trisomies. The extra chromosome

may have a linkage group conferring high solids carried together on the

extra chromosome; the result would be trisomic plants with higher

solids content. Furthermore, the presence of diploid plants with high

percent solids also suggest that introgression for genes from the small

A . fistulosum chromosome found in the trisomic plants can occur during

synapsis and crossing-over of meiosis allowing for sister chromatid

exchange. The occurrence of bivalent pairing and the existence of

homoeologous chromosomes in the two species, which supports the above

suggestion has been reported in interspecific hybrids between A . cepa

and A . fistulosum (6, 12). In crosses between the same two species,

multivalent pairing involving _A. fistulosum chromosomes, which allows

recombination between genomes has also been reported (12, 24, 27, 36).

This supports the hypothesis that genes conferring high solids could be

incorporated into the _A. cepa genome through further generations of

breeding. If this is so, the transfer of genes for high solids to the

commercial onion varieties, through interspecific hybridization using

trisomies may be possible.

CHAPTER V

CONCLUSIONS

1. The observations and data taken under field conditions failed to

provide clear morphological features that allow trisomies to be

distinguished from diploids in the trisomic backeross populations.

2. The trisomic backeross populations had significantly higher

percent solids than cv. 'Temprana' and significantly lower than 'Delta

Giant'.

3. Solids from 5.2 to 17.2% were found in the four trisomic backeross

populations.

4. The distribution of the solids content of the various populations

supports reported research that solids content is quantitatively

inherited. Therefore selection should be effective in increasing

solids.

5. All trisomic plants in the four segregating populations had high

percent solids, suggesting that the extra chromosome, which belongs to

the _A. fistulosum genome, fias genes that confer high solids content.

6. The percent transmission of the extra chromosome in the population

DG 33 was 3.08.

7. The same extra chromosome was present in the trisomic plants found

in the four segregating populations.

8. Alien addition lines (trisomies) can apparently be used to

introgress genes for high solids content from J . fistulosum to

commercial onion varieties.

43

CHAPTER VI

SUMMARY

The objectives of this study were to characterize morphological

features and to determine percent solids in four segregating

populations resulting from interspecific trisomic onion baekcrosses.

Moreover, transmission rate and identification of the extra chromosome

were determined.

The trisomic parents were: DG 11, DG 33, DG 112 and DG 131. The

cultivar 'Temprana' (2n _A. cepa) and the interspecific shallot variety

'Delta Giant' (2n A . cepa + In A . fistulosum), from which the above

trisomic individuals were derived were also included in this study.

Morphological characterization was conducted under field

conditions. On the basis of the data obtained it was not possible to

distinguish trisomic from diploid plants. Percent solids was

determined using the hand refractometer. The segregating populations

had significantly higher solids content than ev. 'Temprana' and

significantly lower than 'Delta Giant'. Percent solids segregated

widely in the trisomic backeross populations from 5.2 to 17.7%. The

distribution of the solids content of the various populations supports

reported research that solids content is quantitatively inherited;

therefore selection should be effective in increasing solids.

Chromosomes were counted and the extra chromosome was identified

in all plants from the backeross population DG 33 and in a group of

plants with high solids in the other segregating backeross populations,

The transmission rate of the extra chromosome in the backeross

44

45

population DG 33 was 3.08%. Karyotype analyses and C-banding technique

revealed that the same extra chromosome was present in all trisomic

individuals from the four backeross segregating populations. It was

determined that all trisomic plants had high percent solids.

The above results suggested that the extra chromosome, belonging

to the A . fistulosum genome, has genes that confer high solids, which

may be incorporated into A . cepa. Therefore, introgression of genes

conferring high solids from A . fistulosum to commercial onion varieties

may be possible through the use of alien addition lines.

LITERATURE CITED

1. Bacon, J.S.D. 1957. The water-soluble carbohydrates of the onion. Allium cepa L. Biochem. J. 67:5-6.

2. Bennet, E. 1941. The effect of storage on the carbohydrates of the Ebenezer onion. Proe. Amer. Soc. Hort. Soe. 39:293-294.

3. Blakeslee, A.F. and A.G. Avery. 1938. Fifteen-year breeding records of 2n + 1 types in Datura stramonium. Carnegie Inst. Wash. Publ. 501:315-351.

4. Burnham, C.R. 1Q74. Discussions in Cytogenetics. 393 pp. Univ. of Minnesota Press.

5. Cochran, F.D. 1950. A study of the species hybrid, Al1ium Ascolonicum and Allium fistulosum and its baekerossed progenies. Am. Soc. Hort. Sci. 55:293-296.

6. Chi-Chang, C. and W.F. Grant. 1968. Morphological and cytological identification of the primary trisomies of Lotus peduneulatus. Can. J. Genet. Cytol. 10:161-179.

7. and . 1968. Trisomic transmission in Lotus penduneulatus. Can. J. Genet. Cytol. 10:648-654.

8. Darbyshire, B. 1978. Changes in the carbohydrate content of onion bulbs stored for various times at different temperatures. J. Hort. Sci. 53:195-201.

9. Dhillon, T.S. and E.D. Garber. 1960. The genus Collinsia. X. Aneuploidy in £. heterophylla. Bot. Gaz. 121(3):125-133.

10. El Gadi, A. and T.T. Elkington. 1975. Comparison of the giemsa C-band karyotypes and the relationships of Allium cepa, Al1ium fistulosum and Allium galanthum. Chromosome 51:19-23.

11. Emsweller, S.L. and H.A. Jones. 1935a. An interspecific hybrid in Allium. Hilgardia 9(5):265-273.

12. and . 1935b. Meiosis in Allium fistulosuiriTTllium cepa and their hybrid. Hilgardia 9:277-288.

13. Endo, T.R. 1986. Complete idenitifieation of common wheat chromosomes by means of the C-banding technique. Jpn. J. Genet. 61:89-93.

46

47

14. Foskett, R.L. and C.E. Peterson. 1950. Relation of dry matter content to storage quality in some onion varieties and hybrids. Proe. Amer. Soc. Hort. Sci. 55:314-318.

15. Gill, A.S. and G. Kimber. 1974. Giemsa C-banded karyotype of Rye. Proe. Nat. Acad. Sci. USA 71, 1247-1249.

16. Gill, B.S., S.S. Virmani and J.L. Minoeha. 1970. Primary simple trisomies in Pearl Millet. Can. J. Genet. Cytol. 12:474-483.

17. Hutchinson, J., T.E. Miller and S.M. Reader. 1983. C-banding at meiosis as a means of assessing chromosome affinities in the triticaeeae. Can. J. Genet. Cytol. 25:319-232.

18. Jones, H.A. and L.K. Mann. 1963. Onion and their allies. Interscience Publishers, Inc. New York.

19. Kalkman, E.R. 1984. Analysis of the C-banded karyotype of Allium cepa L. Standard system of nomenclature and polymorphism. Genetica. 65:141-148.

20. . 1984. Cytotaxonomic studies in the genus Al1ium L. Usefulness of C-banding for description and classification. Proe. 3rd Eucarpia Allium Symposium, Wageningen, Holland, pp. 74-77.

21. Kessel, R. and P.R. Rowe. 1974. Interspecific aneuploids in the genus Solanum. Can. J. Genet. Cytol. 16:515-528.

22. Khush, G.S. and C M . Rick. 1967. Tomato tertiary trisomies: Origin, morphology and use in determining position of centromeres and arm location of markers. Can. J. Genet. Cytol. 9:610-631.

23. 1973. Cytogenetics of aneuploids. Academic Press. New York.

24. Levan, A. 1941. The cytology of the species hybrid Allium cepa x Allium fistulosum and its polyploid derivatives. Heredity. 27:253-272.

25. Liang, G.H. 1979. Trisomic transmission in six primary trisomies of Sorghum. Crop Sci. 19:339-344.

26. Maan, S.S. 1975. Exclusive preferential transmission of an alien chromosome in common wheat. Crop Sci. 15:287-292.

27. Maeda, T. 1937. Chiasma studies in Allium fistulosum, Allium ce£a and their F , F^ backeross hybrids. Jap. Gen. 13:146-159.

48

28. Mann, L.K. and E.J. Hoyle. 1945. Use of the refractometer for selecting onion bulbs high in dry matter for breeding. Proe Amer. Soe. Hort. Sci. 46:285-292.

29. McCollum, G.D. 1966. Heritability and genetic correlation of some onion bulb traits. Estimates from S, offspring on parent regression. J. Heredity 57:105-110.

30. ___ ^ 1968. Heritability and genetic correlation of soluble solids, bulb size and shape in white sweet Spanish onion. J. Genet. Cytol. 10:508-514.

31. Miller, T.E., J. Hutchinson and V. Chapman. 1982. Investigation of a preferentially transmitted Aeqilops sharonensis chromosome in wheat. Theor. Appl. Genet. 61:27-33.

32. Owens, E.W. 1951. The inheritance of dry matter in onion bulbs. M.S. Thesis. Univ. Idaho, Moscow, Ihado. 35 pp.

33. Palmer, R.G. 1976. Chromosome transmission and morphology of three primary trisomies in soybean (Glieine max). Can. J. Genet. Cytol. 18:131-140.

34. Pant, R., H.C. Agrawal and A.S. Kapur. 1962. The water soluble sugars and total carbohydrate contents of onion (Allium cepa), garlic, (Allium sativum) and turnip (Brassica rapa). Flora 152:530-533.

35. Peffley, E.B. 1984. Experimental introgression of Allium fistulosum into Allium cepa. Ph.D. Thesis. New Mexico State Univ. Las Cruees, New Mexico.

36. , J.N. Corgan, K.E. Korak and S.D. Tanksley. 1985. Eleetrophoretie analysis of Al1ium alien addition lines. Theor. Appl. Genet. 71:176-184.

37. Perkins, D.Y., A.E. Kehr, R.T. Brown, E.L. Tims and J.C. Miller. 1958. 'Delta Giant' - a new long season shallot. LSU Circular No. 52.

38. Rajhathy, T. 1975. Trisomies of Avena strigosa Can. J. Genet. Cytol. 17:151-166.

39. Reddi, V.R. and V. Padmaja. 1982. Studies on aneuploids of Petunia. Part I: Cytomorphological identification of primary trisomies. Incor. Appl. Genet. 61:35-40.

40. Rees, H. and R.N. Jones. 1977. Chromosome genetics. R. Lewis and J. Bernard (eds). Edward Arnold Press, pp.151.

49

41. Rick, C M . and D.W. Barton. 1954. Cytological and genetieal identification of the primary trisomies of the tomato. Genetics 39:640-666.

42. Sai, K.R., U.P. Singh, R.B. Singh and R.M. Singh. 1982. Cytomorphological behaviour of primary trisomies in pearl millet (Pennisetum americanum L. Leeke). Cytologia 47:503-510.

43. Sampson, D.R., A.W.S. Hunter and E.C Bradley. 1961. Triploid x diploid progenies and the primary trisomies of Antirrhinum majus. Can. J. Genet. Cytol. 3:184-194.

44. Savitsky, H. 1975. Hybridization between Beta vulgaris and B. procumbes and transmission of nematode (Heterodera schachtii) resistance to sugarbeet. Can. J. Genet. Cytol. 17:197-209.

45. Schertz, K.F. 1966. Morphological and cytological characteristics of five trisomies of Sorghum vulgare. Pers. Crop Sci. 6:519-523.

46. Seal, A.G. 1982. C-banded wheat chromosome in wheat and tritieale. Theor. Appl. Genet. 63:39-47.

47. Texas Department of Agriculture. 1984. Texas Vegetable Statistics.

48. Toole, M.S. and A.E. Clarke. 1944. Chromosome bahavior and fertility of colchieine-indueed tetraploids in Allium cepa and Allium fistulosum. Herbertia 11:295-303.

49. United States Department of Agriculture. 1986. Agricultural Statistics.

50. Van der Meer, Q.P. and J.L. van Bennekom. 1978. Improving the onion crop by transfer of characters from Allium fistulosum L. Biuuletyn Warzywinezy XXII. Instytut Warzynictwa-skierniewice.

51. Vasek, F.C 1962. Phenotypic variation of trisomies of Clarkia unguiculata. Am. J. Bot. Vol. 50-48:308-315.

52. Venkateswarly, J. and V.R. Reddi. 1981. Cytological studies of sorghum trisomies. Theor. Appl. Genet. 60:135-140.

53. Vosa, C G . 1976. Heterocromatic patterns in Allium. I. The relationship between the species of the cepa group and its allies. Heredity 36:383-392.

54. Warid, W.A.B. 1952. Inheritance studies in the onion. Allium cepa L. Ph.D. Thesis. Louisiana State Univ., Baton Rouge, Louisiana. 221 pp.

APPENDICES

50

51

:5-j

i Figure 4. Somatic netaohase chromosomes and karyotype of

the trisomic'plant DG131T6#20. The extra chromosome is arrowed.

52

, H- '.>-"; ^'^•'^. -i'-v*«•/,•.<.. ' .. ••

•/>r-'s-;:5< ',:

- * • • ' ^ . ,

iSki: "^i*

..-??.

r Figure 5. Somatic metaphase chromosomes and karyotype of

the trisomic plant DG33T10#20. The extra chromosome is arrowed.

53

It I Figure 6. Somatic metaphase chromosomes and karyotype of

the trisomic plant DG112T4#32. The extra chromosome is arrowed.

54

1^

I Figure 7. Somatic metaphase chromosomes and karyotype of

the trisomic plant DG11T16#21. The extra chromosome is arrowed.

55

^

• A - i ,a.|!.igi|^%jp<t

Figure 8. C-banded mitotic metaphase chromosomes of the trisomic plant DG112T9#5. The extra chromosome is arrowed, i = intercalary bands

= ^ S_ I ?•»! • ^ — F--^-'^^—= ? " Ill —3F=~ "^ -

5 ^ ^ * ^

Figure 9. C-banded mitotic metaphase chromosomes of the trisomic plant DG11T16#21. The extra chromosome is arrowed.

56

Figure 10. C-banded mitotic metaphase chromosomes of the trisomic plant DG33T10#11. The extra chromosome is arrowed.

Figure 11. C-banded mitotic metaphase chromosomes of the trisomic plant DG131T11#23. The extra chromosome is arrowed.

57

Table 3. Transmission Rate of the Extra Chromosome in the Population DG 33, 1986.

Plants Examined Diploids Trisomies Percent Transmission

130 126 4 3.08

58

Table 4. Chromosome Constituency of Plants With High Solids Content Derived From Interspecific Trisomic Onion Backeross Populations, 1986.

Population Total No. Plants Normal Diploids Trisomies

DG 131 15 10 5

DG 11 10 8 2

DG 112 8 6 2

59

Table 5. Percent Solids of Trisomic Plants in Four Populations of Trisomic Onion Baekcrosses (1985-1986).

Trisomic Plant

DG33T5#18

DG33T10#11

DG33T10#20

DG33T13#35

DG131T6#20

DG131T6#52

DG131T6#55

DG131T11#10

DG131T11#23

DG11T1#26

DG11T16#21

DG112T4#32

DG112T9#5

Percent Solids

15.50

15.50

13.20

13.80

15.95

.15.45

15.15

13.10

13.20

12.80

14.50

13.00

15.20

60

Table 6. Continuous Data of Trisomic Plants in Four Segregating Populations of Trisomic Onion Baekcrosses (1985-1986).

Population

DG33T5#18

DG33T10#11

DG33T10#20

DG33T13#35

DG131T6#20

DG131T6#52

DG131T6#55

DG131T11#10

DG131T11#23

DG11T1#26

DG11T16#21

DG112T4#32

DG112T9#5

Leaf Length

27.0

28.0

41.0

35.0

29.0

29.0

39.6

43.0

31.0

23.0

29.0

39.5

31.5

Leaf Diameter

1.0

1.0

0.9

1.2

0.6

0.9

0.6

0.8

0.8

0.6

1.4

0.9

0.8

Bulb Diameter

4.5

4.0

4.0

4.0

4.5

2.5

4.0

4.0

3.0

3.5

3.5

5.0

3.0

Bulb Height

3.5

3.5

4.0

3.5

4.0

2.5

6.5

5.5

3.5

3.0

3.5

4.0

3.5

61

Table 7. Ordinal Data of Tris urainai uata of Trisomic Plants in Four Segregating Populations of Trisomic Onion Baekcrosses (1985-1986).

Population

DG33T5#18

DG33T10#11

DG33T10#20

DG33T13#35

DG131T6#20

DG131T6#52

DG131T6#55

DG131T11#10

DG131T11#23

DG11T1#26

DG11T16#21

DG112T4#32

DG112T9#5

Plant vigor:

Bulb size:

Bulb shape:

Root vigor:

1

1

1

1

= poor

= small

= eireu

= poor

Plant Vigor

5

5

5

7

6

5

6

7

5

4

6

6

5

vigor, 10 =

bulb, 10 =

h-

Ic

lar, 3 = oval

vigor, 10 = hi

Bulb Size

4

4

4

4

4

3

6

6

3

4

3

5

3

ighly vigo

irge bulb

, 5 = elon

ghly vigo

rous

gated

rous

Bulb Shape

3

2

2

1

1

1

2

Root Vigor

4

7

5

5

9

5

8

9

6

5

5

6

5

62

Table 8. Mean Comparison for Continuous Morphological Characters Between Trisomic and Diploid Plants in the Trisomic Backeross Population DG 33, 1986.

Population

Diploids

Trisomies

Leaf Length

40.90 a

32.75 b

•

Leaf Diameter

0.93

1.025

NS

Bulb Diameter

-cm

5.95 a

4.12 b

*

Bulb Height

5.22 a

3.62 b

*

Solids

%

11.09

14.40

NS

* Significant at P = 0.05

NS = No significance

Means with the same letter are not significantly different (LSD test)

63

Table 9. Kruskal-Wallis Test for Comparison of Ordinal Phenotypic Traits Between Trisomic and Diploid Plants in the Trisomic Backeross Population DG 33, 1986.

Character

Test Statistic T

Plant Vigor

5.46

*

Bulb Size

7.29

*

Bulb Shape

0.27

NS

Root Vigor

3.49

NS

* = Significance at P = 0,05

NS = No significance at P = 0.05

64

Table 10. Analyses of Variance for the Continuous Character Percent Solids in Four Trisomic Backeross Populations, ^. cepa ev. 'Temprana' and interspecific triploid 'Delta Giant"M2"n A. cepa + In A . fistulosum), 1985.

Source

Block 2

Population 5

Experimental Error 10

Sampling Error 627

SS MS

38.97

2052.58

69.83

3081.26

19.48

410.52

6.98

4.91

58.81 *

PR > F

.0001

* = Significance at P = 0.05

65

Table 11. Analysis of Variance for the Continuous Character Leaf Length in Four Trisomic Backeross Populations, 1985.

Source d^ SS MS F PR > F

Block 2 957.95 478.98

Population 3 351.51 117.17 0.27 NS .85

Experimental Error 6 2634.95 439.16

Sampling Error 604 46269.11 76.70

NS = No significance at P = 0.05

66

Table 12. Analysis of Variance for the Continuous Character Leaf Diameter in Four Trisomic Backeross Populations, 1985.

Source

Block 2

Population 3

Experimental Error 6

Sampling Error 604

SS MS

0.21

3.22

1.09

35.25

0.11

1.07

0.18

0.06

5.94

PR > F

0.03

* = Significance at P = 0.05

67

Table 13 . Analysis of Variance f o r the Continuous Character Bulb Diameter in Four Trisomic Backeross Populat ions, 1985.

Source d^ SS MS F PR > F

Block 2

Population 3 69.16 23.05 3.96 NS 0.07

Experimental Er ror 6

Sampling Error 606

19.53

69.16

34.92

1338.80

9.76

23.05

5.82

2.29

NS = No s i g n i f i c a n c e at P = 0.05

68

Table 14. Analysis of Variance for the Continuous Character Bulb Height in Four Trisomic Backeross Populations, 1985.

Source

Block 2

Population 3

Experimental Error 6

Sampling Error 606

SS MS

0.65

5.95

26.61

940.64

.32

1.98

4.44

1.55

PR > F

0.45 NS 0.73

NS = No significance at P = 0.05

69

Table 15. Analysis of Variance for the Continuous Character Leaf Length in Trisomic Plants From Population DG 33, 1986.

Source d^ SS MS F PR > F

Trisomies 1 269.40 269.40 28.06 * .03

Experimental Error 2 19.20 9.6

Sampling Error 123 6813.79 55.40

* = Significance at P = 0.05

70

Table 16. Analysis of Variance for the Continuous Character Leaf Diameter in Trisomic Plants From Population DG 33, 1986.

Source d^ SS MS F PR > F

Trisomies 1 0.049 0.049 7.54 NS 0.11

Experimental Error 2 0.013 0.0065

Sampling Error 123 5.974 0.049

NS = No significance at P = 0.05

71

Table 17. Analysis of Variance for the Continuous Character Bulb Diameter in Trisomic Plants From Population DG 33, 1986.

Source d^ SS MS F PR > F

Trisomies 1 11.16 11.16 131.29 * .008

Experimental Error 2 0.17 0.0085

Sampling Error 124 214.68 1.73

* = Significance at P = 0.05

72

Table 18. Analysis of Variance for the Continuous Character Bulb Height in Trisomic Plants From Population DG 33, 1986.

Source SS MS PR > F

Trisomies 1

Experimental Error 2

Sampling Error 124

9.45

0.28

135.16

9.45

0.14

1.09

67.5 .014

* = Significance at P = 0.05

73

GENERAL DESCRIPTION OF TRISOMIC PLANTS

DG33 T5 #18: Plant vigor 5, leaf with striation and smooth texture,

flat leaf shape, bulb size 4, bulb shape 1, double bulb, bulb color

white, root vigor 4, and solids 15.45%.

DG33 TIO #11: Plant vigor 5, leaf with striation and smooth texture,

flat leaf shape, bulb size 4, bulb shape 1, double bulb, bulb color

white, root vigor 7, and solids 15.15%.

DG33 TIO #20: Plant vigor 5, leaf with striation and texture slightly

undulated, triangualr leaf shape, bulb size 4, bulb shape 1, single

bulb, bulb color white, root vigor 5, and solids 13.2%.

DG33 T13 #35: Plant vigor 7, leaf with striation and texture slightly

undulated, flat leaf shape, bulb size 4, bulb shape 1, single bulb,

bulb color white, root vigor 5, and solids 13.8%.

DG131 T6 #20: Plant vigor 6, leaf with striation and smooth texture,

triangular leaf shape, bulb size 4, bulb shape 2, double bulb, bulb

color white, root vigor 9, and solids 15.95%.

DG131 T6 #52: Plant vigor 5, leaf with striation and texture slightly

undualted, triangular leaf shape, bulb size 3, bulb shape 1, single

bulb, bulb color white, root vigor 5, and solids 15.45%.

DG131 T6 #55: Plant vigor 6, leaf with striation and smooth texture,

leaf with triangular shape, bulb size 6, bulb shape 3, single bulb,

bulb color purple, root vigor 8, and solids 15.15%.

DG131 Til #10: Plant vigor 7, leaf with striation and smooth texture,

triangular leaf shape, bulb size 6, bulb shape 2, double bulb, bulb

color yellow, root vigor 9, and solids 13.2%.

74

DG131 Til #23: Plant vigor 5, leaf with striation and texture slightly

undulated, triangular leaf shape, bulb size 3, bulb shape 2, single

bulb, bulb color white, root vigor 6, and solids 13.2%.

DGll Tl #26: Plant vigor 4, leaf with striation and smooth texture,

triangular leaf shape, bulb size 3, bulb shape 1, single bulb, bulb

color white, root vigor 5, and solids 12.8%.

DGll T16 #21: Plant vigor 4, leaf with striation and smooth texture,

flat leaf shape, bulb size 3, bulb shape 1, single bulb, bulb color

white, root vigor 5, and solids 14.5%.

DG112 T4 #32: Plant vigor 6, leaf with striation and texture slightly

undulated, flat leaf shape, bulb size 5, bulb shape 1, single bulb,

bulb color white, root vigor 6, and solids 13.0%.

DG112 T9 #5: Plant vigor 5, leaf with striation and smooth texture,

triangular leaf shape, bulb size 3, bulb shape 2, double bulb, bulb

color white, root vigor 5, and solids 15.2%.