34

Review of literature

35

2. REVIEW OF LITERATURE

2.1 Cucumis sativus L.

Cucumber (Cucumis sativus L.) is one of the most important member

of Cucurbitaceae family. These are widely grown and consumed all over the

world either raw or in pickled form. Within the species, wide variation with

respect to bearing habits, maturity, yield, shape, size, colour, spines, vine

habit, etc. of the crop has been observed in India. C. sativus houses several

botanical varieties including var. sativus, the cultivated cucumber and the

wild, free-living var. hardwickii (R.) Alef. (Kirkbride, 1993). Wild African

Cucumis species (melon; 2n = 2x = 24) are cross incompatible with

cucumber, which are themselves cross-incompatible (Kroon et al., 1979).

Likewise, the wild, free-living C. hystrix is only sparingly fertile with

cucumber (Chen et al., 1995; 1997a, b). This species is found only in the

Yunnan Province of Southern China, and India, it has a unique genetic

attributes that make its taxonomic determination complex. The contribution

of landraces as source material for crop improvement has been substantial. In

the past, the majority of released cultivars have been developed through

selection from landraces. To meet the challenges in crop improvement, efforts

were made to widen the genetic base by collecting and conserving germplasm

across the world, which led to assembly of large collections at national and

international gene banks. Genetic markers that are associated with

economically important traits can be used by plant breeders as selection tools

(Darvasi and Soller, 1994).

36

Cucumber plant collection expeditions were undertaken by the U.S.

government in the early part of the 20th century to acquire vegetable

germplasm from Asia. These included expeditions led by D. Fairchild in

1901, B. Lathrop and A. Armour in 1902, J. F. Rock in 1920 / 1921, W.

Koelz in 1939 / 1948, and H. S. Gentry in 1953 (U.S. National Agricultural

Archives, Geil and Giel files). Since 1953, cucumber (C. sativus var. sativus

and C. sativus var. hardwickii) germplasm donated by international public

and private sources has resulted in the formation of a U.S. NPGS cucumber

collection consisting of approximately 1,360 accessions (personal

communication, K. Reitsma, NPGS, Ames, Iowa, 1994). Approximately 194

accessions (~14 %) were obtained directly from India. In 1992, the U.S. and

Indian governments sponsored an expedition to collect Cucumis spp. in the

states of Rajasthan, Madhya Pradesh, and Uttar Pradesh, 184 cucumber

collections were made from these states. An assessment of the U.S. NPGS

cucumber collection by Meglic et al. (1996) included 46 accessions of direct

Indian origin acquired before 1972. There were no cucumber accessions

received from India between 1972 and 1992. The 1992 U.S. / India expedition

increased the cucumber collection ~11 % and represented a three-fold

increase in accessions from India (Staub et al., 1997a).

Even in the original home of cucumber, the whole range of variability

has not even been collected and conserved. A collection of only 230 land

races covering 5 taxa of Cucumis are being maintained in different research

institutes in India in comparison to 1043 land races covering maximum

37

available species in U. S. gene bank. Similarly, Russia has 2767 and the

Netherlands has 1930 accessions of cucumber in their respective gene banks

(Esquinas-Alcazar and Gulick, 1983; Sharma and Hore, 1996).

2.1.1 Morphological variability

Genetic diversity in plants has traditionally been established using

morphological and biochemical markers. Phenotypic characterization is the

first step in the description and classification of genetic resources (Smith et

al., 1987). The development of both procedures for characterization of

genetic diversity and reducing collection size to manageable and accessible

levels (core size) are important issues in Gene bank studies. Bio-agronomic

characterization carried out by means of appropriate statistical methods continues to

be a useful tool for the initial description and classification of germplasm, since it

enables plant breeders to identify and select valuable genetic resources for direct use

by farmers or in cucumber breeding programmes (Afangideh and Uyof, 2007;

Hossain et al., 2010; Manohar and Murthy, 2011a; Ngouajio et al., 2006; Staub et al.,

1997b). Unique plant architectural traits (i.e., sex expression, Multiple Lateral

Branching (MLB), fruiting habit, and development) that have potential for increasing

yield in commercial cucumber have been identified in exotic germplasm (Wehner et

al., 1989; Staub et al., 1985). Typically, new, high yielding lines and hybrids are

produced through population development followed by line extraction (Staub and

Bacher, 1997). Serquen et al. (1997b) suggest that few genes (5 to 8) control days to

anthesis, sex expression, main stem length, MLB, and fruit number and fruit weight.

All of these traits are considered to be components of yield in cucumber. Serquen et

38

al. (1997a) found three QTLs (Quantitative Trait Loci) associated with the MLB trait

that explained approximately 60 % of the observed phenotypic variance. These

attributes make MLB a likely candidate for the application of indirect selection

procedures to increase yield in cucumber. The increase in the number of branches

from marker assisted selection was comparable to phenotypic selection after

two generations of backcrossing (Fazio et al., 2003a). Pyramiding QTL for

MLB in cucumber using inbred backcross lines were reported by Robbins et al.

(2008). Lower and Edwards (1986), Wehner (1989), Staub and Bacher (1997)

stated that the effect of sex expression on yield is not in total yield over

multiple harvests, but on early yield and single harvest. The genetics of sex

expression in cucumber has been widely studied and reviewed by several authors

(Lower and Edwards, 1986; Mibus and Tatlioglu, 2004; Staub and Bacher, 1997;

Tatlioglu, 1993), since cucumber is considered a model organism for sex expression

in plants.

2.1.2 Molecular variability

Although morphological (visualized as a phenotype, such as flower

color) and biochemical markers (allelic variants of functional enzymes, also

referred to as isozymes) were historically valuable, their paucity and

variability due to environmental conditions and developmental stages limit

their effectiveness in diversity analysis. The large majority of currently

utilized markers are DNA-based, because they are relatively abundant, not

influenced by the environment, and do not effect the phenotype (Collard et

al., 2005; Gupta et al., 1999; Staub et al., 1996). Molecular markers have

39

been employed to characterize the genetic diversity present in the cucumber

collection (Knerr et al., 1989; Meglic et al., 1996). The degree of genetic

diversity in cucumber is relatively low compared with other cross-fertilized

species of Cucumis (Dane, 1976; 1983; Esquinas-Alcazar, 1977; Knerr et al.,

1989). An assessment of 753 accessions in the NPGS cucumber collection

using 21 isozyme loci revealed that an average of 1.4 loci were polymorphic

per enzyme system and 2.2 alleles were present per polymorphic locus

(Meglic et al., 1996).

Dijkhuizen et al. (1996) compared isozyme (14 loci) and RFLP (30

mapped and 104 random loci) variation in cucumber accession. Staub et al.

(1997b) compared the isozyme and RAPD variation observed in diverse

cucumber accessions of known pedigree. Staub et al. (1997b; 1999) and Mliki

et al. (2003) have studied the variations in accessions among cucumbers in

NPGS collections from Africa, India and China, and stated that all the

collections differ from each other.

Various types of markers are used to identify the genetic variability in

cucmbers: RFLP (Dijkhuizen et al., 1996), RAPD (Horejsi and Staub, 1999;

Manohar and Murthy, 2011a; Staub et al., 1997b, 1999), AFLP (Li et al.,

2004), ISSR (Manohar and Murthy, 2011a; Wang et al., 2007; Yeboah et al.,

2007), SSR (Danin-Poleg et al., 2001) and EST-SSR (Expressed Sequence

Tags- Simple Sequence Repeats; Jainbin Hu et al., 2010). From all these

studies, different estimates for the degree of genetic variation were obtained,

reflecting the differences in the selected sets of genotypes or marker systems.

40

Molecular markers have also been used to characterize the haploids

and diploids among cucumber (Smiech et al., 2008). Molecular markers have

several uses in plant breeding programs, including genetic map construction,

gene tagging, marker-assisted selection (Collard et al., 2005), identification

of QTLs (Bradeen et al., 2001; Fazio et al., 2003b; Kennard et al., 1994;

Knerr and Staub, 1992; Li et al., 2005; Meglic et al., 1996; Park et al., 2000;

Pierce and Whener, 1990; Serquen et al., 1997a; Wang et al., 2005; Sun et

al., 2006; Yuan et al., 2008a, b) and genomic library development (Guan et

al., 2008; Meyer et al., 2008; Nam et al., 2005) in cucumbers. Genome

research of cucumber has made progress recently, and some cucumber genetic

linkage maps have been constructed based mainly on RAPD (Meglic et al.,

1996; Serquen et al., 1997a), RFLP (Park et al., 2000), AFLP (Kennard et al.,

1994; Park et al., 2000), SSR (Bradeen et al., 2001), SRAP (Sequence

Related Amplified Polymorphism, Pan et al., 2005) and SCAR (Fazio et al.,

2003b). These genetic maps are an invaluable resource that can be used not

only to map important agronomic traits or QTL, but also to anchor physical

maps.

2.1.3 Disease resistance

Diseases lead to heavy loss in cucumber production. The most

widespread and damaging pathogens in cucumbers are: Powdery mildew,

Downy mildew, Scab, Blotch or target spot, Angular leafspot, Fusarium wilt

(Lebeda, 1986; Lower and Edwards, 1986; Pivovarov, 1984; Yurina, 1984;

1987; Yurina et al., 1998). In some years, yield loss to disease can be 50-70

41

%. The most cost effective way of combating diseases is the screening for

disease resistance varieties and production of cucumber hybrids with multiple

disease resistance. Thus, collection and screening for various disease

resistance in the own land of cucumber must be the priority. Screening for

disease resistance needs to be confirmed by both molecular markers and field

trial. To fulfill the screening techniques primers specific to disease resistance

or closely linked to it has to be identified.

Block (2005) has screened for resistance to Powdery mildew in 997

cucumber accessions available in the U.S. NPGS in greenhouse condition

following the inoculation technique and identified them. The molecular

marker linked to cucumber Powdery mildew resistance has rarely been

reported. Zhang et al. (2007) found an AFLP marker linked to Powdery

mildew resistance. Liu et al. (2008) has located three QTLs for Powdery

mildew in cucumbers. Park et al. (2004a) used molecular markers tightly linked to

ZYMV resistances from cucumber and melon for comparative mapping. A population

of F7 recombinant inbred lines (RILs) was made from a cross between susceptible

and resistant lines of cucumber in order to study Powdery mildew resistance loci by

Sakata et al. (2006). Susceptibility to Powdery mildew in the F7 RIL individuals

showed a continuous distribution from susceptible to resistant, suggesting that

Powdery mildew resistance is controlled by QTLs. Inheritance of Powdery mildew

resistance in three crosses, and linkage of resistance with AFLP markers were studied

to formulate efficient strategies for breeding cultivars resistant to Powdery mildew by

Zhang et al. (2007). Smiech et al. (2008) identified RAPD molecular markers

42

associated with Downy mildew resistance. The cucumber red beetle, Acalymma

vittatum, is a beetle of the family Chrysomelidae and a serious pest of cucurbit crops

in both larval and adult stages. Cucumber beetles can cause significant amounts of

foliar damage to cucurbit crops, particularly to older plants, and larval root feeding

also damages the plant. Unfortunately, effective control techniques beyond pesticides

are few, which may lead to increased soil pollution. So, screening for resistant variety

is of at most necessary for protection against the beetle.

2.1.4 Fatty acid analysis

The world’s supply of vegetable oils is currently in excess of 100 million

metric ton. The demand is increasing at a rapid pace due to increasing demand for

non-food uses of vegetable oil, for example in biodiesel, oleochemicals, lubricants,

pharmaceuticals, and cosmetics. However, only about 12 of the ~500,000 known

plant species are currently commercially exploited to produce vegetable oils in order

to meet the world’s increasing demand (Mabaleha et al., 2007). Many Cucurbitaceae

seeds are rich in oil and protein, and although none of these oils has been utilized on

an industrial scale, many are used as cooking oil in some African countries and in the

Middle East (Al-Khalifa, 1996). Carreras et al. (1989) studied the chemotaxonomy of

seed lipids of 11 Cucurbitaceae seed oils for physical and chemical viewpoint. The

fatty acids, as methyl esters were studied by Gas Liquid Chromatography (GLC) and

the resulting data were processed by a multivariate statistical analysis for confirming

the taxonomic relations among them. Mariod and Matthaus (2008) studied the

proximate analysis of seeds and physicochemical properties of oils extracted from six

Sudanese Cucurbit seeds C. melo var. agrestis, C. melo var. flexuosus, C. sativus, C.

43

lanatus var. colocynthoides, C. prophetarum, and L. echinata. Abiodun and Adeleke

et al. (2010) evaluated the proximate and mineral analyses from seeds of

Cucumeropsis manni (Naudin), Cucumis sativus, Leganaria siceraria and

Cucumeropsis edulis (Hook). Fokou et al. (2009) studied the chemical properties of

Cucumeropsis manii, Curcubita macima, Cucurbita moschata, Lagenaria siceraria

and Cucumis sativus from different areas in Cameroon and the value for the

saponification, iodine and peroxide index was within recommended levels for edible

oils. These oils have four main fatty acids: Linoleic acid (49-69 %); oleic acid (9-25

%), stearic acid (7-11 %) andpalmitic acid (10-19 %).

2.2 Cucumis melo L.

Melon (Cucumis melo L.) is one of the important horticultural crop

grown worldwide and plays an important role in international trade. Different

forms of melon are known and are morphologically distinct and have

different uses. C. melo is more polymorphic than other species in the genus

(Pitrat et al., 2000). Such polymorphism is highest in the fruit related traits.

There have been several attempts to taxonomically subdivide melons into

sub-species, botanical varieties or groups. Naudin (1859) proposed a

classification of the species into 10 botanical groups after extensive study of

the diverse forms. Naudin’s classification remained a basis for melon intra-

specific classification with amendments being brought about by several

authors (Munger and Robinson, 1991; Robinson and Decker-Walters, 1997;

Whitaker and Davis, 1962). Pitrat et al. (2000) proposed the most recent

classification of the species C. melo following the basic taxonomic rank of

44

the International Code of Botanical Nomenclature (Greuter et al., 1994). C.

melo is subdivided into two subspecies: C. melo ssp. agrestis (Naud.) Pangalo and C.

melo L. ssp. melo. (Greuter et al., 1994; Kirkbride, 1993; Pitrat, 2008; Whitaker and

Davis, 1962). The ssp. agrestis was classified into five botanical varieties,

while the ssp. melo was classified into ten (Pitrat, 2008).

ssp. agrestis ssp. melo

Nonsweet acidulus, conomon, momordica

chate, flesuosus, tibish

Sweet makuwa, chinensis adana, ameri, cantalupensis,

chandalak, reticulates, inodorus

Fragrance dudiam

2.2.1 Morphological variability

The success of any crop improvement programme depends on the

magnitude of genetic variability existing in the germplasm. Genetic diversity

has been estimated for all the major crops (Akashi et al., 2002; Di-Hong et

al., 2004; Park et al., 2004b). The greater range of variability in the initial

material would ensure better chances of producing desirable genotypes

(Vavilov, 1951). With the help of statistical advances in the past, it was

possible to elaborate methods of measuring the variation (Mather, 1952).

The biological variation and technical issues associated with the assessment of

genetic diversity in melon typify the problems inherent in the germplasm

management of Cucurbits. Cultivated melon is a horticulturally important,

45

morphologically diverse, out-crossing species of Cucurbitaceae, because melon

differs widely in plant and fruit characters. Gene banks in different countries are

active in the collection of melons, among them the largest collections are held at

Russia (2900 accession), United States of America (2300 accession), France (1800

accession) and China (1200 accession). Collections are still been made and analysis

of variations are conducted.

The assessment and description of trait variation are important tasks in the

start-up of programme aimed at the selection of genotypes with high-yield

performance and qualitative traits useful to markets. In addition, studies on genetic

variation of genetic resources under safeguard and collecting are of value to perform

efficient phases in conservation and avoid storage of redundant germplasm that

contributes to increase in the cost of germplasm management (Kumar, 1999;

Ricciardi and Filippetti, 2000). Therefore, development of both procedures for

characterization of genetic diversity and reducing collection size to manageable and

accessible levels (core size) are important issues in genebank studies (Brown, 1989;

Frankel, 1984; Marshall, 1990). Although it has been noticed that molecular

characterizations using several classes of molecular markers has resulted in effective

characterization of genetic resources of C. melo (Garcia et al., 1998; 2000; Ricciardi

et al., 2001; 2002; 2003; Silberstein et al., 1999; Staub et al., 2000), bioagronomic

characterization carried out by means of appropriate statistical methods continues to

be a useful tool for the initial description and classification of germplasm, since it

enables plant breeders to identify and select valuable genetic resources for direct use

by farmers or in breeding programmes. There are many reports based on the

46

variations of melons based on agronomic traits (Dhillon et al., 2007a; Escribano and

Lazaro, 2009; Fergany et al., 2010; Garcia et al., 1998; Liu et al., 2004; Staub et al.,

2004; Zalapa et al., 2007).

Swamy et al. (1985) analyzed 20 quantitative characters in 45 genotypes of

muskmelon and reported high variability for netting, fruit shape, flesh thickness,

average fruit weight, total yield per vine and titrable acidity. Khurana et al. (1995)

evaluated 20 lines of long melon (C. melo var. utilissimus L.) for various

characters and reported considerable variation in yield, quality and reaction

to diseases. Pandey et al. (2003) carried out genetic variability, heritability,

character association and path analysis in 63 accessions of snapmelon and recorded

highly significant differences between genotypes for all the characters. Rakhi and

Rajamony (2003) evaluated 42 landraces of culinary melon collected from different

melon growing areas in Kerala and found considerable variation in phenotypic traits.

In addition, some melon varieties were classified as climacteric fruit,

causing a huge market loss within a short time between harvest and

consumption. Poor keeping quality limits their wide commercial acceptance,

and thus long shelf-life has become an indispensable character in modern

cultivars of melon. In fact, the variation of shelf-life existed among varieties

of C. melo has been conducted earlier (Kitamura et al., 1975; Liu et al., 2004;

Miccolis and Saltveit, 1991; Shiomi et al., 1999). In early studies on shelf-

life, researchers generally focused on a few varieties such as inodorus,

reticulatus and cantalupensis (Ayub et al., 1996; Guis et al., 1997; Hadfield

et al., 1995; Lester, 1988; Pratt et al., 1977). Very few published reports are

47

extended to other varieties. Analysis of varietal variation in shelf-life of

melon fruit is of importance for more efficient utilization of a diverse

germplasm.

The most important melon landraces cultivated in Southern India are:

var. acidulus and var. momordica. Snapmelon [Cucumis melo L. var.

momordica (Roxb.) Duthie et Fuller] is native to India, where it is commonly

known as ‘phut’ or ‘phoont’ which means to split. Its fruits invariably crack

at maturity and the flesh tastes mealy. Immature fruits are cooked or pickled

and the mature, low sugared flesh is eaten raw. Snapmelon is cultivated in

many parts of India and in the two Japanese islands (Hachijo and Fukue;

Fujishita, 2004), where it was used as food during the two world wars.

Snapmelon is an excellent source of disease and insect resistance.

From the snapmelon germplasm obtained from India, U.S. breeders isolated

Powdery mildew resistant collections and developed the Powdery mildew-

resistant melon (Pryor et al., 1946; Whitaker and Davis, 1962). The present-

day varieties of muskmelon resistant to race 2 of Podosphaera xanthii and to

Golovinomyces cichoracearum owe their origin to the Indian snaplemon.

Indian snapmelon accessions also provided resistance to various diseases and

pests such as Downy mildew [Pseudoperonospora cubensis (Berk et Curtis)

Rostovzer], Fusarium wilt (Fusarium oxysporum Schltdl. fsp. melonis Snyder

and Hansen), Zucchini Yellow Mosaic Virus, Papaya Ringspot Virus,

Cucurbit Aphid-Borne Yellow virus and Aphis gossypii Glover (Pitrat et al.,

2000; Thomas et al., 1998). Indian snapmelon accessions have also been used

48

for creating mapping populations in various laboratories in Europe and the

U.S. (Baudracco-Arnas and Pitrat, 1996; Wang et al., 1997), to substantiate

taxonomic relationships with other horticultural groups of C. melo (Akashi et

al., 2002; Monforte et al., 2003; Silberstein et al., 1999; Stepansky et al.,

1999a, b). The comprehensive collection and analysis of variation in this

taxon was performed from various locations of India (Dhillon et al., 2007a, b;

2009; Fergany et al., 2010), using snapmelon accessions collected from the

North Western plains of India, hot and humid tropics of Eastern India, humid

tropics of Southern India and central India and are conserved at Punjab

Agricultural University, Ludhiana, India. McCreight et al. (2004) suggested

that the genetic variation in melon germplasm of North and Central India

might be an indication of the genetic diversity present in Eastern India. They

recommended that additional collections of melon germplasm should be made

in entire India with the expectation that genetic diversity not present in the

existing world collections of melon would be found. A similar genetic picture

of Indian melon germplasm has been suggested by Akashi et al. (2002).

C. melo var. acidulus is native to the humid tropics of Southern India

(Karnataka, Kerala and Tamil-Nadu) and is tolerant to Downy mildew

(Rajamony, 1999). Its fruits have very long shelf life and are consumed as

salad or used for ‘Sambhar’ preparation (Fergany et al., 2010). A tremendous

variability exists among landraces of culinary melon in Southern India (Rakhi

and Rajamony, 2003).

49

2.2.2 Molecular variability

Different types of genetic markers have been used to assess genetic

diversity in melon. Isozymes have been used initially (Perl-Treves et al.,

1985; Staub et al., 1987), RFLPs (Neuhausen, 1992), RAPDs (Garcia et al.,

1998; Mliki et al., 2001; Staub et al., 1997b), AFLP (Yashiro et al., 2005),

SSRs (Katzir et al., 1996; Monforte et al., 2003) and ISSRs (Stepansky et al.,

1999a) have been studied. Garcia et al. (2000) used various molecular

markers (AFLP, RFLP and RAPD) and reported that the analysis of different

types of markers showed the similar clustering of six genotypes of melons.

Genetic diversity of melons from different locations were analyzed using

molecular markers: Africa (Mliki et al., 2001), Spanish (Lopez-Sese et al.,

2002; 2003), Greece (Staub et al., 2004), South East Asian (Tanaka et al.,

2007; Yashiro et al., 2005), Japan (Nakata et al., 2005) and India (Dhillon et

al., 2007 a, b; 2009; Fergany et al., 2010). Despite this extensive utilization of

Indian melons, a comprehensive analysis of genetic variation available in this taxon

has not been performed. To increase the usefulness of this type of melon germplasm

for melon conservation, breeders and growers should analyze the morphological,

biochemical and molecular characterization of Indian melons which is of at-most

importance.

Comparative analysis of the genetic variability among Indian snapmelons and

an array of previously characterized reference accessions of melon from Spain, Israel,

Korea, Japan, Maldives, Iraq, Pakistan and India using SSRs showed that Indian

snapmelon germplasm contained a high degree of unique genetic variability which

was needed to be preserved to broaden the genetic base of melon germplasm

50

available with the scientific community (Dhillon et al., 2007b). Fergany et al. (2010)

analyzed the genetic characterization of melon landraces (var. momordica and var.

acidulus) from the humid tropics of Southern India (Kerala and Tamil-Nadu) by

variation at 17 SSR loci, morphological traits of plant habit and fruit, pest resistance,

disease resistance, biochemical composition and mineral content. Comparative

analysis using SSRs of the genetic variability between Indian melons from North,

South, and East regions and reference accessions of melon from Spain, France, Japan,

Korea, Iraq and Zambia showed regional differentiation between Indian melon

accessions and that Indian germplasm was weakly related to the melon accessions

from other parts of the world. This was the first instance where var. acidulus was

used in the evaluation and analysis of genetic diversity.

2.2.3. Disease resistance

Diseases cause great losses to melon crops around the world. Among

them the important fungal diseases are Fusarium wilt, Powdery Mildew,

Downy Mildew, Alternaria Leaf Blight and Gummy Stem Blight. According

to Lecoq et al. (1998) viral diseases that prevail among melons are Cucumber

Mosaic Virus (CMV), Papaya Ringspot Virus (PRSV), Watermelon Mosaic

Virus 2 (WMV 2), Zucchini Yellow Mosaic Virus (ZYMV), Cucurbit Aphid-

Borne Yellows Virus (CABYV), Squash Mosaic Virus (SqMV) and

Watermelon Chlorotic Stunt Virus (WCSV). Different insect species are

known to infest melons, such as white fly, aphids, leaf miner, beetles and

fruit fly (Dogimont et al., 1995).

51

Fusarium wilt of melon (Cucumis melo L.), caused by Fusarium

oxysporum Schlecht f. sp. melonis (Fom; Leach and Currence, 1938), is an

important disease resulting in reduced melon yield and quality all around the

world (Zitter, 1997). Four races of Fom. have been identified and named as 0,

1, 2, and 1,2. Race 1, 2 was further subdivided into 1,2y type, which causes

yellowing symptoms before the death of the plants, and race 1,2w type, which

produces wilting and death without symptoms of yellowing (Risser et al.,

1976). Race specific resistance genes Fom-2 and Fom-1 confer resistance to

races 0 and 1, and races 0 and 2, respectively (Risser et al., 1976). Another

gene, Fom-3, controls resistance to races 0 and 2 in cultivar Perlita-FR (Zink

and Gubler, 1985), but data about its possible allelism with Fom-1 are still

unclear (Danin-Poleg et al., 1999; Risser, 1987). So far, no genes have been

identified in melon that confer high levels of resistance to race 1,2

(Ficcadenti et al., 2002; Perchepied and Pitrat, 2004; Risser et al., 1976).

Identification of DNA markers tightly linked to a resistance gene is a

powerful and useful tool to avoid the previously faced drawbacks in melon

breeding programs. Bulk segregant analysis (BSA) (Michelmore et al., 1991)

is an efficient method to identify molecular markers linked to a specific gene

using DNA bulks from segregating populations. This strategy was previously

used in melon to detect RAPD markers linked to Fom-2 (Wechter et al.,

1995). Those markers have been transformed to more stable and easily

applicable ones, such as Cleaved Amplified Polymorphic Sequences (CAPS;

Zheng et al., 1999) or ‘SCAR’ (Zheng and Wolf, 2000). By combining the

52

BSA strategy with AFLP methodology, Wang et al. (2000) found some AFLP

markers linked to the Fom-2 locus and they were converted into SCAR

markers called AM and FM. Using the RGH method, Garcia et al. (2001)

have identified the first melon resistance gene homologue (MRGH21) linked

to Fom-1. Additional RGH derived marker NBS47-3 has been mapped to the

vicinity of Fom-1 by Brotman et al. (2002). More recently, Brotman et al.

(2005) have identified the 62-RAPD1235 and NBS-1 markers linked to the

Fom-1 locus which were transformed in two CAPS (Cleavage Amplified

Polymorphic Sites) markers ‘62-CAPS’ and ‘NBS1-CAPS’ respectively. Ali

et al. (2008) has developed SCAR markers linked to Fusarium wilt resistance

in melon. Fergany et al. (2010) has screened the South Indian collection for

Fusarium wilt mildew resistance in field level, but the molecular confirmation

of the same has not been conducted.

Powdery mildew caused by Podosphaera xanthii (syn. Sphaerotheca

fuliginea ex Fr. Poll.) and to a lesser degree, Golovinomyces cichoracearum (syn.

Erysiphe cichoracearum DC ex Mérat.) limits the production of melon worldwide

(Sitterly, 1978). Many races of Powdery mildew have been identified and resistant

cultivars or accessions have been reported (Alvarez et al., 2005; Epinat et al., 1993;

McCreight et al., 2005; Sowell and Corley, 1974). Recently, the appearance of new

races of these fungi and the breakdown of disease resistance has been reported

(Hosoya et al., 1999; McCreight et al., 2005). Several genes and QTLs for resistance

to Powdery mildew have been mapped: Pm-w of WMR 29, Pm-x of PI 414723 and

Pm-y of VA 435 (Périn et al., 2002; Pitrat, 1991), PmV.1 and PmXII.1 of PI 124112

53

(Oliver et al., 2001; Perchepied et al., 2005). Morales et al. (2004) and Fukino et al.

(2008) have identified QTLs for resistance and designed CAPs and SCAR primers

specific to Powdery mildew. Fergany et al. (2010) has screened the South Indian

collection for Powdery mildew resistance in field level, but the molecular

confirmation of the same has not been conducted. The cucumber red beetle,

Acalymma vittatum, is a beetle of the family Chrysomelidae and a serious pest of

cucurbit crops in both larval and adult stages. So, screening for resistant variety is of

at most necessary for protection against the beetle.

2.2.4. Fatty acid analysis

Melon seed kernels are major soup ingredients and they are used as a

thickener and flavor component of soups. Melon seeds are less expensive and widely

distributed. They can contribute substantially towards obtaining a balanced diet

(Fokou et al., 2009) and are generally a rich source of oil. Oil seeds are generally

processed to yield condiments such as ‘ogiri’. Despite extensive research on melon

seeds in many part of the world (Abiodun and Adeleke, 2010; Badifu and Ogunsua,

1991; Carreras et al., 1989; Fokou et al., 2009; Hemawathy, 1992; Ismail et al., 2010;

Loukou et al., 2007; Mariod and Matthaus, 2008; Onyeike and Acheru, 2002; Yanty

et al., 2008), there is a dearth of studies among the Indian melon varieties. India

stands sixth in the production of melon and the seeds are generally considered as

waste products (FAO, 2008). If the production of oil from these plants is considered,

then we could meet the increasing demand of the edible oils.

Genetic diversity of concern to agriculture is available in the cultivated form,

which is in the form of several crop varieties. Despite our crucial dependence on it,

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the threat to bio-wealth is increasing everyday. Rapid development of elite cultivars

has hastened the displacement of old varieties and landraces. Thus, in many species a

broad genetic base is needed for crop improvement, thus attempts have to be made for

collecting and preserving the diversity from different locations, which would have

evolved or adjusted to varying climatic and soil conditions. India being a primary

center of origin for cucumber and primer center of diversification of melons, only few

attempts was made in the past for the collections of Cucumis from India, which was

restricted to the Northern states. Recently Dhillon et al. (2007; 2009) and Fergany et

al. (2010) have collected and analyzed the diversity of melons in few states of Eastern

and Southern India, while Karnataka was not included in the study till date and no

attempts were done to analyze the diversity of cucumber in any Southern states as per

as the literature. So in this present study we have collected and analyzed the

phenotypic variations, molecular diversity, screening for disease resistance and fatty

acid profile of the seed oil from the cucumber and melon collections of Karnataka,

India.