Exploiting resistance gene of Cucumis sativus L. var. hardwickii germplasm in Cucumber improvement
Authors: Dinesh Chand, N. Dikshit , N.Sivaraj2 and A D Sharma1
National Bureau of Plant Genetic Resources, Regional Station, Akola 444104,
Maharashtra, India
1 National Bureau of Plant Genetic Resources, Pusa campus, New Delhi-110012
2 National Bureau of Plant Genetic Resources, Regional Station, Rajendra Nagar, Hyderabad, -500030, Telangana

Cucumber and melons are the third most widely cultivated vegetable crops after the tomatoes and onions in the world. In India, cucumber is grown in 41,000 hectares (ha.) with a production of 641,000 metric tonnes (MT) during 2012-13 (Handbook on Horticulture Statistics-2014). It is widely grown for its edible fruits in nearly all the tropical, semitropical and temperate regions of the world. The cucumber is very popular and widely cultivated vegetable in India.. Cucumber and there wild relatives are medicinally important as well, in addition to their great nutritional value. The tender fruits of Cucumis spp. eaten as a vegetable directly in the form of salad, fried and pickled. The flesh of cucumber is mixed with grinded urd dal and mung dal for preparing (cucumber badi) for using as a dal or vegetable in off seasons.

Systematics of Cucumis species

The genus Cucumis belongs to the family Cucurbitaceae (Whitaker, Davis 1962), order Cucurbitales. The Indian sub-continent is considered to be the centre of origin for C. sativus (Cucumber) and a centre of diversity for C. melo (Melon) (Zeven and de Wet 1982). Chakravarthy (1982) recognized five wild taxa of Cucumis namely C. callosus (Rottler) Cogn., C. setosus Cogn, C. prophetarum L., C. hystrix Chakra, and C. sativus var. hardwickii (Royle) Alef. In India, six species of Cucumis with C. melo L. and. C. sativus var. hardwickii (Royle) being cultivated and C. prophetarum L., C. callosus (Rottler) Cogn. et Harms, C. hystrix Chakrav and C. setosus Cogn as truly wild. Both melon and cucumber are represented by wild and weedy forms in their distribution range, the former represented by C. melo subsp. Agrestis (Naud.). Pangalo and the latter by C. sativus var. hardwickii (Royle) Gabaev (Jeffrey 2001.). The plant is a natural component of grasslands especially in farm borders trailing to fences, bushes, and other supports. C. sativus var. hardwickii confined its distribution to foothills of Himalayas (Chakravarthy 1982,; Arora and Nayer 1984), Mount Abu, Rajasthan (Bisht et al. 2004) and distributed in different states of India i.e. Himachal Pradesh, Uttar Pradesh, Uttarakhand, Rajasthan, Madhya Pradesh, Chhattisgarh, Odisha and Western ghats of Maharsahtra (Dikshit, 2014).

Gene pool and crossing ability of Cucumis spp.

The wild species in primary genepool include the wild progenitors of crops, wild and weedy forms and produce fertile hybrids with cultivated types (Harlan and de Wet, 1971). In the secondary genepool the species can only result in some degree of fertility and gene transfer being difficult. The tertiary genepool is represented by distantly related species or unrelated taxa of different genera/ species and hence the crossing is difficult. This includes the genepool having little direct value. But valuable genes of this gene pool can be used by application of gene transfer methodologies. In terms of utilization of wild relatives, primary and secondary genepools are easy to exploit because they are wild progenitors/ closer/ relatively closer to their respective crop groups. On the basis of the data from morophology, cross fertility test, cytogenetics and physiology, the wild taxon, Cucumis sativus var. hardwickii (2n= 2X=14) is shown to be the progenitor of C.sativus (Deakin et al., 1971). Successful hybridization between several accessions of cultivated C. sativus and its wilds forms by (Kho et al., 1980) and (Staub and Kupper 1985) have also indicated their close genetic relationship.

Source of desirable traits

Wild species of Cucumis have been found to possess useful morpho-agronomic characters as well as resistance against pest and diseases and therefore, emphasis has been laid on the utilization of the variability in the wild species of Cucumis for improvement of cucumber and muskmelon (Deakin et al.1971). It is a potential source for increased yield in pickling cucumbers (Horst and Lower 1978). A single recessive gene for resistance (mjlmj) to the root- knot nematode (Meloidogyne javanica) was identified in Cucumis sativus var. hardwickii (Walters, SA. et al. 1997). It could be incorporated easily into elite inbreds using back cross methods and benefit the cucumber growers. Cucumber mosaic virus (CMV),

Recent Initiatives in augmenting the germplasm

Wild Cucumis sativus L. var. hardwickii germplasm were collected from diverse agro-ecological niches covering Raigadh and Ratnagiri districts in Maharashtra region. The collected germplasm exhibited very interesting variation in the qualitative characters of fruits such as shape, luster, blossom end, ridges etc. Four types of fruit shape were recorded in wild germplasm viz.,small, round, elongate, oval etc. Wide range of variability were recorded in the quantitative traits viz., fruit length, fruit width , perimeter of the fruits, green fruits weight, flesh rind thickness, number of seeds / fruit, seed length, seed width, number of stripes/ placenta present and spread from anterior to posterior end and 100 seed weight. Promising genotypes for fruit weight (152.80 g) was observed in IC0614594 (ND/DC-16) â€" a collection from Kumbawe village under Dapoli mandal (Ratnagiri), Maharashtra (Fig-1).

Fig.- 1. IC-0614594 (ND/DC-16) â€" A promising accession of C. sativus var. hardwickii collected
from Kumbawe , Dapoli , Ratnagiri, Maharashtra

Future thrust

Study shows that Cucumis sativus var. hardwickii in India is very divergent and enrich in variability. It can be helpful in successful use of germplasm in modern breeding programme for most important diseases of Cucumis spp. including Cucumber mosaic virus (CMV), Zucchini yellow mosaic virus (ZYMV), Cucumber downy mildew (Pseudo peronospora cunsis) and the economically important pests of cucumber. Augmentation of Cucumis genetic resources should be taken up in a consortium mode and a wide range of samples from different regions of the India be collected, characterized. the changes in spatial and temporal variation could be associated with geographical origin for its distribution, variability and diversity. In order to discover distribution of cultivated and wild forms in the current climate change regime. Hence, the collection and conservation of these valuable resources assumes great importance in the cucumber breeding programme in the country.


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About Author / Additional Info:
I am working as Senior Scientist (Eco. Botany & Plant Genetic Resources) at NBPGR Regional Station , Akola, Maharashtra. The mandate crops are cereals, millets, pulses, vegetables and oilseeds and their wild relatives. I am responsible for germplasm exploration, evaluation, maintenance,conservation, documentation and supply of Plant Genetic Resources.