Potential Usefulness of SSR Markers for Studying Infraspecific Variability in Cucurbita pepo

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Cucurbit Genetics Cooperative Report 23:71-72 (article 24) 2000

Nurit Katzir, Neta Mozes-Daube, Yael Danin-Poleg, and Harry S. Paris
Department of Vegetable Crops, Agricultural Research Organization, Newe Ya-ar Research Center, P.P. Box 1021, Ramat Yishay 30-095, Israel

Simple sequence repeats (SSRs), also known as microsatellites, consist of variable numbers of tandem repeats of up to five nucleotides, forming highly informative, locus-specific genetic markers. SSRs are often conserved among closely related species of animals and plants and may be useful as tools for evolutionary studies. SSR markers have proven to be informative and polymorphic in Cucumis (3). Some of the cucumis primers have also been found to be functional and polymorphic in Cucurbita (4). Based on the methodology already described (3,4), we observed Cucumis SSR markers that also simplified specific products in Cucurbita. Of 50 SSR markers tried in Cucurbita pepo, eight gave distinct amplification products, and six were polymorphic. The banding pattern obtained from one of them on a sequencing gel is presented in Figure 1.

The results presented in Figure 1 are fairly consistent with the classification of Cucurbita pepo into subspecies (2) and cultivar-groups (5). The monomorphism, expressed in the right half of the figure is for accessions of the Cocozelle, pumpkin, Vegetable marrow, and Zucchini Groups and the ‘Orange Ball’ gourd, all C. pepo spp. pepo. Just to their left is the unique banding of the wild Mexican accession, C. pepo spp. fraterna. To its left are accessions classified as C. pepo spp. ovifera. The lane at the extreme left is of the Cucumis melo accession. Next to it are three lanes of cultivars of the Acorn Group. The seventh and ninth lanes, for the modern hybrid ‘Golden Girl’ (Straightneck Group) and the ‘Striped Pear’ gourd, show two sets of bands, indicative of polymorphy within each. The remaining accessions are cultivars of the Scallop and Crookneck Groups and wild gourds from Arkansas and Texas,

C. pepo ssp. fraterna has been suggested by Andres (1) to be the wild ancestor for the species as a whole. It was suggested by Paris (6) that the Acorn Group may be derived from introgression of genes from the Pumpkin Group into the Scallop Group. The results presented in Figure 1 combined with the results obtained using ISSRs (4) are generally supportive of these two ideas on the evolution and crop development of C. pepo.

Figure 1

Acknowledgement: Contribution No. 124/00 from the Institute of Field & Garden Crops, Agricultural Research Organization, Bet Dagan, Israel.

Literature Cited

  1. Andres, T.C. 1987. Cucurbita fraterna, the closest wild relative and progenitor of C. pepo. Cucurbit Genet. Coop. Rep. 10: 69-71.
  2. Decker, D.S. 1988. Origin(s), evolution, and systematics in Cucurbita pepo (Cucurbitaceae). Econ. Bot. 42: 4-15.
  3. Katzir, N., Y. Danin-Poleg, G. Tzuri, Z. Karchi, U. Lavi, and P.B. Cregan. 1996. Length polymorphism and homologies of microsatellites in several Cucurbitaceae species. Theor. Appl. Genet. 93: 1282-1290.
  4. Katzir, N., Y. Tadmor. G. Tzuri, E. Leshzeshen, N. Mozes-Daube, Y. Danin-Poleg, and H.S. Paris. 2000. Further ISSR and preliminary SSR analysis of relationships among accessions of Cucurbita pepo.In: Proceedings of Cucurbitaceae 2000: the 7th Eucarpia Meeting on Cucurbit Genetics & Breeding, pp. 433-439. N. Katzir and H.S. Paris, eds. I.S.H.S., Leuven, Belgium.
  5. Paris, H.S. 1986. A proposed subspecific classification for Cucurbita pepo. Phytologia 61: 133-138.
  6. Paris, H.S. 1989. Historical records, origins, and development of the edible cultivar groups of Cucurbita pepo. Econ. Bot. 43: 423-443.