Cucurbit Genetics Cooperative Report 7:96 (article 43) 1984

Trisomic Identification of Linkage Groups of Cucurbita

Graham, J.D., N.F. Weeden and R.W. Robinson

Department of Horticultural Sciences, New York State Agricultural Experiment Station, Geneva, NY 14456

Bemis (1) synthesized trisomic stocks of Cucurbita, having 40 chromosomes of C. moschata and one from C. palmata. The five different trisomics we obtained from him are morphologically very similar but not identical to 'Butternut', the C. moschata parent (2). Starch gel electrophoresis of young leaf extracts in combination with specific isozyme stains was used to develop an improved method of identifying Cucurbita trisomics.

Trisomic P2 is characterized by a hard, lignified fruit rind, similar to that of C. palmata, and a hybrid fumarase phenotype. The fumarase phenotype gave activity at positions corresponding to the bands observed in each parent plus the space between these two bands. Thus, the fumarase and hard rind genes are both on the C. palmata chromosome present in the P2 trisomic.

Trisomic P3 had unique phenotypes for aspartate aminotransferase (AAT) and glucose phosphate isomerase (GPI) isozymes. The trisomic had at least two AAT bands not present in C. moschata, one of them corresponding to one in the C. palmata zymogram and the other apparently a hybrid molecule consisting of one moschata and one palmata subunit. Trisomic P3 differed from each parental species for both the plastid specific form and cytosolic form of GPI. Two GPI and one AAT isozyme genes are therefore linked on the extra chromosome of the P3 trisomic.

No phenotype differences in isozymes from C. moschata were detected in P1, P4, and P6 trisomics. The parental species exhibited at least 20 allelic differences in the 12 enzyme systems investigated. Thus at least 15 of the loci, those for which a C. palmata allozyme was not observed in the trisomics, appear to be situated on chromosomes not represented in the selection of trisomics available to us.

Literature Cited

1. Bemis, W.P. 1973. Interspecific aneuploidy in Cucurbita. Genet. Res. 21:221-228.
2. Graham, J.D. 1984. Phenotypic effects and transmission rates of Cucurbita palmata chromosomes in Cucurbita moschata aneuploids. Ph.D. Thesis, Univ. of Arizona, Tucson.