Cucurbit Genetics Cooperative Report 7:96 (article
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 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.
- Bemis, W.P. 1973. Interspecific aneuploidy in Cucurbita. Genet.
- Graham, J.D. 1984. Phenotypic effects and transmission rates of Cucurbita palmata chromosomes in Cucurbita moschata aneuploids.
Ph.D. Thesis, Univ. of Arizona, Tucson.