Multiple allelism at the D locus in squash

Abstract

Early Prolific Straightneck, a squash (Cucurbita pepo) cultivar having dark stems and lightly colored young fruits that intensify in color later in development, was crossed with an accession of Vegetable Spaghetti, a cultivar having light stems and lightly colored fruits throughout development conferred by genotype d/d I-1/I-1 I-2/I-2. All F1 plants, regardless of the direction of the cross, and all plants of the backcross to Early Prolific Straightneck were similar in stem color and developmental fruit color intensity to Early Prolific Straightneck. These characteristics segregated independently in the F2 and in the backcross to Vegetable Spaghetti. Each appeared to be under the control of a single gene, but a lower proportion than expected of individuals having a dark stem were observed in the backcross to Vegetable Spaghetti. In a test for allelism, Early Prolific Straightneck was crossed with a tester stock nearly isogenic to Vegetable Spaghetti, but which had dark stems and fruits of intense coloration later in development and was known to be of genotype D/D I-1/I-1 I-2/I-2;, this F1 was then crossed with Vegetable Spaghetti. All of the resulting progeny (n = 211) had dark stems, indicating that the dark stem of Early Prolific Straightneck is conferred by an allele of D, designated D(s). Unlike D, D(s) does not darken fruit color. D(s) is recessive to D but dominant to d.