Another gene affecting fruit and stem color in squash, Cucurbita pepo

Of the 13 genes described as affecting fruit color in Cucurbita pepo, one, D (Dark stem), also markedly affects stem color. The D allele confers dark stems and dark intermediate-age fruits, is dominant to the d allele for light stems and fruits, and epistatic to two recessive genes conferring light fruit coloration, l-1 and l-2. However, a gene for light fruit coloration, W (Weak fruit color), is epistatic to D in the fruits. We observed variation for stem color in a scallop squash cultivar having light-colored fruits, some plants having dark stems and others light stems. Two true-breeding inbreds of this cultivar, one having dark stems and the other light stems, were developed and, when these inbreds were crossed, the progeny had light stems. In order to elucidate the genetic basis of the dominant light-stem characteristic, these two inbreds were crossed with two near-isogenic tester lines, one of genotype D/D l-1/l-1 l-2/l-2 and the other of genotype d/d l-1/l-1 l-2/l-2. Also, the dominant light stem and light fruit color were introgressed into a third near-isogenic line of genotype D/D l-1/l-1 l-2/l-2, resulting in two new near-isogenic lines, and these lines were then intercrossed. The results showed that the variation in stem color of the scallop squash cultivar derives from segregation of alleles at the W locus, with a newly designated top-dominant allele, W ^S , conferring both, light stems and light fruits. This allele may be genetically unstable and sub-vital.