Interaction of Three Loci, l-1, l-2, and d, in Conferring the Reverse Stripe Phenotype in Egg Gourd

There are more than a dozen described genes that govern rind color and rind color patterns in fruit of Cucurbita pepo L. (9), and expression of such traits is complex because colors and patterns can change at different stages of fruit development (11) and many of the gene loci affecting fruit pigmentation have multiple alleles. In addition, two or more genes affecting fruit color may interact to produce novel patterns of fruit coloration. Three such independently assorting loci are l-1, l-2 and d (10). When both l-1 and l-2 are recessive, fruit are pale green. When either allele is dominant, the fruit are green; when both alleles are dominant, the fruit are darker green. There are additional alleles at the l-1 locus which in the presence of L-2/L-2 result in different degrees of striped fruit characterized by narrow stripes of light pigmentation over the vein tracts and green pigmentation between the vascular tissue (6, 8). One such pattern that I have introgressed into egg gourd is referred to as broad normal stripes (BNS), and is conditioned by the l-1BSt allele (6). The allele l-1BSt is recessive to L-1, but dominant to l-1. There is also a reverse striping pattern characterized by narrow green stripes over the vein tracts, with white pigmentation between the narrow stripes, a striping pattern conferred by the complementary interaction of alleles at two loci, l-1BSt together with a newly described allele, l-2R, at the l-2 locus (7). The D gene affects both stem and fruit color, but is not expressed until about 15 to 18 days after pollination (10). Plants carrying recessive d/d have light stems and peduncles throughout development; whereas, those with dominant D develop dark stems and peduncles (10). Also, D is epistatic to l-1 and l-2, resulting in a change in fruit pigmentation from pale green to moderately dark green. When l-1 and l-2 alleles are combined with the Wf allele for white flesh, the fruit rind becomes white early in development (5).

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