Heterotic patterns in hybrids involving cultivar-groups of summer squash, Cucurbita pepo L.

Heterotic response for total yield among five cultivar-groups of summer squash, Cocozelle, Vegetable Marrow, Zucchini, Crookneck and Straightneck, was studied in two sets of diallel crosses evaluated in two harvest seasons. Each diallel cross included two representatives of each the five cultivar-groups. Griffing and diallel GGE biplot (genotype main effect and interaction) analyses were carried out. The relative importance of the specific combining ability variance on total variance was greater than that reported earlier for intragroup crosses. Highly significant heterosis was manifested only in combinations of Crooknecks or Straightnecks crossed to Cocozelles, Vegetable Marrows or Zucchinis. GGE biplots showed a consistent arrangement where testers of ssp. texana interacted with cultivars of ssp. pepo and vice versa. We propose that the heterotic pattern of texana-pepo crosses could be potentially used to achieve increased yields in hybrids by introgressing one group into another in a manner that would maintain fruit attributes of the cultivar-group.