Reciprocal effects suggest maternal and extranuclear influences on fruit traits in winter squash breeding

Abstract Winter squash ( Cucurbita moschata ) seed oil holds significant nutritional and pharmacoeconomic value, yet genetic studies on combining ability and reciprocal cross effects in this species remain scarce. This study assessed genetic variability and estimated general combining ability (GCA), specific combining ability (SCA), reciprocal effects, and gene action for 13 morpho-agronomic traits related to earliness, plant architecture, and seed and oil yield, using a complete diallel mating design with five parents analyzed via Griffing’s Method III and the Cockerham and Weir decomposition. Significant genetic variability was detected in 8 of the 13 evaluated traits. GCA effects predominated for growing degree days to male and female flowering, indicating additive gene action and potential for effective parental selection, while SCA was significant for fruit mass, pulp thickness, and transverse diameter of the internal cavity, reflecting non-additive gene effects for these traits. Significant specific reciprocal effects were observed for fruit mass ( p < 0.05), pulp thickness ( p < 0.05), and longitudinal diameter of the internal cavity ( p < 0.01), suggesting maternal or extranuclear influences that render cross orientation a critical factor for these traits. Parents 301 and 516 showed the greatest potential for reducing the crop cycle, and hybrid combinations involving at least one of the parents 117, 301, or 516 were consistently superior across traits of interest. Base populations derived from crosses 117 × 301, 301 × 516, and 516 × 447 are recommended as foundational material for line extraction and recurrent selection in functional oil-oriented breeding programs.