Generation Mean Analysis of Key Earliness-Related Traits in Cucumber (Cucumis sativus L.)
Understanding the genetic control of earliness-related traits is essential for developing early maturing cucumber varieties and hybrids. The present investigation was undertaken to elucidate the nature of gene action governing the node at which the first female flower appears (NFFF) and days to first fruit picking (DFFP) using generation mean analysis in two reciprocal crosses, PBRK-11 × Punjab Naveen and Punjab Naveen × PBRK-11. Six basic generations, namely P1, P2, F1, F2, BC1P1 and BC1P2, were evaluated for both traits. The results revealed sufficient genetic variability among the generations for both traits. For NFFF, additive gene action was predominant in the cross PBRK-11 × Punjab Naveen, whereas its reciprocal cross Punjab Naveen × PBRK-11 exhibited significant dominance effects along with duplicate type of epistasis, indicating the influence of non-additive gene action. The contrasting behaviour of the reciprocal crosses suggested a possible reciprocal cross effect for NFFF; however, this effect cannot be attributed to maternal or cytoplasmic inheritance without further validation. In contrast, the DFFP trait was mainly governed by dominance gene action with duplicate type of epistatic interactions in both reciprocal crosses, indicating no clear reciprocal difference for this trait. The estimates of dominance ratio indicated partial to complete dominance for NFFF and over-dominance for DFFP. Significant negative heterosis for DFFP over better-parent indicated the superiority of hybrids for early fruit development, whereas contrasting heterotic responses for NFFF suggested limited direct exploitation of heterosis for NFFF. The predominance of non-additive gene effects and duplicate epistasis indicates that selection for earliness would be more effective in later segregating generations. Overall, the findings indicate that hybridization followed by selection in advanced generations would be an effective breeding strategy for developing early maturing cucumber varieties.