Genetic and developmental aspects of breeding for early maturity of mungbean (Vigna radiata (L.) Wilczek)

Field experiments involving variation in sowing date revealed a consistent ranking of these lines for flowering time over a wide range of environments. Both UT1 and KPS1 flowered later than the two early lines. There were also substantial variation in the duration of pre and post-anthesis development phases: sowing to floral initiation (SF1), floral initiation to first open flower (FISF), first open flower to first mature pod (SFFMT), first open flower to mean maturity (FMTMMT), as well as in plant growth: number of leaves formed at first open flower (LN) and leaf appearance rate prior to first open flower (LAR). All lines flowered more late under sowing date conditions with decreasing temperature and increasing photoperiod, which in turn delayed in maturity. The two late lines were more responsive to variation in sowing date. Flowering time of all lines decreased with successive delays in sowing, then again increased in later sowing dates so that differences among the population were greatest in the early day season. Controlled environment experiments indicated relatively little variation among the lines in response to photoperiod at 25 deg C than in 15 deg C. Variation in photoperiod and temperature had relatively little effect on time to floral initiation and leaf number. Differences among populations in flowering time appeared to be the responses to photoperiod which largely reflected variation in post-initiation development. Also, late lines had substantially longer SFI than the two early lines. Analysis of genetic variation in earliness and related characteristics were conducted with populations (P1, P2, F1, F2, B1 and B2) derived from 5 crosses among these lines in early rainy season. Substantial variation in flowering time, first mature pod, leaf number formed, seed yield and yield components were detected in the F2 and backcross populations of all crosses. Individual plants flowering much earlier than the early flowering parent were detected in the F2 and backcross populations of most crossess indicating the transgressive segregation. Gerneration mean analyses of segregating populations of all crosses showed polygenic with additive gene effect was most important in conditioning these characteristics. Among the non-additive gene actions, the additive x additve gene effects was also detected in most cases.