Study on pre-anthesis developmental variation in soybean (Glycine max (L.) Merr.)

Studies on pre-anthesis developmental variation of 9 soybean varieties differing in maturity including early, intermediate and late maturity, were undertaken. In field experiment, seeds were sown in 3 different seasons: dry season (Jan-Apr, 1996), late rainy season (Aug-Nov, 1996), and early rainy season (Jun.-Sep., 1997). the results clearly revealed the effects of variety and season on days to floral initiation (Fl), days from floral initiation to first open flower (FISF), days to first open flower (SF), number of leaves formed at first flower open (LN), leaf appearance rate (LAR), number of leaf primordia formed at first open flower (LP) and rate of leaf primordia formed on main stem (LPR). The early maturity varieties developed to each of the developmental characteristics at the fastest rate. Whereas, the late maturity varieties developed at the slowest rate, and the intermediate maturity varieties developed at the intermediate rate. Substantially variation was detected due to different seasons that would hasten these pre-anthesis developments. It was noticed, however, less environmental effects on days to floral initiation, number of leaves at first open flower and leaf appearance rate, indicating that these developmental characteristics would be governed predominantly by the genetic effects. Controlled environment study in the extent to examine for the influence of photoperiod revealed that the increased photoperiod (13 hours) would increase the number of leaves espetially for the late-maturity varieties. But daylength had no effect on leaf appearance rate. This clearly indicated that other environmental factors (i.e. temperature) rather than photoperiod would confine to the developmental event. For FI, FISF and SF, similar results to the field experiment were obtained by which the early maturity varieties were less responsive whereas the late maturity varieties were greatest responsive and the intermediate maturity varieties were intermediate responsive. The analysis study on genetic controlling of pre-anthesis development were conducted. Three F2 populations derived from the crosses between early maturity varieties (NS 1 and KUSL 20004) and late maturity varieties (CPAC 98-76 and Santa Maria) were grown in the field. Results indicated that delay in days to first open flower (SF) and greater number of leaves at first open flower (LN) were governed by a single dominant gene. According to the significantly positive correlation between floral initiation and days to first open flower obtained from the previous sowing date study, it is suggested that floral initiation would also be controlled by a single dominant gene. The findings that environmental factors had lesser effects on floral initiation, number of leaves at first open flower and leaf appearance rate than genetic effects, these three characteristic should be condidered as main criteria for selection of soybean genotypes better pre-anthesis development.