Abstract
This study was conducted to determine reproductive development of soya bean [Glycine max (L.) Merr.] genotypes of Maturity Groups (MG) Ill-VI grown under different photoperiods in Puerto Rico to establish the appropriate light regimes required for crossing. Three genotypes of each MG Ill-VI were planted in replicated experiments at three field environments and in growth chambers. In the field, photoperiods were natural conditions (unlighted) or 13-h, 14-h, and 15-h lighted photoperiods. In lighted treatments, genotypes were exposed to continuous light for two weeks, and appropriate photoperiods were then used until the end of flowering, after which plants grew in natural conditions. In the growth chamber, photoperiods of 12 h, 13 h, 14 h, and 15 h were used. Dates of full bloom (R2) and of full seed (R6), number of nodes at R2 and R6, and percentage of cleistogamous flowers were recorded. Environmental, photoperiod, and MG effects were significant on days and nodes at R2, but the MG × photoperiod effect was not. Under natural field conditions, all genotypes flowered approximately 30 days after planting (DAP) and had five nodes. They reached R6 56 DAP and had eight nodes. In the 14-h photoperiod, genotypes flowered 46 DAP. Genotypes of MG III flowered 37 DAP which was the shortest time. Within photoperiods, lines of each MG flowered within short periods of time from each other. Cleistogamy was at least 90% in all MGs in natural field conditions and in the 13-h photoperiod for MG Ill. The crossing of genotypes of MGs Ill-VI will require photoperiods of 14 h. A 6-day flowering difference of genotypes of MG Ill and VI suggests that several planting dates in the season will be needed, with the late maturing lines planted first.
