GENETIC-ANALYSIS OF GROWTH OF DETERMINATE SOYBEAN GENOTYPES UNDER 3 PHOTOPERIODS

Soybean is a short day plant highly influenced by photoperiod. Response to day length is determined by the genotype, and the genetic control of flowering and growth is distinct and independent for long and short day conditions. In this work four parents, including three with a classical type of response to photoperiod (BR85-29009, FT-2 and BR-13) and one long juvenile trait carrier (OC-8), were crossed in all combinations to obtain six sets of F2 and F3 generations. The parental response to final plant height, days to flowering, trifoliolate leaf number and average length of the internode and the genetic mechanisms controlling photoperiodic response of these traits in the six crosses were studied. Variation in day length was obtained by sowing in September, October and November at Londrina (23-degrees and 22, of latitude). Results showed that additive genetic effects predominated in the control of all traits. For adequate progress, selection for plant adaptation must be done for days to flowering and/or final plant height at each sowing. There is probably a single genetic mechanism, involving several loci, controlling days to flowering in the three photoperiods in soybeans.