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

Soybean is a short day plant highly influenced by photoperiod. Respons e to day length is determined by the genotype, and the genetic control of flowering and growth is distinct and independent for long and shor t day conditions. In this work four parents, including three with a cl assical type of response to photoperiod (BR85-29009, FT-2 and BR-13) a nd one long juvenile trait carrier (OC-8), were crossed in all combina tions to obtain six sets of F2 and F3 generations. The parental respon se to final plant height, days to flowering, trifoliolate leaf number and average length of the internode and the genetic mechanisms control ling photoperiodic response of these traits in the six crosses were st udied. Variation in day length was obtained by sowing in September, Oc tober and November at Londrina (23-degrees and 22, of latitude). Resul ts showed that additive genetic effects predominated in the control of all traits. For adequate progress, selection for plant adaptation mus t be done for days to flowering and/or final plant height at each sowi ng. There is probably a single genetic mechanism, involving several lo ci, controlling days to flowering in the three photoperiods in soybean s.