Selection for later flowering in soybean (Glycine max L. Merrill) F-2 populations cultivated under short day conditions

Several different selection strategies were used to estimate expected gain of days to flowering and other related characters in two F-2 soybean (Glyci ne max (L.) Merrill) populations. The sample originated from crosses of lin es whose seeds do not contain the three lipoxygenase isozymes with the comm ercially cultivated IAC-12. IAC-12 is a gene carrier for an extended juveni le period. This study was conducted during the winter of 1994 in ViSosa, Mi nas Gerais. The plants were grown under natural photoperiod. One population was grown in a heated greenhouse, and the other in the field under natural temperature conditions. Lower temperatures early in the field planting cau sed a delay in flowering. Delayed flowering caused a broader amplitude in a ll characters evaluated, and resulted in higher selection gains for the fie ld-grown plants than for the greenhouse-grown plants. Direct selection for number of flowering days proved to be efficient far improving this characte r in both populations. Gains were also obtained for other characters. Inter actions of temperature and photoperiod and temperature and genotypes affect ed soybean flowering time and produced alterations in other correlated agro nomic characters, including productivity.