Several different selection strategies were used to estimate expected gain of days to flowering and other related characters in two F2 soybean (Glycine max (L.) Merrill) populations. The sample originated from crosses of lines whose seeds do not contain the three lipoxygenase isozymes with the commercially cultivated IAC-12. IAC-12 is a gene carrier for an extended juvenile period. This study was conducted during the winter of 1994 in Viçosa, Minas 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 caused a delay in flowering. Delayed flowering caused a broader amplitude in all characters evaluated, and resulted in higher selection gains for the field-grown plants than for the greenhouse-grown plants. Direct selection for number of flowering days proved to be efficient for improving this character in both populations. Gains were also obtained for other characters. Interactions of temperature and photoperiod and temperature and genotypes affected soybean flowering time and produced alterations in other correlated agronomic characters, including productivity.
