Comparison of vegetative development in soybean cultivars for low-latitude environments

Soybean production has been expanded into northern Brazil by the introduction of long-juvenile genes. These genes cause flowering to be delayed but specific changes in the sensitivity of plant development to temperature and photoperiod have not been resolved in these commercial cultivars. This study was undertaken to resolve possible changes in long-juvenile plants associated with rates of plant emergence, leaf appearance, and flowering. Eight cultivars, including three long-juvenile cultivars, were sown each week throughout a year in a plastic greenhouse so that the plants would develop under differing temperature and photoperiod. While there were differences among cultivars in the cumulative temperature required for plant emergence and the rate of leaf appearance, these differences were not necessarily associated with the long-juvenile trait. An extended duration to flowering was confirmed for the three long-juvenile cultivars but this delay was not associated with any difference in sensitivity to temperature and photoperiod. The trait that distinguished the long-juvenile cultivars was a much lower maximum development rate towards flowering than that found in the other cultivars. However, cultivar differences were identified among the long-juvenile cultivars indicating the possibility of further selection of genotypes to fit specific environments in low-latitude regions.