The Role of Genetics and Photoperiod in Soybean Development and the Control of the Plant Life Cycle.

The rate of soybean development and the life cycle of the plant are critical to its geographic distribution and adaptation to different latitudes. An understanding of the mechanisms that control this phase can help breeders tailor soybean cultivars to their environment.  Previous studies have found that a series of genes known as the E-genes as well as seasonal photoperiod can condition time to flowering as well as the duration of the post-flowering phase. The objective of the current study is to determine how E-genes and photoperiod regulate each of the post-flowering phases of development.  A randomized complete block experiment with treatments arranged in split-plots was conducted in 2009.  Four E-gene near-isogenic lines were grown under four photoperiod treatments in a replicated experiment.  The photoperiod treatments were imposed after flowering of all genotypes was synchronized under an 11 h short day photoperiod imposed under controlled environment conditions.  Once all genotypes were flowering they were transplanted into ambient or ambient +2h day length extension treatments that corresponded approximately to 15-h, 16-h, 17-h and 18-h day lengths.  The target photoperiods were obtained by having two different planting dates, and day length extension using incandescent bulbs suspended over the field plots. Detailed phenology and daily temperature data will be collected, and growing degree days and average photoperiod will be calculated.  The role of dominant versus recessive alleles at the E-gene loci, and their impact on reproductive development and control of life cycle through a photoperiod mediated response shall be discussed.