Modeling genetic effects on the photothermal response of soybean phenological development

The identification of genes that affect plant growth and development has played a prominent role in modern plant research. Mathematical modeling can be a useful tool in this process of quantifying the effects of individual genes. In soybean [Glycine mar (L.) Merr.], seven loci (E1 to E7) have been identified that condition time to flowering and maturity and photoperiod sensitivity. Twenty-nine near-sogenic lines with different combinations of alleles at six of these loci in either 'Clark' or 'Harosoy' background were used in this study. Days from planting to first flower were observed in these lines over 2 yr at two locations (Ottawa, ON, Canada, and Urbana, IL, USA) under natural daylength and a 20-h photoperiod. A mathematical model was developed to simulate the effect of average daily temperature, photoperiod, and the temperature X photoperiod interaction. A photoperiod coefficient was calculated for each isoline, which resulted in an R-2 of 0.93 when calculations of times to first flower were correlated with observations. A submodel was developed to calculate photoperiod coefficients by adding contributions from each locus with dominant alleles. This reduced the 29 isoline coefficients to seven coefficients (one for each locus plus an additional value for unknown genes) but with a reduction of the R-2 of from 0.93 to 0.89. The El coefficient was approximately twice the size of the other five allele coefficients. Time from planting to first flower can be calculated from the average daily temperatures and latitude of a given location using the gene model if the genetic makeup of the line is known.