Is the yield change due to warming affected by photoperiod sensitivity? Effects of the soybean E4 locus

Abstract

Modeling studies predict that global warming will shorten growth duration and reduce seed yield of early-maturing soybean (Glycine max) cultivars, but that late-maturing cultivars could mitigate this reduction. This is widely discussed but has not been validated experimentally. Time of soybean maturation is determined by several photoperiod-sensitive loci. Here, we focused on the E4 locus, and tested the hypothesis that this locus would mitigate the growth period shortening and yield reduction due to warming. We sowed cv. Enrei with the dominant E4 allele and a near-isogenic line with recessive e4 allele (NIL-e4) on two dates (normal vs. late, with a shorter photoperiod) and grown under three temperature regimes (near-ambient, and 2.0 and 4.6°C above ambient) in sunlit greenhouses in a cool region of Japan. The period from sowing to flowering (R1) decreased with increasing temperature, regardless of genotype and sowing date. However, increased temperature prolonged the period from R1 to the beginning of pod filling (R3) in Enrei but not in NIL-e4 for either sowing date. This indicates that increasing temperature shortened the period before R1, exposing Enrei with E4 to a longer photoperiod and therefore slowing its development. For both sowing dates, pod number and seed yield increased with warming in Enrei. Since the days from R1 to R3 and the cumulative radiation for this period were positively correlated with pod number in Enrei, the greater yield response was explained mostly by the prolongation of this period caused by warming. However, the yield increase resulted partially from the current mean growing season temperature, which was near or below the optimum for yield. We conclude that the E4 locus can increase seed yield under future warming in cool regions of Japan. This result demonstrates the potential importance of modifying photoperiod sensitivity to increase soybean yield under future warming.