Effect of high temperature during the late seed filling period on green stem disorder in soybean

Abstract

ContextGreen stem disorder (GSD) in soybeans is a condition wherein delayed leaf and stem maturation at harvest negatively affects harvest efficiency and seed quality. Biotic and abiotic stresses promote GSD, which is mediated by sink limitations at the flowering and pod setting stages. Previous studies have suggested that high-temperature stress promotes GSD. However, the critical growth period and its mechanisms have not yet been elucidated. ObjectiveThe present study investigated the relationship between temperature and GSD severity in growth chambers and fields. MethodsThe study was conducted in two parts. First, the effects of high temperature on GSD (30/25 ℃, day/night) at different growth stages were analyzed in growth chambers. Second, field experiments were conducted to verify the relationship between temperature during the late seed-filling period and GSD severity. Three near-isogenic lines (NILs) with different combinations of maturation genes, E1, E2, and E3, were cultivated on three sowing dates (June, July, and August) for two years. ResultsHigh temperatures in the late seed-filling period significantly promoted GSD severity, whereas high temperatures in the early seed-filling period had no effect on GSD. Sink size did not decrease with high-temperature treatments. The field experiment in 2019 also revealed a positive correlation between GSD severity and mean temperature during the late seed-filling period, whereas mean temperature before the seed-filling period showed no correlation with GSD. Temperatures during the late seed-filling period accounted for GSD suppression in the late-maturation genotype and late sowing dates, whereas the early maturation genotype had an unknown mechanism to promote GSD. On the other hand, in the field experiment in 2020, ratio of source ability to sink size became lower than in 2019 because of higher solar radiation during sowing to R1 period increased sink size. As a result, in 2020, the effect of temperature relatively low compared to the effect of source-sink ratio. ConclusionThe findings indicate that high temperatures during the late seed-filling period promoted GSD. Sink limitations were not the cause of the phenomena. Annual variation of GSD occurrences could be explained by considering effects of both temperature and solar radiation in the specific growth stage. The late seed-filling period corresponds to autumn during the soybean cropping season. Therefore, the phenomena revealed in this study could be responsible for the GSD occurrences promoted by global warming in soybean fields. ImplicationsThis study facilitates selecting appropriate soybean cropping seasons and cultivars for each area to avoid GSD occurrence.