Cool temperature caused by late planting affects seed vigor via altering kernel biomass and antioxidant metabolism in cotton (Gossypium hirsutum L.)

Abstract

Cotton in double cropping systems (rapeseed-cotton or wheat-cotton) is often late-planted and experiences a much longer period of cool temperature at the late growth stage, which impairs seed quality. A two-year field experiment with two planting dates (normal and late planting date) was conducted to investigate the effects of late planting on cottonseed vigor and its relationship with seed biomass accumulation and kernel antioxidant metabolism during seed development. With the delay of planting date and the increasing height of fruiting branches, the mean daily temperature during boll period decreased from 25.9 °C to 20.7°C. Meanwhile, the seed, kernel and vigor index decreased by 2.6–12.1%, 4.7–15.0% and 2.5–16.0% respectively. The direct path coefficient of growing degree days (GDD) and the indirect path coefficients via GDD for seed, kernel and vigor index were positive and high. Seed vigor was more sensitive to the change of kernel index than seed index and the cool temperature limited the accumulation of kernel biomass mainly via reducing the maximum velocity of kernel biomass accumulation (Vmax), which led to a significant decline in seed vigor especially in the late planting date. Under cool temperature caused by late planting, the time of the maximum activity for each H2O2-scavenging enzyme was postponed with their maximum activities being decreased, which caused slow reduction in the content of malondialdehyde and H2O2 content during the late stage of seed development. In addition, peroxidase (POD) had the closest correlation with cottonseed vigor compared with catalase, ascorbate peroxidase and glutathione reductase. Altogether, low seed vigor occurred in late planting could be attributed to the decreased kernel biomass and prolonged duration of oxidative damage on membranes caused by cool temperature. The GDD of boll period is valuable for estimating cottonseed harvesting time especially under late planting conditions and seeds with high POD activity are more tolerant to cool temperature.