Impacts of high temperature, relative air humidity, and vapor pressure deficit on seed set of contrasting maize genotypes during flowering

Abstract

Heat stress is a main constraint to current and future maize production at the global scale. Male and female reproductive organs both play major roles in increasing seed set under heat stress at flowering, but their relative contributions to seed set are unclear. For this purpose, a 2-year field experiment including three sowing dates in each year and 20 inbred lines were conducted. Seed set, kernel number per ear, and grain yield were all reduced by more than 80% in the third sowing dates compared to that in the first sowing dates. Pollen viability, silk emergence ratio, and anthesis-silking interval were the key determinants of seed set under heat stress; their correlation coefficients were 0.89***, 0.65***, and -0.72***, respectively. Vapor pressure deficit (VPD) and relative air humidity both had significant correlations with pollen viability and silk emergence ratio. High relative air humidity can alleviate heat impacts on maize seed set by maintaining high pollen viability and high silk emergence ratio. Under warming climate from 2020 to 2050, VPD will decrease as a result of increased relative air humidity. Based on pollen viability and silk emergence ratio, 20 genotypes fell into four different groups. The group with high pollen viability and high silk emergence ratio performed better under heat stress, which can be further improved by combining improved traits in flowering pattern.