Pollen Viability, Pollen Shedding, and Combining Ability for Tassel Heat Tolerance in Maize1

Abstract

High temperatures during maize (Zea mays L.) pollination limit kernel number. Knowledge is limited on the effect of heat stress on both pollen viability and tassel shedding characteristics or of possible heat tolerance sources and testers. The purpose of this research was to determine the tassel response to heat stress, as measured by in vitro pollen viability and shedding characteristics, and the combining ability for these traits using a diallel of four heat‐tolerant and three heat‐intolerant inbreds. Tassels from field‐grown plants were excised at the beginning of anthesis, immediately placed in sufficient water to cover the base, and transferred to growth chambers. The growth chambers were maintained at light period temperatures of 29 and 38°C and dark period temperatures of 24 and 32°C, respectively. In vitro germination, anther emergence, and tassel color were determined after 24 h in the growth chamber. Due to bursting, low levels of germination were obtained, but the percentage of nongerminated pollen increased greatly at the high temperature (65% mean increase). The increase in nongerminated pollen varied among the genotypes, and all except B73 × Mo17 and N28 × Mo17 had statistically significant increases at the high temperature. Mo17 had the most desirable general combining ability (GCA) effect at the high temperature for nongerminated pollen. Specific combining ability effects were significant for nongerminated pollen and accounted for 51% of the genotype and genotype × temperature sum of squares. Anther emergence of the central tassel spike decreased differentially among the hybrids at the high temperature. Mo17 had the most desirable GCA effect for anther emergence. Anther emergence and pollen viability did not always respond the same to high temperature. Results from this study indicate pollen shed and viability must be considered in tassel heat tolerance and hybrids involving Mo17 had the most heat tolerant tassels.