High temperatures during endosperm cell division in maize: A genotypic comparison under in vitro and field conditions

High temperature during endosperm cell division reduces grain yield of maiz e (Zea mays L.). The objective of the study was to determine if there were differences in tolerance of two inbred lines (B73 and Mo17) to exposure to brief high temperature treatments (HTTs). Beginning 5 d after pollination ( DAP), kernels were exposed to a continuous 35 degreesC temperature for eith er 4 or 6 d. The effects of HTTs on kernel development, ultrastructure, and sink capacity were evaluated under both in vitro and field conditions. In B73, the 4 and 6 d HTT reduced final kernel dry weights > 40 to 60% under i n vitro and 79 to 95% under field conditions, compared with the controls. T he HTT-induced reduction in kernel mass was due mainly to reduction in star ch granule number, since by 16 DAP the endosperm cell number had recovered and was not significantly different from the controls. In contrast, in Mo17 both the number of endosperm cells and starch granules were reduced by > 4 5 to 80% by the 4 and 6 d HTT imposed under the two growing conditions. Hen ce, these data and kernel ultrastructure evidence confirm that kernel devel opment is more tolerant to high temperature in B73 than in Mo17. The differ ence appears to be due mainly to the ability of B73 to maintain a higher ke rnel sink capacity after exposure to HTT during endosperm cell division. Ex ploiting the differential response of these genotypes appears to be a viabl e approach to further elucidate the physiological basis for heat tolerance during early kernel development.