Abnormal Sporogenesis in Wheat (Triticum aestivum L.) Induced by Short Periods of High Temperature

Plants of Triticum aestivum L. cv. Gabo, grown at 20 °C, were exposed to 30 °C for short periods during the time between the beginning of meiosis in the pollen mother cells and anthesis. Plant water deficit at this temperature was avoided by maintaining a high atmospheric relative humidity and tissue water potential did not change. This temperature treatment applied for 3 days, at the time of reduction division and tetrad break up in the male tissue, lowered grain yield through a drastic reduction in grain set, but was without effect at other stages of development. Grain set was also reduced by exposing plants to 30 °C for 1 day only or to a 30 °C day, 20 °C night (16 h photoperiod) regime for 3 days during the sensitive period. A reduction in grain set did not result in a compensatory increase in the weight of remaining grains. The female fertility of previously heat-stressed plants was assessed by pollinating with pollen from plants grown at a lower temperature (20 °C). Grain set in such plants was less than that in plants grown at the lower temperature and hand pollinated with similar pollen, indicating that female fertility was reduced by high temperature. This was not the sole reason for reduced grain set, however, as some anthers on heat-stressed plants were small and neither extruded nor dehisced normally. Such anthers contained pollen grains that were mostly shrivelled, had abnormal cytoplasm and showed no reaction to 2, 3, 5-triphenyl tetrazolium chloride. Similar effects were also noted in pollen from apparently normal anthers on heat-stressed plants.