Drought Stress and Its Effects on Maize Reproductive Systems¹

Moisture stress during pollination of maize (Zea mays L.) can greatly reduce kernel set, yet little quantitative information is available on the effects of plant water status on male and female floral development. The purpose of this study was to establish different drought stress regimes during pollination and to measure synchronization of male and female floral development, pollen viability, and diurnal silk elongation rates. Single cross hybrids were field‐grown in large pots and exposed to different soil moisture treatments at the time of tassel emergence. Compared to well‐watered control plants, mild (no visible wilting) and severe (visible wilting) drought treatments increased the interval from initial silking to initial pollen shed by an average of 3 and 4 days, respectively. Increasing moisture deficits caused no change in in vitro pollen germination even though the severest drought treatment caused visible symptoms of midday wilting and of lower leaf senescence. Diurnal silk elongation measurements indicated that on clear days the majority of silk elongation occurs at night when ear leaf water potentials are highest. At similar morning leaf water potentials, stressed plants maintained a lower silk elongation rate than well#x2014;watered plants. Positive silk elongation ceased at ear leaf water potentials of about #x2014; 9 bars in droughted plants and at #x2014; 14 bars in well—watered plants, suggesting that factors other than water potential may also regulate rate of silk growth. It is concluded that drought beginning at anthesis has a greater effect on female than male floral development.