Night Temperature at Silking Affects Set in Maize

Maize ( Zea mays L.) grain yield is primarily associated with variation in the number of mature kernels which, in turn, depends on crop growth at silking. This study was conducted to determine whether night temperature at silking could affect kernel set in maize. Two night thermal conditions: (i) ambient and (ii) ambient plus 5°C, imposed from 1 wk before to 3 wk after silking in a well‐watered and fertilized maize crop, were investigated in a field experiment at Balcarce, Argentina during the 1994‐1995 growing season. Development rate was hastened by heating; tassels and silks appeared 1 d earlier and the lag phase of grain filling was shortened by 5 d. Control plots required seven more days to achieve the same thermal sum than heated plots during the heating period. Plant growth per day at silking did not differ between treatments since both the crop radiation interception and radiation use efficiencies remained unchanged. Differences in respiration losses were insignificant. Spikelet morphogenesis was not affected by heating. Nevertheless, kernel abortion was increased in heated plots (36 vs. 28% for controls, P < 0.02). Final kernel number was associated with plant growth rate at silking when rate was expressed per unit of thermal time. Thus, increased night temperature at silking affected kernel set in maize mainly through increasing development rate that reduced photoassimilate production per unit of thermal time, limiting photoassimilate availability to support kernel growth at the ear tip.