Yield components of wheat grown under high temperature stress during reproductive growth

High temperature is a major determinant of wheat (Triticum aestivum L.) dev elopment and growth, decreasing yields by 3 to 5% per 1 degrees C increase above 15 degrees C in plants under controlled conditions. Even greater yiel d differences have been reported between favorable and unfavorable temperat ure conditions in the field. The objective of this study was to identify th e yield components of the hard red,winter wheat cultivar Karl 92 that are a ffected by controlled high temperature during maturation of intact plants u nder simulated field populations. Plants at a final density of 144 m(2) wer e grown in the greenhouse until anthesis and transferred to growth chambers for temperature treatment. Day/night temperatures of 20/20, 25/20, 30/20, and 35/20 degrees C were imposed from 10 and 15 d after anthesis until ripe ness in two experiments, and temperatures of 25/20, 30/20, and 35/20 degree s C were applied from 20 d after anthesis until ripeness in a third experim ent. Grain yield was reduced by 78%, kernel number was reduced by 63%, and kernel weight was reduced by 29% at 35/20 degrees C compared,vith 20/20 deg rees C from 10 d after anthesis until ripeness. The yield loss from high te mperature applied during this period was much greater than for previous con trolled-environment studies. Kernel numbers in treatments applied during ea rly reproductive growth in our study were as sensitive to high temperature as wheat plants in previous field studies. High temperature applied 15 d af ter anthesis until ripening reduced grain yield 18%, Since kernel number wa s set by this time, the loss was exclusively due to decreased kernel weight . High temperature imposed from 20 d after anthesis decreased kernel weight by 18%.