Wheat cultivars adapted to post-heading high temperature stress

The existence of genetic variation in wheat for tolerance to high temperature stress has been reported but cultivars released for a particular production system often are not characterized. The objective of this study was to identify and describe the characteristics of wheat cultivars adapted to production systems with risks of high temperature during the post-heading period. Fifteen diverse wheat cultivars and one unreleased genotype were evaluated at the Texas A&M University Agricultural Research and Extension Center, Uvalde, TX, during two seasons characterized by daily maximum temperatures as high as 36 degrees C. Measurements during both seasons included days to heading, days to physiological maturity and grain yield. Large and significant (P < 0.05) grain yield differences were measured among cultivars within each season. Yield varied between 2979 and 4671 kg ha(-1) in the first season and between 1916 and 5200 kg ha(-1) in the second season. Late planting in the second season delayed heading date resulting in the post-heading period to coincide with periods of high temperatures. Cultivars that headed early, in general, yielded better than cultivars that headed later within each season with yield reduction of 35.3 kg ha(-1) in the first season and 91.0 kg ha(-1) in the second season for every 1 day delay in heading after mid-March. Early-heading cultivars outperformed later-heading cultivars because of two distinct advantages: the early-heading cultivars had longer post-heading and, therefore, longer grain filling period than the later-heading cultivars. In addition, early-heading cultivars completed a greater fraction of the grain filling earlier in the season when air temperatures were lower and generally more favourable. The advantage of earlier-heading cultivars was also manifested in the amount of green leaves retained to anthesis. Earlier-heading cultivars produced fewer total leaves per tiller but retained more green leaves and lost fewer leaves to senescence at anthesis than later-heading cultivars. The results suggest that early heading is an important and effective single trait defining wheat cultivars adapted to production systems prone to high temperature stress during the post-heading period.