Effect of Timing of Heat Stress During Grain Filling on Two Wheat Varieties Differing in Heat Tolerance. I. Grain Growth

Abstract

Short periods of very high temperature (> 35�C) are common in many of the world's wheat growing areas and can be a significant factor in reducing yield and quality of wheat. This study was designed to determine the stage at which grain growth is most sensitive to a short period of high temperature and to examine whether varietal differences in heat tolerance are expressed throughout the whole grain-filling period. Two varieties of wheat differing in heat tolerance (cvv. Egret and Oxley) were exposed to a short (5 days) period of very high temperature (40�C max. for 6 h each day) at 5-day intervals throughout grain filling, starting from 15 days after anthesis (DAA) and concluding at 50 DAA. Responses of grain dry matter accumulation and water content to high temperature were monitored throughout grain filling, and the results compared with controls maintained at 21/16�C day/night. Varietal differences in heat tolerance were expressed throughout the grain-filling period. Mature individual kernel mass was most sensitive to heat stress applied early in grain filling and became progressively less sensitive throughout grain filling, for both varieties. Reductions in mature kernel mass resulted primarily from reductions in duration rather than rate of grain filling.

Response of floret fertility and individual grain weight of wheat to high temperature stress: sensitive stages and thresholds for temperature and duration

“…For every 1 C above the optimal growing temperature of 15À20 C, the duration of grain filling was estimated to be reduced by 2.8 days in wheat (Streck 2005). However, slight increase in grain filling rates were not sufficient to compensate the losses caused by shorter grain filling periods (Stone and Nicolas 1995;Prasad et al 2008b). Similar results were observed with grain sorghum (Prasad et al 2006b(Prasad et al , 2008a.…”

“…High temperature (40 C daytime maximum) during the early grain filling stage caused maximum decrease in individual grain weight; the negative effects became progressively less at later stages of grain filling (Stone and Nicolas 1995). Stone and Nicolas (1998) reported that a day of high temperature (40/21 C day/night) during grain filling decreased the individual grain weight by 14% compared with a control (21/16 C day/night).…”

“…Similarly, Hays et al (2007) showed that a day of HT (40/18 C day/night) at 10 days after anthesis caused a 10-30% reduction in individual grain weight of wheat. Decreases in individual grain weight generally result from shortening of grain filling duration (Stone and Nicolas 1995;Prasad et al 2008b).…”

Truncation of grain filling in wheat (Triticum aestivum) triggered by brief heat stress during early grain filling: association with senescence responses and reductions in stem reserves

“…A similar impact of heat on grain filling (i.e. GFD was affected with little effect on the grain filling rate) was observed by Stone and Nicolas (1995) after applying a similar heat treatment to ours (40 C : 19 C day : night at 15 DAA for 5 days). Sofield et al (1977) tested the effect of source supply on grain filling dynamics by subjecting wheat to three different light intensities during grain filling from 4 DAA onwards.…”

“…Under similar treatment conditions, Tashiro and Wardlaw (1990) have reported that a treatment at 10 DAA was late enough to avoid producing any 'sterile', 'parthenocarpic', 'abortive' or 'shrunken'(wrinkly) wheat grains, but was not late enough to make some grains appear abnormal in other ways (notched, split or opaque). Such a treatment is still early enough to substantially reduce the final grain dry mass of susceptible varieties (Stone and Nicolas 1995). Pots were placed in trays of water to~2-cm depth while in the chamber to minimise drought stress.…”