Effect of heat stress on grain yield stability, chlorophyll content and cell membrane stability of flag leaf in commercial rice cultivars in Khuzestan

To study the effect of heat stress on physiological and structural characteristics of rice cultivars, an experiment was carried out in a split-plot arrangement using randomized complete blocks design with three replications in 2006 and 2007 cropping seasons at Shavoor Agricultural Research Station, Ahwaz, Iran. For exposing rice cultivars to different higher temperature regimes, main plots were assigned to three sowing dates from 5 May with 20 days intervals and cultivars; Hoveizeh, Hamar (heat tolerance) Red Anbori, Champa (heat sensitive) and Danial (relatively heat tolerant) were randomized in sub-plots. The results of combined analysis of variance showed that sowing date had significant effect on grain yield. The highest grain yield was harvested from the second sowing date (26 May). cv. Hoveizeh with grain yield of 4977.6 Kg.ha-1 was the superior cultivar. Chlorophyll content at 50% heading and harvesting time were also affected by sowing date and cultivars. The first sowing date (5 May) had the highest chlorophyll content, however, the lowest chlorophyll content was measured for cv. Hoveizeh. The simple analysis of variance also indicated that the third (15 June) and first (5 May) sowing dates had the highest and lowest cell membrane stability, respectively. Cv. Hoveizeh had greater cell membrane stability when compared with the other cultivars, in all three planting dates. cv. Hoveizeh had also the lower environmental sensivity, hence, higher grain yield stability.