Evaluating the Effects of Sowing Dates on the Peduncle Anatomy and Grain Yeild of Rice Cultivars in the Climatic Condition of Khuzestan Province

This experiment was carried out to determine the effects of heat stress, due to different planting dates, on the peduncle anatomy of rice cultivars and their grain yields. It was performed in a split-plot experiment using randomized complete blocks design with three replications in 2006 and 2007 cropping seasons at the Shavoor Agricultural and Natural Resources Research Center of Khuzestan. Three planting dates (May 5th. with 20 days intervals), to expose rice cultivars to different tempratures, were assigned to main plots and cultivars (Hoveizeh, Hamar, heat tolerant, Ghermez Anbori, Champa, heat sensitive, and Danial, relatively heat tolerant) to sub-plots. The results of combined analysis showed that the effects of planting date× variety interactions were significant for all of traits, including air channel surface, large vascular bundles surface, xylem and phloem. This indicates that cultivars reacted differently to planting dates. Lowest and highest airchannels surface levels were related to 1st and 2nd planting dates (15492.23 and 21144.38 µm2) and to Hoveizeh and Champa cultivars (15492.23 and 23411.18 µm2) respectively. Lowest and highest xylem surface obtained in 3rd and 1st planting dates (741.37 and 898.03 µm2) respectively. But, lowest and highest level of large vascular bundles were optained in 2nd and 3rd planting dates (15514.20 and 15983.93 µm2)and for phloem (3121.68 and 3437.55 µm2)respectively. Based on these results it can be said that the reduction of large vascular bundles surface and phloem in 1st and 2nd planting date are mechanisms of water conservation and maintaining cell turgor pressure. Increasing xylem vascular bundle surface also, would facilitate availability of water to plant under drought stress conditions.