The Role of Spike Photosynthesis and Foliar Application of IAA on Grain Yield and its Components of Two Wheat Cultivars in Late Season Drought Stress

Drought stress is a major cause of reduction in crop production. According to the role of various plant parts, especially the spike photosynthesis in grain filling and the regulatory roles of IAA in formation of grain yield, a split plot-factorial experiment based on randomized complete block design (RCBD) with three replications was conducted at the experimental field of the Campus of Agriculture and Natural Resources, University of Razi, Kermanshah, in 2010-2011 growing season using two wheat cultivars (Marvdasht and Pishtaz). Results indicated that water stress after pollination significantly decreased grain yield and 1000 grain weight but it did not affect grain no. spike-1, number of fertile and infertile spikelet per spike and spike length as compared well-watered conditions. Drought stress caused 25.7 and 22.6 percent reduction in grain yield and 1000 grain weight of varieties under study respectively. Cultivars differed in grain no. spike-1, 1000 grain weight, number of fertile and infertile spikelet per spike and spike length significantly. Water stress also reduced grain yield of Marvdasht cultivar (31.8%) as compared to Pishtaz cultivar (18.7%). Pishtaz cultivar possessed larger spikes which resulted in grain yield increase under drought stress. Photosynthesis of spike during grain filling stage increased yield under well watered condition by 42.5% and under post-anthesis drought stress by 23.8%, respectivly. Foliar application of IAA did not have any effect on yield reduction when photosynthesis was stopped. This shows the importance of spike photosynthesis in increasing grain yield.