Effect of Water Stress and Source Limitation on Accumulation and Remobilization of Photoassimilates in Wheat Genotypes

In order to study dry matter accumulation in different developmental stages and photoassimilates remobilization in bread wheat genotypes, a field experiment was carried out using a split split plot design based on a randomized complete block design with three replications in Torogh Agricultural and Natural Resources Research Station (Mashhad, Iran) in 2006-2007 and 2007-2008. Main plots were assigned to two levels of water stress treatments; D1: optimum irrigation, and D2: cessation of watering from anthesis to maturity stages. Sub plots were assigned to eight bread wheat genotypes: 9103, 9116, 9203, 9205, 9207, 9212, C-81-10, and Cross Shahi; and source limitations with two levels; P1: no source limitation and P2: inhibition of current photosynthesis from anthesis were in sub-sub plots. Results of combined analysis showed that, grain yield, accumulation of dry matter in different developmental stages (soft dough stage and physiological maturity stage), amount of remobilized dry matter (DMT), remobilization efficiency (RE), remobilization percentage (CPAAG), canopy temperature depression (CTD) and leaf relative water content (RWC) in anthesis and grain watering stages was significantly affected by water stress treatment. Water stress increased DMT, RE, and CPAAG by 15%, 18%, and 50.6%, respectively; compared with well-watered treatment. Current photosynthesis inhibition increased CPAAG by 43.1%, and decreased DMT and RE by 44% and 60.8%, respectively; compared with P1 treatment. Postanthesis water stress and current photosynthesis inhibition caused source and sink limitations, and decreased CTD and RWC. Considering that C-81-10, 9103 and 9116 genotypes showed the highest grain yield and translocated dry matter under different moisture conditions; thus, these genotypes could be introduced as promising lines in breeding programs for arid and semi-arid regions. Significantly positive correlations between CTD and RWC with grain yield, particularly at grain watery stage, showed that CTD and RWC can be used for selection criteria in breeding programs