Determination of susceptibility of developmental stages in bread wheat to water stress and its effect on yield and yield components

In order to study the effect of water stress on yield and yield components of bread wheat and determine the critical developmental stages under stress conditions, a field experiment was conducted in Torogh Agricultural Research Station (Mashhad, Iran) in 2000/01 and 2001/02 cropping seasons, using a split plot design based on a randomized complete block design with 3 replications. Main plots were assigned to 7 levels of water stress treatments D1, full irrigation D2, cessation of watering from one leaf stage to floral initiation, and in other treatments, cessation of watering under rain shelter D3, one leaf stage to floral initiation D4, floral initiation stage to early stem elongation D5, early stem elongation stage to emegence of flag leaf D6, emegence of flage leaf stage to anthesis D7, anthesis stage to late grain filling (soft dough). Sub-plots were assigned to four bread wheat cultivars: Roshan, Ghods, Marvdasht and Chamran. Results of combined analysis of variance showed, biological yield, grain yield, yield components, harvest index and other traits were significantly affected by water stress treatments. Under D5, D6 and D7 treatments, grain yield decreased compared to D1 by 36.7, 22.8 and 45.6%, respectively. There were also significant differences between genotypes for yield and yield components. Significant correlation coefficients were found between grain yield and number of spike per m2,number of grains per spike, harvest index, spike weight at anthesis and seed set percentage. Under water stress conditions, grain yield was more affected by number of grain per unit area. Results showed, susceptibility of developmental stages of bread wheat to water stress were different. Exposing to water stress in each developmental stages, lead to decrease in yield. Grain filling (D7) and stem elongation (D5) stages were the most critical stages under water stress conditions. The effect of water stress in early pre-anthesis (D6) and tillering (D3) stages was also considerable.