Photosynthesis and Remobilization of Dry Matter in Wheat as Affected by Progressive Drought Stress at Stem Elongation Stage

With increasingly erratic rainfall patterns particularly in drought‐prone production systems, the capacity of plants to recover productively from drought spells becomes an important feature for yield stability in rainfed agriculture. Consequently, effects of water management at the stem elongation stage on partitioning and remobilization of dry matter, alteration in photosynthesis and water‐use efficiency (WUE), and yield components of wheat plants were studied in a glasshouse pot experiment. The plants were subjected to three soil moisture regimes: well watered during all phenological stages (WW), drought affected during stem elongation and post‐anthesis stages (DD) and drought affected during stem elongation and rewatered at post‐anthesis stage (DW). Total dry weight substantially decreased by both drought treatments. However, DD plants allocated relatively higher assimilates to roots whereas DW plants remobilized them to the grains. Drought applications resulted in a decrease of grain yield and thousand grain weight while reduction was more pronounced in DD treatment. Relative contribution of post‐anthesis photosynthesis to dry matter formation in grain was higher in WW treatment (72.6 %) than DD (68.5 %) and DW (68.2 %) treatments. Photosynthetic rate, gas exchange and transpiration decreased whereas leaf (photosynthetic) and plant level WUE increased with drought applications. However, all these parameters were rapidly and completely reversed by rewatering. Our findings showed that partitioning of dry weight to grain increases with rewatering of wheat plants subjected to drought during stem elongation phase, but the relative contributions of remobilization of stem reserves and post‐anthesis photosynthesis to grain did not change. Moreover, rewatering of plants at booting stage after a drought period lead to full recovery in photosynthesis and WUE, and a significant although partial recovery of yield components, such as grain yield, TGW and harvest index.