The objective of this study was to assess changes in proline, Glycine Betaine (GB), photosynthetic pigment concentration, Membrane Stability Index (MSI), and grain yield of wheat cultivars induced by Supplemental Irrigation (SI) in the terminal growth stages. Two field experiments with four irrigation levels (rainfed, SI at booting stage, SI at booting and anthesis stages, SI at booting, anthesis, and grain filling stages) and five cultivars (Rejaw, Sardari, Homa, Azar2, and Sirwan) were conducted during the 2015- 2017 growing seasons. Results indicated that, overall, SI increased cultivars' chlorophyll concentration, MSI, and grain yield. Proline and GB highly accumulated under drought stress, but rapidly decreased after SI; the severity of the decrease in proline concentration was more remarkable. Sardari and Azar2 cultivars exhibited greater MSI, proline, and GB accumulation during drought stress and more rapid recovery from drought. Our results suggest that the ability of the wheat cultivars to maintain functions during drought and recover after SI during the terminal growth stage is essential for determining final grain yield.
