Physiological and yield responses of rainfed grapevine under different supplemental irrigation regimes in Fars province, Iran

• Half of rainfall was used by evaporation under rainfed condition.
• Two times supplemental irrigation did not increase significantly grape yield compared to no irrigation.
• Supplemental irrigation in May yielded more grape berries.

Supplemental irrigation, which provide minimum amount of water under rainfed farming systems, improves the physiological characteristics and yield production of plants especially in arid and semi-arid regions. However, the amount and timing of supplemental irrigation are of utmost importance and challenging with the recent drought occurrences. A two-year field experiment was carried out to study the effect of different supplemental irrigation timings (March, April, May, June, March + April and no irrigation, denoted I1, I2, I3, I4, I5 and I6, respectively) on stomatal conductance (gs), photosynthesis rate (An) and leaf water potential of rainfed seedless Table grape, cv. Yaghooti. The I1, I2, I3 and I4 treatments received 500 l of water, while I5 treatments received 1000 l of water during the growth season, respectively. The significant maximum berry weight was obtained in the I3 treatment in both years indicating the efficient use of applied water. Maximum and minimum values of An and gs were 12.10 μmol m−2 s−1 and 0.133 mol m−2 s−1 in I4 (in 114 days after first irrigation initiation), and 6.54 μmol m−2 s−1 for I5 and 0.068 mol m−2 s−1 for I1, respectively. It is concluded that supplemental irrigation during May (I3) yielded more grape production, although it received less water compared to I5 treatments.