Gas-exchange response of almond genotypes to water stress

We studied water relations and gas exchange in six almond genotypes grafted on GF677 in response to withholding irrigation for 14 days and a subsequent 10-day rehydration period. The responses to drought stress significantly differed in the almond genotypes; the tolerant plants were distinguished and monitored. Leaf relative water content (RWC) decreased by more than 23%, leaf water potential dropped to less than -4.3 MPa, and electrolyte leakage increased to 43% in dehydration-sensitive genotypes. Photosynthesis (P (N)) and stomatal conductance (g (s)) of drought-sensitive genotypes were significantly reduced by 70% and 97% in response to water deficiency. Water stress significantly enhanced wateruse efficiency up to 10 folds in drought-tolerant almonds. The difference between leaf temperature and its surrounding air temperature (Delta(T)) increased significantly to more than 187% under water stress in drought-tolerant genotypes. In addition, the reduction in the g (s) and further ability to preserve RWC were involved probably in drought-tolerance mechanism in almond. Negative significant correlations were found between Delta(T), P (N), and g (s). Based on the correlations, we suggested that Delta(T) could be used as a simple measurement for monitoring water stress development in the irrigation management of almond orchards. In conclusion, 'Supernova' and the Iranian genotypes '6-8' and 'B-124', were found to be more droughttolerant compared with other genotypes in this experiment.