PHYSIOLOGICAL AND BIOCHEMICAL RESPONSES IN SOME ALMOND (PRUNUS AMYGDALUS BATSCH.) GENOTYPES (GRAFTED ON/GN15) SUBMITTED TO DROUGHT STRESS

The concept of plants reactions to drought conditions is important for improving water-use efficiency (WUE). In this research several physiological traits including: relative water content (RWC), leaf water potential (psi(W)), photosynthesis rate (P-N), stomatal conductance (g(s)), leaf temperature (Delta(T)), electrolyte leakage (E-L) of five almond genotypes grafted on/GN15 rootstock, which exposed to drought stress were studied. Drought tolerance according to some parameters was specified in different genotypes. In all genotypes, as the level of drought severity increased, RWC (up to 32%), psi(W) (up to -3.38Mpa), photosynthesis rate (up to 70%) and leaf stomatal conductance (up to 75%) significantly decreased; whereas, electrolyte leakage (up to 53%), and leaf temperature increased. Water deficit significantly elevated WUE more than 7 times in the drought-resistance genotypes. The differences in Delta T in the early morning and midday significantly decreased in drought tolerant genotypes. Significant (p >= 0.01) correlation between Delta T, P-N and gs were found. It can be concluded that AT might be utilized as an easy evaluation in order to estimate drought stress in almond genotypes and controlling drought stress in the irrigation programs of almond trees. In other words, in comparison, "Ferragness" cultivar, "Sahand" and H genotypes on GN15 rootstock could act more efficiently than other genotypes, especially during severe drought stress conditions. This is related to decreases in stomatal conductance and more ability to maintain RWC.