Effect of Foliar Application of Some Bioregulators on Biochemical, Vegetative Characteristics and Fruit Yield of Tomato (Lycopersicon esculentum Mill.) Under Drought Stress Conditions

Recently, the use bioregulators to ameliorate the effects of environmental stresses on agricultural products has been considered. This split plot experiment was conducted as a randomized complete block design to investigate the moderating effect of some bioregulators on vegetative, biochemical and yield characteristics of greenhouse tomatoes under drought stress in the research greenhouse of University of Hormozgan. Experimental factors were three drought stress levels as the main factor, were include full irrigation as control, moderate and severe drought stress, respectively, irrigation of plants based on providing 100, 75 and 50% readily available water, and foliar application of 0.5 g per plant of biological compounds (the first time one day before applying drought stress and the second time before flowering begins) as a sub-factor including control (without the use of compounds), proline, chitosan and N-Succinyl and N, O dicarboxymethylate chitosan (NSC and NOC, respectively). Application of bioregulators at each water stress level increased the of proline content and catalase and peroxidase enzymes activity in comparison with the control, which in most cases the highest increase in enzyme activity related to NSC. Chitosan derivatives, on the other hand, were able to reduce the amount of malondialdehyde (MDA) and hydrogen peroxide in tomato leaves. Among the biological compounds, NSC and chitosan had the greatest improving effect on the fruit yield via increasing the number and diameter of fruit. So that foliar application with NSC increased fruit yield in control, moderate and severe water stress by 5.33, 17.91 and 33.24%, respectively. Therefore, according to these results, under deficit irrigation conditions, chitosan and its derivatives can reduce the effects of drought stress on tomatoes more efficiently than proline.