Effect of Spray Application of Calcium Compounds Combined with Free Polyamines at Different Growth Stages on Physiological Problems and Yield of ‘Ahmad-Aghaii’ Pistachio (Pistacia vera L.)

Introduction: Pistachio is one of the most important horticultural crops in Iran, USA, Turkey and some Mediterranean countries. Some physiological problems such as abscission of inflorescence buds, blankness, non-splitting, early splitting, cracking and nut deformation reduce the pistachio yield and quality. A proper nutrition management of pistachio orchard might decrease the physiological problems and increasing the yield. Calcium is an essential plant macro-nutrient that has several distinct functions within plants. These functions can be divided into main areas including effects on membranes, enzymes, cell walls, and interactions of calcium with phytohormones. Free polyamines (putrescine, spermine, spermidine), are the widely distributed of N containing organic molecules binding to the intracellular anions (DNA, RNA, chromatin and proteins). They are also known to possess several regulatory functions. In plants, they have been associated with regulating many physiological processes, such as organogenesis, embryogenesis, floral initiation and development, leaf senescence, fruit development and ripening, and abiotic and biotic plant stress responses. Although the spray application of calcium compound and free polyamine has been investigated separately, application of calcium compounds combined with free polyamines has not been investigated yet. Therefore, the aim of this study was to evaluate the effect of combined treatments of calcium and free polyamines on decreasing the physiological problems and improving the yield of ‘Ahmad-Aghaii’ pistachio trees. Materials and Methods: This experiment was carried out in a commercial 20-year old ‘Ahmad-Aghaii’ pistachio orchard in Rafsanjan, Iran. It was arranged as factorial based on randomized completely block design with three replications. The treatments were control, calcium compounds (calcium nitrate and calcium chloride at concentration of 0.5%) combined with free polyamines (putrescine, spermidine and spermine at concentration of 0.5 mM). Spraying were applied at different growth stages including two weeks after full bloom (stage 1), six weeks after full bloom (just before endocarp hardening) (stage 2) and the combination sprays of stage 1 and stage 2. Different traits including the percentages of abscission of inflorescence buds, cracking, blankness, early splitting, nut deformation, non-splitting and splitting as well as yield, leaf area and vegetative growth were measured. The individual shoot was the experimental unit and analyses of variance were performed using the General Linear Models procedure of SAS. Means were separated by Duncan’s multiple range test (P < 0.05). Results and Discussion: Results showed that the main physiological problems of pistachio crop were decreased by application of calcium compounds combined with free polyamines. Spray application of the mentioned treatments was more effective at combined stages of 1 and 2 rather than the stages separately. It was resulted that calcium nitrate combined with spermine and spermidine treatments at combined stages of 1 and 2 reduced the abscission of inflorescence buds, blankness, nut deformation and non-splitting. Also, it was found that calcium nitrate combined with spermidine at combined stages of 1 and 2 reduced the percentage of early splitting while splitting and yield were increased. Spray application of free polyamines combined with calcium compounds did not affect the length and diameter of current-year shoots but significantly increased the leaf area. It seems that calcium plays a key role in conjunction with free polyamines especially spermidine and spermine in decreasing the abscission of inflorescence buds via improving the stability of cell wall and preventing abscission layer formation. It also seems that polyamines reduce the abscission of inflorescence buds by antagonism with ethylene, possibly by competing for S-adenosylmethionine (SAM), a common precursor of both plant bioregulators. Increasing the shoot yield and decreasing the percentage of blankness might be due to improving leaf photosynthesis as well as regulating kernel growth and development. It was found that free polyamines and calcium might promote a regulatory system against environmental stresses especially heat, drought and salinity which are the main concerns of pistachio growers. Conclusion: According to the results, the application of calcium compounds combined with free polyamines could reduce the physiological problems and increased the yield of ‘Ahmad-Aghaii’ pistachio. Among calcium treatments, calcium nitrate was significantly more effective than calcium chloride. In the case of free polyamines, both spermidine and spermine were more effective than putrescine. It was concluded that application of calcium nitrate combined with spermidine or spermine at both stages (stage 1 + 2) was the most effective treatments in reducing physiological problems and increasing the yield of pistachio trees