Increasing the Efficiency of Supplemental Foliar Nutrition on Improving Reproductive Disorders of Pistachio by Application of Plant Growth Regulators

Abstract

Severe environmental stress and nutrient deprivation cause reproductive disorder in pistachio trees. In this study, the effect of some plant growth regulators on increment the efficiency of supplemental foliar nutrition on reducing these complications was investigated. A factorial experiment (4 × 2) was carried out with exogenous foliar spray of three plant growth regulators included control (without treatment), nitric oxide (DETA/NO, 0.05 mM), 24-epibrassinolide (0.1 mM), Spermine (1 mM), and supplemental foliar nutrition at two levels contained untreated (control) and foliar nutrition with urea (5 gL−1) + zinc chelate (2 gL−1)+calcium chelates (2 gL−1) + boric acid (0.5 gL−1) + KNO3 (40gL−1) + Ca(NO3)2 (20gL−1). Plant growth regulators were applied along with urea, zinc and calcium chelate and boric acid a week before full bloom and 2 weeks after full bloom. They were also used in combination with potassium and calcium nitrate at the shell hardening, beginning and middle of pistachio kernel filling, respectively. The interactive effect of 24-epibrassinolide with supplemental foliar nutrition had the greatest effect on the reduction of fruit abscission (19.1%), blank nuts (53.9%) and inflorescence bud abscission (20.6%) as the main effective variables in reducing the yield of ‘Ahmad-Aghai’ pistachio. This treatment had the highest effect on the increasing the efficiency of supplemental foliar nutrition on improving the reproductive disorders, decreasing the alternate bearing intensities (30.2%) and enhancing fruit yield per tree (79.1%) in ‘Ahmad-Aghai’ pistachio.