Effects of Gibberellic Acid Application on Reduction of Hull Splitting, Aflatoxin Content and Quality of Pistachio Nut

Green skin (hull) of pistachio fruits is a barrier against the penetration of fungi and insects into the kernel of pistachio. Splitting of husk facilitates the entry of fungi and infection of pistachio kernels during the harvest. So far no effective way has been reported for controlling this problem. To evaluate the effects of gibberellic acid on hull spliting the present research was conducted in a commercial orchard of pistachio during 2001-2002 in Rafsanjan, Iran. Gibberellic acid (GA3) at 0,25,50 and 100 mg –1 was applied on 25-year-old of “Owhadi” pistachio cultivar. Two branches of each tree was sprayed during two years of study. GA3 at 25,50 and 100 mg –1 significantly reduced hull splitting and penetration by Aspergillus spp. into pistachio fruits. There was a positive correlation between the hull splitting and fungi penetration (r=0.92*). The exocarp, mesocarp and endocarp of pistachio fruits cultured on selective medium of Aspergillus spp. showed no infection of pistachio kernel by Aspergillus spp. The highest concentration of aflatoxin was detected in the kernel of non-treated fruits (6.25 ppb) and the lowest (0.5 ppb) fruits treated by GA3 . GA3 reduced husk slippery of pistachio fruits at harvest. The rate of husk slippery was reduced by increasing the concentration of GA3. Gibberellic acid treatments had no significant effect on dehiscence, weight of 100 fruits, total soluble solids, but significantly increased fat and chlrophyll content of kernel of pistachio fruits. The results of the study is recommended for commerical pistachio production in Iran.