PREVENTION OF BLACK SPOT DISEASE IN PERSIMMON FRUIT BY GIBBERELLIC-ACID AND IPRODIONE TREATMENTS

Black spot disease (BSD) in persimmon fruit, caused by Alternaria alte rnata, develops primarily in the high humidity environment beneath the calyx. Three treatments with gibberellic acid (GA(3), 20 mu g/ml) app lied during fruit development at 30, 20, and 10 days before harvest, r educed decay more effectively than the single commercial treatment of GA(3) (50 mu g/ml) applied 10 days before harvest. As a result of GA(3 ) treatment, the calyx of the fruit remained erect till harvest. The c orrelation coefficent between BSD under the calyx and calyx erectness was r = -0.72. Persimmon fruits treated with GA(3) in the orchard and stored at 0 C for 3 mo showed less fruit area becoming covered with bl ack spot during storage compared with untreated fruit. Increasing the number of sprays from one to three resulted in a decreased infected ar ea. Sprays of GA(3) also inhibited fruit softening, with a correlation coefficient of r = -0.63 between decayed area and fruit firmness. GA( 3) at concentrations up to 200 mu g/ml had no effect on fungal develop ment in vitro and in vivo on inoculated fruits. GA(3) apparently affec ts decay development by enhancing resistance of the fruit. Preharvest treatment with GA(3) and the fungicide iprodione further reduced the p ercentage of fruits unmarketable due to BSD.