CHANGES IN ENZYMATIC-ACTIVITIES AFTER HARVEST AND IN EARLY STAGES OF BOTRYTIS-CINEREA INFECTION OF KIWIFRUIT

Mature unripe kiwifruit were harvested on 19 May 1992, inoculated with Botrytis cinerea conidia, stored at 22 degrees C and subsampled up to 168 h. Phenylalanine-ammonia lyase (EC 4.3.1.5) activities in the stem end tissues peaked at 4 h with 4.0 and 7.3 times the initial values for control and inoculated fruit, respectively. Endochitinase (EC 3.2.1.14) activity increased in inoculated fruit only from 24 h after harvest, reaching 3.3 times the initial value at 168 h. A number of isoforms of endochitinase were detected at the time of harvest. Exochitinase activity was present in both inoculated and control fruit. Lipoxygenase (EC 1.13.11.12) activity increased at 4-8 h to 1.4 times the initial activity. Peroxidase (EC 1.11.1.7) activities in inoculated and control fruit at 168 h were, respectively, 2.6 and 1.3 times the original values. Catechol oxidase (EC 1.10.3.1) activity increased from 2 h after harvest and peak values were 3.3 and 2.6 times the initial values for inoculated fruit and controls, respectively. The peroxidase and catechol oxidase activities of rotted stem end tissues were very low. High activities of pathogenesis-related enzymes in fruit on the vine suggests that their expression is governed by environmental or maturity factors rather than by postharvest infection. The changes occurring in the early post-harvest period appear to be related to the early post-harvest decline in susceptibility to infection.