Mechanical wounding and abscission in citrus

leaf drop were determined in Citrus sinensis for periods up to 96 h after mechanical wounding. Injury by removing a thin section of mature fruit flavedo reduced FDF, increased ethy-lene evolution and promoted abscission. Injuring flavedo 1 cm below the calyx was more effective at reducing FDF than injuring flavedo at the equator or the blossom-end of mature fruit. Injuring the calyx or peduncle of mature fruit, or injur-ing three leaves closest to the mature fruit did not reduce FDF. Immature fruitlets either did not abscise or underwent low rates of abscission in response to mechanical wounding, depending on age. Inhibiting ethylene binding in wounded mature fruit with 1-methylcyclopropene (1-MCP) increased ethylene evolution compared with wounded fruit alone, but the reduction in FDF was similar. When an ethylene biosynthesis inhibitor (aminoethoxyvinylglycine, AVG) was used, reduc-tion in FDF of wounded mature fruit exposed to AVG was similar to that of wounded fruit alone but ethylene production was markedly reduced. Wounding mature leaf blades in the presence or absence of 1-MCP resulted in elevated but equal ethylene evolution up to 48 h after wounding, however, no leaf drop occurred. Thereafter, ethylene evolution was higher in 1-MCP-treated wounded leaves. Removing up to 77 % of the total mature leaf area did not cause leaf drop, nor did wound-ing tissue across the laminar or petiolar abscission zones. Leaflets of 5mm length reached nearly 100 % abscission after mechanical wounding, whereas wounding leaves 20mm length resulted in 15 % abscission. The data suggest that mechanical wounding of flavedo results in mature fruit abscis-sion, and ethylene binding may not be mandatory to initiate abscission in citrus fruit. The differential response of fruit and leaves at different ages to wounding may be related to poten-tial contribution to carbohydrate accumulation, and produc-tion and sensitivity of tissues to an abscission signal(s)