PHYTOTOXOCITY OF VAPOR-PHASE HYDROGEN-PEROXIDE TO THOMPSON SEEDLESS GRAPES AND BOTRYTIS-CINEREA SPORES

The tolerance of Botrytis cinerea Pers. spores and Thompson Seedless grapes (Vitis vinifera L.) to vapour phase hydrogen peroxide (H2O2 vapour) at various concentrations and temperatures was determined. The germination rate of botrytis spores decreased logarithmically with exposure time to H2O2 vapour. Treatments of 0.27 and 0.55 mg l(-1) H2O2 vapour at 20 or 30 degrees C, respectively, required 10.5 and 5.7 min to kill 99% of the spores. Grapes did not develop visible injury until they were exposed to 0.55 mg l(-1) H2O2 vapour for 6 h at 40 degrees C. Injury developed as a yellow-brown discoloration of the fruit and stems. Discoloration increased with time of exposure and concentration of H2O2 vapour. High treatment temperatures also increased the rate of discoloration. Prolonged exposure to H2O2 vapour caused increased water loss and loss of firmness of the grapes. Grapes were able to tolerate exposures of 0.27 mg l(-1) H2O2 vapour at 40 degrees C for 24 h with no visible injury. The difference in the tolerance of botrytis spores and grapes to H2O2 vapour may allow its use to control botrytis bunch rot in stored table grapes.