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

The tolerance of Botrytis cinerea Pers. spores and Thompson Seedless g rapes (Vitis vinifera L.) to vapour phase hydrogen peroxide (H2O2 vapo ur) at various concentrations and temperatures was determined. The ger mination rate of botrytis spores decreased logarithmically with exposu re time to H2O2 vapour. Treatments of 0.27 and 0.55 mg l(-1) H2O2 vapo ur at 20 or 30 degrees C, respectively, required 10.5 and 5.7 min to k ill 99% of the spores. Grapes did not develop visible injury until the y were exposed to 0.55 mg l(-1) H2O2 vapour for 6 h at 40 degrees C. I njury developed as a yellow-brown discoloration of the fruit and stems . Discoloration increased with time of exposure and concentration of H 2O2 vapour. High treatment temperatures also increased the rate of dis coloration. Prolonged exposure to H2O2 vapour caused increased water l oss and loss of firmness of the grapes. Grapes were able to tolerate e xposures 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 an d grapes to H2O2 vapour may allow its use to control botrytis bunch ro t in stored table grapes.