EFFECT OF INTERRUPTED LEAF WETNESS PERIODS ON SUPPRESSION OF SPORULATION OF BOTRYTIS-ALLII AND BOTRYTIS-CINEREA BY ANTAGONISTS ON DEAD ONION LEAVES

Saprophytic antagonists were evaluated for suppression of sporulation of Botrytis allii and B. cinerea on artificially killed segments of onion leaves that were pre-inoculated with the pathogens. During incubation of the antagonist-treated leaf segments in moist chambers, periods of leaf wetness and leaf dryness were alternated to simulate conditions in the field. Interruption of humid conditions with dry periods had a differential effect on antagonists. Alternaria alternata, Chaetomium globosum, Ulocladium atrum and U. chartarum suppressed sporulation of B. allii almost completely under continuously wet conditions, and when the leaf wetness periods were interrupted with drying periods of 9h imposed 16, 40, and 64 h after the antagonists were applied. When leaf wetness was interrupted 16 h after antagonist application, the number of conidia of B. allii produced cm(-2) leaf surface after eight days was under the detection limit of 5.2 x 10(3) conidia on leaves treated with these antagonists compared to 3.7 x 10(5) conidia on leaves that were not treated. On the other hand, Gliocladium roseum, G. catenulatum and Sesquicillium candelabrum, all highly efficient under continuously wet conditions, were of low to moderate efficiency when leaf wetness periods had been interrupted 16 h after application of the antagonists. The antagonists showed the same differentiation and sensitivity to interrupted wetness periods when tested with B. cinerea.