Effect of Interrupted Wetness Periods on Spore Germination and Apple Infection byBotryosphaeria obtusa

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Abstract
Conidia of Botryosphaeira obtusa were allowed to germinate in water for 4 hr at 24 C, were air-dried, and were rewetted following dry periods ranging from 0 to 8 hr. No increse in germ tube length was observed 4 hr after rewetting in any treatment. Mean germ tube length was similar (approximately 126 .mu.m) for all drying treatments. Mean germ tube length was 532 .mu.m when conidia were allowed to germinate in water for 8 hr without interruption. Apple [Malus .times. domestica] seedlings were inoculated with conidia of B. obtusa in aqueous suspension and were exposed to 24-hr wetness periods, which were interrupted after 12 hr for 1, 2, 3, and 4 hr. Infection of apple foliage stopped irreversibly with interruptions of 1 or more hr in the wetness period. Interrutpons as short as 1 hr also resulted in reduced infection of fruit.