Effects of Humidity and Leaf Wetness on Infection and Incubation Periodof Strawberry by Podosphaera aphanis var. aphanis

Abstract

The leaves of strawberry seedlings were sprayed with a conidial suspension of Podosphaera aphanis var. aphanis within one week of their complete unfolding. In all four strawberry cultivars tested, lesions first developed on the 5th day post-inoculation, and new lesions, which were originated from inoculated conidia, appeared continuously until the 9th day post-inoculation, possibly for a few more days. The number of lesions that appeared on the 5th day was <5% of the total lesions developed during the 13-day post-inoculation period in the three cultivars, “Mo-ikko,” “Nyoho,” and “Saga-honoka.” In the cultivar “Sanuki-hime,” 14.6% of the total lesions appeared on the 5th day post-inoculation, while the number of lesions that developed each day between the 9th and 13th days was <11% of the total. Thus, depending on the cultivar, more lesions developed over two to three days between the 5th and 8th days post-inoculation. Considerably greater levels of infection occurred at a relative humidity of 100% than at 50% (p < 0.05). Twenty-four or forty-eight hours of leaf wetness post-inoculation with a conidial suspension neither significantly reduced nor increased the infection levels in the seedlings of “Mo-ikko” and “Nyoho” cultivars (p < 0.05).