Irradiation with UV-B fluorescent bulbs suppresses strawberry powdery mildew

W. Sugeno, Y. Iwasaki, Y. Hachiya
Strawberry powdery mildew [caused by Sphaerotheca aphanis (Wallr.) U. Braun] is a serious disease of strawberry (Fragaria × ananassa). It is difficult to control this disease using fungicides, because S. aphanis is adept at developing fungicide resistance. However, UV-B lights have been reported to induce resistance in strawberry plants against powdery mildew. In this study, we investigated the ability of a new type of UV-B fluorescent bulb (recently developed by the Panasonic Lighting Devices Co., Ltd., Japan) to suppress strawberry powdery mildew under greenhouse conditions. Strawberry plants were irradiated daily with UV-B (light intensity 4.0-13.4 μW cm-2) for 3 h during the night from the time of transplanting to the end of cultivation. We found that the number of fruits infected with powdery mildew declined by 84.3% relative to the control treatment (no irradiation). UV-B radiation (light intensity 4.3-15.3 μW cm-2) for 4 d week-1 for 3 h during the night lowered the percentage of infection by 54.8% relative to controls. Because daily UV-B irradiation significantly suppressed the mildew, we investigated whether incorporating a daily UV-B radiation regime could reduce the required frequency of fungicide application. Under a daily 3-h, UV-B radiation regime (intensity 8.0-18.8 μW cm-2), the percentage of powdery mildew infection on strawberry fruits was 0.1%, even when fungicide spraying was reduced to four times (compared with 16 times in the control). Our results indicate that using a UV-B lighting system for inhibiting powdery mildew in strawberry plants could substantially reduce fruit loss and the cost of fungicide spraying.
Sugeno, W., Iwasaki, Y. and Hachiya, Y. (2018). Irradiation with UV-B fluorescent bulbs suppresses strawberry powdery mildew. Acta Hortic. 1227, 549-554
DOI: 10.17660/ActaHortic.2018.1227.69
Fragaria × ananassa, Sphaerotheca aphanis (Wallr.) U. Braun, UV-B lighting system, greenhouse, induced resistance

Acta Horticulturae