Control of Powdery Mildew Disease in Cucumber and Tomato Seedlings by Supplemental UV-B Irradiation

Abstract

Ultraviolet-B (UV-B; wavelength, 280–315 nm) is known to induce resistance against various plant diseases. In this study, irradiation of UV-B was examined to determine optimal conditions in cucumber and tomato seedlings using a UV-B fluorescent lamp. Powdery mildew was suppressed by daily 2-hour irradiation of UV-B at 50 and 100 mW・m^–2 in both species, but visible leaf injury occurred on UV-B irradiation at 100 mW・m^–2. Daily 1-hour UV-B irradiation had insufficient effects; on the other hand, 2 or 3-hour treatment had the same effects as conventional chemical protection. As a result, optimal conditions of UV-B irradiation were considered to be 50 mW・m^–2 for 2 hours daily in cucumber and tomato seedlings, and UV-B irradiation is considered to be an alternative method for practical protection from powdery mildew.