Ultraviolet B radiation from a compact fluorescent lamp for tomato disease control

We previously produced an ultraviolet B (UV-B) lighting system to control strawberry powdery mildew. Since then, Panasonic Corp. has produced a new compact fluorescent lamp that can provide continuous illumination longer than a previous version of the lamp, and at a lower price. We have begun applying this new compact lamp to control tomato diseases. For this study, tomato was grown in the winter over two growing seasons using a nutrient flow technique (NFT) system in a 300-m2 greenhouse. The compact UV-B fluorescent lamp was suspended from the ceiling, approximately 1-2 m above the tomato plants. Tomato plants were irradiated using compact UV-B fluorescent lamps daily during 23:00-23:30 and 0:00-0:30 from Oct 2014 to Mar 2015, and during 23:00-2:00 from Oct 2015 to Feb 2016. Plants received light energy of 0.1-1.5 kJ m-2 d-1 in 2014 and 0.2-1.4 kJ m-2 d-1 in 2015. Diseased leaves or fruits that had been infected with powdery mildew (Oidium neolycopersici) or gray mold (Botrytis cinerea) were hung at approximately 2 m height as inocula 1-2 months after starting irradiation. Both diseases were suppressed effectively. The best control values against powdery mildew were 92.0% the first year and 91.2% the second year. The control value against gray mold was 65.6% in the first year. The UV-B radiation applied did not suppress germination of tomato powdery mildew conidia in laboratory tests. Furthermore, crude extracts from radiated tomato leaves exhibited antifungal activity. From these findings, we conclude that the compact UV-B fluorescent lamp can induce tomato plant resistance against fungal pathogens. Future studies are expected to produce a new radiation system to control tomato diseases.