Abstract
Supplementary lighting with blue-violet light-emitting diodes (LEDs) was tested to reduce the onset of pathogenic disease in tomato plants grown in the greenhouse. Tomato plants (cvs. Reika and Momotaro) were cultivated on rockwool under drip irrigation without the application of any agricultural chemicals. Supplementary lighting systems consisting of LED units fitted with 12 LED lamps (peak wavelength 405 nm) were developed to irradiate the plants. Supplementary lighting was provided in the early morning (from before sunrise) and early evening (till after sunset) at a power consumption of 6–12 W per plant. The onset of pathogenic disease was visually inspected and compared with that of control plants cultivated without supplementary lighting. Supplementary lighting of 405 nm LED reduced the onset of black leaf mold (Pseudocercospora fuligena). As a result of analysis of the relationships between environmental factors and the suppressive effect of LED irradiation, it was observed that supplementary lighting with 405 nm LED was effective in disease suppression at high temperature. These findings indicate that 405 nm LED irradiation has the potential to provide tomato plants protection from disease, and this technique is therefore expected to contribute to a reduction in the use of agricultural chemicals in protected cultivation.
