Effects of different LED light wavelengths on the resistance of tomato against Botrytis cinerea and the corresponding physiological mechanisms

New types of light-emitting diode (LED) sources were applied to irradiate Botrytis cinerea mycelium and tomato leaves that were inoculated with B. cinerea to assess the effect of different LED light wavelengths on the infection of tomato with B. cinerea, to determine the optimum light wavelengths to control B. cinerea, and to explore the mechanism of LED influence on the development of gray mold. The results showed that purple light and blue light irradiation significantly inhibited the growth of B. cinerea mycelium, and the inhibition rates were 22.3 and 15.16%, respectively, and purple light exhibited a better inhibitory effect than blue light. The lesion development of B. cinerea on tomato leaves was significantly inhibited upon irradiation with red and purple light with inhibition rates of 32.08 and 36.74%, respectively. Irradiation with red light inhibited the oxidative burst of superoxide anion (O2−) that was caused by infection with B. cinerea, and red light regulated the H2O2 content in the tomato leaf, which increased and rapidly returned to a lower level. In addition, red light irradiation improved the activity of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) in tomato leaves. However, purple light irradiation did not make tomato leaves exhibit this kind of physiological response. Therefore, red light and purple light can suppress gray mold in tomatoes, but the disease suppression mechanisms of these two types of LED light are different. In general, red light suppresses gray mold primarily by regulating the tomato defense mechanism for disease, whereas the suppression of tomato gray mold by purple light can be partially explained by the photo-inhibition of B. cinerea.