Light quality influences the virulence and physiological responses of Colletotrichum acutatum causing anthracnose in pepper plants

Aims: To explore the effects of light quality on the physiology and pathogenicity of Colletotrichum acutatum, we analysed the morphological traits, melanin production and virulence of the pathogen under different light wavelengths. Methods and Results: The influence of light wavelength on the mycelial growth and conidial germination of C.acutatum was investigated using red, green, blue and white light sources. Red and green light reduced the mycelial growth in comparison with blue and white light, and dark conditions. The least percentage of conidial germination was observed under blue light, while the germination rate among white, red and green light, as well as in the dark, was insignificant. In comparison with its influence on mycelial growth and conidial germination, light wavelength significantly affected the pathogen's virulence towards hot pepper fruits. The highest disease severity was observed under blue light, which was at least a twofold increase compared with the disease severity under other light conditions. To elucidate the effect of light on the disparity in virulence, scytalone was assayed by HPLC, and scd1 gene expression was examined with real-time PCR. The highest and lowest scytalone production was observed in the cultures incubated under blue (109mAU) and green light (15mAU), respectively. Higher scd1 gene expression (similar to 40-fold increase) was observed in cultures incubated under blue and white light in comparison with those incubated in the dark. Conclusions: This study revealed that light affects the growth, colonial morphology and virulence of C.acutatum. The pathogen needs light for its active melanin production and also to attain higher virulence. Significance and Impact of the Study: This is the first report on the effect of light quality on the virulence of C.acutatum. The findings of this study will broaden our knowledge of the influence of light on physiological responses of fungal pathogens.