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

Abstract

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 (10Á9 mAU) and green light (1Á5 mAU), respectively. Higher scd1 gene expression (~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.

Fungal photobiology: visible light as a signal for stress, space and time

“…Even visible light itself can be a source of oxidative stress for the fungal cell as was shown most recently in Botrytis cinerea , in which a white light (400–720 nm)-dependent reduction in growth rate could be rescued simply by the addition of the antioxidant ascorbate to the medium (Canessa et al 2013). A similarly slight reduction in mycelial growth by light has also been noted in numerous fungi including, Aspergillus fumigatus (Fuller et al 2013), Cordyceps militaris (Yang and Dong 2014), Fusarium graminearum (Kim et al 2014a) and Colletotrichum acutatum (Yu et al 2013). …”

“…Photo-induced melanization has been observed in numerous ascomycetes including Aspergillus fumigatus (Fuller et al 2013), Magnaporthe oryzae (Kim et al 2011b), Cercospora kikuchii (Bluhm et al 2010), Botrytis cinerea (Canessa et al 2013) and Colletotrichum acutatum (Yu et al 2013), as well as in the basidiomycete mushroom Lentinula edodes (Sano et al 2009). The WCC is presumed to play a major role in melanization for these fungi based on the action spectrum for the response and, in the case of A. fumigatus , has been demonstrated directly through deletion analysis.…”

“…Surprisingly, however, a blue light-to-dark- driven melanin banding pattern in B. cinerea persists in the wc-1 deletion mutant, indicating that additional blue-light receptors are operative (Canessa et al 2013). Moreover, red light, in addition to blue light, was shown to have an inducing effect in C. acutatum , but the role of a phytochrome in this response is unknown (Yu et al 2013). …”

“…The induction of photolyases and/or UV endonucleases by blue light has been shown in the ascomycetes Neurospora , A. fumigatus (Fuller et al 2013), A. nidulans (Ruger-Herreros et al 2011), Fusarium oxysporum (Ruiz-Roldan et al 2008) and Cercospora zeae-maydis (Yu et al 2013). In C. neoformans , endonuclease (Uve1) induction is dependent upon the WCC as is light-induced UV resistance (Verma and Idnurm 2013).…”

Seeing the world differently: variability in the photosensory mechanisms of two model fungi

“…However, understanding photobiology may have merit in its own right, as the importance of light on agriculturally, industrially and even medically important fungi becomes appreciated. For example, light enhances plant lesion size during infection with Colletotrichum acutatum and Cercospora zeae-maydis , but represses infection with Magnaporthe oryzae (Kim et al , 2011a; Kim et al , 2011b; Yu et al , 2013). It is difficult to dissect the influence of light on the pathogen versus the host in these experiments, but at least in the case of M. oryzae , the light effect is lost upon deletion of wc-1 .…”