Light Intensity Alters the Behavior of Monilinia spp. in vitro and the Disease Development on Stone Fruit-Pathogen Interaction

Effect of Different Light Wavelengths on Zymoseptoria tritici Development and Leaf Colonization in Bread Wheat

The wheat pathogen Zymoseptoria tritici can respond to light by modulating its gene expression. Because several virulence-related genes are differentially expressed in response to light, different wavelengths could have a crucial role in the Z. tritici-wheat interaction. To explore this opportunity, the aim of this study was to analyze the effect of blue (470 nm), red (627 nm), blue-red, and white light on the in vitro and in planta development of Z. tritici. The morphology (mycelium appearance, color) and phenotypic (mycelium growth) characteristics of a Z. tritici strain were evaluated after 14 days under the different light conditions in two independent experiments. In addition, bread wheat plants were artificially inoculated with Z. tritici and grown for 35 days under the same light treatments. The disease incidence, severity, and fungal DNA were analyzed in a single experiment. Statistical differences were determined by using an ANOVA. The obtained results showed that the different light wavelengths induced specific morphological changes in mycelial growth. The blue light significantly reduced colony growth, while the dark and red light favored fungal development (p < 0.05). The light quality also influenced host colonization, whereby the white and red light had stimulating and repressing effects, respectively (p < 0.05). This precursory study demonstrated the influence of light on Z. tritici colonization in bread wheat.

Deciphering the Effect of Light Wavelengths in Monilinia spp. DHN-Melanin Production and Their Interplay with ROS Metabolism in M. fructicola

Pathogenic fungi are influenced by many biotic and abiotic factors. Among them, light is a source of information for fungi and also a stress factor that triggers multiple biological responses, including the activation of secondary metabolites, such as the production of melanin pigments. In this study, we analyzed the melanin-like production in in vitro conditions, as well as the expression of all biosynthetic and regulatory genes of the DHN-melanin pathway in the three main Monilinia species upon exposure to light conditions (white, black, blue, red, and far-red wavelengths). On the other hand, we analyzed, for the first time, the metabolism related to ROS in M. fructicola, through the production of hydrogen peroxide (H₂O₂) and the expression of stress-related genes under different light conditions. In general, the results indicated a clear importance of black light on melanin production and expression in M. laxa and M. fructicola, but not in M. fructigena. Regarding ROS-related metabolism in M. fructicola, blue light highlighted by inhibiting the expression of many antioxidant genes. Overall, it represents a global description of the effect of light on the regulation of two important secondary mechanisms, essential for the adaptation of the fungus to the environment and its survival.