Streptomyces pratensis S10 Inhibits the Spread of Fusarium graminearum Invasive Hyphae and Toxisome Formation in Wheat Plants.

Fusarium head blight (FHB) of wheat, mainly caused by Fusarium graminearum, leads to severe economic losses worldwide. Effective management measures for controlling FHB are not available due to a lack of resistant cultivars. Currently, the utilization of biological control is a promising approach that can be used to help manage FHB. Previous studies have confirmed that Streptomyces pratensis S10 harbors excellent inhibitory effects on F. graminearum. However, there is no information regarding whether invasive hyphae of F. graminearum are inhibited by S10. Thus, we investigated the effects of S10 on F. graminearum strain PH-1 hypha extension, toxisome formation, and TRI5 gene expression on wheat plants via microscopic observation. The results showed that S10 effectively inhibited the spread of F. graminearum hyphae along the rachis, restricting the infection of neighboring florets via the phloem. In the presence of S10, the hyphal growth is impeded by the formation of dense cell wall thickenings in the rachis internode surrounding the F. graminearum infection site, avoiding cell plasmolysis and collapse. We further demonstrated that S10 largely prevented cell-to-cell invasion of fungal hyphae inside wheat coleoptiles using a constitutively green fluorescence protein-expressing F. graminearum strain, PH-1. Importantly, S. pratensis S10 inhibited toxisome formation and TRI5 gene expression in wheat plants during infection. Collectively, these findings indicate that S. pratensis S10 prevents the spread of F. graminearum invasive hyphae via the rachis.