Visualization of the early infection stage of Sporisorium scitamineum in sugarcane cultivars

Abstract:

[Objective] Sporisorium scitamineum isa pathogenic fungus that causes sugarcane smut, the most important disease of sugarcane in China. Tracing the infection progression of the disease will help to reveal the mechanism of resistance to smut and lay a foundation for the selection of resistant cultivars and the control of smut. [Methods] We labeled the basidiospores of the pathogen with a gene that encodes the enhanced yellow fluorescent protein (eYFP) by Agrobacterium tumefaciens-mediated transformation (ATMT). We tested the mating and pathogenicity of the transformants. To visualize the early stage of infection, we injected the eYFP-tagged strains into smut susceptible sugarcane cultivar ROC22 and smut resistant cultivar Zhongzhe 1, Zhongzhe 6, Zhongzhe 9. [Results] The eYFP-tagged strains were indistinguishable to the wild-type strain in mating and pathogenicity, and the fluorescence was able to inherit into the teliospores. Laser confocal microscopic examination showed that at 5 days post inoculation, a few aggregated as well as separated mycelia were observed in the susceptible sugarcane cultivar ROC22, but only a small amount of single mycelium was found at the same time in the resistant Zhongzhe cultivars. Much more aggregated mycelia were found at 35 days post infection in ROC22 than in Zhongzhe cultivars, with the lowest number in Zhongzhe 1. [Conclusion] A fluorescent tracer system for sugarcane infection by S. scitamineum was successfully constructed, and there may be a mechanism to constrain the mycelial growth of S. scitamineum in Zhongzhe cultivars.