Sugarcane red rot is a critical constraint threatening the stability and sustainability of sugarcane production in Southwest China, where Yunnan and Guangxi Provinces are the core cultivation regions. To provide a scientific basis for targeted disease management and ensure sugarcane production security, 40 symptomatic red rot samples were collected from 10 sugarcane varieties across 7 locations in these two provinces. A total of 57 fungal isolates were obtained, and they were identified through morphological characterization, multigene phylogenetic analysis (ITS/ACT/TUB2 for Colletotrichum sp. and EF-1α/RPB2 for Fusarium sp.), and pathogenicity tests on the susceptible cultivar Yuetang 93-159 using three representative isolates per species. The results show that 36 isolates were identified as Colletotrichum falcatum and divided into light and dark morphotypes. Phylogenetic analysis revealed that Yunnan and Guangxi isolates clustered in Clade I and Clade II, respectively. The remaining 21 isolates were identified as Fusarium madaense, and no sequence polymorphisms were detected in either EF1α or RPB2 among these isolates, which clustered with the F. madaense strain isolated from sugarcane in Brazil. Pathogenicity tests on leaf midribs and stalks of this cultivar showed that the representative isolates of C. falcatum and F. madaense induced typical red rot symptoms consistent with field observations. Among the representative isolates tested, preliminary findings suggest that light-type C. falcatum isolates were more virulent than dark-type ones, and the C. falcatum isolates Cf16 and Cf1 showed higher stalk virulence than the tested F. madaense isolates. To our knowledge, this is the first report of F. madaense causing typical red rot symptoms on sugarcane in China.
Li et al. (Fri,) studied this question.