Sorghum Sheath Blight Caused by Fusarium spp. in Sinaloa, Mexico

Sorghum (Sorghum bicolor) leaf sheath blight was observed for the first time in Sinaloa, Mexico in the summer of 2020. Fungal isolates were obtained from symptomatic tissue in potato dextrose agar. Fusarium spp. were associated with symptomatic plants in 10 sampling sites under field conditions. No root and stalk rot was observed during the sampling period. Analysis of fragments of the translation elongation factor alpha and RNA polymerase II second largest subunit genes indicated that all isolates belong to the Fusarium fujikuroi species complex (FFSC). Five groups were delineated from this complex: F. thapsinum, F. verticillioides, Fusarium sp. (four isolates), Fusarium sp. 4 (Fus4), and Fusarium sp. (Fus16), which is closely related to Fusarium madaense. The morphological characteristics (colony color and morphometry of conidia) of isolates with sequence similarities to those of F. thapsinum and F. verticillioides were in the expected range for these species. The morphology of isolates Fus7a, Fus7b, Fus11, and Fus17, as well as Fus4 and Fus16, were similar to those of the FFSC, specially to F. andiyazi and F. madaense. Inoculations of sorghum with representative isolates of F. thapsinum, F. verticillioides and the unidentified Fusarium species resulted in reddish brown lesions similar to those observed under field conditions; the original isolates inoculated were reisolated fulfilling the Koch's postulates. Although leaf sheaths on sorghum plants were heavily damaged, root and stalk rot were not observed in the greenhouse inoculations or under field conditions. Future research should focus on determining the identity of the unknown Fusarium spp. to design control measures for the disease. This is the first report of Fusarium spp. causing sorghum leaf sheath blight in Mexico.