High Diversity of Species Associated with Leaf Spot on Italian Ryegrass in Southwestern China: Six New Records and Three New Species.

Italian ryegrass is widely cultivated for the production of forage, hay, and silage because of its high nutritional value and good palatability. Leaf spots caused by fungi pose a serious threat to forage crops. In order to expand the knowledge of fungi causing leaf spots in ryegrass () in Sichuan, Yunnan, Chongqing, and Guizhou of southwestern China, a comprehensive survey was undertaken from 2015 to 2022. The survey discovered that Epicoccum leaf spot (ELS) was a common and widespread disease, more serious at the late stage of growth (after late May). Symptomatic leaf samples collected from the four different provinces were analyzed, and a total of 202 isolates were obtained. Based on both multilocus phylogeny (ITS, LSU, , and ) and morphology, 10 species were finally identified, including three novel species ( sp. nov., sp. nov., and sp. nov.), six new host records (, , , , , and ), and an unknown species ( sp.1). Pathogenicity tests showed that , , and sp.1 were nonpathogenic to Italian ryegrass, which were confirmed as endophytes in this study; the other six species could infect Italian ryegrass and cause leaf lesions to different degrees, of which was more aggressive ( ≤ 0.05). Coupled with the isolation rates and geographical distributions of these species, it was found that was the predominant pathogen in Yunnan while and were the predominant pathogens in the other three provinces. This work provides an initial understanding of the taxonomy, virulence, and distribution of species associated with ELS in southwestern China and lays a solid foundation for the diagnosis in the field and scientific control of ELS on Italian ryegrass.