Characterization of Pestalotiopsis species causing black leaf spot on Italian ryegrass in southwestern China

Italian ryegrass (Lolium multiforum Lam.) is widely cultivated as a vital forage crop in southern China due to its exceptional quality and yield, good palatability, and rapid early growth. A survey found that black leaf spot (BLS), caused by Pestalotiopsis species, is a prevalent and emerging disease of Italian ryegrass, typically manifesting as black spots or net blotches. This study isolated 70 Pestalotiopsis strains from diseased leaves of Italian ryegrass planted in the Chongqing, Yunnan, and Guizhou provinces of southwestern China between 2021 and 2022. Based on morphological features and multi-locus phylogenetic analyses (ITS, TUB2, and TEF1), five new records and one unknown species were identified in association with Italian ryegrass. These are Pestalotiopsis australasiae, P. biciliata, P. telopeae, P. trachycarpicola, P. tumida, and Pestalotiopsis sp.1. Together with the isolation rates and geographical distributions of these species, pathogenicity tests showed that P. trachycarpicola is the most important causal agent of BLS on Italian ryegrass in southwestern China. These findings form the basis for diagnosis, detection, pathogen identification, and scientific control of BLS on Italian ryegrass.