Pathogen Identification and Factors Influencing Infection Frequency and Severity of Fungal Rust in Four Native Grasses in Hulunber Grassland, China

Abstract

A serious rust infection present in 2014 and 2015 on the dominant grass species (Leymus chinensis) in the Hulunber grassland of Inner Mongolia, China, and also present on three other grass species (Agropyron cristatum [wheat grass], Bromus inermis, and Festuca ovina) was investigated. Field surveys, laboratory determination of morphological characteristics, pathogenicity tests, and molecular identification methods were integrated to identify two rust-causing pathogens on L. chinensis. It was found that Puccinia elymi was the major pathogen of L. chinensis, and also infected A. cristatum and F. ovina. This is the first report of P. elymi on A. cristatum in China. P. striiformis caused stripe rust on L. chinensis and B. inermis. The incidence and severity of rust infection increased through the growing season, presumably from asexual spread by urediniospores, and was higher on grass species phylogenetically more closely related to common crop hosts of the pathogens. High host grass density and presence of a potential alternate host for P. elymi, Thalictrum squarrosum, were two further factors promoting rust incidence. These results provide insight into ecological factors linked to the rust epidemic and provide a theoretical basis for the formulation of control strategies.