Cattle grazing alters the interaction of seed-borne fungi and two foliar pathogens of Leymus chinensis in a meadow steppe

Intensive grazing by herbivores lead to major ecological changes in natural grasslands, including severe degeneration. However, the understanding of how grazing affects the incidence of pathogenic and saprotrophic fungi on leaves and seeds of dominant plant species in grasslands is limited. In this study, the presence of two fungal pathogens that cause lesions on leaves of a dominant grass species of the Hulunber meadow steppe in northeast China, Leymus chinensis, as well as saprotrophic fungi associated with lesions, was investigated in plots with different grazing intensities treatments (0, 0.42, 0.63, 0.83, 1.25, and 1.67 cattle ha(-1)). In addition, seeds of L. chinensis were harvested from plants of the different grazing intensities and the presence of seed-borne fungi, including pathogenic and saprotrophic fungi, were examined by fungal isolation. The results indicated that with the increase of grazing intensity, the incidence of two fungal diseases on leaves of L. chinensis, leaf blotch diseases caused by Leptosphaeria avenaria and Parastagonospora nodorum, decreased. On seeds, the two most frequently isolated fungi were Le. avenaria and P. nodorum, from 57.2% and 40.6% of seeds respectively. At the highest grazing plots, the frequency of isolation of these two fungi to 23.1 and 15.6% respectively. By contrast, the frequency of isolation of Epicoccum nigrum in the highest grazing plots was 88.9%, approximately 10-fold of that in control plots. In dual-culture studies, E. nigrum isolates had inhibitory effects on the growth of isolates of the two leaf pathogens.