Epichloid endophytes confer resistance to the smut Ustilago bullata in the wild grass Bromus auleticus (Trin.)

Abstract

In this work it was studied for the first time whether asexual Epichloe ( Neotyphodium ) endophytes of Bromus auleticus , protect their host plants against the pathogenic fungus Ustilago bullata. Seeds of two different ecotypes of B. auleticus , one of them infected with the endophyte Neotyphodium pampeanum (NpE+) and the other infected with the endophyte Neotyphodium tembladerae (NtE+) and their respectively endophyte-free (NpE−/NtE−) counterparts were used. Seeds of each ecotype and endophytic status were superficially disinfected and were randomly assigned to different treatments named: S+ (smut fungus inoculated) and S− (mock-inoculated). It was evaluated the effect of U. bullata infection on plant characteristics in every stage of their life cycle: seedling emergence, vegetative growth, mortality and smut symptoms in the florets. In NtE+ infected plants, smut disease was almost completely suppressed, whereas in their endophyte-free counterparts (NpE−) the incidence of smut symptoms reached 64%. In NpE+ infected plants smut incidence was significantly lower (7%) than in endophyte-free plants (39%). Although U. bullata infection decreased the emergence rate of both endophyte-infected and endophyte-free plants, neutral or protective effects of the endophytes were observed in seedling development and survival. The survival during the first year of NtE+ plants was higher than in their NtE− counterparts. These results indicate a strong beneficial effect of vertically transmitted endophytes against this pathogen.