Evidence for leaf endophyte regulation of root symbionts: effect of Neotyphodium endophytes on the pre-infective state of mycorrhizal fungi

Abstract

Neotyphodium endophytes and arbuscular mycorrhizal (AM) fungi are common constituents of natural grasslands. The plant?endophyte symbiosis can introduce changes in soil conditions that affect the density and activity of different functional groups of soil organisms. A few experiments have reported that leaf endophytes can reduce mycorrhizal sporulation and colonization of host roots in agronomic hosts, contrasting with the studies we have conducted in native grasses from Argentina. In the present work we performed in vitro assays to evaluate the effect of root and endophyte exudates on the pre-infective state of mycorrhizal fungi (Gigaspora margarita and G. rosea). Plant roots of Bromus setifolius, from populations of Patagonia and four strains of Neotyphodium were used to obtain the exudates. Root exudates of infected plants, at a high concentration, significantly increased AMF hyphal branches and length. The effect of endophyte exudates on AMF mycelia lenght, varied depending on strain and the concentration used, suggesting a differential interaction between endophyte and AMF species. AMF hyphal branches were increased by fungal exudates in both mycorrhizal species. This study reports the direct and positive effect of Neotyphodium endophytes on AMF pre-infective state, supporting previous information on native grasses.