Positive association between Neotyphodium endophytes and arbuscular mycorrhiza fungi: a widespread trait in native grasses

M.V. NOVAS; L.J. IANNONE; M.V. VIGNALE; J.M. SCERVINO

Lexington, Kentucky, USA

Simposio; International Symposium on Fungal Endophyte of Grasses; 2010

The potential impact of foliar endophytes on below-ground process, in particular on arbuscular mycorrhiza fungi (AMF), has received little attention, and the existing results are contradictory. Here we, firstly, review the research performed on the endophyte-AMF interaction in three native grasses, from different environmental regions in Argentina, at field conditions. Secondly, we report the results obtained from in vitro assays to test the effect of the endophyte on the preinfective state of AMF. AMF roots colonization was studied in Neotyphodium-infected (E+) and uninfected (E-) plants in natural populations of Bromus setifolius and Poa bonariensis, while roots of B. auleticus were obtained from plants in an experimental field were the effect of N fertilization was also studied. In vitro assays were performed using four different strains of Neotyphodium, isolated from B. setifolius, and two species of AMF: Gigaspora margarita and G.rosea. The AMF colonization was significantly higher in plants from E+ populations than in plants from E- populations for all three hosts. No significant differences were detected between E+ and E- plants when they coexist in the same population. Infected plants of B. auleticus showed higher mycorrhization and arbuscules rate than E- plants, regardless the fertilization level. In vitro assays revealed that root exudates from E+ plants and exudates from endophyte strains significantly enhanced hyphal length and the number of hyphal branches in AMF. However, this effect varied depending on the endophyte strain and the AMF species couple. Our results suggest that the positive effect of Neotyphodium endophytes on AMF, increasing the root plant colonization, would be a widespread phenomenon in native grasses. Furthermore, regarding the in vitro assays, the higher colonization could, at least, be partially explained by the positive effect of the endophyte strains on the pre-symbiotic stages of the AM fungi.