Control of clavicipitaceous anamorphic endophytes with fungicides, aerated steam and supercritical fluid CO2-seed extraction
The effects of soil drenches with systemic fungicides on viability of clavicipitaceous anamorphic endophytes, non-choke inducing endosymbiotic fungi of the genus Neotyphodium that systemically infect grasses, were tested in endophyte-infected seedlings of Hordeum brevisubulatum subsp. violaceum, Lolium perenne and Festuca arundinacea germplasm. None of the endophytes of these grasses were sensitive to benomyl at 3-5 ppt. The endophyte of H. brevisubulatum was sensitive only to propiconazole. The viability of the F. arundinacea endophyte (N. coenophialum) was reduced, but not completed eliminated by prochloraz, imazalil and propiconazole in the 2-3 ppt range. Aerated-steam seed treatments at 60 C for 5 min were effective in reducing viability of the perennial ryegrass endophyte (N. lolii) by 83%, although some reduction in seed germination and negative growth effects were observed. A novel disease-control method, supercritical fluid carbon dioxide extraction (SFE-Cod, for the elimination of Neotyphodium-endophytes in grass seeds is reported here for the first time. The endophyte N. lolii was completely controlled in seeds of L. perenne cv. Ellett by extracting the seeds at 400 atmospheres for 10 or 20 min. Only minor reductions in seed germination resulted from the SFE-CO2, seed-extraction treatment and no appreciable effects on growth of seedlings or mature plants were observed. Several potential applications of these disease-control technologies for seedborne fungal pathogens are discussed.