Optimal cultivated conditions for Epichloё endophyte isolation from dominant grass Elymus tangutorum in Qinghai Plateau

The morphological characteristics, including conidial size and speed rate, of colonies isolated from five ecotypes of Elymus tangutorum in Qinghai plateau were examined under cultivation conditions supplied with different carbon and nitrogen sources. Our results indicated that the optimum carbon and nitrogen sources for the growth of Epichloё endophytes isolated from different ecotypes significantly differ. Sucrose and tryptone were the optimal carbon and nitrogen sources for the colony growth of strains 1 and 3, respectively; in contrast, the most suitable carbon and nitrogen sources for the colony growth of strains 2 and 4 were amylum and peptone, respectively. Furthermore, maltose and tryptone were the optimum carbon and nitrogen sources in accelerating the growth of strain 5. In contrast, the colony morphologies of strains 2, 3, and 5 were similar, a white protrusion emerged at the center of the surface and a distinct circle formed at the edge, and the color of colonies was white centrally to light yellow at the margin under different carbon sources. The colony edge of strain 1 was irregular in the condition that amylum was the carbon source, however, strain 4 slowly grew when fructose was provided as the carbon source. The colony morphology of the five strains was commonly white convex at the center of the surface; conversely, the converse color of isolated colonies tan centrally to light tan at the edge when cultivated under different nitrogen sources. Interestingly, only small white dots on the colony surface were observed when ammonium was used as the nitrogen source. However, sparse and transparent aerial mycelium appeared on the edge of the colony when no nitrogen source was supplied. The shape of the spores was characterized as oval, round, reniform, or asymmetrical in shape. However, the spore and conidiophore sizes of the same strain significantly differed when different carbon and nitrogen sources were supplied. Our results suggested that the colony growth and morphological traits of Epichloё endophytes isolated from different ecotypes of E. tangutorum varied when different carbon and nitrogen sources were supplied, and the optimal carbon and nitrogen sources for accelerating the growth of Epichloё endophytes isolated from E. tangutorum were clarified. These findings on E. tangutorum could clarify the optimal cultivation conditions for Epichloё endophytes, which will facilitate the process of breeding new germplasms of the Elymus genus through the inoculation of Epichloё endophytes into cool seasonal grasses such as E. tangutorum.