Plants, fungi, and culture conditions
Seeds ofA. sibiricum were collected from the experimental field of the Inner Mongolia Grassland Ecosystem Research Station of the Chinese Academy of Sciences (43° 38′ N, 116° 42′ E). We separately prepared E. sibiricum -infected seeds and endophyte-free seeds according to the methods reported in a previous article (Shi et al ., 2020). Plump surface-sterilized seeds of EI and EF plants were sown in square pots (length × width × height was 10×10×12 cm; one seed was sown in one pot) filled with vermiculite. After 30 days of cultivation, the endophytic infection status of each plant was inspected by trypan blue staining (Latch and Christensen, 1985). The endophytic infection rate in the EF plants was 0, and that in the EI plants was 100%. Identical sizes of EF and EI seedlings were selected and cultured for subsequent tests.
C. lunata was provided by the Agricultural Culture Collection of China (ACCC) and cultured on potato dextrose agar (PDA) culture medium at 25 °C for 15 days. To obtain a spore suspension of the pathogen, the hyphae of the pathogenic fungus were washed with sterile water (containing 0.02% Tween 20) and filtered through a double layer of sterile gauze. The concentration of the pathogen spore suspension quantified with a hemocytometer was 1.2 × 105spores/mL, and the spore germination rate was 80%.