Response of Diploid Perennial Ryegrass to Fungal Endophyte AR29 Infections under Water Stress

Asexual fungus Neotyphodium spp. are often associated with aboveground parts of different grasses. Perennial ryegrass (Lolium perenne L.), dominant cool-season grass species in New Zealand, is frequently infected by endophytic fungus (Neotyphodium lolli). To evaluate the growth, nutrient status, and avoidance to dehydration stress, clones of diploid perennial ryegrass either infected with Neotyphodium lolii AR29 endophyte (E+) or not infected (E-) were grown in a potted Andisol with intermittent wetting-drying cycles in a controlled growth chamber. Results showed that endophyte infection (E+) significantly reduced plant height, tiller number, shoot and root dry weights, and root volume with an associated increase in root/shoot ratios of ryegrass. The E+ plants showed a greater shoot and lower root avoidance to dehydration stress than the E- plants. The negative values of relative interaction intensity index between the diploid ryegrass and AR29 endophyte association suggested that these host-endophyte associations were parasitic under intermittent soil wetting-drying cycles. While the nitrogen (N) and phosphorus (P) concentration, plant production index, and water-use efficiency were significantly greater in E+ plant than in E- plants, the N and P efficiency ratios were greater in E- plants than in E+ plants. Results suggested that the endophyte mediation may have synergistic or antagonistic effects which depend on particular host genotype-endophyte combinations and environmental conditions to promote drought tolerance in grasses for degraded land restoration or forage production.