Host-endophyte (Epichloë occultans) interaction impacts on annual ryegrasses (Lolium persicum and Lolium rigidum): ecological and breeding implications

Grass endophytic symbionts interact with the host depending on the host's genetic background and environmental pressures, aiming for survival. Lolium persicum, a self-pollinating annual grass, is suggested for studying such an interaction. Most grasses host endophytic fungi, co-evolved organisms that can interact with their hosts from antagonism to mutualism. This study examined the impact of mating systems on host-endophyte interactions by utilizing endophyte-infected (E+) and endophyte-free (E-) populations of self-pollinating Lolium persicum and open-pollinating Lolium rigidum, collected from three regions of Iran. The evaluations in a pre-breeding process and two experiments were conducted on 1400 plants screened to select 126 half-sib (L. rigidum) and full-sib (L. persicum) families based on a limited space stress, morphological traits, and seed dormancy, respectively. It was found that endophytes generally have a significant and positive effect on reproductive traits and promoting effects in plants to strive for survival. Their impacts were population-dependent, and the E+ plants were superior when a population had higher biomass production and seed yield-related traits. Endophytes help to maintain the host's genetic structure over generations, particularly in L. persicum. In this way, E+ populations exhibited the highest heritability and genetic advance for endophyte-host survival traits such as seed weight, number of seeds, plant height, and days to tillering in both species. In L. persicum, this also included acid-detergent fiber, neutral detergent fiber, crude protein, fat content, phosphorus content, number of tillers, and days to emergence. We demonstrated that artificial selection of morphological traits influenced plant-fungal fitness, such that selecting against seed dormancy significantly increased seed shattering but decreased fungal fitness.