Functional Analysis of Lolium perenne L. in Response to Fungal Endophyte Inoculation and Salinity Stress

Abstract Lolium perenne L., is a widely cultivated cool-season grass, is an important turf and forage species worldwide, with moderate salt tolerance. However, soil salinity resulting from poor water management, inadequate drainage of fields and high temperatures significantly impair its yield. This study explores effects of two endophytic fungi on enhancing the growth of non-host L. perenne under salt stress. Two salt-tolerant, plant growth-promoting fungal endophytes, Stereum gausapatum (ENDO_1) and Parasarocladium gamsii (ENDO_2), were inoculated in L. perenne under salt stress conditions (0 mM, 150 mM, and 300 mM NaCl). The plant growth performance, physiological responses, and transcriptomic changes were analyzed in two ryegrass varieties, Indiana and Greensky, to assess the endophytes’ effects on plant resilience and adaptation to salinity stress. The two fungi significantly increased growth and biomass with beneficial physiological effects in L. perenne : ENDO_1 reduced lipid peroxidation and increased total antioxidants, while ENDO_2 increased proline accumulation. Weighted gene correlation network analysis revealed that stress-responsive pathways were differentially regulated in plant organs (leaves and roots) and after fungal inoculation in both varieties. The representative processes included amino acid metabolism, cell wall macromolecule metabolism or biogenesis, organic acids and compatible solutes, plant stress-related, generation of precursor metabolites and energy, transport, and plant nutrition. Salinity-induced growth reductions were ameliorated by fungi leading to greater biomass and increased plant growth compared to non-inoculated plants. Salinity stress-related pathways namely lipid metabolism, carboxylic acid biosynthesis, alpha amino acid catabolism were regulated by endophytes, which can be potential biomarkers used for bioinoculant selection.