Neotyphodium fungal endophytes confer physiological protection to perennial ryegrass ( Lolium perenne L.) subjected to a water deficit

Abstract

While it is generally accepted that Neotyphodium lolii and related epichloë endophytes are mutualists that provide important benefits to their perennial ryegrass ( Lolium perenne) host plants under conditions of biotic stress, relatively little is known about the effect of endophyte on the host under conditions of abiotic stress. Using genetically identical endophyte infected (E+) and uninfected (E−) clones of perennial ryegrass from a natural and a synthetic association grown under conditions of water stress in a controlled environment, we show that N. lolii had minor effects on morphological responses (leaf elongation rate and ground biomass production) but had more pronounced effects on physiological responses (water use efficiency, relative water content and osmotic potential) by the host. The effects were most marked in the natural association. While levels of proline increased in response to water stress, the presence of endophyte had no effect on those levels. The effect of water stress on endophyte bioprotective metabolites was also examined. Ergovaline levels in pseudostem tissue increased in response to increasing water stress for both N. lolii/ L. perenne associations but lolitrem B levels only increased in the natural association. No differences in steady state levels of transcripts from genes known to be required for the synthesis of these alkaloids were observed in response to water stress. This study demonstrated that N. lolii can confer protection to perennial ryegrass from water stress and that levels of the bioprotective metabolites, lolitrem B and ergovaline were altered in response to this abiotic stress in a manner that was specific for each symbiotic association.