Assessment of germination and endophyte viability in perennial ryegrass and tall fescue seeds following accelerated ageing treatment

Temperate pasture grasses form symbiotic associations with asexual fungal endophytes of the genus Epichloë. Viabilities of both seed and endophyte were assessed in cultivars of perennial ryegrass and tall fescue following different accelerated ageing (AA) treatments based on variations of relative humidity (RH) (80-100%) and duration at elevated temperature (42°C), to identify particularly stable and compatible host-endophyte associations. The cultivars were inoculated with three endophytes (NEA10, NEA11 and NEA12) isolated from perennial ryegrass and belonging to distinct taxa (E. festucae var. lolii, LpTG-2 and LpTG-3, respectively), and two endophytes isolated from tall fescue (belonging to the taxon E. coenophiala). Consistent with previous studies, endophyte viability following AA treatment was inversely correlated with both increasing RH and duration of treatment in both species. Significant interaction effects between cultivar variety, endophyte genotype, humidity level and treatment duration were observed for both seed germination and endophyte viability. NEA12 consistently displayed higher viability following AA treatment than NEA10 and NEA11 in each of the perennial ryegrass cultivars. Stable host-endophyte combinations were observed for 'Alto'-NEA10, 'Bealey'-NEA11 and 'Trojan'-NEA12, 'Bronsyn' being the least compatible host population. The applicability of AA for selecting stable host-endophyte associations, or to identify and eliminate unstable associations, is discussed.