Finding Benefit in Endophytes to Mitigate the Effects of Freezing Stress in Perennial Ryegrass.

The fungal endophyte Epichloe festucae var. lolii has a mutualistic relationship with perennial ryegrass (Lolium perenne) that enhances the survival of the host.  If a grass stand has a high percentage of plants infected with endophytes the result can be a decrease in several abiotic and biotic stresses.  Perennial ryegrass grown in northern climates often suffers  from winterkill, which can completely destroy stands in severe years.  This problem has been difficult to remedy through traditional breeding.   Research has shown that endophyte interactions can differ based on abiotic stresses present in the area they coexist with their host.   Therefore, it is hypothesized that endophytes would reduce freezing stress if plants infected with endophytes evolved in areas where severe freezing temperatures are common.  To test this hypothesis seven diverse accessions with varying freezing tolerances were selected. Plants were tested for endophyte infection and populations were then created with and without endophytes.  The effect of the endophytes within each of the accessions was determined on a population basis.  Comparisons between endophyte infected (E+) and non-infected (E-) populations determined if the endophyte had an effect on the freezing tolerance of the perennial ryegrass accessions.  Freezing tolerance was determined by the population’s lethal temperature 50 (LT50).  Each E+ and E- population within each accession contained 10 genotypes.  The genotypes were then cloned to fulfill four reps of each temperature treatment in the freezing test.  Six different temperature treatments ranging from -10^oC to -20^oC encompassed 100% survival to 100% death for all populations respectively.  Results show that the endophytes effect on freezing tolerance varies greatly between accessions.  Endophyte infection had a favorable association with three of the accessions.