TEMPERATURE AND SEASONAL EFFECTS ON EXPRESSION OF ACREMONIUM ENDOPHYTE-ENHANCED RESISTANCE TO SCHIZAPHIS-GRAMINUM (HOMOPTERA, APHIDIDAE)

Temperature and seasonal changes affected endophyte concentration, peramine concentration, and antixenosis to greenbug in perennial ryegrass infected with Acremonium lolii Latch, Christensen & Samuels. Endophyte and peramine concentrations and degree of greenbug antixenosis to endophyte-infected tillers were lower at 7 and 28-degrees-C compared with 14 and 21-degrees-C in three genotypes of perennial ryegrass; antixenosis was related to peramine and to endophyte concentration. Genotype differences were greater than differences associated with temperature. Field data collected every 3-6 wk indicated highest endophyte concentrations in spring and fall, when mean daily temperatures averaged 15-degrees-C in the previous 4 wk. These data suggest that it is possible to produce cultivars with low or high endophyte concentrations as needed for pastures or turf.