Influence of Neotyphodium lolii and barley yellow dwarf virus, individually and combined, on the growth of Lolium perenne

The effect of infection by either of two strains of the endophyte Neotyphod ium lolii with or without infection by barley yellow dwarf virus (BYDV) on the growth of eight perennial ryegrass genotypes was investigated in a gree nhouse trial. Herbage production was significantly influenced by plant geno type. Infection with BYDV reduced dry matter and tiller production of most perennial ryegrass plants and although there was no significant plant genot ype x virus interaction, the genotypes differed in their response to virus infection. Infection with endophyte induced an increase in plant dry weight of 42% in one genotype, whereas the others were not significantly affected . Presence of BYDV did not influence production of the alkaloids ergovaline , lolitrem B or peramine, nor was there a significant interaction between t he two strains of endophyte and the virus. However, with some genotypes vir us infection masked the effect of endophyte on the dry matter production of plants.