Field performance of perennial ryegrass (Lolium oerenne) infected with toxin-free fungal endophytes (Neotyphodium spp.)

Abstract

A national series of six small plot trials were sown in 1996 and four in 1997 to evaluate the performance of six novel fungal endophytes in Grasslands Nui perennial ryegrass. These endophytes do not produce the mammalian toxins, ergovaline and lolitrem B, but produce peramine, a feeding deterrent to the major ryegrass pest, Argentine stem weevil (ASW). Trials included the naturally occurring endophyte (wild-type) which produces both toxins, and an endophyte-free (nil) treatment. Pasture production was measured regularly and samples were taken at least once each summer-autumn from all trials for assessment of ASW damage. Black beetle larval damage was recorded on three trials. The toxin-free endophytes, AR1, AR12, AR22 and the wild-type were equally effective at reducing ASW adult feeding and larval damage significantly below that which occurred in nil treatments. Ryegrass infected with AR1, AR12, AR22 and the wild-type endophyte was damaged less by black beetle larvae than ryegrass without endophyte. The effect of AR24 on insect damage was variable and two other toxin-free endophytes, AR17 and AR506, which had low infection rates, seldom reduced either ASW or black beetle damage. Yield differences between treatments were found on two of 21 sampling occasions between October and December and 12 of 30 sampling occasions between January and April. During summer-autumn, wild-type, AR1, AR12 and AR22 gave higher ryegrass yields than the nil, AR17 and AR506 treatments. In the second year of the 1996-sown trials, productivity of ryegrass with AR1 in the summer-autumn tended to be lower than that of the wild-type with significant differences occasionally occurring. Yield differences were correlated with either ASW or black beetle damage in North Island trials and with percent endophyte infection at all sites. Differences in yield at Lincoln, Canterbury, were attributed to pasture mealy bug. Three conclusions were drawn from these results: 1. Endophytes are very important for maximising ryegrass yield during summer and early autumn. 2. The effect of endophytes on yield is at least partly due to the insect resistance they impart. 3. The field performance of three toxin-free endophytes, AR1, AR12 and AR22, equalled that of the wild-type in terms of increased insect resistance but did not always match it in plant growth. Keywords: AR1, Argentine stem weevil, black beetle, endophyte strain, ergovaline, insect damage, lolitrem B, Neotyphodium lolii, ryegrass yield