Field resistance to Argentine stem weevil(Listronotus bonariensis)in different ryegrass cultivars infected with an endophyte deficient in lolitrem B

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Abstract
A spaced plant trial, a small plot trial, and a field trial evaluated an endophyte (Acremonium spp.) (AR6) which does not produce lolitrem B in the tetraploid cultivars Grasslands Moata (Lolium multiflorum) and Grasslands Greenstone (L. multiflorum × perenne), and in the perennial cultivars (L. perenne) Grasslands Pacific and Grasslands Nui. The endophyte was compared to three lolitrem‐producing isolates viz. AR41, Waiau, and the wildtype. In all trials Argentine stem weevil (ASW) (Listronotus bonariensis) adult feeding, oviposition, and larval damage were recorded at regular intervals between October and March. ASW attack was highest on the tetraploid cultivars, Greenstone and Moata. In most instances, all endophytes reduced adult ASW feeding and oviposition in the different cultivars compared with their respective endophyte‐free (E‐) controls. Feeding and oviposition on endophyte‐infected (E+) Moata and Greenstone was in some instances similar to, or higher than, that on E‐ Nui or Pacific. All endophyte isolates also significantly reduced the incidence and severity of ASW larval damage. ASW damage levels were higher in summer than in spring. Differences as a result of endophyte infection were much greater in summer than in spring. In summer on E+ plants nearly all ASW oviposition and larval damage occurred on Moata and/or Greenstone. There were few significant differences between the different endophyte isolates. In the field trial, the AR6 endophyte gave protection against ASW attack similar to that provided by the wildtype endophyte.