RYEGRASS STAGGERS: FURTHER SUBSTANTIATION OF A LOLIUM ENDOPHYTE AETIOLOGY AND THE DISCOVERY OF WEEVIL RESISTANCE OF RYEGRASS PASTURES INFECTED WITH LOLIUM ENDOPHYTE
An experiment was planned and undertaken to obtain further evidence on the association of the Lolium endophyte (a fungus parasitic in some perennial ryegrass) with the occurrence of ryegrass staggers in sheep (Fletcher & Harvey, 1981). In the experiment, 39 sheep grazing four plots established with perennial ryegrass seed (Lolium perenne) highly (>90%) infected with the endophyte all developed clinical ryegrass staggers over a 26 day grazing period. The same number of sheep grazing plots established from seed found to have negligible (<3X) endophyte infection showed no evidence of ryegrass staggers. The results clearly confirm that Lo/&m-endophvte infested ryegrass pastures are closely associated with the occurrence of ryegrass staggers in sheep. Observations made during regrowth of the ryegrass plots at the end of the grazing period showed that there was a 3 to 4-fold greater production of dry matter from the high endophyte plots than from the low endophyte plots. The poor regrowth and low production recorded in low endophyte plots was found to be largely due to pasture predation by the Argentine stem weevil (Lisfronotus bonariensis). There is a firm indication that Lolium-endophyte infection of ryegrass confers resistance to stem weevil predations. This finding is discussed in relation to the field control of ryegrass staggers. It will clearlv have implications in relation to plant selection and seed production, as well as to pasture production trials conducted over many years during which seed and pasture of unknown endophyte status was evaluated.
