Effects of heading date and Epichloe endophyte on persistence of diploid perennial ryegrass (Lolium perenne). 2. Endophyte strain and interactions with heading date

Context. Data are lacking on the effects of selected endophytes of perennial ryegrass (Lolium perenne L.) on ryegrass persistence. Aim We aimed to determine the impact of Epichloe endophyte on the persistence of mid- and late-heading perennial ryegrass cultivars. Method. Two mid-heading (Samson, Bronsyn) and two late-heading (One50, Rohan) cultivars, infected with selected endophytes (AR37, nea2/6) or with standard toxic endophyte, were established in a replicated plot study grazed by cattle in a subtropical environment of the upper North Island of New Zealand. Persistence characteristics were quantified at least five times per annum, over 4 years. Key results. Endophyte strain had an effect on persistence; infection with standard endophyte resulted in higher ryegrass ground cover percentage, ryegrass content in pasture dry matter and autumn yield than infection with nea2/6 on many occasions, and with AR37 on some occasions. There were negligible impacts on ryegrass tiller density or nutritive value. Trends were dominated by the main effect of endophyte; interactions with heading date were inconsistent. Conclusions. Cultivars were more persistent when infected with standard endophyte than with selected endophytes, although persistence declined over 4 years for all cultivars and irrespective of heading date. Implications. Reliance on selected endophyte is unlikely to prevent persistence decline of perennial ryegrass in a subtropical environment. Other strategies will be required to maintain the persistence of high-quality pastures based on perennial ryegrass.