Effects of heading date and <i>Epichloë</i> endophyte on persistence of diploid perennial ryegrass (<i>Lolium perenne</i>). 2. Endophyte strain and interactions with heading date

<p dir="ltr"><b>Context</b>: Data are lacking on the effects of selected endophytes of perennial ryegrass (<i>Lolium perenne</i> L.) on ryegrass persistence.</p><p dir="ltr"><b>Aim</b>: We aimed to determine the impact of <i>Epichloë</i> endophyte on the persistence of mid- and late-heading perennial ryegrass cultivars.</p><p dir="ltr"><b>Method</b>: 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.</p><p dir="ltr"><b>Key results</b>: 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.</p><p dir="ltr"><b>Conclusions</b>: 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.</p><p dir="ltr"><b>Implications</b>: 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.</p>