Research Summary• The relationship between cool-season grasses and fungal endophytes is widely regarded as mutualistic, but there is growing uncertainty about whether changes in resource supply and environment benefit both organisms to a similar extent.• Here, we infected two perennial ryegrass ( Lolium perenne ) cultivars (AberDove, Fennema) that differ in carbohydrate content with three strains of Neotyphodium lolii (AR1, AR37, common strain) that differ intrinsically in alkaloid profile. We grew endophyte-free and infected plants under high and low nitrogen (N) supply and used quantitative PCR (qPCR) to estimate endophyte concentrations in harvested leaf tissues.• Endophyte concentration was reduced by 40% under high N supply, and by 50% in the higher sugar cultivar. These two effects were additive (together resulting in 75% reduction). Alkaloid production was also reduced under both increased N supply and high sugar cultivar, and for three of the four alkaloids quantified, concentrations were linearly related to endophyte concentration.• The results stress the need for wider quantification of fungal endophytes in the grassland-foliar endophyte context, and have implications for how introducing new cultivars, novel endophytes or increasing N inputs affect the role of endophytes in grassland ecosystems.

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Tall fescue [Lolium arundinaceum (Schreb.) Darbysh. syn. Festuca arundinacea Schreb.] and perennial ryegrass (Lolium perenne L.) are important perennial forage grasses utilized throughout the moderate- to high-rainfall temperate zones of the world. These grasses have coevolved with symbiotic fungal endophytes (Epichloë/Neotyphodium spp.) that can impart bioactive properties and environmental stress tolerance to the grass compared with endophyte-free individuals. These endophytes have proven to be very important in pastoral agriculture in the United States, New Zealand, and Australia, where forage grasses are the principal feed for grazing ruminants. In this review, we describe the biology of these grass-endophyte associations and implications for the livestock industries that are dependent on these forages. Endophyte alkaloid production is put in context with endophyte diversity, and we illustrate how this has facilitated utilization of grasses infected with different endophyte strains that reduce livestock toxicity issues. Utilization of tall fescue and use of perennial ryegrass in the United States, New Zealand, and Australia are compared, and management strategies focused predominantly on the success of endophyte-infected perennial ryegrass in New Zealand and Australia are discussed. In addition, we consider the impact of grass-endophyte associations on the sustainability of pasture ecosystems and their likely response to future changes in climate.

The agronomic merits of a perennial ryegrass (Lolium perenne) cultivar infected with a new endophyte (Neotyphodium lolii), AR37, were compared with the same cultivar infected with currently available endophytes (AR1, Standard) at two sites in northern New Zealand for at least 3 years. AR37-infected ryegrass was the highest yielding treatment at both sites (11 080 kg DM/ ha/yr) producing more dry matter than either AR1 or Standard-infected ryegrass which yielded similar amounts (8870 kg DM/ha/yr). Yield advantages of AR37-infected ryegrass were greater at Kerikeri (36%) than Hamilton (17%), with differences increasing over successive years at both sites. At Hamilton, tiller populations were lowest in AR37-infected ryegrass in Year 2, and lowest in AR1- infected ryegrass 3 and 5 years after sowing. At both sites AR37-infected ryegrass had the lowest infestation scores for root aphid. At Hamilton in Year 4, more damage by African black beetle larvae occurred to AR1-infected plants than to AR37 and Standard-infected plants. These pests are likely to have contributed to the differences in agronomic performance observed. These agronomic results suggest AR37-infected ryegrass cultivars will be a useful choice for farmers in northern New Zealand. Keywords: endophyte, Neotyphodium lolii, perennial ryegrass, Lolium perenne, dry matter yields, plant persistence, root aphid, Aploneura lentisci, African black beetle, Heteronychus arator

Pasture mealybug (Balanococcuspoae) was found infesting two field trials evaluating the performance of selected strains of the endophyte Neotyphodium lolii in ryegrass (Lolium spp.) in Canterbury, New Zealand. Deterioration of endophyte-free plots relative to endophyte-infected plots had been observed. In Trial A, pasture mealybug were sampled in plots of the perennial ryegrass cultivar 'Grasslands Nui', without endophyte (nil), or infected with the wild-type endophyte, or the selected strains, AR1 and AR37. In Trial B, mealybug numbers on six ryegrass cultivars infected with AR1 or wild-type were compared with those on the same cultivars without endophyte. In sampling these trials, the presence of a root aphid, Aploneura lentisci, was also noted. Populations of mealybug in both trials were similar on all endophyte-infected treatments and significantly lower than populations on nil treatments. Neither AR1 nor wild-type appeared to reduce root aphid numbers, while AR37 may have had some effect. The amount of dead grass was significantly greater in nil than in endophyteinfected plots in Trial A, and yield of ryegrass was correlated with numbers of mealybug and root aphid present. Pasture productivity in nil treatments had recovered by spring, in the year of the outbreak. The presence of endophyte, strain of endophyte and cultivar were all significant factors affecting both total dry matter and green yield in Trial B. Pasture mealybug accounted for 55% of the variation in a decline in growth rate that occurred in this trial over the summer-autumn periods between 2000 and 2001, particularly in the nil treatments. Two years after the outbreak there was 25% less ryegrass and persistently lower pasture yields in nil plots. We conclude that pasture mealybug are capable of inflicting severe damage to endophyte-free ryegrass in Canterbury, particularly during dry summer-autumn periods.