D. E. Hume

The exploitation of epichloae endophytes for agricultural benefit

Epichloae endophytes of family Clavicipitaceae (comprising genera Epichloë and Neotyphodium) are fungal symbionts of Pooideae grasses. The associations formed, range from mutually beneficial to antagonistic and the nature of this relationship is dependent upon the importance of vertical (via host seeds) versus horizontal (ascospore mediated) transmission of the fungus. These endophytes can enhance their hosts’ survival through protection from abiotic and biotic stresses and can thus be utilized in an agricultural context. Animal-safe grass-endophyte associations that confer bio-protective properties for increased pasture persistence and productivity have been developed and commercialized. One of the crucial drivers underpinning the selection of epichloae strains for commercial development is endophyte derived bioactivity. The potential of next generation endophytes is determined by testing a number of attributes such as agronomic fitness, animal and food safety as well as compatibility with host plants of interest. Strategic research supports these activities by focusing on elucidating mechanisms of compatibility between host and fungal symbiont, as well as investigating other molecular drivers of symbiosis such as siderophore mediated iron-uptake, fungal signalling, fungal growth in host plants and fungal secondary metabolism. This review weaves together the different strands of multidisciplinary research aimed at ultimately exploiting epichloae endophytes for increased pasture performance.

Occurrence and impact of pasture mealybug (Balanococcus poae) and root aphid (Aploneura lentisci) on ryegrass (Lolium spp.) with and without infection by Neotyphodium fungal endophytes

Abstract 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 endo‐phyte‐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 endophyte‐infected 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.

Effect of Growth Conditions on Alkaloid Concentrations in Perennial Ryegrass Naturally Infected with Endophyte

A preliminary study of the effect of water stress on alkaloid concentrations in endophyte-infected perennial ryegrass (Lolium perenne) focused on artificial infections with selected endophyte strains (Barker et al., 1993). This paper reports the results of studies of the impact of environmental factors (nitrogen, water, temperature) on the concentration of alkaloids in “Nui” perennial ryegrass naturally infected with Neotyphodium lolii, a more typical component of New Zealand pastoral forage.

Evaluation of ‘Grasslands Puna’ chicory (Cichorium intybus L.) in various grass mixtures under sheep grazing

Abstract Growth of chicory (Cichorium intybus) in mixtures with different companion grass species and white clover (Trifolium repens) was examined over 4 years in a trial rotationally grazed by sheep. A mixture containing red clover (T. pratense) instead of chicory, and ryegrass (Lolium perenne), was also included. Over summer and autumn, pastures were either grazed frequently (every 3–4 weeks) or infrequently (4–6 weeks), and at other times of the year every 4 weeks. Chicory establishment was high (82% of viable seed sown), with 46 plants/m2, declining to 15/m2 by Year 4, whereas red clover plant numbers declined from 101/m2 to 13/m2. Dry matter (DM) yields of chicory and red clover increased from Year 1 to Year 3, then declined in Year 4. Over the 4 years, chicory contributed 34, 80, 85, and 57%, respectively, to green DM yield; red clover contributed 9, 24, 77, and 13%. Yields of sown grass were inversely related to chicory or red clover yields (P < 0.001, r= 0.82), particularly for chicory‐based pastu...

Evaluating the performance of endophytes in farm systems to improve farmer outcomes – a review

Abstract. The main plant species relied on for forage supply to grazing animals in New Zealand and south-eastern Australia is perennial ryegrass (Lolium perenne L.). Perennial ryegrass has evolved with a fungal endophyte (Neotyphodium lolii, Latch, Christensen & Samuals) that occupies intercellular spaces, and is nourished by its host. The endophyte (referred to as standard or wild-type) provides the plant with protection from a range of insect pests by producing alkaloids, some of which are also toxic to grazing animals, causing ryegrass staggers and/or exacerbating heat stress. Over the last 20 years naturally occurring perennial ryegrass endophytes have been found in Europe that produce less of the alkaloids that cause animal health problems but have similar or enhanced effects as the standard endophyte on deterring insect attack on infected plants, when introduced into New Zealand and Australian-bred ryegrasses. This review provides a summary of endophyte research in New Zealand from the perspective of insect pests, plants (particularly perennial ryegrass) and the animals grazed on ryegrass-dominant pastures. The protocols used to evaluate perennial ryegrass/endophyte associations over the past 30 years are also discussed. Future testing of new grass/endophyte associations should include the utilisation of more environments for agronomic and entomological experiments; routinely carrying out small animal toxicology assays, and the running of short-term indoor feeding experiments with sheep and cows. Implementation of these changes provides the minimum requirements for strengthening the evaluation of new endophyte associations so farmers using these technologies, gain optimal benefits from their adoption.

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

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 ...

Development of a bird-deterrent fungal endophyte in turf tall fescue

Abstract Two Neotyphodium fungal endophyte strains (AR601 and AR604) that produce high levels of ergovaline and loline alkaloids were inoculated into turf tall fescue for the purpose of producing symbioses that deter birds. The endophyte–grass associations were shown to be stably transmitted and, in preliminary experiments, reduced insect and bird numbers at an airport and reduced faecal contamination of a sports field by birds. Cultivar ‘Jackal’ infected with endophyte strain AR601 has been released commercially.

Mutualistic fungal endophytes in the Triticeae – survey and description

Grasses of the tribe Triticeae were screened to determine the presence of mutualistic epichloae fungal endophytes. Over 1500 accessions, from more than 250 species, encompassing 22 genera within the Triticeae were screened using immunodetection and direct staining/microscopy techniques. Only two genera, Elymus and Hordeum, were identified as harbouring epichloae endophytes with accessions native to a range of countries including Canada, China, Iran, Kazakhstan, Kyrgyzstan, Mongolia, Russia and the USA. Genetic analysis based on simple sequence repeat data revealed that the majority of endophytes cluster according to geographical regions rather than to host species; many strains isolated from Hordeum grouped with those derived from Elymus, and amongst the Elymus-derived strains, there was no clear correspondence between clustering topology and host species. This is the first detailed survey demonstrating the genetic diversity of epichloae endophytes within the Triticeae and highlights the importance of germplasm centres for not only preserving the genetic diversity of plant species but also the beneficial microorganisms they may contain.

Agronomic advantages conferred by endophyte infection of perennial ryegrass (Lolium perenne L.) and tall fescue (Festuca arundinacea Schreb.) in Australia

Abstract. Perennial ryegrass and tall fescue are key grasses of sown pastures in the high-rainfall zone of south-eastern Australia. Ryegrass in naturalised pastures, and in sown seed, is widely infected with Neotyphodium fungal endophytes, with toxic endophyte strains occasionally causing toxicosis in livestock. Endophyte infection is also beneficial in sown grasslands, assisting ryegrass hosts to overcome biotic stresses, and tall fescue hosts to overcome biotic and abiotic stresses. We review the literature for Australia and present new data, to examine the agronomic effects of endophyte. Frequency of endophyte infection in old, perennial ryegrass pastures and ecotype-based cultivars is high and, in all pastures, increases with time, providing evidence for endophyte-infected plants having an agronomic advantage over endophyte-free plants. Within a cultivar, agronomic field experiments have compared endophyte-infected with endophyte-free swards. Endophyte significantly improved ryegrass establishment in seven of 19 measurements taken from 12 trials. In mature ryegrass pastures, over half of the experiments found advantages to endophyte infection. Tall fescues infected with a selected endophyte (‘AR542’) had improved agronomic performance relative to endophyte-free in a majority of experiments, and on occasions, the endophyte was essential for tall fescue persistence. Cultivar × endophyte interactions occurred but were inconsistent. In high-stress environments, endophyte was more important for agronomic performance than difference between cultivars. The relative importance of cultivar and endophyte is discussed, with elite cultivars that are adapted to the region and are infected with elite endophytes being the best avenue to capture the benefits and minimise detrimental endophyte effects on livestock. The major drivers are likely to be insect pests and drought, but evidence is limited.

Agronomic performance and water-soluble carbohydrate expression of selected ryegrasses at two locations in New Zealand

Abstract Agronomic trials at cool (Gore) and warm (Palmerston North) temperate sites in New Zealand tested ten United Kingdom-bred (six diploids, four tetraploids) and two New Zealand-bred diploid (‘Bronsyn’, ‘Impact’) perennial and long-term hybrid ryegrasses (Lolium perenne, L. boucheanum) over two trial periods. Dry matter (DM) yields and persistence were better at the cool site but differential expression among cultivars for water-soluble carbohydrates (WSC) and yields was small compared with the warm site. The tetraploid cultivars generally had the highest concentrations of WSC but also on occasions had higher levels of crown rust, moderate DM yields and poorer persistence compared with diploids. Two of the tetraploid cultivars will be of value for their high WSC and good agronomic performance at the cool site. Some of the diploid UK cultivars expressed higher WSC and had similar or higher annual DM yields than some of the NZ-bred cultivars, and had high levels of resistance to crown rust. Overall, differences among cultivars in expression of WSC were small. Some differences occurred for seasonal DM yields with some UK cultivars having lower winter yields.