The most recent novel endophyte, AR37 does not contain the alkaloid compounds of lolitrem B, peramine, or ergovaline, but does have a unique set of compounds called epoxy-janthitrems...
What is endophyte?
Endophyte is a naturally occurring fungus whose complete life cycle occurs within grasses such as perennial ryegrass and tall fescue. Most New Zealand ryegrass pastures are infected with endophyte. The endophyte fungus grows between the cells of the host plant, drawing nutrients from it but in return conferring resistance to insect pests, providing some drought tolerance, and protection from overgrazing – a relationship know as a symbiosis. In the early 1980s it was discovered that an endophyte (Standard Endophyte) in perennial ryegrass was responsible for staggers and heat stress in sheep and cattle. However, just removing the endophyte wasn’t a solution in many regions of New Zealand as perennial ryegrass persistence is poor when endophyte is absent, and these fungi produce a range of insect-deterring chemical compounds, which may also affect grazing animals.
Endophytes produce chemical compounds known as alkaloids some of which confer pest resistance to ryegrass, although some may also cause animal health problems. Peramine is a compound that deters feeding and egg laying of Argentine Stem Weevil, a serious pest affecting ryegrass persistence and protects against pasture mealy bug, but has no known effects on animal health when that ryegrass is grazed. Lolitrem B deters Argentine Stem Weevil larval feeding but causes Ryegrass Staggers. Ergovaline gives resistance to African Black Beetle, but causes heat stress in animals, especially in warm humid conditions
Novel endophytes are selected endophyte strains that have a known and understood alkaloid chemical compound profile. It is known what impact these compounds have on; insect pests; the agronomic performance and persistence of the ryegrass plant, and the health; and performance of animals grazing ryegrass plants containing the novel endophyte strain. Novel endophytes can be incorporated into elite cultivar germplasm either by an inoculation process or by breeding and selecting with plants that contain the novel endophyte strain. Novel endophytes are naturally occurring and are not genetically modified organisms.
Standard Endophyte contains the compounds lolitrem B, peramine and ergovaline. AR1 novel endophyte contains peramine which protects against Argentine Stem Weevil and pasture mealy bug and provides some tolerance to adult African Black Beetle after the plants are established. AR1 does not contain lolitrem B or ergovaline and as such there is enhanced animal performance over Standard Endophyte. Endo 5 endophyte contains peramine but not lolitrem B. It has some level of ergovaline production which allows for agronomic robustness, especially in areas where African Black Beetle is an issue.
The most recent novel endophyte, AR37 does not contain the alkaloid compounds of lolitrem B, peramine, or ergovaline, but does have a unique set of compounds called epoxy-janthitrems. Epoxy-janthitrems confer resistance to a wide range of insect pests (Argentine Stem Weevil larvae, African Black Beetle adults, root aphid, pasture mealy bug and porina). Testing to date has shown perennial ryegrass plants with AR37 to be more persistent and productive than perennial ryegrass with Standard Endophyte and with livestock performance levels similar to AR1 and nil endophyte. While AR37 does not produce the alkaloid LolitremB it can cause ryegrass staggers in grazing livestock. In grazing trials at Lincoln the incidence of ryegrass staggers on pure ryegrass with AR37 has been less frequent and usually only half as severe as on ryegrass with standard endophyte. However, these trials have shown than spasmodically AR37 can cause serious staggers (Fletcher & Sutherland 2009: Proc NZ Grassland Assn, 71: 127-33.
How AR37 came about - The search for pest tolerant endophytes
While AR1 endophyte was shown to have better animal performance than Standard Endophyte, it was also shown to have limited pest resistance - it controls only Argentine Stem Weevil and pasture mealy bug. Reports were soon received that ryegrasses infected with AR1 were not persisting in some areas of New Zealand, particularly where African Black Beetle or root aphid were present. This reduced persistence was clearly seen where there were dry conditions and the increased insect pest pressure. This was because this insect pressure increase the susceptibility of ryegrass to drought.
As a result of this reduced persistence, AgResearch set about seeking more pest tolerant endophytes that did not contain lolitrem B or ergovaline. The new technology identified was AR37 - a naturally occurring endophyte strain that deterred a wide range of insects and provides increased persistency, but did cause ryegrass staggers. AR37 was developed in direct response to feedback from farmers and pastoral industries, aiming to improve perennial ryegrass persistence over that of ryegrasses with AR1, and even delivering greater persistence than Standard Endophyte.
The science behind AR37
AR37 was first identified through agronomic trialing in the mid-1990s. In 11 trials sown in 4 regions of the country, a range of endophytes were tested against endophyte free and standard endophyte ryegrass in the same cultivar with AR37 delivering better ryegrass production and persistence. On average, these 11 trials showed that over a 3-4 year period, annual dry matter was 12% better for AR37-infected ryegrass compared with the same ryegrass cultivar infected with Standard Endophyte. Differences were greatest in northern regions of New Zealand and greater in late summer/ autumn. Further work with different cultivars sown in other years has confirmed these results are repeatable.
AR37 effects on insects
Several insect pests attack ryegrass. These include Argentine Stem Weevil larvae, pasture mealybug, African Black Beetle (adult), porina, root aphid and grass grub. All of these insects, except porina and grass grub, feed on ryegrass and not on clover. Porina and grass grub feed on all pasture species.
Argentine Stem Weevil - Argentine stem weevil is a significant pasture pest for nil endophyte rygrass. It is not uncommon for over 20% of endophyte-free ryegrass tillers to be damaged by Argentine Stem Weevil larvae in summer whereas both AR1 and AR37 will reduce this level to less than 5%.
Pasture Mealy Bug - Pasture mealy bug can be a major problem in Canterbury and Hawke’s Bay but is also found in the Marlborough and Nelson districts, Manawatu, Waikato and Northland. These insects suck plant sap from around the base of the plant causing plants to wilt and brown-off in autumn. Both AR1 and AR37 reduce populations of mealybug to very low levels (Pennell et al, 2005: NZ Journal of Agricultural Research, 48: 329-37
African Black Beetle - AR37 is also very effective against African Black Beetle adults resulting in lower populations of the very damaging root-feeding larvae in summer and early autumn (Popay & Thom, 2009: Proc NZ Grassland Assn 71: 121-27).
Porina - AR37 is also both deterrent and toxic to porina larvae in laboratory trials (Jensen & Popay, 2004: NZ Plant Protection, 57: 323-28). In a field trial, no porina were found in plots of AR37 whereas endophyte-free and AR1 plots contained 10 larvae/m2 (A.J Popay, Unpublished Data). This field trial result confirm laboratory evidence of tolerance of ryegrass with AR37 to porina, compared with AR1 and endophyte free ryegrasses.
Root aphid - Root aphid is a tiny insect that sucks the plant sap from roots of grasses which is present all year. Because it has many generations in a year it can build up to high numbers when conditions suit it. AR37 endophyte reduces populations of this aphid to very low levels, however, this aphid is considered to be responsible for reduced vigour of ryegrass with AR1 and Standard Endophyte.
Grass Grub - Grass grub numbers in AR37 pastures have been noted to be lower in trials in the Waikato (Popay & Thom, 2009: Proc NZ Grassland Assn 71: 121-27) and Canterbury (Winchmore) (A.J Popay, Unpublished data) than AR1 and Standard Endophyte pastures. While AR37 does not provide resistance to grass grub, lower numbers indicate there will be less severe pressure from this pest under AR37 than under AR1 or Standard Endophyte. This does not mean that AR37 will not be damaged by grass grub.
Broad Pest Protection - The increases in persistence and production of ryegrass from AR37 are largely due to the protection it provides against this broad range of insects. In an outdoor pot trial, the growth of ryegrass with different endophytes was compared when plants were treated or not treated with an insecticide. Insecticide treatment did not increase the growth of plants with AR37 but markedly increased the growth of endophyte-free ryegrass and of ryegrass infected with AR1 and the Standard Endophyte (see graph below). In the field, protection against African Black Beetle adults and root aphid are thought to be the main reasons for the high yield of AR37 ryegrass in field trials in Hamilton and Kerikeri (Hume et al, 2007: Proc NZ Grassland Assn, 69: 201-05) and greater persistence of AR37 ryegrass over AR1 and Standard Endophyte in a Waikato dairy trial (Popay & Thom, 2009: Proc NZ Grassland Assn, 71: 121-27).
These graphs show how insecticide treatment of perennial ryegrass with AR37 does not increase its growth, but insecticide applications does increase the growth of endophyte-free ryegrass, and ryegrass infected with the AR1 and Standard Endophytes.
AR37 – Agronomic Performance
The agronomic trialing of AR37 began in the mid-1990s. In 11 trials sown over 3-4 years and 4 regions of the country, a range of endophytes were tested in the same cultivar (in clover free pastures) against endophyte-free and the Standard Endophyte. The outstanding feature of this research was the better production and persistence that AR37 imparted on the ryegrass (see graph below).
On average, these 11 trials showed that over a 3-4 year period, annual dry matter was 12% better for AR37-infected perennial ryegrass compared with the same ryegrass infected with Standard Endophyte. Differences were greatest in northern regions of New Zealand, and greater in late summer/autumn.
More recent trials show that the time it takes for the advantages of AR37 to be seen will differ between years and regions Hume et al 2007: Proc NZ Grassland Assn, 69: 201-205
AR37 provides increased ryegrass tiller numbers, root mass & depth, persistence and yields (12% more than Standard Endophyte) with more at critical times of the year.
The DairyNZ trial on Scott Farm (Waikato) compared Commando perennial ryegrass-based pasture infected with AR37, AR1, Standard (HE) or without endophte (Nil). The project aimed to measure ryegrass persistence and pasture yields and to assess any effects of the AR37 endophyte on cow health and milk production. In the fourth and final milking season white clover was removed to test the effect of endophyte/ryegrass association in isolation from any effect on clover content of pastures. The following bullet points present a summary of results from the four seasons.
- AR37 ryegrass was clearly more persistent than either AR1 or Standard (HE) ryegrass. This supports findings from previous work.
- The greater persistency translated into a reduced need for renovation of AR37 pastures after the 2008 drought, but in the three years before that time there was no difference in total pasture yield.
- There was no sign of ryegrass staggers or any other animal health issues in cows grazing AR1 or AR37 pastures – even at times when cows grazing HE were affected by ryegrass staggers.
- With ryegrass/white clover pastures, there was a trend for slightly lower milksolids (MS) production over summer from cows grazing AR37 or HE compared with AR1. With pure ryegrass pastures there were no significant differences in MS production. These results suggest that the higher clover content of the AR1 mixed pasture was a contributing factor to the observed MS production differences.
- Where pasture persistence is the top priority then AR37 will clearly deliver benefits. Where persistence of AR1 ryegrass is not a problem, continuing to sow AR1 is advised. DairyNZ cannot envisage any situation in which farmers should sow HE ryegrass.
A larger trial in Victoria, Australia on pure perennial ryegrass pastures has also shown similar milk yield per cow for AR1 and AR37 over the first and second lactations, and there have been no incidences of ryegrass staggers grazing AR37 pastures.
Animal health and performance responses to grazing perennial ryegrass infected with AR37 have been measured in weaned lambs and hoggets over 10 years at AgResearch Lincoln. Results from the first 6 years were published in 2005 (Fletcher et al 2005: In: Neotyphodium in Cool Season Grasses: 229-241). These results are updated to 2008 in the tables below.
Sheep growth rates over summer and autumn, when endophyte toxins are likely to be highest, have been better on AR37 than on the same ryegrass cultivar infected with the Standard Endophyte containing no clover. Growth rates on AR37 are similar to the same ryegrass without endophyte or with the AR1 endophyte (see Table 1). Overall lambs grazing AR37 have liveweight gains similar to that of AR1 and nil endophyte and superior to lambs grazing Standard Endophyte when the average ryegrass staggers score is less than 2. In grazing trials at Lincoln the incidence of ryegrass staggers on pure ryegrass with AR37 has been less frequent and usually only half as severe as on ryegrass with Standard Endophyte. However, these trials have shown that spasmodically AR37 can cause serious staggers.
(Fletcher and Sutherland 2009: Proc NZ Grassland Assn, 71: 127-33).
Epoxy-janthitrems which are produced by ryegrass infected with AR37, are tremorgenic and can cause ryegrass staggers. Ryegrass staggers is a neuro-muscular disorder which is scored on a 0-5 ascending scale, with 5 being very serious staggers (see Table 2). It should be noted that there is considerable variation between animals in their susceptibility to ryegrass staggers.
Apart from ryegrass staggers, animals grazing ryegrass with AR37 show none of the adverse responses often associated with grazing ryegrass with Standard Endophyte, such as increased body temperatures and respiration rates, more dags and flystrike and lower plasma prolactin concentrations.
|TABLE 2: Ryegrass staggers scoring criteria: after being driven briskly over 300m|
|1||Slight muscle spasms around neck, shoulders and flank.|
|2||Severe muscle spasms and shaking of the head after stress but no loss of co-ordination.|
|3||As in 2, but with lack of co-ordination when moving.|
|4||Muscle tremors beginning early in the run (<30 m), soon followed by lack of co-ordination resulting in staggering gait which progresses to the animal falling down. The animal regains its footing after a short period of severe spasms and is able to walk off.|
|5||Severe muscle tremors following short movement (<10 m) or after slight disturbance. The animal collapses in severe tetanic spasms which may last in excess of 10 minutes, before the animal attempts to regain its footing.|
|From Keogh, R.G. 1973 Induction and prevention of ryegrass staggers in grazing sheep. New Zealand Journal of Experimental Agriculture 1: 55-57|
|TABLE 3: Effect of endophytes on mean ryegrass staggers scores
(0-5 ascending scale) at Lincoln 1999-2008
|2006 trial A||4.0||1.2|
|2006 trial B||4.0||0.6|
|* summer and autumn grazing combined|
Does AR37 live up to its claims?
The persistence that AR37 ryegrass plants has exhibited in the recent severe droughts in the North Island of NZ would indicate that AR37 endophyte is living up to its claims. Compared to AR1, Standard and nil Endophyte ryegrasses, ryegrasses containing AR37 have been able to withstand the drought because of lower pest pressure - predominantly from Argentine Stem Weevil, African Black Beetle and root aphid.
No perfect solution - No one-endophyte-fits-all
Currently there is no perfect solution when it comes to ryegrass endophyte. The decision of which endophyte farmers choose depends on their region and farm. While AR1 has been a success story for its high animal performance compared with Standard Endophyte, its agronomic performance in some regions of New Zealand can be lower. AR37 endophyte does provide better persistence and good animal performance but with a recognized risk of ryegrass staggers. Where farmers are concerned with their ryegrasses agronomic performance, AR37 can be a good alternative.
AR37 is a great example of what can be achieved by world-leading, New Zealand based science. It was born out of the need to do better — to build on the successes of AR1 and offer farmers, dealing with drought conditions and pest infestations, a more enduring solution.
AR37 is a significant breakthrough for farmers, and for the New Zealand economy.