AR37 - The Facts

Article from the April 2008 issue of AgResearch InTouch magazine (see magazine).

You may have seen media coverage in recent weeks of AR37 - an AgResearch developed/PGG Wrightson Seeds marketed endophyte that was recently launched onto the market. There has been some confusion and misinformation about it. What follows are the facts:

How AR37 came about

AR37-infected ryegrass seeds

In the early 1980s it was discovered that an endophyte (standard wild type) in 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 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.

AgResearch’s advanced research found the chemical compound lolitrem B was the cause of ryegrass staggers, ergovaline caused heat stress, and peramine provided resistance to a major pasture pest - Argentine stem weevil. But it was also found that in ryegrasses from around the world there were many different variants of endophyte and some did not produce either lolitrem or ergovaline, but did produce peramine. One of these was commercialised non-exclusively in 2000 as ‘AR1’ and is now incorporated into about 70 to 80% of all proprietary ryegrasses sown in New Zealand.

AR1’s limitations

AR1, however, has 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. Increased insect pest pressure also increases the susceptibility of ryegrass to drought.

The search for pest tolerant endophytes

AgResearch set about seeking more pest tolerant endophytes that did not contain lolitrem or ergovaline. The new technology identified was AR37 - a naturally occurring endophyte strain that has limited effects on cows and sheep, yet deters insects, thus possibly providing increased drought tolerance. AR37 was developed in direct response to feedback from farmers, aiming to improve ryegrass persistence over that of AR1 ryegrasses, and even delivered greater persistence than the standard endophyte.

No perfect solution

AR37 didn’t produce any of the known bioactive compounds (lolitrem, ergovaline [which depresses animal growth rates] or peramine), but after many years of research AgResearch discovered that the chemicals responsible for AR37’s wide ranging pest resistance are a group of compounds called epoxy-janthitrems - which can also cause staggers.

The science behind AR37

AR37's robustness is primarily due to large improvements in insect resistance, compared with the same ryegrass cultivar infected with other endophyte strains

AR37 was first identified through agronomic trialling 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. AR37 delivered better 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 ryegrass 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 (see figures attached) has confirmed these results are repeatable.

Does AR37 live up to its claims?

If you take the recent severe Waikato drought, the unequivocal answer is ‘yes’. Compared to AR1, standard and nil endophyte ryegrasses, AR37 has been able to withstand the drought because of lower pest pressure - predominantly from Argentine stem weevil, African black beetle and root aphid.

Why a commercial partner is so important to AR37

The endophyte technology is not a product itself. It is the combination of commercial ryegrass seed and AgResearch-endophyte technology that delivers the benefit.

No one-endophyte-fits-all

Which endophyte farmers choose depends on the region and farm. While AR1 has been a success story for its high animal performance compared with the standard endophyte, its agronomic performance can be lower. AR37 can be a good alternative in these cases.

The milk production debate

No claim has been made about an AR37-containing grass giving rise to more milk than AR1. One might hope that such a grass would give rise to more milk if there is more grass and it persists for longer.

A trial presently being conducted by DairyNZ at Newstead compares milk production from cows grazed on ryegrass-clover pastures containing nil, standard, AR1 or AR37 endophytes. This finds no statistically significant difference in milk production between AR1 and AR37 over the course of a whole season or lactation, but within a season has found more milk produced from AR1-grassed pastures in summer and autumn. This trial is continuing and will produce more information on milk production and the persistence of pasture following the current drought. A larger trial in Victoria, Australia, has also shown similar milk yield per cow for AR1 and AR37 over the first lactation.

In summary

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 our economy.

It is valuable for farmers and for every New Zealander who prospers as a result of its success.

Relative ryegrass yields for ryegrass infected with AR1 endophyte and AR37 endophyte compared with Standard endophyte (=100) for each season at two sites in northern New Zealand. Error bars show the LSD value when significant differences (P<0.05) occurred between endophyte strains within a season. Hume et al 2007. NZGA Proceedings 69: 201-205.