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In The Paddock
Seasonal sheep flock management tips – January 2003

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Ryegrass endophytes – both friend and enemy

Key points

  • Endophytes are fungi that exist inside plants.
  • They produce a wide range of compounds. The main ones are peramine, lolitrem B and ergovaline.
  • Peramine helps protect plants from insect attack, especially Argentine stem weevil.
  • Lolitrem B is a neurotoxin that causes ryegrass staggers in animals.
  • Ergovaline lowers blood prolactin levels and causes heat stress.
  • Some of these chemicals, in combination with other as yet unidentified compounds, depress intake and liveweight gain, and cause scouring and dags in sheep.
  • Non-toxic strains of endophyte have been identified.
  • The most promising, AR1, produces peramine and is commercially available. It protects the plant from insect attack and has no ill-effects on grazing animals.

Endophytes are fungi that grow inside plants in a symbiotic relationship.

Beneficial effects include the protection they give grasses from attack by some insects, nematodes, and plant diseases.

They can make their hosts more drought-tolerant and in some plants, can trigger enhanced growth and tillering. Their presence may also discourage over-grazing by mammals.

Negative effects include the production of alkaloids which affect the health and production of grazing animals.

Effects on pasture growth and yield

Endophytes are essential because they protect ryegrass from pests, notably Argentine stem weevil (ASW). In 1991, this pest was estimated to be costing New Zealand $46-200 million in pasture damage each year.

Endophytes also protect perennial ryegrass from other invertebrates, such as black beetle, which in some seasons can be a serious pest in northern New Zealand.

Endophyte-free ryegrass can be quickly destroyed by black beetle. If endophyte is present, feeding by adult beetles is deterred, and egg and larval numbers are reduced.

Ryegrass has greater tolerance to stresses like drought when infected with endophyte. It's also less likely to be severely grazed. And most importantly, endophyte-infected ryegrass pastures produce more dry matter than endophyte-free pastures.

On the down-side, clover growth tends to be poorer in endophyte-infected pasture. This effect may be compounded by the tendency for livestock to preferentially graze clover in a mixed sward and actively avoid the infected ryegrass.

Before 1980, it was thought that a fungus was involved with ryegrass staggers, and research aimed to isolate the chemical(s) responsible. The discovery of endophytes hastened this process.

Several related compounds were identified, and of these, lolitrem B proved to be the most abundant and most potent. The main compound responsible for protection from ASW was shown to be peramine.

Ergovaline was also found. This lowers blood prolactin levels, causing a host of animal health problems including heat stress. Ergovaline and lolitrem B also protect against insect pests.

Because the endophyte and the host have evolved together, there is an array of compounds present in endophyte-infected grasses. These may be a cause of scouring, dags and other symptoms of ill-thrift in stock.

In the laboratory, it is possible to select or develop endophyte strains with varying levels – as low as nil – of particular alkaloids.

Endophyte strains have been identified which produce peramine but are free of ergovaline and/or lolitrem B. The novel endophyte (AR1) is one of these.

AR1, which is produced by AgResearch, significantly reduces the risk of animal health problems. Trials show animal performance on AR1 pastures to be similar to those on endophyte-free pasture.

The main alkaloids in ryegrass endophyte, their occurrence and effects on plant pests and grazing animals
Endophyte Option Definition Produced Main Chemicals Properties
Wild Naturally infected with an endophyte Lolitrem B, Ergovaline, Peramine Protects against ASW and black beetle, can cause ryegrass staggers, heat stress and dags.
Nil Contains no endophyte Nil No protection against insects. No ryegrass staggers, heat stress and dags.
AR-1 Novel endophyte Peramine Protects against ASW, offers some protection against black beetle but not as much as wild endophyte. No ryegrass staggers, heat stress and dags.

More information

Ryegrass endophyte – an up-to-date review of its effects, WoolPro Report, 2001.

Your local farm consultant or veterinarian can provide useful advice about ryegrass endophytes. Alternatively, contact your local Meat & Wool Innovation specialist:

Northern North Island: Sally Hobson tel 07-827 3818 or 025-924 751
Hawkes Bay/East Coast: Lew Willoughby tel 06-835 1888 or 025-434 417
Southern North Island: Richard Gavigan tel 06-376 0005 or 025-499 851
Nelson/Marlborough/Canterbury: Alan Marshall tel 03-325 6911 or 025 329 399
South Canterbury: Julia Mackenzie tel 03-680 6782 or 025-782 353
Otago: Robert Pattison tel 03-489 9021 or 025-323 094
Southland: Aaron Meikle tel 03-203 9071 or 025-846 377
 

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