Endophytes

What is an endophyte?

An endophyte is a naturally occurring fungus that is found in ryegrass and tall fescue pastures. Endophytes are essential for persistence in most New Zealand pasture as it protects the plant from insect attack.

The endophyte produces chemical compounds which help protect plants from a range of insects but can be associated with animal health problems, especially ryegrass staggers. There are different types of endophyte and each varies in persistence, yield, and insect protection.

How does endophyte work?

Perennial ryegrasses have a mutually beneficial arrangement with an endophyte fungus. “Endo“ means inside implying that the endophyte lives entirely within the plant (in fact it can only be detected by microscopic examination of leaf sheath tissue or seeds that have been specially stained). The fungus obtains nutrients from the plant and the plant in return gets protection from insect and animal feeding by the fungus producing chemical deterrents or toxins.

The fungal strands or mycelium are concentrated in the leaf sheath of vegetative tillers at the base of the plant. However, the fungus grows up seed heads in spring infecting the newly formed seeds, thereby transferring itself to the next ryegrass generation as the seeds germinate. This elevation of the endophyte in seed heads causes some management issues as it becomes more accessible to grazing animals.

Perennial ryegrass in old dairy pastures will be infected with the Standard (Wild-type) endophyte. This endophyte produces 3 main chemicals, two of which are toxic to animals. Other endophyte strains have different chemical deterrents.

Selecting an endophyte

The decision of which endophyte to choose depends on your region and farm. 

• Most perennial ryegrass plants in NZ pastures contain an endophyte fungus that grows inside the plant and is passed to the next generation via the seed.
• Endophytes provide varying levels of protection against pasture pests so you need to know which is best for your situation. AR37, NEA2 and NEA4 are recommended in perennial ryegrass for the Upper North Island because of black beetle and argentine stem weevil.
• Novel (or selected) endophytes provide a way of avoiding animal health problems associated with ryegrass infected with the Standard (or Wild type) endophyte (Neotyphodium lolii), while maintaining positive effects on plant persistence.
• Sowing treated seed in insect-prone areas is essential to protect seedlings for a few weeks after germination when the endophyte is not active against insects.

What are the endophyte options?

When selecting endophyte for diploid perennial ryegrass, here are some things to consider:

AR1 is a selected endophyte strain that produces only peramine. It was found in perennial ryegrass in France by AgResearch (the AR portion of the name). Plants are protected from Argentine stem weevil and pasture mealy bug with only weak protection against black beetle and no protection against root aphid, porina, and grass grub. AR1 is not recommended for the upper North Island, in an invasion by black beetle, all ryegrass is destroyed.

NEA, NEA2 and NEA4 are selected endophyte strains (sometimes called novel endophytes) that produce peramine and small quantities of ergovaline. They do not cause ryegrass staggers, and offer protection from pasture mealy bug, some protection against Argentine stem weevil and black beetle, and weak protection against root aphid.

AR37 is another novel endophyte found by AgResearch in France. AR37 does not contain the alkaloid compounds of lolitrem B, ergovaline and peramine but does have unique compounds janthitrems. It provides a wide spectrum of insect resistance.

SE refers to 'standard endophyte' (SE).  It is sometimes referred to as ‘high’ or ‘wild type’ endophyte. This is a naturally occurring endophyte in old ryegrass pastures, and is still available in some cultivars.

Standard endophyte (SE) causes ryegrass staggers in spring/summer. Plants are protected from Argentine stem weevil and pasture mealy bug, have some protection against black beetle and only weak protection against root aphid and Porina. Plants have no protection against grass grub.

U2 is a meadow fescue endophyte that produces lolines. At present it is not available in the Forage Value Index, because National Forage Variety Trial (NFVT) DM yield and persistence data is not yet available on the performance of the cultivars containing this endophyte.

WE refers to seed 'without endophyte' ****and LE refers to 'low endophyte'.

Endophyte type and protection against insect pests

Pasture in New Zealand is subject to feeding and damage by a number of insect pests. The control of these pests is mediated through the endophyte within perennial ryegrass, Italian and short term (hybrid) ryegrass, festulolium, and tall fescue.

Notes on tables

No control

+ Low level control: Endophyte may provide a measurable effect, but is unlikely to give any practical control.

++ Moderate control: Endophyte may provide some practical protection, with a low to moderate reduction in insect population.

+++ Good control: Endophyte markedly reduces insect damage under low to moderate insect pressures. Damage may still occur when insect pressure is high.

++++ Very good control: Endophyte consistently reduces insect populations and keeps pasture damage to low levels, even under high insect pressure.

( ) Provisional result: Further results needed to support the rating. Testing is ongoing.

Edge endophyte currently has no industry-agreed ratings for animal health and performance or insect control. Testing is ongoing.

1 AR37 endophyte controls Argentine stem weevil larvae, but not adults.  While larvae cause most damage to pastures, adults can damage emerging grass seedlings. In Argentine stem weevil-prone areas it is recommended to use treated seed for all cultivars with novel endophyte.

2 AR1 plants are more susceptible to root aphid than plants without endophyte.

3 Also active against black beetle adults and larvae.

Endophyte effect on animal health and performance

Traditionally most New Zealand pastures contained endophyte now called 'Standard' endophyte which on occasion has caused 'ryegrass staggers' in animals. Today there is a selection of new or 'novel' endophytes with superior animal health.

Dairy and beef cow performance by endophyte type

All trialling for ryegrass staggers occurs under simulated worst-case scenario management and does not represent normal farm practice, although the likely hood for ‘ryegrass staggers’ to occur is reduced, the risk still may exist if rated below the 4-star rating ‘freedom from staggers’. The risk of ryegrass staggers can reduce if cows are supplied a mixed diet, such as other non-ryegrass species, clover, crops, or supplements.

What are the chemical compounds produced by endophytes?

Peramine protects the plant from attack by Argentine stem weevil and pasture mealy bug. Adult Argentine stem weevil will not lay eggs on plants where they detect peramine, but their larvae are less sensitive to the chemical. Peramine is not toxic to animals.

Ergovaline protects the plant from black beetle feeding and moderate protection against root aphid. As a vasoconstrictor causing reduction in blood vessel diameter, ergovaline may occasionally interact with the weather conditions, precipitating heat stress in cows, but this has not been proven to occur in New Zealand

Lolitrem B causes ryegrass staggers in cattle and acts on the nervous system and affected animals appear drunk and uncoordinated when suffering from ‘Ryegrass Staggers’. Effects of lolitrem B on livestock is most pronounced in summer and autumn as chemical concentration is highest in warm, moist climatic conditions. Seed head production also occurs in late spring/early summer when lolitrem B concentrations at the top of the plant are 4 times that of the base. Animals grazing wild-type endophyte in summer are most at risk if they eat seed head or if they graze very low into the sward. Lolitrem B is also toxic to Argentine stem weevil larvae.

Janthitrems are alkaloids produced only by AR37 endophyte and provide protection against a wide range of insect resistance. Janthitrems levels follow a seasonal; pattern of other alkaloids, low in winter and high in summer.

Lolines are alkaloids produced by meadow fescue endophyte and offer protection for a wide spectrum of insects.

How do I manage contamination of standard or wild type endophyte?

In situations where a farm has old pastures, new novel endophyte pastures can be contaminated by standard (wild type) endophyte.

Sources of contamination of novel endophyte-infected pastures

Novel endophyte-infected pastures will only give the intended benefits if contamination with the wild endophyte is low. The greatest source of contamination is from:

• Surviving endophyte-infected ryegrass plants
• Natural reseeding (seed on soil surface)
• Seed carried in hay and cow dung

A small insignificant source of contamination is from buried ryegrass seed, which usually survives for less than one year.

Pre-sowing pasture management

The aim of pre-sowing pasture management is to:

• Kill all existing vegetative ryegrass plants
• Deplete levels of ryegrass seed on the soil surface

Seed shed on to the soil surface from mature seed heads (natural reseeding) the summer before sowing can germinate after rain in autumn. Natural reseeding is minimised by:

• Growing a crop over summer (e.g. turnips, maize) – most effective means
• Topping after grazing when there are green, immature seed-heads present
• Not making hay

Establishment methods

• Provide a seedbed that favours rapid establishment of the sown ryegrass
• Spray/cultivate - kill existing ryegrass plants using herbicide then plough to bury surface seeds.
• Double-spray/fallow - apply herbicide in late summer to kill existing plants, then fallow, surface seed germinates after autumn rain. Kill these seedlings with a second herbicide application.