Ryegrass staggers cause is confirmed

Press, 5 March 1982, Page 19

Ryegrass staggers cause is confirmed

By

HUGH STRINGLEMAN

First the bad news; ryegrass staggers in sheep and cattle is very bad in. North Canterbury this year. Now the good news; a research breakthrough within recent days has confirmed the cause of staggers as the fungus folium endophyte, which lives within ryegrass. There should be some consolation for North Canterbury farmers who are watching their stock stagger, and in some cases’ die, in the news of the research confirmation of the cause of the problem, but unfortunately widespread prevention is still a way down the track. Just as the research breakthrough came from the efforts of what is described as a unique combination of scientific disciplines, the battle to treat and eventually eliminate ryegrass staggers will probably take place on several fronts. But none of this work will help the afflicted farmer and his stock this season, and the management practices of controlled grazing and supplementary feeding remain the best ways of treating the problem. (See accompanying story.) The research into the cause of staggers has all the elements of a good detective story and although plenty of detail has been released within the last six months by the scientists concerned, it is only in the last week that another piece of very conclusive evidence has confirmed folium endophyte as the cause of the annual scourge. A freshly harvested ryegrass seed line has been found to contain the folium endophyte in an active state and the cells of the endophyte to contain the crystaline material suspected of carrying the neurotoxins (called lolitrem A and B) which cause staggers. The Canterbury seed line was forwarded to Dr Rex Gallagher, Ministry of Agriculture and Fisheries Ruakura. who found that crude extracts from this seed, when injected into mice, proved' highly toxic, producing symptoms' similar to those induced when known toxic ryegrass leaf sheath , preparations were adminis- , tered.’ Physiologically, the toxins i are believed to prevent the i operation of normal neuro- i logical chemicals which con- i trol or moderate nerve im- i pulses, so that infected animals tremble, have spasms, < and show the behaviour i farmers know as the ; staggers. i Dr lan Harvey, plant i

I ' pathologist at the Plant [ Health Diagnostic Station of ; the Ministry of Agriculture ■ and Fisheries at Lincoln, has explained the significance of this latest discovery with the toxic seed line. "Since ryegrass seed is not formally toxic to animals, and normally contains no crystaline inclusions, these results strongly implicate the crystaline inclusions as the site of the accumulation of the toxins (lolitrem A and B) and adds strong weight to the ryegrass staggers and folium endophyte association," he said. Dr Harvey has been coordinating the intensive and comparatively speedy research into folium endophyte and ryegrass staggers. Experts in mycology (the study of fungi), electron microscopy and toxicology have worked on raw materials and data collected by agronomists, veterinarians and plant pathologists and the pieces fitted together like a jigsaw to give a picture of the unusual microscopic fungus which causes all the trouble. Involved have been scientists at Ruakura, Lincoln and the University of Canterbury. “It has been very exciting," said Dr Harvey, "and we can now say that we have confirmed the" theory that folium endophyte causes ryegrass staggers but there is substantiating work still going on. “Various groups will turn their attention to combating the problem, now that we know what causes it. “It is my hope that with a combination of pasture seed selection, seed storages, fungicide treatments, animal breeding, and even animal remedies we will eventually eliminate ryegrass staggers," he predicted. But amid the excitement among researchers over the latest breakthrough there is a realisation of the irony that a previous generation of New Zealand researchers in the 1950 s were (continuing the detective thriller analogy) only one step away from solving the mystery. li has been known for many years that ryegrass contains the fungus ’ folium endophyte and it was strongly suspected of being the cause of staggers. Considerable research was done into the fungus during the 1950 s but it was eventually rejected as a cause of staggers for the following reasons:

0 Lolium endophyte-infected ryegrass seed when fed to animals had not been found to be toxic. ® Pure cultures of the folium endophyte are not toxic. 0 The fungus is found throughout New Zealand seed lines and is too widespread to account for sporadic outbreaks of staggers. In the New Zealand Veterinary Journal in 1959 a paper by I. J. Cunningham and W. J. Hartley said in part: “Lolium endophyte was found in 10 out of 14 ryegrass plants examined and there was nc other fungus. “It was considered by J. C. Neill in the Plant Diseases Division of the D.5.1.R.. Auckland, that a widely distributed fungus such as lolium endophyte could not be responsible for localised outbreaks of ryegrass staggers.” But no blame can be attached to these researchers for turning their backs on the fungus when they were within one fact of nailing it as the culprit. The one fact that was needed, and which those researchers did not have, even if they suspected its existence. was only provided by the electron microscope. Dr Harvey did his Ph.D. in electron microscopy and he asked that the " electron microscope of the University of Canterbury, under Dr Brian Fineran and Mr Manfred Ingelfeld. Botany Department, should probe the fungus cells. It uncovered some unusual characteristics. The lolium endophyte cyto-

plasm, or contents of its cells, taken from ryegrass leaf sheaths, which are known to be highly toxic, contain crystaline inclusions. When grown in artificial culture the cytoplasm of the folium endophyte does not contain these inclusions and the fungus in rye seeds is normally in a dormant state, also containing no crystaline inclusions. Obviously the crystaline structure was then suspected of being connected with the high incidence of staggers in stock which are allowed to intensively graze ryegrass, or in other words to eat a high concentration of leaf sheath material. It was reasoned that if the crystaline inclusions contain the neurotoxins which produce the staggers then this would explain why staggers could not be produced by feeding stock ryegrass seed or extracts of folium endophyte.

The electron microscope work proved that the fungus has a norma! state, without crystaline inclusions, when it is not dangerous, and another state when the lolitrem neurotoxins which cause staggers are present in the crystaline structures.

Although present in the greatest, and most dangerous. concentration in the leaf sheath, the fungus also in-' habits other parts of the plant, but in all cases with no ill-effects to the plant.

It is in the seeds of ryegrass, but its viability diminishes with the length' of time that th 6 seed is stored.

Research work by Mr Lester Fletcher. ’ technical officer with the Grasslands Division. D.5.1.R., Lincoln, on different cultivars of ryegrass had shown that the length of storage of the seed was connected to the subsequent incidence of staggers. It appeared that storing seed 18 months or longer eliminated the possibility of subsequent ryegrass staggers. The latest breakthrough in positively identifying neurotoxins and their undesirable effects in freshly harvested ryegrass seed, referred to at the beginning of this article, has confirmed Mr Fletcher’s field observations. The multi-disciplined nature of the research will now be repeated in the search for remedies

A rapid detection method for lolium endophyte in plant and seed samples is being developed by Dr David Musgrove. Plant Diseases Division, D.5.1.R.. and will probably find very useful application at the Seed Testing

Station in Palmerston North. Fungicides-are being used to treat ryegrass seed to kill the fungus and one, marketed under the name of Till, shows promise. There is evidence that there is a variation in susceptibility to ryegrass staggers between breeds and even sires within breeds of the animals which are prone to staggers; sheep, cattle and horses. There is also potential for genetic selection work to breed up animals which are tolerant to the neurotoxin. ■Tolerance also builds with age and it appears that there is scope for animal remedies to be developed which would assist the ability of the livers of animals to cope with infections of the lolitrem neurotoxins.

But the extent of perennial ryegrass pastures throughout New Zealand, particularly in the regions of the country, like North Canterbury, where ryegrass staggers has been a problem, makes a concerted effort to eliminate the problem through pasture replacement. a mammoth undertak ing.

Instead it appears that the various remedies being worked on at present will eventually be available te farmers troubled by staggers to use if they wish. The costs of such, remedies may induce farmers to remain with management techniques to combat staggers