Microbe of the Month: Friendly fungus to grass, but poison to grazing animals
Monday 15 November 1993
These qualities, which have made tall fescue particularly attractive to farmers in the upper South and lower Midwest of the United States, come from a fungus, Acremonium coenophialum, which grows inside the plant. The infection does not harm the grass, which shows no visible signs of the fungus within. Seeds carry Acremonium from generation to generation. Soon after germination, thread-like filaments of the fungus begin to spread through the plant, particularly in the leaf sheaths. As flowering approaches, they concentrate in the tissues where the flower heads are to form.
But there is a paradox behind the agricultural success of tall fescue. The microbe responsible for the grass's robust characteristics also has toxic effects, the chemical basis of which is becoming clear, on grazing animals. Because some less hardy varieties of tall fescue do not carry Acremonium, there are hopes that they can be infected with novel strains, genetically engineered to confer benefits but not disadvantages. Meanwhile, as Donald Ball of Auburn University, Alabama, and colleagues report in the current issue of American Scientist, farmers must accept the harm to their livestock or switch to a grass with much less robust characteristics.
The earliest indications of problems came to light after tall fescue first began to be planted in the US during the Forties. There were reports of declining health and productivity in cattle, sheep and horses grazing on the grass. But only in 1973 was the fungus incriminated, when Department of Agriculture scientists investigated a farm near Mansfield in Georgia, where cattle in one field of tall fescue were perfectly healthy while those on apparently identical pasture nearby were sick. They found that 10 per cent of the grass in the first field was infected with fungus, compared with virtually 100 per cent in the second.
We can now discern a symbiosis between the grass and the fungus. The plant provides nourishment for Acremonium, which confers benefits in return. One example is the 'leaf roll' of infected fescue when, during periods of drought, the blades of grass curl inwards to minimise water loss. Uninfected plants, unable to retain water in this way, may die under identical conditions. Acremonium also makes the fescue toxic to both insects and grazing livestock. Analysis indicates that this is attributable to substances known as peptide ergot alkaloids, produced by the fungus. Although Acremonium does not grow into the leaf blades, the toxic alkaloids travel there through the tissues from elsewhere in the plant.
One of the most striking effects of the infected grass in cattle is 'summer slump'. In high temperatures, the animals become lethargic, salivate excessively and spend much of their time seeking water and shade. Recent studies have also shown that cows and sheep grazing on infected fescue produce less milk and have lower pregnancy rates. A conservative estimate of the total losses among livestock in the US is dollars 500m to dollars 1bn a year.
But considerable difficulties face a farmer who decides to plant uninfected fescues or totally different grass. Not only does this mean relinquishing the benefits of pest resistance, a long growing season, the capacity to grow in land impoverished in nutrients, and tolerance of drought and a wide range of acidity and alkalinity. There is also the considerable expense of destroying the existing grass, sowing new seed, sustaining livestock while the pasture is being replaced and, almost inevitably, encouraging soil erosion.
Whether science can create a fungus that benefits the plant without accompanying drawbacks remains to be seen. Given that the natural association between Acremonium and tall fescue is so intimate, efforts to modify it for human benefit may prove more difficult than the genetic engineers imagine.
- 1 Five-year-old Iris Grace is raising awareness of autism through her extraordinary paintings
- 2 Expert urges cat lovers to own just one animal each
- 4 Yes, the iPhone 6 is a miracle, but it's Apple's tax affairs that deserve a double take
Sainsbury's '50p challenge' poster telling staff to encourage customers to spend more placed in shop window instead of staff room
Five-year-old Iris Grace is raising awareness of autism through her extraordinary paintings
Car tax disc changes: Two days to go - and they affect you much more than just not displaying a piece of paper
Isis an hour away from Baghdad - with no sign of Iraq army being able to make a successful counter-attack
British man raped while urinating in bushes at Oktoberfest beer festival in Germany
Isis, we are told, is a 'clear and dangerous threat to our way of life'. I’m sorry, but I just don’t buy it
Exclusive: 'Putin's Russia has been my biggest regret,' says Nato's outgoing Secretary General
The Osborne Ultimatum: Chancellor’s benefits freeze bombshell will affect ten million households
'Women, walk wherever you want' posters taken down in Stamford Hill following 'unacceptable' signs separating men and women
There’s no excuse for Dave Lee Travis’s behaviour, but we need to keep a sense of proportion
Should gay sex be illegal? 16% of Britons think so
- < Previous
- Next >
Very Competitive Salary: Austen Lloyd: NORTH HAMPSHIRE NQ to MID LEVEL - An e...
Highly Attractive Pakage: Austen Lloyd: MANCHESTER - A highly attractive oppor...
£40000 - £50000 per annum: Ashdown Group: Marketing Manager (Campaigns, Offlin...
£90000 - £135000 per annum: Ashdown Group: Head of Marketing (B2C, Acquisition...