Microbe of the Month: Friendly fungus to grass, but poison to grazing animals

Anyone driving around Kentucky and adjoining states is bound to notice the lush green of much of the turf and pasture land. It is the colour of tall fescue, a grass that grows vigorously to produce stunning green swards and is exceptionally resistant to attack by insects and nematode worms. It also survives well in areas subject to drought and in soil depleted of nutrients.

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.

(Photograph omitted)

Suggested Topics
News
More than 90 years of car history are coming to an end with the abolition of the paper car-tax disc
newsThis and other facts you never knew about the paper circle - completely obsolete today
News
people'I’d rather have Fred and Rose West quote my characters on childcare'
Life and Style
The new Windows 10 Start Menu
tech
Arts and Entertainment
There has been a boom in ticket sales for female comics, according to an industry survey
comedyFirst national survey reveals Britain’s comedic tastes
PROMOTED VIDEO
Travel
Bruce Chatwin's novel 'On the Black Hill' was set at The Vision Farm
travelOne of the finest one-day walks you could hope for - in Britain
Sport
footballManchester City 1 Roma 1: Result leaves Premier League champions in danger of not progressing
Arts and Entertainment
Gay and OK: a scene from 'Pride'
filmsUS film censors have ruled 'Pride' unfit for under-16s, though it contains no sex or violence
News
i100
Life and Style
Magic roundabouts: the gyratory system that has excited enthusiasts in Swindon
motoringJust who are the Roundabout Appreciation Society?
Arts and Entertainment
Hilary North's 'How My Life Has Changed', 2001
booksWell it was good enough for Ancient Egyptians and Picasso...
News
ebooksAn unforgettable anthology of contemporary reportage
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Commercial Litigation NQ+

Very Competitive Salary: Austen Lloyd: NORTH HAMPSHIRE NQ to MID LEVEL - An e...

MANCHESTER - SENIOR COMMERCIAL LITIGATION -

Highly Attractive Pakage: Austen Lloyd: MANCHESTER - A highly attractive oppor...

Senior Marketing Manager - Central London - £50,000

£40000 - £50000 per annum: Ashdown Group: Marketing Manager (Campaigns, Offlin...

Head of Marketing - Acquisition & Direct Reponse Marketing

£90000 - £135000 per annum: Ashdown Group: Head of Marketing (B2C, Acquisition...

Day In a Page

Ebola outbreak: The children orphaned by the virus – then rejected by surviving relatives over fear of infection

The children orphaned by Ebola...

... then rejected by surviving relatives over fear of infection
Pride: Are censors pandering to homophobia?

Are censors pandering to homophobia?

US film censors have ruled 'Pride' unfit for under-16s, though it contains no sex or violence
The magic of roundabouts

Lords of the rings

Just who are the Roundabout Appreciation Society?
Why do we like making lists?

Notes to self: Why do we like making lists?

Well it was good enough for Ancient Egyptians and Picasso...
Hong Kong protests: A good time to open a new restaurant?

A good time to open a new restaurant in Hong Kong?

As pro-democracy demonstrators hold firm, chef Rowley Leigh, who's in the city to open a new restaurant, says you couldn't hope to meet a nicer bunch
Paris Fashion Week: Karl Lagerfeld leads a feminist riot on 'Boulevard Chanel'

Paris Fashion Week

Lagerfeld leads a feminist riot on 'Boulevard Chanel'
Bruce Chatwin's Wales: One of the finest one-day walks in Britain

Simon Calder discovers Bruce Chatwin's Wales

One of the finest one-day walks you could hope for - in Britain
10 best children's nightwear

10 best children's nightwear

Make sure the kids stay cosy on cooler autumn nights in this selection of pjs, onesies and nighties
Manchester City vs Roma: Five things we learnt from City’s draw at the Etihad

Manchester City vs Roma

Five things we learnt from City’s Champions League draw at the Etihad
Martin Hardy: Mike Ashley must act now and end the Alan Pardew reign

Trouble on the Tyne

Ashley must act now and end Pardew's reign at Newcastle, says Martin Hardy
Isis is an hour from Baghdad, the Iraq army has little chance against it, and air strikes won't help

Isis an hour away from Baghdad -

and with no sign of Iraq army being able to make a successful counter-attack
Turner Prize 2014 is frustratingly timid

Turner Prize 2014 is frustratingly timid

The exhibition nods to rich and potentially brilliant ideas, but steps back
Last chance to see: Half the world’s animals have disappeared over the last 40 years

Last chance to see...

The Earth’s animal wildlife population has halved in 40 years
So here's why teenagers are always grumpy - and it's not what you think

Truth behind teens' grumpiness

Early school hours mess with their biological clocks
Why can no one stop hackers putting celebrities' private photos online?

Hacked photos: the third wave

Why can no one stop hackers putting celebrities' private photos online?