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The complex co-dependency of microfungi and grass
08 March 2010
Natural Resources Institute Finland
Plants harbour many different microbes, fungi and bacteria that take advantage of their hosts. However, the host can also benefit from these little organisms, which are known as endophytes. The relationship is extremely complex.
According to a thesis published by Susanna Saari, Research Scientist at Agrifood Research Finland, endophyte infections are common in the meadow fescue cultivars found in Finland, although the frequency varies considerably both between and within cultivars. European tall fescue cultivars, on the other hand, were found to be practically endophyte-free.
Microfungi were extremely common in natural meadow fescue populations found in the Åland Islands, Estonia, the coastal area of Södermanland in Sweden, and Gotland.
"The high level of infection indicates that endophytes are beneficial to their natural grass hosts at least in these areas," Ms Saari explains.
"The reason behind the varying infection levels found in cultivars may be that where an endophyte affects one of the agriculturally important characteristics of its host grass, plant breeders may have inadvertently promoted or restricted the prevalence of the endophyte by favouring or rejecting individual plant characteristics."
Ousts Aphids And Protects Voles From Predators
The toxins produced by endophytes affect the pest-resistance of grass in many ways. The study concluded that endophytes increased the resistance of meadow fescue to bird cherry-oat aphids, overriding the effects of seed lot and cultivar. Endophytes did not affect the body mass or population size of voles that consume endophyte-infected grass, but they did reduce the voles' mobility.
"In predation tests, immobility and calmness appeared to protect voles from weasels, as they were no longer able to detect voles among the grass. This is a common way for voles to avoid predation," Ms Saari explains.
More Seeds, Less Growth
Fungal endophytes can also affect grass reproduction and growth. The fungi appeared to increase seed production in meadow fescue but to stunt growth after mowing in some circumstances. "Endophytes appear to affect the competition between certain growth functions inside the plant," Ms Saari speculated.
Endophytes have been found to benefit their hosts especially in fertile agricultural environments. In natural infertile environments, however, the fungus can be an enemy. The plant has to share the little resources that it collects from the soil with the fungus, which in turn may produce fewer toxins. This prevents the fungus from protecting its host effectively against pests.
Potential In Agricultural Production
Endophytes have caused serious toxic symptoms in cattle fed on infected grass in the US and in New Zealand. Seed production companies in these countries now routinely examine animal feed for endophytes in order to prevent these problems from recurring.
"Endophytes affect many agriculturally important characteristics of the host grass, which is why they should be acknowledged in agricultural management in Finland and elsewhere in Europe as well," Ms Saari concludes.
The thesis ‘Plant endophyte in food chain - friend or foe?' by Ms Susanna Saari, MSc, will be examined at the University of Turku in Finland at 12 noon on 19 March 2010. Professor Michael Müller from the Finnish Forest Research Institute will act as the opponent and Professor Kai Norrdahl from the University of Turku will act as the custodian.