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Fungi, Invisible Protectors of Tropical Grasses

What do a farmer in Colombia, a golfer in the Philippines, a soccer player in Italy, and a tribesman in Amazonia have in common? They all walk on grasses that carry endophytes—invisible fungi that offer enormous potential for industry, medicine, and agriculture.

Endophytes live in the microscopic spaces found between plant cells, creating mutually beneficial relationships with their host plants. As the plants offer shelter and nutrients, the fungi enhance plant vigor and improve resistance to pests, diseases, and drought.

While the swards covering a golf course or soccer field are healthier and more resistant to natural enemies, thanks to the presence of these invisible allies, the farmer may not be so happy with this association, as it seems to make his livestock ill. Livestock that consume plants (at least some temperate grasses) carrying endophytes can lose weight, produce less milk, become weak and tremulous, lose fertility, or even suffer from gangrene. Because these endophytes cannot be seen, the grasses carrying them have acquired notoriety for being poisonous.

These effects have been extensively studied in the temperate world, but largely ignored in the tropics, that is, until the end of 1996. Then, a team of scientists from the International Center for Tropical Agriculture (CIAT), with financial support from the Japanese Government, began searching for endophytes in tropical grasses.

This multicultural and interdisciplinary team, headed by Ethiopian phytopathologist Segenet Kelemu, with support from Japanese scientists, and assistance from Colombian personnel, achieved significant progress, opening up enormous possibilities for science.

Among their efforts-for the first time, an endophyte was identified in the Brachiaria grasses, which comprise the most important pastures of tropical America. This fungus—Acremonium implicatum—, when associated with Brachiaria, protects its host plant against pests and diseases, and provides the plant with resistance to drought.

The fungus, when in association with the plant, can be transmitted through seed. "If a plant has this fungus, its seed also carries it and the fungus is reproduced generation after generation, provided the seed is well stored", says Dr. Kelemu.

As the research progressed, other advances were made. The scientists consider their last achievement to be very important—a biotechnology technique to determine, at the DNA level, whether a plant is carrying endophytes. The methodology took three years to develop.

"This method will be very useful for testing Brachiaria seed lots and establishing the presence or absence of endophytes", adds Dr. Kelemu. "At first, we used only the microscope, which was very difficult, because there are so many fungi and we had to know the endophyte really well to find it. Our biotechnology method now makes identification easy."

However, much remains to be done. Nothing is known of the effect this type of fungus has on livestock that consume it during grazing. The CIAT research team has requested collaboration from colleagues at the University of Kentucky, USA, to exclusively examine the toxicity of some endophytic strains from Colombia.

"Probably, at the end of the year, we will know whether they are toxic to animals", says Dr Kelemu. "Preliminary data suggest that they do indeed produce toxins that attack pathogenic fungi, but we don't know if these toxins are also bad for livestock."

What will happen if these toxins are found to affect livestock? The research that will follow will not be easy, because the scientists will then have to examine the possibility of eliminating the toxicity for the animals while retaining the beneficial effects for the plant.

However, if the toxins prove not to adversely affect animals, then research will focus on artificially inoculating endophytes into more plants and thus exploit, on a large scale, the benefit of resistance in pastures.

These fungi also have medicinal properties. In Europe and North America, pharmaceutical companies use them to produce sedatives and anticoagulant agents. Some Amazonian and Ecuadorian tribes use and cultivate endophyte-carrying grasses for birth control and to facilitate delivery, for other medicinal uses, and for religious rites.

All this opens up a huge panorama for industry and agriculture, attracting the interest of scientists throughout the tropics.

Captions to photos

1. A trial with Brachiaria plants inoculated with a pathogen. The plant on the left has endophytes and is disease free, whereas the other plant, which is endophyte-free, is diseased. Environmentally, endophytes are significant as they can help discourage pesticide abuse for pest and disease control.

2. Microscopic image of an endophyte, magnified ×10-3 times.