Clash Of Microbes To Help Scientists Fight Rice Fungus

24 December, New Delhi

Pitting one microbe against the other,” plant scientists are uncovering more clues critical to disarming a fungus that is the number one killer of rice plants.The findings, published in Frontiers in Plant Science and in Current Opinion in Plant Biology, may lead to a more effective control for Magnaporthe oryzae, the fungus that causes rice blast disease.

The studies were led by the laboratory of Indian scientist Harsh Bais, associate professor of plant and soil sciences in College of Agriculture and Natural Resources of University of Delaware.

While the first author of both research articles was graduate student Carla Spence, co-authors included postdoctoral researcher Venkatachalam Laksmanan and Nicole Donofrio, associate professor of plant and soil sciences, besides Bais.Rice blast or rotten neck epidemics plague India on a regular basis, resulting in 11 to 30 per cent crop losses annually.

In India, about 5,64,000 tonnes of rice is lost due to blast in Eastern India alone. “Rice is a food the world relies on – it accounts for about one-fifth of all the calories humans consume,” says Bais.”So it’s critical to find ways to reduce the impact of rice blast disease Previously, Bais and his research team had isolated Pseudomonas chlororaphis EA105, a bacterium that lives in the soil around the roots of rice plants and found that this beneficial microbe can trigger a system-wide defense against the rice blast fungus.

Now, they have identified a stress hormone that appears to play a crucial role in increasing the virulence of the fungus.When little water is available, rice plants make more abscisic acid in their roots. This stress hormone travels up to the plant leaves to close off tiny pores, halting the evaporation of water from the plant to the atmosphere.

Bais and his team have shown that when the rice blast fungus invades a rice plant, an increase in abscisic acid occurs.But rather than boosting the plant’s defence mechanisms, the abscisic acid actually suppresses them, making the pathogen even more potent.”It’s like a double-edged sword,” Bais says.

“Abscisic acid can save the plant during drought; but when a pathogen is present, this same molecule blocks the plant’s innate defence response.”In studies, Bais and his team treated spores of the rice blast fungus with abscisic acid.In 10 hours, 84 per cent of these spores had germinated and formed a specialised infection structure called the appressorium, which acts like a battering ram, exerting pressure on a rice leaf until the fungus punches through the surface.

However, when spores of the fungus were treated with both the beneficial bacterium EA105 and abscisic acid, only about 23 per cent of the spores formed this attack machinery.”The rice blast fungus uses abscisic acid to its own advantage, which is absolutely wild,” Bais says.”

People have been struggling to find targets for controlling rice blast, and now we have one, with abscisic acid, the scientist said.It’s one of those classic holy grails because this fungus affects not only rice, but also barley and wheat.”