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Genetically mapping the spread of black sigatoka

New research confirms that black sigatoka disease may have originated in South-east Asia.

The spread of the disease, which has been termed "an unprecedented global scenario of invasion," has been mapped by following genetic markers across 37 different countries.

One of the authors of the recent study, Stephanie Robert, said "The historical hypothesis was that it came from South East Asia."

When the disease was first noticed, in Fiji in 1963, it was initially believed that the disease may have commenced its attack from Papua New Guinea or the Solomon Islands.

The study now suggests that anywhere within the whole of the South-east Asian region could be the source. The area, which is home to a diverse array of wild bananas and plantains, is "the area of banana and plantain domestication that began several thousand years ago".

The exact point of origin of the host plant could not be pinpointed without further comparison between wild and domesticated banana plants. Ms Robert says fungal spores cannot travel more than a few metres and are very sensitive to UV rays, but when travelling on the wind spores can be dispersed up to several hundred kilometres.

But this does not explain the spread of the disease around the world.
"I don't think the disease would have spread so far without human contribution, says Ms Robert. "It's very difficult to understand exactly how the disease is dispersed - it's currently proceeding through the Caribbean and has just invaded Martinique," she says.

Originally it was thought that the fungus travelled through Africa after just a few introductions, but the research suggests it was spread through a single source near the South China Sea.

In the Americas, the fungus is thought to have been derived from mingling between genetically different sources in South East Asia and Oceania, through multiple introductions in the same place, or at different times and places. The pathogen was first identified in Honduras in 1972 but would have been present in the 60s, it is thought.

Ms Robert says she hopes the study will help the banana industry reduce fungicide use and develop better control strategies. "It's very important for the creation of pathogen-resistant varieties in a sustainable way because the pathogen does adapt," she says.

The study calls for more precise investigation into the disease.


Publication date: 3/7/2012


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