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Scientists have developed improved methods for identifying a bacterium devastating banana crops in East Africa, where the fruit is a staple part of the diet and an important part of the rural economy.

Their research was published in the journal Plant Disease last month (May).

Until now, banana Xanthomonas wilt (BXW) was diagnosed by symptoms alone. These include a progressive yellowing and wilting of leaves, premature ripening of fruit, brown discoloration of fruit and pale yellow ooze coming from cut surfaces, says Leena Tripathi, the study's lead author.

The research team, including Steffen Abele, head of the Banana and Plantain Systems Program and research director at the new Dar es Salaam branch of the International Institute of Tropical Agriculture (IITA) in Tanzania, tried a variety of biochemical tests to identify the BXW pathogen in the laboratory.

Tests that amplify and identify the pathogen's DNA were "most reliable, as the infected plants can be tested even before the symptoms develop", says Tripathi, a biotechnologist at the IITA in Uganda.

Tripathi says the team has also developed a method for effectively growing the BXW bacterium in the laboratory. Using conventional techniques, the bacterium grows slowly and can be overcome by other bacteria or fungi. The new method uses a specific growth medium on which the BXW pathogen grows easily.

Tripathi says the researchers are also testing genetically-modified bananas inserted with a single disease-resistant gene from sweet peppers to resist the disease (see GM bananas to fight wilt in Africa).

BXW, first reported in Uganda in 2001, has since spread to Burundi, the Democratic Republic of Congo, Kenya, Rwanda and Tanzania, according to Ranajit Bandyopadhyay from the IITA in Ibadan, Nigeria. It is spread by insects, wind-driven rainfall, infected planting materials and contaminated planting tools.

"But the disease can be contained through using tissue cultures and plant material which is free of infection, disinfecting farm tools and early removal of male flowers because insects spread this disease through male flowers so they are an entry point for infection,'' says co-author Maina Mwangi, from IITA in Uganda.

"This study stands to educate researchers as well as farmers on ways to detect the disease and avoid its spread," says IITA Kenya biotechnologist Dong-Jin Kim, who was not a member of the research team. Kim says the diagnosis is "cost effective and fast".

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