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Green pepper to the rescue of African bananas

By Godwin Atser

In a major breakthrough, crop scientists have successfully transferred genes from green pepper to bananas that enable the crop to resist the Banana Xanthomonas Wilt (BXW), one of the most devastating disease of banana in the Great Lakes region of Africa that causes about half a billion dollars worth of damage yearly. The researchers are poised to begin confined field trials in Uganda soon.

The transformed banana, infused with plant ferredoxin-like amphipathic protein (Pflp) or hypersensitive response-assisting protein (Hrap) from green pepper, have exhibited strong resistance to BXW in the laboratory and screenhouses. Some of the findings of the research have been published in the Molecular Plant Pathology Journal.

Scientists from the International Institute of Tropical Agriculture (IITA) and the National Agricultural Research Organization (NARO) of Uganda, in partnership with African Agricultural Technology Foundation (AATF), would soon be evaluating these promising resistant lines under confined field trials after the Ugandan National Biosafety Committee recently approved the conduct of the tests.

Dr Leena Tripathi, a biotechnologist with IITA and the lead author of the paper, says that although there is still a long way to go before the transgenic bananas find their way onto farmer's fields, this breakthrough is a significant step in the fight against the deadly banana disease.

“The Hrap and Pflp genes work by rapidly killing the cells that come into contact with the disease-spreading bacteria, essentially blocking it from spreading any further. Hopefully, this will boost the arsenal available to fight BXW and help save millions of farmers' livelihoods in the Great Lakes region,” she said.

“Furthermore, the mechanism - known as Hypersensitivity Response - also activates the defense of surrounding and even distant uninfected banana plants leading to a systemic acquired resistance," she adds.

The Hrap and Pflp are novel plant proteins that give crops enhanced resistance against deadly pathogens. They can also provide effective control against other BXW-like bacterial diseases in other parts of the world such as “Moko”, Blood, and “Bugtok”. The genes used in this research were acquired under an agreement from the Academia Sinica in Taiwan.

The highly destructive BXW affects all varieties including the East African Highland bananas and exotic dessert, roasting, and beer bananas causing annual losses of more than US$500 million across East and Central Africa. The crop is also under threat from another deadly disease, the banana bunchy top.

Dr Tripathi adds that there are presently no commercial chemicals, biocontrol agents or resistant varieties that could control the spread of BXW. She emphasized that even if a source of resistance is identified today, developing a truly resistant banana through conventional breeding would be extremely difficult and would take years, even decades, given the sterile nature and long gestation period of the crop.

BXW was first reported in Ethiopia 40 years ago on Ensete, a crop relative of banana, before it moved on to bananas. Outside of Ethiopia, it was first reported in Uganda in 2001, then rapidly spread to the Democratic Republic of Congo, Rwanda, Kenya, Tanzania, and Burundi, leaving behind a trail of destruction in Africa's largest banana producing and consuming region.

The disease causes yellowing and wilting of the leaves, uneven and premature ripening of the fruit, and withering and rotting of the whole plant.

BXW can be managed by debudding the banana plant and sterilizing farm implements used. However, the adoption of these practices has been inconsistent at best as farmers feel that debudding affects the quality of the fruit and sterilizing farm tools is too tedious.

The research to fortify banana against BXW using genes from sweet pepper was initiated in 2007.