Field Trial of Xanthomonas Wilt Disease-Resistant GM Bananas in East Africa

A field trial experiment was conducted to evaluate 65 transgenic lines of banana cv. ‘Sukali ndiizi’ (apple banana; AAB group) and ‘Nakinyika’ (East Africa Highland banana; AAA group) using a randomized block design at the National Agriculture Research Laboratories, Kawanda, Uganda. The site and the experimental plan had been previously approved by the Uganda National Biosafety Committee. The transgenic banana lines had been generated to over express the sweet pepper Hrap or Pflp genes and pre-evaluated in greenhouse experiments where they showed 100% resistance against  Xanthomonas campestris  pv.  musacearum  (Xcm) which causes the banana xanthomonas wilt (BXW) disease currently ravaging banana production in the Great Lakes countries of East Africa (Uganda, Kenya, Tanzania, DRC, Rwanda and Burundi). The disease affects all cultivated bananas, and is highly destructive, killing whole plants and leading to complete yield crops loss. It is estimated to have caused $2-8 billion of economic losses over the past decade in Uganda alone. The mother and first ratoon plants of transgenic lines and non-transgenic lines were evaluated for BXW resistance by artificial inoculation. The inoculated plants were assessed every day for disease symptoms including necrosis of leaves and finally as complete wilting of plants, until harvest time. At harvesting, the number of leaves wilted was counted and also internal symptoms in pseudostem, rachis and fruits were observed and disease severity was scored. Fourteen of the transgenic lines showed high levels of resistance, 7 Hrap  lines showed 100% resistance, 2 Hrap lines showing partial resistance, 3  Pflp  lines showed 100% resistance and 2  Pflp lines showed partial resistance. These were further analyzed for gene expression using qRT-PCR. As expected there were no significant differences in plant morphology and production. These results provide a proof of concept for control of banana bacterial wilt disease through transgenic Hrap - and Pflp mediated resistance in banana. These plants will be further evaluated toward the development of varieties that can be released to farmers as part of the arsenals to fight this disease epidemic and save livelihoods in Africa.