Banana Xanthomonas wilt

The banana Xanthomonas wilt disease (Fig. 1) caused by the bacterium Xanthomonas campestris pv. Musacearum (Xcm) has threatened the livelihood of millions of Ugandan farmers. The disease has also been reported in the Democratic Republic of Congo, Rwanda and more recently has been identified in Tanzania. Bacterial diseases are difficult to control. Resistant varieties have been the best and most cost-effective method of managing bacterial diseases. Attempts to develop bacterial disease resistant varieties through conventional breeding have resulted in only limited success, as no source of germplasm exhibiting resistance has been identified against Xcm. Transgenic technologies for banana may provide a timely and cost-effective measure to address the dangers of the spread of this disease.

Genetic Transformation of East African highland bananas

Genetic transformation systems (both Agrobacterium-mediated transformation and micro-projectile bombardment) were developed for production of transgenic East African highland bananas. The apical shoot tips were transformed with binary vector pCAMBIA 1201 (Fig. 2) having the hygromycin resistance gene as a selection marker and GUS-INT as a reporter gene. Transient expression of the b-glucuronidase (uid A) gene was achieved in transformed explants. The transformed explants were regenerated on selection medium containing hygromycin. The stable expression of the uid A gene was checked through a GUS histochemical assay. The integration of the uid A gene was confirmed by PCR and southern blot analysis.

Development of banana varieties resistant to banana Xanthomonas wilt

The genetic transformation system developed and optimized at IITA can be used for the production of bacterial wilt resistant varieties of banana, using transgenes already demonstrated to confer resistance against bacterial wilt in other crops. Ferredoxin-like amphipathic protein (pflp), isolated from sweet pepper, is a novel plant protein that can intensify the harpin-mediated hypersensitive response (HR) (Fig. 3). This protein has dual function; an iron depletion antibiotic action, and a harpin triggered HR enhancement. pflp has been shown to delay HR response induced by various pathogens such as Erwinia, Pseudomonas, Ralstonia, and Xanthomonas spp. in non-host plants through the release of the proteinaceous elicitor harpin in various crops, including dicots such as tobacco, potato, tomato, broccoli, orchids, and monocots like rice.

Since the transgene pflp, isolated from sweet pepper, has been shown to function in monocots such as rice with demonstrated efficacy against bacterial pathogens including Xanthomonas, its usefulness as a transgene for resistance to Xcm in banana has a high probability of success. The disease-resistant varieties of banana can contribute significantly to food security and poverty alleviation in the region.

The development of resistant varieties of banana using the pflp transgene is in progress under a joint IITA/NARO project.