Banana Xanthomonas Wilt (BXW), caused by the bacterium Xanthomonas campestris pv. musacearum (Xcm), is threatening banana production across the Great Lakes region of East and Central Africa. No banana cultivar has resistance to the disease, yet the people of this region are highly dependent on the crop for food security and income generation.
In collaboration with national research and regulatory partners, we led regional surveillance initiatives to map the presence and spread of BXW. To overcome the problem of BXW symptoms being confused with those of other diseases and abiotic factors, diagnostic methods have been developed using serological and molecular-based techniques that are both rapid and sensitive – able to detect BXW in recently infected banana plants or suckers that have not yet shown any symptoms.
Since not all countries have the technical capacity to implement lab-based diagnostics, systems have been established to collect DNA from banana plants using novel portable kits that are cheap and easy to use and transfer across country borders. The kits are being used to facilitate simultaneous high throughput testing of several samples using the same protocols to produce directly comparable results.
Once the disease is confirmed in a location, disease awareness campaigns are mediated through SMS (text messaging), factsheets, booklets, radio messages, and community-based action to identify and manage the disease through cultural practices. These include the routine removal of the male bud (to prevent infection from insects), use of sterilized farm tools (using household bleach) and destruction of single infected stems (recently revised from the recommendation of destroying whole plants based on experimental work undertaken by IITA and observations by NARO). However, the level of BXW control by cultural practices can be inconsistent as it is dependent on the individual growers and traders implementing them.
A more robust solution is to develop cultivars that are resistant to the disease. Our researchers, in partnership with NARO-Uganda and AATF, have done just that by using transgenic lines of banana containing genes from sweet pepper that confer resistance against BXW. The transgenic banana plants have exhibited strong resistance to BXW in the laboratory and screenhouse tests. The best 65 resistant lines have been planted in a confined field trial at NARO’s National Agricultural Research Laboratory (NARL) in Kawanda, Uganda, for further evaluation. Twelve transgenic lines have been found to be completely resistant to BXW after the evaluation of three generations of crops. Furthermore, the transformed lines also showed characteristics of flowering and yield (bunch weight and fruit size) comparable to those of non-transgenic varieties.
The wilt-resistance genes from pepper, Pflp and Hrap, were obtained under an agreement from Academia Sinica in Taiwan and the proteins they confer are not listed as being a potential allergen in AllergenOnline and should be safe for human consumption. These proteins are widely distributed across a broad range of plant species including rice and fruits that are eaten raw. Even so, the transgenic lines will be tested for food and environmental safety in compliance with biosafety regulations. The risk of gene flow from banana to another crop species will not be an issue as most edible banana are sterile and the clonal mode of propagation does not make this possible.
Given the rapid spread and devastation of BXW across the continent, genetic transformation through the use of modern biotechnology tools offers — at least for the time being — the most effective, fast, safe, and viable way to develop resistant varieties and help save the livelihoods of millions of smallholder banana growers.