Status of Banana Xanthomonas Wilt in Western Kenya and Factors Enhancing Its Spread

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Status of banana Xanthomonas wilt in western kenya and factors enhancing its spread

J.N. MBAKA1, V.G. NAKATO2, J.AUMA3 & B. ODERO4 1Kenya Agricultural research Institute, National Horticultural Research Centre, PO Box 220-01000, Thika, Kenya 2 International Institute for Tropical Agriculture (IITA), PO Box 7878, Kampala, Uganda 3 Rural Energy and Food Security Organisation, PO Box 342, Busia, Kenya 4Catholic Relief Services, PO Box 49675-00100, GPO, Nairobi, Kenya

Abstract Banana Xanthomonas Wilt (BXW) caused by Xanthomonas campestris pv musacearum was reported in Uganda in 2001. It spread fast to Democratic Republic of Congo in 2003, Rwanda in 2004 and Tanzania in 2005. Infected plants die, fruits are rendered inedible. Disease spread between plants is mainly by insect pollinators and contaminated farm tools. To establish the status of BXW in Western Kenya, a disease survey was conducted in September, 2006 in 14 districts located in Western and Nyanza Provinces. Wilted bananas were observed in Teso, Bungoma, Nyamira and Busia districts. Symptoms were similar to those previously reported in Uganda. Pathogenicity tests confirmed the causal organism as Xanthomonas campestris pv. musacearum. The outbreak in western Kenya is significant because this region produces over 60% of bananas in Kenya and, therefore, could have serious consequences on food and income security of small-scale banana farmers.

Key words: Bacterial disease, incidence, Xanthomonas campestris

Introduction for pollen and nectar (Tinzaara et al., 2006). Infection through the flower leads to rotting and total destruction Bananas in Kenya are grown for food and income on 0.32 of fruits, as well as wilting of the entire foliage. All banana of the total arable land (Kahangi et al., 2003). Distribution cultivars are susceptible but some cultivars escape insect of the wide range of genetic diversity is influenced by transmitted disease due to their floral morphology local tastes, eating habits, market demand and (persistent bracts). The most susceptible cultivar is Pisang environmental conditions (Nguthi, 1998). Adoption of Awak probably due to the high sugar content in the nectar tissue culture technology to address banana production which makes them more attractive to the insects constraints (pests, diseases and lack of adequate clean (Tushemereirwe et al., 2003; Kagezi, et al., 2006; Welde et planting materials) led to increased yields, higher demand al., 2006). for planting material and commercialization of banana According to Eden-Green (2004), banana tissue culture laboratories (Kahangi, 2003). In 2007, 505.258 Xanthomonas wilt containment depends on prompt metric tones valued at nearly 4 billion Kenya shillings removal of sources of inoculum and reducing and (about 5 million US dollars) were produced (MoA, 2007). eliminating opportunities for spread. A number of However, the recent spread of banana Xanthomonas wilt technologies targeting removal of infection sites and (BXW), since its first report in Uganda in 2001 elimination of disease inoculum have been recommended (Tushemereirwe et al., 2003, 2004) is a big threat to banana (Biruma et al., 2007). Breaking off the male bud has been production in the country. The disease is caused by the recommended to remove bacterial entry sites in male buds. bacterium Xanthomonas campestris pv. musacearum Sterilisation of garden tools in Sodium hypochlorite, or (Xcm). Outside Uganda, the disease was reported in flaming them after use on a plant has been recommended Democratic Republic of Congo in 2003 (Ndungo et al., (Mwangi et al., 2007a). Cutting down and heaping diseased 2004, 2006), Rwanda in 2004 and Tanzania in 2005 (Mgenzi plants as a way of eliminating inoculum sources has also et al., 2006). been recommended (Tushemereirwe et al., 2003). Infected Many sources of infection are known or suspected for plants can be injected with 1.2 ml of 2, 4- BXW including standing infected plants, plant residues, Dichlorophenoxyacetic acid (2, 4-D). This method is much contaminated tools, contaminated soil and water, traded easier than manually rouging and burying infected plants products such as fruits, leaves and planting materials (Blomme, et al., 2006). (Tumushabe et al., 2006; Biruma et al., 2007). Transmission Establishment of disease status and identification of to the male bud is the primary means of spread by pre -disposing factors are the initial steps in tailoring pollinators (Eden-Green, 2004; Tinzaara et al., 2006). responses for management of the particular disease Banana cultivars become most vulnerable to BXW (Karamura et al., 2005). To establish the status of BXW in infection at flowering stage since the pathogen can be Western Kenya, a disease survey was conducted in transmitted between plants by insects that visit flowers 674 J.N. MBAKA et al. September, 2006 in 14 districts located in Western and banana stems were found standing in the field even when Nyanza Provinces. they had long died. None of the farmers reported disinfection of farm tools after use in the orchards. When Materials and methods replacing the diseased mats, farmers got suckers from the same field or from neighbours as far away as the The survey team was composed of scientists from the neighbouring Uganda. At the Busia and Malaba border Kenya Agricultural Research Institute (KARI), towns, banana bunches wrapped in leaves and pseudo- International Institute for Tropical Agriculture (IITA), stem sheathes were ferried on wheelbarrows from the Kampala, Uganda and Rural Energy and Food Security Ugandan side. Organization (REFSO), a non governmental organization (NGO) in Busia, Kenya. The target areas were selected Discussion districts in Western and Nyanza provinces. The survey was undertaken in two stages, both designed to capture The presence of wilting of the inflorescences on most of information on factors that could accelerate disease spread the Xcm infected plants in Western Kenya indicated or increase vulnerability of farming communities to the insect-transmitted infection (Eden-Green, 2004). It is disease. The first stage was the administration of the possible that initial inoculum was introduced through designed questionnaire through an oral interview with the infected bunches, leaves, pseudo-stem sheaths or suckers farmers. Farmers were randomly selected on the basis of brought from the neighbouring affected districts in their having at least 60 banana mats older than two years Uganda. This could be supported more by the presence and near the homestead for adequate sampling. The of disease along a road connecting the Malaba border questions addressed, banana cultivars grown, presence town with Busia. of BXW and other diseases, farmer awareness of BXW Although there is considerable diversity of banana management practices, sources of planting material, cultivars in Kenya (Nguthi, 1998), all banana cultivars have cultural practices (e.g. trashing, weeding, de-suckering, been reported to be susceptible to banana Xanthomonas de-budding, intercropping) and any other issues that could (Biruma et al., 2007). The key trait that influences disease be relevant to disease spread and management. infection in different banana cultivars is the inflorescence. The second stage involved visiting the banana plot to Cultivars with persistent bracts tend to escape insect inspect the plants for disease symptoms. In each farm, 30 transmission. This is because scars created when the plants were randomly selected by making two diagonal bracts fall are the entry points for the bacteria that cause transect walks. The banana cultivar types were identified infection (Biruma et al., 2007). and plants assessed for BXW and other diseases and Cultivars with dehiscent male buds become more pests. Samples of plants with disease symptoms similar to susceptible to insect transmitted disease. Pisang Awak, those of banana bacterial wilt previously reported in Kivuvu (ABB genome) and ‘Sukari Ndizi’ (AB genome) Uganda were collected, put in polythene bags, sealed, that have higher sugar content in their nectar are more labeled and put in cold boxes for disease confirmation in attractive to the insect vectors hence more susceptible to the laboratory. Protocols on the isolation and insect transmitted BXW (Kagezi et al., 2006). These same characterization of Xcm already published (Tushemereirwe cultivars were dominant in the survey areas. The existence et al., 2003: Mwangi et al., 2006) were used. Bacterial of ecological conditions suitable for insect vectors is also colonies were sent to the Central Science Laboratory (CSL), believed to influence infection (Mwangi et al., 2006). United Kingdom (UK) for molecular characterisation. Debudding immediately the last hand is formed has been recommended as an effective control method Results

Wilted bananas were observed in Bungoma, Busia, Table 1. Incidence of banana Xanthomonas wilt in Western Kenya. Nyamira and Teso districts. Disease incidence is showed in Table 1. Most of the infected plants had wilted male District No. of farms Percentage buds. The isolated bacteria caused wilt on test banana seedlings in the pathogenicity tests. The bacterium was Busia 20 5.0 Teso 21 61.9 identified as Xanthomonas campestris pv musacearum Bungoma 14 14.0 similar to that earlier reported in Uganda according to the Butere 17 0.0 fatty acid analysis (Tushemereirwe et al., 2003; 2004). Kuria 11 0.0 The main banana cultivars grown in the survey area Migori 19 0.0 were Kayinja (AB genome, syn. ‘Pisang Awak’), Bluggoe Kisii 12 0.0 (ABB genome, syn ‘Kivuvu’), ‘Sukari Ndizi’ (AB genome), Nyamira 15 7.0 East African Highland Banana (EAHB) cultivars (AAA Rachuonyo 12 0.0 genome) and the Cavendish group (Fig. 1). The banana Gucha 10 0.0 production practices (de-budding, de-suckering and Vihiga 10 0.0 Siaya 6 0.0 source of planting material are shown in Fig. 2). Forty five percent of the farmers practiced de-budding but not Total 167 regularly and not to control bacterial wilt. The infected Status of banana Xanthomonas wilt 675

45 40 35 30 25 20 15 Percentage 10 5 0 Pisang Kivuvu Sukari ndizi EAHB Cavedish Others Awak Cultivars Figure 1. Banana cultivars grown in Western Kenya by percentage.

Figure 2. Banana production practices in Western Kenya.

(Bagamba et al., 2006). Only 45% of the farmers in Western Conclusion Kenya practiced de-budding but not regularly and not with the intention to control BXW. The main reason of The spread of BXW in Western Kenya is due to presence removing the male bud was to use it as a stopper for water of cultivars prone to insect transmitted disease in an fetching containers. This too could serve to spread environment suitable for the insect vectors and banana disease from one area to the other. production practices. Due to lack or ignorance of the Suckers are an important means of spread for systemic importance of clean planting material, farmers could spread bacterial diseases (Hayward, 2006). Over 90 % of the disease through use of potentially infected banana farmers in western Kenya were planting suckers either suckers. The extension field officers lack the skill to from the same field or from neighbours’ fields. The latent diagnose disease, hence, cannot initiate the management nature of Xanthomonas wilt especially in the early stages strategies. Technologies developed and validated in may lead to farmers planting the already infected suckers Uganda can be used to stop the spread of banana and these may serve to spread diseases across farms and Xanthomonas wilt in Kenya. These include: timely removal regions. The presence of other diseases that manifest of male buds, disinfection of tools and use of clean above ground symptoms similar to Xanthomonas wilt may planting material. complicate correct diagnosis. This may lead to incorrect decisions on measures to be taken and as such Acknowledgement contributing to disease spread. 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