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THE STATUS of BANANA XANTHOMONAS WILT (Xanthomonas Campestris Pv Musacearum) in WESTERN KENYA 1 J.N

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THE STATUS of BANANA XANTHOMONAS WILT (Xanthomonas Campestris Pv Musacearum) in WESTERN KENYA 1 J.N THE STATUS OF BANANA XANTHOMONAS WILT (Xanthomonas campestris pv musacearum) IN WESTERN KENYA 1 J.N. Mbaka, 2 M. Mwangi, 2 V.G. Nakato, 3J.Auma and 4B. Odero 1Kenya Agricultural research Institute (KARI) National Horticultural Research Centre, Thika P.O. Box 220-01000, Thika, Kenya Tel. +254 67 24332 E-Mail [email protected] 2 International Institute for Tropical Agriculture (IITA) P.O Box 7878 Kampala, Uganda Tel +256 41 223445, 221009 Fax: +256 41 223494, 220217 Email: [email protected]:[email protected] 3 Rural Energy and Food Security Organisation (REFSO) P.O.Box 342, Busia, Kenya 4Catholic Relief Services (CRS) P.O. Box 49675-00100, GPO, Nairobi, Kenya Email: [email protected] Tel: 0733 401401 Mode of presentation in the KARI Conference 2008: ORAL Author for correspondence Jesca Njeri Mbaka National Horticultural Research Centre P.O. Box 220-0100, Thika, Kenya Email: [email protected] Tel: + 254 722 88 24 22 Mbaka et al Status of banana Xanthomonas wilt2 in Kenya- ABSTRACT Banana Xanthomonas Wilt (BXW), caused by the bacterium Xanthomonas campesris pv musacearum was reported in a single farm in Mukono district of Uganda in 2001. By early 2006 it was confirmed in 33 districts of Uganda, parts of Democratic Republic of Congo, Rwanda and Tanzania. Disease spread between plants is mainly by insect pollinators and contaminated farm tools. The main mode of long distance spread is banana trade (fruits, leaves and planting material). Insect transmitted infections lead to wilting and rotting of the banana male bud, pre-mature ripening and rotting of fingers that become unpalatable. Infections from contaminated tools and infected suckers start as wilting of leaves that eventually dry. Infected plants die within two weeks. Yield losses can be up to 100%. Due to its rapid spread, BXW poses a great threat to banana production in the East and Central Africa region. Understanding of the disease status and establishment of farmer practices that may pre-dispose bananas to BXW are crucial to preparedness for effective disease management. The objectives of this study therefore were to establish, the status of BXW and the existing banana production practices in banana orchards in Western Kenya. A survey was conducted in September, 2006 in 14 districts located in Western and Nyanza Provinces. A questionnaire was administered by face to face interview with the farmers to capture data on banana production practices. Wilted bananas were observed in Teso, Bungoma and Busia districts in western Kenya. Symptoms were similar to those previously reported in Uganda. Pathogenicity tests confirmed the causal organism as Xanthomonas campestris pv mucasearum. 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 2 Mbaka et al Status of banana Xanthomonas wilt3 in Kenya- security of small-scale banana farmers. Technologies developed and validated in Uganda can be used to stop disease spread. Key words: bacterial, banana, control, disease INTRODUCTION Banana (Musa spp. L) is the fourth most important global food crop after rice, wheat and maize in terms of gross value of production (FAOSTAT, 2003). About 20 million people in the East and Central Africa region depend on banana for food. A wide range of genetic diversity of bananas is found in different areas of Kenya. Factors such as local tastes, eating habits, market demand and environmental conditions tend to influence their distribution (Nguthi, 1998). Diffusion, dissemination and adoption of the tissue culture technology aimed to address banana production constraints (pests, diseases and lack of adequate clean planting materials) has led to increased yields, higher demand for planting material and commercialization of tissue culture laboratories (Kahangi, 2003). By end of year 2006, Kenya had 82,518 hectares under bananas from this 505,258 metric tones valued at nearly 4 billion Kenya shillings were produced (MoA, 2006). However, the recent spread of banana Xanthomonas wilt (BXW), since its report in Uganda in 2001 (Tushemereirwe et al., 2003) is a big threat to banana production in The disease is caused by the bacterium Xanthomonas campestris pv. musacearum (Xcm) that was for long considered a problem of enset (Ensete ventricosum (Welw) Cheesman), in Ethiopia (Thwaites et al., 2000). Enset is a Musa species mainly grown in Ethiopia for its importance for extraction of industrial starch from its corm. The first outbreaks outside Ethiopia were reported in a single farm in Mukono district of Uganda in October, 2001 3 Mbaka et al Status of banana Xanthomonas wilt4 in Kenya- (Tushemereirwe et al., 2003). By October 2003, the disease was confirmed in 10 more districts and is in 33 districts by early 2006 (Tushemereirwe and Kubiriba, 2006). Outside Uganda, the disease was first reported in North Kivu province of the Democratic Republic of Congo (DRC) in 2003 (Ndungo et al., 2004, 2006), Rwanda in 2004 and Tanzania in 2005 (Mgenzi et al., 2006). Many sources of infection are known or suspected for BXW including standing infected plants, plant residues, contaminated tools, contaminated soil and water, traded products (fruits, leaves and planting materials). Observations at advancing disease fronts in Uganda suggest that transmission to the male bud is the primary means of spread by pollinators (Eden-Green, 2004). Banana cultivars become most vulnerable to BXW infection at flowering stage since the pathogen can be transmitted between plants by insects that visit flowers for pollen and nectar. Infection through the flower leads to rotting and total destruction of fruits, as well as wilting of the entire foliage. All banana cultivars are susceptible but some cultivars escape insect transmitted disease due to their floral morphology (persistent bracts). The most susceptible cultivar is Pisang Awak (Tushemereirwe et al., 2003). Banana Xanthomonas wilt containment depends on two key actions: prompt removal of sources of inoculum and reducing and eliminating opportunities for spread. Establishment of diseases status and identification of pre - disposing factors are the initial steps in tailoring responses for management of the particular disease. The objective of this study therefore was to ascertain the status of BXW and factors pre-disposing bananas to the disease in Western Kenya region. It was hoped that effective disease management strategies developed and evaluated in Uganda 4 Mbaka et al Status of banana Xanthomonas wilt5 in Kenya- would be applied in Kenya to stop disease spread to new areas and to reduce levels of severity in any affected areas. MATERIALS AND METHODS Disease surveys A banana disease survey was carried out in Western Kenya region in August and September 2006. The region was targeted due to its close proximity to Uganda, the banana trade and unrestricted movement of banana materials across the porous boundaries. The survey team was composed of two plant pathologists, one from Kenya Agricultural Research Institute and one from the International Institute for Tropical Agriculture, Kampala, Uganda and a horticulturalist from Rural Energy and Food Security Organization, Busia, Kenya. The target areas were selected districts in Western and Nyanza provinces. A questionnaire was designed to capture data on banana cultivars grown, disease incidence and prevalence, soil types, banana production practices, banana marketing systems and utilization. The exact locations of the survey areas and sample collection sites were marked by use of a Geographic Positioning Satellite (GPS) instrument Magnum ®. The survey team visited the District Agricultural Officers (DAOS) of the respective districts for desk top information on banana production. In every district, two main banana growing divisions were selected. A stratified random sampling was used to select 15 farmers from each division. A stratum was taken to be a farmer with at least 30 banana mats in production. The questionnaire was administered through face to face interview with the farmers. Thirty mats in each farm were scored for diseases and pests by the enumerators. Clear pictures of symptoms (diseases, pests and 5 Mbaka et al Status of banana Xanthomonas wilt6 in Kenya- physiological problems) of banana laminated and filed were used as visual aids for field diagnostics. A total of 365 farms were visited and respective farmers interviewed. Isolation of Xcm on synthetic growth medium Banana samples (pseudostem and fruits) suspected to have Xcm were put in polythene paper bags, sealed and put in a cold box. In the laboratory, the samples were thoroughly cleaned under running tap water and surface sterilized by dipping in 5 % sodium hypochlorite for 2 minutes, rinsed in distilled water and blotter dried. Isolation of Xcm was done on Yeast Peptone Glucose Agar (YPGA). The medium was poured onto 90 mm Petri dishes and allowed to cool overnight. The following day, bacteria were picked from the infected samples with a sharp needle and plated on the medium. The plates were incubated at 25 0C for 72 hours. To obtain pure colonies, isolation was done on Cephalexin Cellebiose Agar (CCA) according to Mwangi et al. (2006). Pathogenicity tests To determine if the isolates suspected to be Xcm were pathogenic to a susceptible banana cultivar, pathogenicity testing was done on three-month old tissue-cultured banana plantlets of cultivar Pisang Awak. The pathogen was introduced to the plant by injecting a 1 ml cell suspension (2 x 108 cells/ml) into the stem. The control was plantlets injected with a similar amount of sterile distilled water. The plants were kept under a shade net for three weeks. Disease symptoms were recorded every three days. In the second week, the first wilt was observed and re-isolation of the pathogen done as above. Bacterial colonies were sent to the Central Science Laboratory (CSL), United Kingdom (UK) for molecular characterization. 6 Mbaka et al Status of banana Xanthomonas wilt7 in Kenya- RESULTS The main banana cultivars grown in Western Kenya are shown in Figure 1.
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