Identification of Xanthomonas vasicola (formerly X. campestris pv. musacearum), causative organism of banana xanthomonas wilt, in Tanzania, Kenya and Burundi

Xanthomonas campestris pv. musacearum (Xcm) causes a disease on banana (Musa spp.) and enset (Ensete spp.) known as banana xanthomonas wilt (BXW).Recent studies have shown that Xcm is a strain of X. vasicola (Aritua et al., 2008). However, the status of pathovars within the species remains unclear. Prior to its discovery in Uganda in October 2001, the disease had been limited to Ethiopia (first reported 1968).Since then the disease has spread to the Democratic Republic of Congo and Rwanda (observed in May 2004 and September 2005 respectively). BXW can cause high yield losses and is a high priority concern within the Great Lakes region.A comprehensive review of the pathogen and disease was recently published by Smith et al. (2008). Thus far, outbreaks in Tanzania, Kenya and Burundi have only been referred to in symposium proceedings and on various websites. These new records are thus officially reported here for the first time.

In Tanzania, the disease was first reported in the Kagera region of north west Tanzania, bordering Lake Victoria, Uganda, Rwanda and Burundi, in September 2005 (Mgenzi et al., 2006). Spread has continued, but not to other major banana growing areas. In Kenya, the disease was first reported in September 2006 in the Teso District, of western Kenya, bordering Uganda (Anon., 2006).Spread has since been reported as slow. In Burundi the disease was first observed during October 2006 (Anon., 2006). The current status of BXW in Burundi is unclear with no recent substantiated reports.

Bacterial cultures were isolated from diseased racemes from Tanzania and Burundi at CABI UK and from Kenya at KARI (NARL).All cultures were identified to species level at CSL by fatty acid profiling (MIDI system) and DNA analysis using X. vasicola specific primers (Aritua et al., unpublished) and partial sequencing of the gyrase B gene (Parkinson et al., 2007). Koch’s postulates were fulfilled for all strains at CSL by stem inoculation of banana plants (height approximately 30 cm) with a bacterial suspension (200ml with ~10⁷ cfu/ml) under controlled environmental conditions (minimum temperature 27º C). Identification of Xcm isolates from Burundi and Kenya was further supported by Ohio State University and KARI, respectively, using X. vasicola specific primers (Lewis-Levy Miller, unpublished) that have a different target site to those of Aritua et al. (unpublished).

Reference cultures are held by the UK National Collection of Plant Pathogenic Bacteria, Accession Nos. NCPPB 4392-5 (Tanzania), 4434 (Kenya) and 4433 (Burundi).