Presence of banana bacterial wilt (Xanthomonas campestris pv. musacearum) in Rwanda

In September 2005, visits were made to five sites within the Gisenyi province in northern Rwanda to investigate reports of a damaging banana disease affecting brewing, dessert and cooking varieties. Symptoms included progressive yellowing and wilting of leaves (Fig. 1), shrivelling of male buds (Fig. 2), premature ripening and internal discoloration of fruits (Fig. 3) plus a characteristic yellow ooze from the vascular tissue of cut pseudostems (Fig. 4). These symptoms resembled those of banana bacterial wilt (BBW) caused by Xanthomonas campestris pv. musacearum (Xcm).

A yellow-pigmented bacterium was consistently isolated on YDC (yeast extract dextrose calcium carbonate agar) from the internal tissues of flower stalks. Four isolates were identified as Xanthomonas campestris by fatty acid (Microbial ID Inc. [MIDI]) and metabolic (Biolog, Inc, Hayward, CA, USA) analyses [ID probability score approx. 0.9]. Molecular studies using rep-PCR (Louws et al., 1994) with ERIC and BOX primers confirmed that isolates had an identical DNA fingerprint to other Xcm isolates from Musa spp. in Ethiopia*, Uganda* and the Democratic Republic of Congo (DRC) and Enset(Ensete ventricosum) from Ethiopia*. Pathogenicity was confirmed by injecting bacterial suspensions of isolate (IMI 393640)* into the stems of six young banana plants. Typical wilt symptoms were observed after three weeks. Bacteria were re-isolated from symptomatic plants and their identity confirmed by rep-PCR analysis.

Xcm was first described from Ethiopia in the 1960s, infecting ensete and cultivated banana (Yirgou & Bradbury, 1968) but was only recently confirmed infecting bananas in Uganda and the DRC (Tushemereirwe et al. 2004; Ndungo et al.2004). In Gisenyi, banana is extensively cultivated in the highland plateaux. The wilt disease has been reported from three districts (Cyanzarwe, Gisenyi, Kanama), though it may have spread more widely. Local farmers report that wilt symptoms were first seen around 2002-2003. The disease may have spread from the DRC when Congolese people fled to Ruhengeri and Gisenyi provinces following the eruption of Mount Nyiragongo in January 2002. There is a regular interchange of people and goods across the Rwanda-DRC border and the first confirmed outbreak of Xcm in the DRC was in Masisi region (Lacs Mokotos), which is close to Gisenyi.

This is the first report of BBW in Rwanda and poses a serious threat to banana production, endangering the livelihoods of banana growing households throughout the country.

*held in the CABI Genetic Resource Collection