First report of Xanthomonas campestris pv. musacearum on banana in Uganda

Abstract

In October 2001, a wilting disorder of new aetiology was reported affecting banana ( Musa sp.) within the Mukono district of Uganda. The disorder was characterized by a rapid yellowing and wilting of the younger leaves, a discoloration of the internal vascular vessels, occasionally a dieback initiating from the male floral parts with internal rotting of banana fruits. These symptoms were notably distinct from fusarium wilt ( Fusarium oxysporum ) and 'Matooke wilt' (a wilt-like disorder of unknown aetiology), but strongly resembled Moko disease caused by Ralstonia solanacearum , although this particular pathogen had not previously been recorded on banana in Africa.A bacterium was isolated on nutrient agar that was identified by fatty acid (Microbial ID Inc. [MIDI]) and metabolic (Biolog, Inc, Hayward, CA, USA) analyses as Xanthomonas axonopodis (ID probability score < 0·4) and Xanthomonas campestris (ID probability score ∼ 0·9), respectively. The presence of the Xanthomonas specific fatty acids 11:0 ISO, 11:0 ISO 3OH and 13:0 ISO 3OH was recorded. Pathogenicity tests on disease-free tissue culture-derived banana plantlets by stem inoculation with a bacterial suspension induced wilt symptoms consistent with field observations after 3 weeks. Reisolation and identification, as outlined above, confirmed Koch's postulates. Reference to the literature suggested the bacterium was Xanthomonas campestris pv. musacearum (Yirgou & Bradbury, 1968). However, this bacterium is relatively poorly described and not contained within either the MIDI or Biolog databases. To support the identification, rep-PCR (Louws et al ., 1994) using ERIC and BOX primers was performed on the Ugandan banana isolate, cultures of X. campestris pv. musacearum from Ensete and Musa in Ethiopia (IMI 349461, IMI 349986, IMI350025) and other cultures of Xanthomonas spp. from Africa. These analyses revealed an identical DNA fingerprint for all isolates from Musa and Ensete , but distinct fingerprints for the isolates from other hosts. This is the first report of X. campestris pv. musacearum outside of Ethiopia, where it is recorded as a pathogen of ensete and, to a lesser extent, banana. Accordingly, this pathogen has been given the common name of ensete bacterial wilt, although the aptness of this now looks questionable. The risk posed by this new disease record to the contiguous banana plantation of Uganda is undetermined, but significant spread is already being observed. The causative organism for this new disease record has been deposited within the CABI Genetic Resource Collection as IMI 386970. References

Agronomic performance of local and introduced plantains, dessert, cooking and beer bananas (Musa spp.) across different altitude and soil conditions in eastern Democratic Republic of Congo

“…musacearum. It was first officially reported in 1968 in Ethiopia (Yirgou and Bradbury, 1974), where it remained confined until 2001 when the disease appeared in both Central Uganda and the North Kivu province of the DR Congo and all banana cultivars planted in these areas are susceptible to XW (Tushemereirwe et al, 2004;Ndungo et al, 2006). Black leaf streak (BLS), the most important foliar disease in banana, caused by an airborne fungus called Mycosphaerella fijiensis Morelet, reduces functional leaf area and thus can cause yield losses of 30 to 50% (Mobambo et al, 1996;Ploetz, 2004).…”

Symptomless banana suckers sourced from Xanthomonas wilt infected fields are a viable alternative for seed within infected banana-based landscapes lacking access to clean planting materials.

“…First observed in central Uganda and the North Kivu province, Democratic Republic of Congo (DR Congo) in 2001 (Tushemereirwe et al, 2004;Ndungo et al, 2006), XW has since rapidly spread to the entire East African Great Lakes region (Mbaka et al, 2007;Reeder et al, 2007;Karamura et al, 2008;Carter et al, 2010). Its indiscriminate infection of all Musa cultivars and ability to cause up to 100% yield loss, severely compromises livelihoods and food security for banana farming households in East and Central Africa (Kagezi et al, 2006;Ssekiwoko et al, 2006;Blomme et al, 2014).…”

“…No resistant cultivated Musa varieties are yet known (Thwaites et al, 2000;Ssekiwoko et al, 2006). The cultural practices that include rouging and destroying infected plants/mats, early removal of male buds, disinfection of farm tools and use of clean planting materials are so far the most effective ways of reducing the inoculum in infested fields (Yirgou and Bradbury, 1968;Tushemereirwe et al, 2004). The adoption of rouging and complete destruction of infected mats, early male bud removal and disinfection of farm tools has been poor because they are cumbersome and costly (Jogo et al, 2013;Ocimati et al, 2013a).…”

Evaluation of banana genotype resistant to Xanthomonas wilts disease (Xanthomonas campestris pv. musacearum) in south east of Ethiopia

“…However, in recent years, the epidemics of Xanthomonas wilt with significant damage have been reported on banana in Uganda in 2001 (Tushemereirwe et al, 2004). Further outbreak and establishment were also confirmed on banana in eastern Congo, in the Lake Victoria region of Tanzania, Rwanda and Kenya (Aritua et al, 2008;Biruma et al, 2007 andNdungo et al, 2006).…”