Survey and Characterization of Xanthomonas campestris pv. musacearum, the Cause of Enset Bacterial Wilt in Southern Ethiopia

Enset bacterial wilt (EBW) is a major disease threatening enset production in Ethiopia. The objectives of the study were to assess the distribution and intensity of EBW across locations and altitude gradients, identify biophysical factors that affect EBW intensity and characterize the Xanthomonas campestris pv. musacearum isolates. For this purpose, EBW disease survey was carried out in Gedeo, Gurage, Sidama, Silte and Wolayta from July to November 2021. In addition, 20 Xcm isolates were collected from across altitude gradients and their characteristic features were assessed in laboratory tests and by inoculating them on a susceptible enset clone (Arkiya) in a pot experiment. The disease was prevalent across all the surveyed areas albeit at different intensities. From 300 enset fields assessed, 74.7% farms were affected by EBW. The disease was most prevalent in Silte (88.3%) followed by Gurage zone (80%). The highest EBW incidence of 24.3% was recorded at intermediate elevation (2001-2500 m.a.s.l). The highest (20%) and lowest (11.4%) mean incidence were recorded in Wolayita and Gedeo zones, respectively. Altitudes, clonal diversity, sites for raising suckers and exchanging of planting materials are factors that significantly influence EBW intensity in the study areas. The Xcm isolates were creamy to yellow mucoid, with dome-shaped colonies, gram-negative, KOH and catalase positive and slimy mucoid to mucoidal yellow colonies on nutrient agar with 5% glucose. All the strains were positive to hypersensitivity test on tobacco leaves and found to be pathogenic, on enset clone Arkiya. However, significant differences (P≤0.05) were recorded among the isolates in terms of DAI, DI, PSI and AUDPC. Isolates from Hula and Damot Gale districts were more aggressive than the others. It is recommended that isolate variations should be considered in future enset improvement to manage the disease in a sustainable manner. Future studies should also give due attention to genetic differences among the isolates to verify current results.