Abstract:
Xanthomonas campestris pv. musacearum (Xcm) is a deadly bacterial pathogen causing wilt of enset
and banana plants since the first record in Keffa province in Southwest Ethiopia as early as the 1960s.
The disease remains a dominant constraint to enset production although its impact on banana has
declined over the past four decades. The disease is ravaging banana plantations and spreading at
alarming rates since its recent outbreak in other east and central African countries, including Uganda,
Democratic Republic of Congo, Rwanda, Tanzania and Kenya. Enset wilt management strategies such
as sanitation have been recommended although it is tedious for farmers to apply them for various
reasons. The efforts to develop enset clones tolerant/resistant to Xcm strains have not been efficient for
inconsistent reactions/performance of the selected materials, mainly attributed to variations in the
bacterial isolates used across the studies. Thus, it is important to determine ranges of variation within
the pathogen and host populations for developing resistant varieties and further breeding work. The
objectives of this study were to collect and characterize Xcm strains from enset and banana plants in
three major enset growing zones of Southwest Ethiopia and determine host-pathogen interactions.
Nineteen (19) Xcm strains were selected from a total of 72 isolates collected from leaf petioles of enset
and banana plants infected with bacterial wilt in six districts of Sheka, Keffa and Bench-Maji zones. The
bacterial strains were typically creamy to yellow mucoid, circular with dome-shaped colonies. The
strains were Gram-negative, KOH and catalase positive, suppressed on asparagine medium and
negative for nitrate reduction; most isolates (84.2%) were insensitive to 2% NaCl while few strains
(15.8%) were retarded by 1% NaCl concentration. All the strains were positive to hypersensitivity test
with reaction varying from chlorosis to necrosis on tobacco leaves. Six enset and two banana strains of
Xcm were pathogenic to the susceptible enset ‘Yeko’ and banana ‘Butuza’ (AAA) clones. The banana
strains induced typical bacterial wilting symptoms on both hosts that ultimately led to complete death
(100%). The host-pathogen interaction evidenced differences mostly among the enset clones in their
resistance/tolerance and variation in aggressiveness (virulence) between the bacterial strains. The
enset clones ‘Nobo’ and ‘Gudiro’ were consistently resistant while ‘Yeko’ was highly susceptible to the
three Xcm strains, namely: Xcme-9, Xcme-10 and Xcme-19, whereas ‘Chikaro’ was moderately tolerant
to two strains (Xcme-10 and Xcme-19) but most susceptible to strain Xcm9. The strains were less or
non-aggressive to the resistant clones ‘Nobo’ and ‘Gudiro’ but most aggressive on the susceptible
plants while ranges of aggressiveness were demonstrated on ‘Chikaro’.
