Physiological characteristics and pathogenicity of Xanthomonas campestris pv. musacearum strains collected from enset and banana in Southwest Ethiopia

Abstract

Xanthomonas campestris PV. Musacearum (Xcm) is a deadly bacterial pathogen coursing 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’.

Keywords: Banana, Ensete ventricosum, enset bacterial wilt, Xanthomonas campestris pv. musacearum, Ethiopia.

African Journal of Biotechnology, Vol 13(24) 2425-2434