Abstract:
Bacterial wilt [Xanthomonas campestris pv. musacearum (Xcm)] is a very destructive disease that
attacks enset (Ensete ventricosum). The objective of this study was to characterize Xcm isolates
morphologically, biochemically, physiologically and pathogenically. The objective of this study
was to determine the morphological, biochemical, physiological and pathogenic characteristics of
Xcm isolates collected from Southwestern Ethiopia. One hundred and twenty Xcm isolates were
collected from 120 infected enset fields in 10 major enset growing districts, namely Andiracha,
Bita, Chena, Decha, Gimbo, Maji, Masha, Semen-Bench, She-Bench and Yeki, in southwestern
Ethiopia during 12 June to 08 August 2017, and were isolated on yeast peptone sucrose agar
(YPSA) medium in the laboratory. From each sample, a loopful of the suspension was streaked on
yeast peptone sucrose agar (YPSA) medium. The plates were arranged in complete randomized
design and incubated at 28 oC for 48–72 hours. The isolates were characterized on the bases of
their colony growth, morphological, physiological and pathogenic features, and their responses to
various biochemical tests. Morphologically, variability among isolates was observed in
appearances in colony color that varied from light to deep yellow, and growth as its’ growth type
that ranged from low to highly mucoid colony. Moreover, variability in tolerance abilities within
isolates was observed under different NaCl concentrations (0–5%) and temperature variation (26,
28, 30 and 32 oC). On the contrary, all the 14 biochemical tests showed similarities amongst the
isolates. Thus, potassium hydroxide solubility test revealed that all the isolates were Gram-
negative. All the isolates were catalase and oxidase positive, could hydrolyze casein and gelatin,
produce H2S, and utilized citrate and malate while the isolates could not reduce nitrate to nitrite,
could not hydrolyze Tween 80 (about 92.5% of the isolates) and starch, and could not produce
indole. Morphological and biochemical tests in combination with the pathogenicity test confirmed
the isolates were Xcm, and suggested the presence of population diversity among Xcm isolates
tested. However, further studies that target the genetic diversity of the pathogen using large number
of isolates are essential to draw a meaningful inference.
