Biochemical Characteristics and Pathogenicity of Xanthomonas campestris pv. musacearum Isolates Associated with Enset (Ensete ventricosum) Bacterial Wilt from Southwestern Ethiopia

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 °C 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 °C). 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.