Phenotypic and genotypic diversity of Xanthomonas axonopodis pv. manihotis causing bacterial blight disease of cassava in Kenya

Abstract

Cassava bacterial blight (CBB), caused by Xanthomonas axonopodis pv. manihotis (Xam), is the most important bacterial disease of cassava. There is no information available on the morphological and genetic variability of Xam isolates from Kenya. The aim of this study therefore, was to determine the diversity of Xam isolates from different cassava growing regions of Kenya using phenotypic characteristics and repetitive DNA polymerase chain reaction-based fingerprinting (rep-PCR). Thirty three isolates were recovered from infected cassava leaf samples collected from farmers' fields in cassava growing regions. The dendrogram generated from analysis of phenotypic characteristics of the isolates produced two major clusters at 75% similarity level. Analysis of 19 isolates with repetitive extragenic palindromic (rep) primers yielded characteristic fingerprint pattern with bands ranging between 400 and 2000 bp in size and their numbers ranged from 1 to 6 bands per isolate. Cluster analysis using unweighted pair group method with arithmetic averages (UPGMA) did not reveal any significant differences in clustering and relationship to the geographical origin, with exception of a single isolate that had unique fingerprints. These findings indicate that Xam population in Kenya evolved from the same origin and is a uniform population, and this may prove useful in future breeding programmes.