Diversity and Phylotype Analysis of Ralstonia solanacearum Strains Causing Tomato and Potato Bacterial Wilt in Ethiopia

Abstract

Ralstonia solanacearum is the causative agent of bacterial wilt on economically important
crops. The occurrence and importance of the disease has been recognized in Ethiopia. The
pathogen is known for its high variability and adaptability to various geographical regions
of the world. The biovar and race classification system has been considered as insufficient
to encompass the diversity within the R. solanacaerum species complex. A classification
scheme based on phylotype specific multiplex PCR from an internal transcribed spacer
(ITS) region and an endoglucanse gene sequencing has been reported to fill the limitation.
The study was intended to characterize R. solanacearum strains from Ethiopia based on both
conventional approaches and determination of phylotypes. On the basis of the conventional
approach R. solanacearum strains from Ethiopia were identified as biovars 1 and 2
complementing the recent report of biovar 1 in Ethiopia. Rep-PCR analyses also revealed
three clonal lines at about 80 % similarity level and overall 9-fingerprint types at 100 %
similarity level among the studied strains. Phylotype grouping revealed the occurrences of
phylotype II and III and further confirmed by partial endoglucanse gene sequencing. The
association of biovar and phylotyping indicate that phylotype II consists of only biovar 2
and phylotype III comprises biovar 1 and 2. This is the first formal report on the occurrence
of phylotypes II and III in Ethiopia. The genetic variability of R. solanacearum requires
proper consideration in future research work in the country. The findings also would
contribute to update the existing information on R. solanacearum strains in Ethiopia and can
help to discriminate and assess emerging pathogens or strains that could be potentially
introduced into the country.