Abstract

In Africa, cultivation of potato (Solanum tuberosum) represents an important food source and income generation. However, its productivity is constrained by biotic and abiotic stresses. Bacterial wilt caused by Ralstonia solanacearum is an important constraint to the world potato industry. In Kenya, the disease affects 77% of potato farms causing yield losses of up to 100%. Control methods are limited mainly due to the broad diversity and wide spread of its pathogen. Understanding the population structure and geographical distribution of this pathogen is an important starting point in the development of effective control strategies. In this study, R. solanacearum strains affecting potato cultivation in Nakuru county were successfully isolated and characterized. Kelman’s triphenyl tetrazolium chloride media were used to isolate the pathogen and 20 isolates were selected based on their virulence for further characterization and confirmation of their status at the molecular level through polymerase chain reaction using 759/760 primers and sequencing of partial endoglucanase (egl) gene. The phylogenetic assay was done using specific primers and it was found that the phylogenetic diversity was highly heterogeneous, since all the four phylotypes of R. solanacearum were identified. Phylotype I was the most prevalent phylotype and represented 50% of the collection. Based on their ability to utilize sugars and alcohols, all the isolates were grouped as biovar III except 2 (Rs18 and Rs49). The aggressiveness of isolated bacteria was then evaluated using a hypersensitive reaction test on tobacco and their virulence was further confirmed on a susceptible potato variety Shangi under greenhouse conditions. All isolates elicited a reaction in tobacco with different grades. They also showed varying levels of virulence with Rs6 isolate being the most virulent. Taken together, these findings provide baseline information for improvement programs targeting host-based resistance to multiple strains causing bacterial wilt of potato in this region.

Keywords: Bacterial wilt, Biovar, hypersensitive reaction, pathogenicity, phylotype, potato, Ralstonia solanacearum.