Abstract:
Ralstonia solanacearum is a bacterium recognized as a major wilt causing
phytopathogen with an unusual broad host range. This study aimed at determining the
distribution of the bacteria along the coast of Tanzania and environmental factors
influencing incidence and disease severity. It also aimed to define the population
structure of the strains in terms of its biology and phylogenetic make up in order to
effectively screen for variety tolerance. The study revealed that contaminated
irrigation water and temperature are the key environmental factors determining
incidence and severity. Bacterial wilt was found in Tanga, Pwani, Unguja ukuu and
Morogoro where temperature varied within the range of 25°C to 32°C. R.
solanacearum was detected in river water by DAS-ELISA. At a temperature of 18
20°C, no infected plants were found in Mtwara and Lindi. Due to high diversity in its
genotypic and phenotypic traits, Ralstonia solanacearum is considered a species
complex. Strains from different locations vary in virulence, hence its control using
resistant varieties is usually strain specific. The study also included characterization of
R. solanacearum isolates in order to determine strains present in the selected study
areas. The strains were tested for their ability to utilize hexose sugars and alcohols and
found to be biovar 3. Multiplex PCR showed that strains found along the Tanzanian
coast are phylotype I which are predominantly Asian. A representative strain from
each region was chosen and inoculated on tomato lines from AVRDC bred for
resistance to R. solanacearum. Lines AVTO 1010, 9221, 0301, and 1226 had varying
levels of resistance against different strains but were significantly resistant to the
pathogen compared to the susceptible variety Cal J. These lines can be disseminated
appropriately for farmers' seed testing and used to improve yield. The collection of
strains can be used for selection purposes when screening for available local sources
of resistance and mapping genes strongly linked to strain virulence.
