TITLE:
Screening and Phenotypic Characterization of Presumptive Avirulent Ralstonia-Like Isolates from Tomato Rhizosphere Soils for Bacterial Wilt Management in Northern Tanzania
AUTHORS:
Athumani Ally Muya, Ernest R. Mbega, Emmanuel J. Mrema, Agatha Aloyce
KEYWORDS:
Avirulent Isolates, Bacterial Wilt, Ralstonia solanacearum, Colony Morphology, Antagonism
JOURNAL NAME:
Agricultural Sciences,
Vol.17 No.11,
November
3,
2026
ABSTRACT: Bacterial wilt caused by the Ralstonia solanacearum species complex is among the most damaging constraints to tomato (Solanum lycopersicum L.) production in Tanzania, and available management options give only partial control. Naturally occurring isolates that have lost pathogenicity are of interest for biological control because they occupy the same niche as virulent strains. This study aimed to recover and characterize isolates with a non-fluidal colony phenotype from tomato rhizosphere soils in bacterial wilt-affected areas of Arusha District Council. Thirty samples (27 composite rhizosphere soil samples from asymptomatic plants and three symptomatic plants) were collected from nine fields in three wards and plated on triphenyl tetrazolium chloride (TZC) medium. Twelve small, dry, deep-red, non-fluidal isolates were recovered from soil and three fluidal presumptive virulent isolates from symptomatic stems. None of the 12 caused wilt on the tomato varieties Tanya and Tengeru 97 in a screen house up to 35 days after inoculation, whereas the presumptive virulent control caused severe wilt (mean severity 4.50 and 3.50 on a 0 - 5 scale). Inference was confined to wilt incidence, which separated the positive control from all other treatments (Fisher’s exact test, p