THE DEVELOPMENT OF A BIOLOGICAL CONTROL AGENT AGAINST RALSTONIA SOLANACEARUM RACE 3 IN KENYA.
Smith J.J1., Offord L.C1., Kibata G.N2, Muimi Z. K2., Trigalet A3., Saddler G.S1.
1 International Mycological Institute, Egham, Surrey, United Kingdom.
2 Kenyan Agricultural Research Institute, Nairobi, Kenya.
3 Institute National de la Recherche Agronomique, Toulouse, France.
In Kenya, potato cultivation occurs between 1200 and 2800m over an area of 75000-100000 ha per year. Socio-economic pressures result in near continuous potato cultivation in these areas and losses due to bacterial wilt (Ralstonia solanacearum race 3 biovar 2-A) have been serious in recent years. Accordingly, control strategies that are affordable to the farmer are urgently required. This research addresses the potential of biological control of bacterial wilt in Kenya by pre-inoculation with non-pathogenic mutants of the wild type organism.
From a survey of R. solanacearum race 3 comprising 46 isolates from Kenya, 10 isolates were selected for development as biocontrol agents against the wild type by mutation to non-pathogenic forms. Selection was based on a multi-faceted approach evaluating siderophore, bacteriocin, pectinase and cellulase production by agar plate methods, pathogenicity and genomic fingerprinting by macro-restriction analysis; the fragments resolved by pulsed field gel electrophoresis. Whereas agar plate and pathogenicity assessments proved poorly discriminatory, the genomic fingerprinting revealed hitherto unrealised genetic diversity within R. solanacearum race 3 that allowed a rational selection of Kenyan isolates for mutagenesis. Non-pathogenicity was induced by one of two methods 1) Transformation by a omega (W ) interposon that shared homology to the hrp region; 2) Sequential insertion and forced eviction of the sacB gene of Bacillus subtilis. Preliminary biocontrol assessments under growthroom conditions recorded a significant level of protection, with a delay in disease onset of 50%.
