Evaluation of the role of fluorescent siderophore in the biologicalcontrol of bacterial wilt in tomato using Tn(5) mutants of fluorescentPseudomonas sp.

摘要

Fluorescent pseudomonads have been recognized as biocontrol agents against certain soil-borne plant pathogens. They are characterized by the production of yellow-green pigments termed pyoverdines, which fluoresce under UV light and function as 'siderophores'. Pyoverdines chelate iron in the rhizosphere and deprive pathogens of iron which is required for their growth and pathogencsis. Involvement of iron competition m biological control has been inferred from experiments in which mutants deficient in siderophore production were compared with the wild type with respect to biocontrol activity. A number of fluorescent pseudomonads with biocontrol activity against Ralstonia solanaceraum causing bacterial wilt disease in tomato, have been reported. In order to assess the mechanism of' biocontrol in these strains, the forward genetic approach of developing random mutants was attempted using a tranposable element, Tn, borne on the suicidal plamid PGS 9 maintained in E. coli WA 803. The mutagenesis of fluorescent siderophore producing Pseudomonas strains, RBL 101 and RSI 125, was performed following the method of Mahesh Kumar et al.. The putative mutants were checked for fluorescence under UV as well as for siderophore production following CAS plate assay. The colonies that did not fluoresce were designated as Flu mutants and those which fluoresced brighter than the wild type as hyperactive (Flu~(++)) mutants. The colonies which did not produce yellow zone of colouration on CAS plates were designated as Sid mutants. Those which produced small zones were designated as Sidd mutants and those which produce large-sized zones as Sid~(++) mutants. The putative mutants were tested for their in vitro inhibition of R. solanacearum following the dual culture assay? and for itl vitro suppression of the bacterial wilt disease in tomato following the plant growth assay.