SELECTION OF RHIZOSPHERE-COMPETENT PSEUDOMONAS STRAINS AS BIOCONTROL AGENTS IN TROPICAL SOILS

Pseudomonas strains were isolated from the rhizosphere of maize grown in yellow-red latosol from Rio de Janeiro, Brazil, to serve as a deliv ery system for heterologous genes and for risk assessment studies in t ropical soils. Selected strains were modified by insertion of the cryI VB gene from Bacillus thuringiensis and tested for pathogenicity gene expression against larvae of a susceptible model species, Anopheles aq uasalis. Modified strains Br8 and Br12 showed similar survival perform ance to their parental strains, and presented a viable density of 10(7 ) c.f.u./g dry soil 30 days after release. A strain of P. fluorescens (Br12) that presented positive results for gene expression and the bes t survival performance, was selected for risk assessment studies in so il microcosms.