Detection, isolation and baseline characterization of indigenous PhlD+ fluorescent Pseudomonas species for the control of bean root rot and coffee wilt disease in Uganda

Abstract

Fluorescent Pseudomonas spp. which produces antibiotics such as 2,4-diacetylphloroglucinol (DAPG/phl) have biocontrol activity against many important soil-borne fungal pathogens. We isolated several Pseudomonas spp. carrying genes for DAPG synthesis (phlD) from coffee and bean rhizospheres from different sites in Uganda. RFLP analysis using Hae III and MspI revealed one dominant genotype in the coffee fields and two dominant genotypes in the bean fields. The three genotypes were unique and novel. In vitro antifungal assay against Fusarium xylaroides, Fusarium oxysporum, Fusarium solani and Pythium ultimum revealed strong inhibition by phlD+ isolates against all four pathogens. However, some phlD-negative isolates from coffee showed strong inhibition against the Fusarium spp. Furthermore screen-house experiments showed good disease control against coffee wilt disease (Fusarium xylaroides) and bean root rot (Pythium ultimum). The bio-control potential of the phlD+ isolate against the two diseases appeared to increase with time compared to chemical control which reduced with time.
Keywords: 2,4-diacetylphloroglucinol, biocontrol, coffee wilt disease, fungal root rots, fluorescent Pseudomonas bacteria, phlD+ gene, Uganda