Phylogenetic diversity and antagonistic traits of root and rhizosphere pseudomonads of bean from Iran for controlling Rhizoctonia solani

Abstract

Fluorescent pseudomonads from bean root and rhizosphere in Iran were investigated for biocontrol of the fungal pathogen Rhizoctonia solani. Phylogenetic analysis of concatenated 16S rRNA, gyrB and rpoD sequences for 33 Pseudomonas isolates showed that 15 belonged to four clusters within the 'P. fluorescens' group, i.e. one corresponding to P. thivervalensis, two others including P. moraviensis or P. baetica, and the last one without closely-related established species. The 18 other isolates belonged to five clusters within the 'P. putida' group, one including P. mosselii and P. entomophila, another including strains currently described as P. putida, and three without closely-related species described. Ten isolates were selected based on in vitro inhibition of R. solani. Cellulase activity was identified in three pseudomonads, chitinase activity in two pseudomonads, extracellular protease activity in nine pseudomonads and hydrogen cyanide production in two pseudomonads. Genes coding for production of phenazine, pyoluteorin, pyrrolnitrin and 2,4-diacetylphloroglucinol were not found, whereas the 1-aminocyclopropane-1-carboxylate deamination gene acdS was present in three pseudomonads. The antagonistic acdS⁺ strain VKh13 from the 'P. putida' group effectively protected soil-grown bean from R. solani AG 4-HGI. Results show that pseudomonads from uncharacterized taxa were readily obtained from Iranian soils and displayed biocontrol potential against R. solani.

Keywords: Biocontrol; P. fluorescens; P. putida; Pseudomonas; Rhizoctonia solani.