Pseudomonas cepacia and Pseudomonas putida as winter wheat inoculants for biocontrol of Rhizoctonia solani

Abstract

Pseudomonas cepacia R55 and R85 and Pseudomonas putida R104, antagonistic towards plant pathogenic fungi in vitro, were assessed as seed inoculants for winter wheat (cv. Norstar) grown in a growth chamber in soil infested with Fusarium solani or Rhizoctonia solani isolate AG-1, AG 2-1, or AG-3. Infestation of soil with R. solani AG-1 or AG 2-1 reduced root dry weight of uninoculated plants by 62 and 78%, respectively, whereas R. solani AG-3 or F. solani had no effect on plant biomass. Pseudomonad inoculants increased (relative to plants subjected to disease) the winter wheat root dry weight by 92–128% and shoot dry weight by 28–48% in the soil infested with R. solani AG-1. The shoot material of all plants inoculated with pseudomonads also had significantly (P < 0.05) higher total Fe contents than the uninoculated treatment in the R. solani AG-1 infested soil. Pseudomonas cepacia R55 produced the highest (P < 0.01) total Fe contents in the shoots, but it had no effect on N and P content. Pseudomonas cepacia R85 significantly increased total N (P < 0.05) and total P (P < 0.01) of wheat shoots, and P. putida R104 increased the percentage (P < 0.05) and (or) total P content (P < 0.01) in the soil infested with R. solani AG-1. Pseudomonas cepacia R85 also significantly (P < 0.05) increased wheat shoot biomass in R. solani AG-3 infested soil. All three pseudomonads produced fluorescent siderophores when cultured in a low-iron medium. These results suggest an in situ antibiosis activity of three fluorescent pseudomonad strains towards phytopathogenic fungi and suggest that the plant growth response was probably due to protection against damage caused by R. solani. Key words: biocontrol, pseudomonads, Rhizoctonia solani, winter wheat, siderophores.