Interactions between a fluorescent pseudomonad, an arbuscular mycorrhizal fungus and a hypovirulent isolate of Rhizoctonia solani affect plant growth and root architecture of tomato plants

Abstract

Although Rhizoctonia solani is a cosmopolitan soilborne pathogen, the genus includes isolates with different pathogenicity ranging from high virulence to avirulence. The biocontrol strain Pseudomonas fluorescens P190r and the arbuscular mycorrhizal (AM) fungus Glomus mosseae BEG12 were inoculated alone or in combination in tomato plants infested by the mildly virulent pathogen R. solani #235. Plant growth as well as root morphometric and topological parameters were evaluated. The infection of R. solani was significantly reduced by all the combinations of the beneficial microorganisms. Root systems of R. solani‐infected plants were weakly developed but highly branched with a herring‐bone pattern, while those inoculated with the AM fungus, alone or in combination with the bacterial strain, were longer and more developed, and displayed a dichotomous pattern. The interactions among these three microorganisms affected plant growth and root architecture of tomato plants.

Keywords:

• Arbuscular mycorrhizal fungi
• fluorescent pseudomonads
• hypovirulent Rhizoctonia solani
• root architecture
• root topology

Acknowledgements

This work was supported with funds from the MIUR (Co.Fin PRIN) Project “Plant‐microorganism symbioses: interactions with aprofound ecological impact”. The authors are grateful to Dr Rosemary Warren and Mrs Barbara Hall (South Australian Research and Development Institute, Adelaide, Australia) for providing the R. solani #235 strain, and to Dr Alberto Escande (Instituto Nacional de Tecnologia Agropecuaria, Balcarce, Argentina) for providing the P. fluorescens P190 strain.