Evaluation of the effectiveness of biocontrol bacteria against avocado white root rot occurring under commercial greenhouse plant production conditions

• Selected bacteria from a previous collection were chosen for this study.
• In vitro biocontrol experiments allowed selection of promising biocontrol bacteria.
• Rhizospheric soil persistence is different for Pseudomonas spp. and B. subtilis strains.
• Pseudomonas chlororaphis PCL1606 and B. subtilis CB115 reduced disease.

Avocado white root rot (WRR) is a disease of significant importance in the Mediterranean area and is caused by the emerging pathogen Rosellinia necatrix. Five Pseudomonas spp. and three Bacillus subtilis strains were selected for this study based on their rhizospheric soil survival, antagonistic and biocontrol activities under experimental conditions. After a single inoculation, Pseudomonas spp. showed higher persistence in rhizospheric soil, and B. subtilis strains were not detected for longer than ten days. In biocontrol assays, B. subtilis CB115 protected the plants against WRR under experimental growth chamber conditions at a similar level to the biocontrol reference strain Pseudomonas chlororaphis PCL1606. The strains B. subtilis CB115, P. chlororaphis CB254 and PCL1606 and Pseudomonas fluorescens CB306 were further selected to explore their biocontrol abilities under commercial greenhouse conditions. B. subtilis CB115 showed consistent biocontrol with protection levels similar to the biocontrol strain P. chlororaphis PCL1606. Although B. subtilis CB115 did not show persistence features, repeated applications by direct soil drenching led to the detection of a stable population that was mainly composed of spores in the avocado rhizospheric soil after 74 days. Our results indicate that both P. chlororaphis PCL1606 and B. subtilis CB115 can help control R. necatrix under commercial greenhouse conditions. This is the first study investigating the performance of biocontrol bacteria against avocado WRR under commercial greenhouse settings.

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