Use of Bacteria Isolated from Berry Rhizospheres as Biocontrol Agents for Charcoal Rot and Root-Knot Nematode Strawberry Diseases

Strawberry is a high-value crop in Spain, where fruits for fresh consumption are produced off-season and exported to central and northern European countries. Soil-borne pathogens (SBP), such as Macrophomina phaseolina and Meloidogyne hapla, are widely spread in strawberry crops in Spain. The prevalence of these pathogens is a significant barrier to producing strawberries of premium quality and at profitable yields. The current ban on fumigant pesticides drives the search for alternative SBP control methods that can simultaneously control both SBP. Twenty-nine bacterial strains were isolated and identified from strawberry and blueberry rhizospheres and screened for plant growth promotion activities as well as for biocontrol potential on M. phaseolina and M. hapla. Two of these bacterial strains (Bacillus velezensis FC37 and Pseudomonas aeruginosa AC17), together with Brevibacterium frigoritolerans Hvs8 coming from IFAPA's bacterial collection, were selected and evaluated in planta for their biocontrol potential on strawberry SBP diseases caused by M. phaseolina and M. hapla. The three tested bacterial strains reduced charcoal rot disease severity, crown incidence and severity, and petiole colonization by M. phaseolina. Root-knot nematode (RKN) symptoms were reduced by P. aeruginosa AC17 and B. velezensis FC37, but RKN reproduction was only reduced in plants inoculated with P. aeruginosa AC17. Pseudomonas aeruginosa AC17 showed the greatest potential as a biocontrol agent candidate to be included in integrated disease management programs to control the two most prevalent soil-borne pathogens of strawberry in Spain.