In vitro and in vivo screening of bacteria that have antagonistic and elicitation effects on potato pathogens

Liépin, Maxime [UCL] Gillis, Annika [UCL] Desoignies, Nicolas [UCL] Bragard, Claude [UCL] Mahillon, Jacques [UCL] Legrève, Anne [UCL]

The increase in organic farming adhering to European regulations on the sustainable use of pesticides has stimulated research into new strategies for controlling plant pathogens. A high-throughput screening method was used to select bacterial strains for potential use as growth promoting bacteria or as biopesticides. More than 2,600 strains of Pseudomonas spp. and Bacillus spp. were isolated from soils, compost and potato plants sampled in the Walloon region. Their antagonistic effects on Phytophthora infestans, Fusarium solani, Streptomyces scabies and Pectobacterium carotovorum were assessed in vitro. Fifty-four strains of Bacillus spp. and 16 strains of Pseudomonas spp. with antagonistic effects on at least one of the tested pathogens were selected. The elicitation effect of these strains was tested using mutant Arabidopsis plants expressing the GUS reporter system fused with the plant defensin gene PDF1.2. The induced systemic resistance (ISR) of nine bacteria inducing high defensin expression in Arabidopsis was tested on potato under greenhouse conditions. Potato tubers were coated with powder composed of lyophilized bacteria and the gene expression involved in ISR was quantified by RT-qPCR. The antagonistic effects of the 70 strains were also assessed in vivo. Bacterial suspensions were sprayed on the leaves of potato plants grown in the greenhouse and in the field. Their antagonistic effects on P. infestans were assessed by quantifying the progression of late blight disease after inoculation with P. infestans. In vivo tests were also conducted on the antagonistic effects of some strains on three tuber diseases caused by F. solani, S. scabies and P. carotovorum. The potential of using such bacteria for protecting potato against plant pathogens is discussed.