Specificity of Pseudomonas Isolates on Healthy and Fusarium Head Blight-Infected Spikelets of Wheat Heads

The specificity of culturable bacteria on healthy and Fusarium head blight (FHB)-infected spikelets of wheat heads was investigated to find a candidate of biocontrol agents against FHB. The bacterial genus Pseudomonas was commonly isolated from the tissues, and phylogenetic analysis using 16S ribosomal RNA gene sequences of isolates of the genera revealed that particular phylogenetic groups in the genus specifically inhabited either healthy or infected spikelet tissues. The specificity of each group was suggested to be due to differences in the ability to form biofilms and colonize spikelet tissues; isolates originated from healthy spikelets formed biofilms on polyvinyl chloride microplate wells and highly colonized the spikelet tissues. Other bacterial groups obtained from FHB-infected spikelets less formed biofilms and attached with low densities on the spikelet tissues. Their colonization on the tissues, however, was promoted when co-inoculated with the causal pathogenic fungus, Fusarium graminearum, and several isolates were observed to smash the mycelia in vivo. Moreover, based on results of in vitro mycelial growth inhibition activity, the diseased tissue-originated isolates were verified to have a negative effect on the fungal growth. These results suggest that Pseudomonas isolates obtained from infected spikelet tissues were highly associated with the FHB pathogen and have potential as candidates for biological control against FHB.