The Use of the Bacterial Antagonist Bacillus subtilis and the Plant Defense Enhancer Fosetyl-Al against Fire Blight on Pear

Since the use of the antibiotic Streptomycin is forbidden in Belgium, new strategies to control fire blight have been developed like the use of Plant Defense Enhancing (PDE) molecules. Aliette (fosetyl-Al) has been registered against fire blight in Belgium in 2012 as a PDE molecule with applications starting in the post-floral period on pear and at the end of bloom on apple. A PDE molecule like fosetyl-Al should be positioned preventively, prior to the infection, so that the defense mechanisms of the plants can be switched on in time. A reduction in the disease progression and a clear reduction in the ooze formation on the infected tissues were observed on plants treated 3 times preventively with fosetyl-Al and this is considered to be a very interesting factor in the fire blight epidemiology. Furthermore, after hail during the summer period, fosetyl-Al can interfere with the ooze formation on the infected immature fruits and lower the disease spread. To protect the flowering period, the efficacy of the bacterial antagonist Bacillus subtilis, is tested. The antagonistic bacteria Bacillus subtilis can act against fire blight through a competition with Erwinia amylovora for site and nutrients on the stigma of the flowers and through the production of antimicrobial peptides. In 2013 and 2014, the efficacy of different formulations of Bacillus subtilis QST 7013, applied alone or in combination with fosetyl-Al, was assessed against artificial inoculations of flower clusters and young, active growing shoots on potted ‘Conference’ pear trees under optimal infection conditions in the quarantine greenhouse. The results showed interesting activity of the bacterial antagonist against Erwinia amylovora: a reduction in the disease progression as necrosis and a limitation of the ooze formation on the infected tissue was observed. A combination of the protection of blossoms with Bacillus subtilis followed by the PDE activity of fosetyl-Al looks promising.