Biological control of Sclerotinia sclerotiorum (Lib.) de Bary by Pseudomonas and Bacillus species on canola petals.
Four bacterial strains, Pseudomonas chlororaphis (PA-23), Bacillus amyloliquefaciens (BS6), Pseudomonas sp. (DF41) and B. amyloliquefaciens (E16) which had been found to have biocontrol activity in vitro assays against Sclerotinia sclerotiorum, the causal agent of stem rot of canola, were tested for their efficacy in greenhouse and field conditions. Microscopic studies showed that P. chlororaphis strain PA-23 inhibited the germination of S. sclerotiorum ascospores on petals while complete colonization of petals was observed 48 h after application of ascospores alone. Double application of PA-23 on canola plants challenged with the ascospores of S. sclerotiorum triggered increased levels of hydrolytic enzymes including chitinase and β-1,3-glucanase in canola plants. In addition, it also triggered the expression of the pathogenesis-related protein PR3. Field studies over a period of two years indicated that disease control with PA-23 and BS6 was comparable to that achieved with the fungicide Rovral Flo® (iprodione). There was no significant difference between single- and double-spray application of PA-23 and BS6 in the management of canola stem rot. Results suggest that P. cholororaphis PA-23 and B. amyloliquefaciens BS6 can be used to control Sclerotinia stem rot of canola under field conditions.