Abstract
Powdery mildew is a fungal disease found in a wide range of plants and can significantly reduce crop yields. Bacterial strain LJ02 is a biocontrol agent (BCA) isolated from a greenhouse in Tianjin, China. In combination of morphological, physiological, biochemical and phylogenetic analyses, strain LJ02 was classified as a new member of Bacillus amyloliquefaciens. Greenhouse trials showed that LJ02 fermentation broth (LJ02FB) can effectively diminish the occurrence of cucurbits powdery mildew. When treated with LJ02FB, cucumber seedlings produced significantly elevated production of superoxide dismutase, peroxidase, polyphenol oxidase and phenylalanine ammonia lyase as compared to that of the control. We further confirmed that the production of free salicylic acid (SA) and expression of one pathogenesis-related (PR) gene PR-1 in cucumber leaves were markedly elevated after treating with LJ02FB, suggesting that SA-mediated defense response was stimulated. Moreover, LJ02FB-treated cucumber leaves could secrete resistance-related substances into rhizosphere that inhibit the germination of fungi spores and the growth of pathogens. Finally, we separated bacterium and its fermented substances to test their respective effects and found that both components have SA-inducing activity and bacterium plays major roles. Altogether, we identified a BCA against powdery mildew and its mode of action by inducing systemic resistance such as SA signaling pathway.
Highlights
Cucurbits powdery mildew caused by Sphaerotheca fuliginea is a common disease of cucurbits under field and greenhouse conditions in most areas of the world (Perez-Garcia et al, 2009)
The results proved that strain LJ02 inhibited the occurrence of cucurbits powdery mildew under greenhouse condition
We further found a large body of evidences that LJ02 could induce SAmediated systemic acquired resistance (SAR) as one of its major mode of actions
Summary
Cucurbits powdery mildew caused by Sphaerotheca fuliginea is a common disease of cucurbits under field and greenhouse conditions in most areas of the world (Perez-Garcia et al, 2009). Copper, and various classes of fungicides or combinations of them are widely used to control those infections (Reuveni et al, 1996). Due to long-term extensive use of fungicides, pathogens have gradually evolved resistance to those fungicides. The pesticide residues are of major concern because of their detrimental effects on human health and the environment (Zhang et al, 2015). To circumvent those undesirable effects, the application of biocontrol agent (BCA) is considered as a promising alternative treatment that can reduce both environmental pollution and the rise of fungicide resistance (Alamri et al, 2012)
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