Plant Biologicals Network Sympossium 2021, Kobenhavn, Denmark, 11 - 12 November 2021, pp.1
Biological control agents (BCA) of crop diseases are gaining considerable attention as an alternative to synthetic fungicides. Antibiosis is a feature widely exploited to develop biofungicides based on the ability of BCAs to produce fungitoxic compounds. A less recognised and utilised attribute of plant-associated microorganisms is their ability to stimulate the plant immune system, providing long-term systemic self-protection against different types of pathogens. The term ‘priming’ of the plant defence denotes the situation where the plant treated with the BCA shows no apparent defence activity and no energetic costs in the absence of pathogen infection. However, primed plants are prepared to respond faster and stronger upon pathogen attack.
By using conventional antifungal in vitro screening coupled with in planta assays, we found antifungal (AF) and non-antifungal (NAF) bacterial strains that protected the ornamental plant Kalanchoe against the soil-borne pathogen Fusarium oxysporum in experimental and commercial production settings. Further examination of one AF and one NAF strain indicated that high protection efficacy in planta did not necessarily correlate with antifungal activity in vitro. Whole genome sequencing showed that the NAF strain lacks the biosynthetic gene clusters for typical antimicrobial compounds. Instead, this bacterium mediates the activation of plant defence through defence priming. Additional in planta assays showed that this NAF strain also confers high protection in tomato against F. oxysporum f.sp. lycopersici and in wheat against the foliar pathogen Zymoseptoria tritici through priming of the host defence system. We suggest that priming of plant defence is a promising target in the development of novel biological crop protection products.