Evaluation of Biofungicides and Plant Defense Elicitors against Bacterial Pathogens of Agronomic Importance

Abstract

Plant bacterial diseases are nowadays routinely managed with scheduled treatments based on heavy metal compounds or, in the worst cases, on antibiotics; to overcome the environmental consequences linked to the use of these chemical compounds, such as pollution or selection of antibiotic resistant pathogens, an integrated control management is required. The use of bacterial antagonists, biological agents, plant defence response elicitors or resistant host plant genotypes play an important role in the frame of sustainable agriculture. In this work, the activity of plasma activated water (PAW) and different bioagents aimed to the control of the two bacterial pathogens Xanthomonas vesicatoria and Pseudomonas syringae pv. actinidiae, causal agents of tomato bacterial leaf spot and kiwifruit bacterial canker, respectively, were studied. All these tools were assayed for their direct efficacy and for their ability, as elicitors, to trigger the plant immune system against these two bacterial pathogens. Moreover, a study on several Actinidia sp. accessions was carried out to evaluate their susceptibility against bacterial canker of kiwifruit. PAW resulted unable to direct inhibit X. vesicatoria growth in in vitro assays, however it showed the ability to trigger tomato plant immune system by reducing disease severity up to approx. 38% when tested in three experiments on two tomato genotypes conducted under greenhouse conditions. When tested in in vitro and in vivo experiments against X. vesicatoria and P. syringae pv. actidinidiae, the tested bioagents, based on natural extracted compounds or on different strains of Bacillus sp., showed a direct efficacy against both bacterial pathogens. Moreover, they were also able to elicit the plant defence response by significantly lowering the disease severity on tomato and kiwifruit leaves. In addition, the A. chinensis accession NPK3 resulted the less susceptible to the bacterial canker in comparison to more than 20 accessions tested.