A novel promising bioproduct to control bacterial plant diseases

The control of bacterial diseases is nowadays still limited to copper compounds, whose use is regulated by European Union since 2020 for its environmental impact, or to few biological control agents (BCAs). In this study, the efficacy of the foliar fertilizer Probaction® at 0.3% and 0.4% was tested in vitro by macrodilution method against strains of Xanthomonas vesicatoria (Xv), X. fragariae (Xf), Pseudomonas savastanoi subsp. savastanoi (Pss) and Erwinia amylovora (Ea). Probaction® at 0.3% was also tested in planta under climatic chamber conditions against bacterial leaf spot of tomato (BLST) caused by Xv. In particular, tomato plants cv. VF10 were treated with the product at the leaves or at the root apparatus; after 24 h, the plants were experimentally inoculated by spraying the Xv suspension (ca. 107 CFU/mL) at the leaves. Streptomycin sulphate (100 ppm) and sterile distilled water (SDW) were used as positive and negative controls, respectively. In vitro, Probaction® inhibited the growth of Xf, but it was not effective against Xv, Pss and Ea. In planta, the tomato plants treated at leaves or at roots showed a lower BLST severity (ca. 18 and 14 spots/leaf, respectively), in comparison to that on negative control plants (SDW, ca. 27 spots/leaf). The efficacy of Probaction® in reducing BLST severity, associated to its inability in inhibiting Xv growth in vitro, may suggest its role in triggering the plant immune response.