Bacterial angular leaf spot disease (Xanthomonas fragariae) is an important strawberry disease and responsible for significant yield losses. The efficacy of emulsions containing tea tree or palmarosa essential oils (EO) against angular leaf spot, seeking to elucidate their mode of action, was evaluated in this study. Tea tree or palmarosa EO were added in an aqueous suspension of aloe polysaccharide (AP) and tea tree EO emulsion (TAP) and palmarosa EO microemulsion (PAP) were obtained. The antimicrobial potential of AP, TAP and PAP were evaluated in plants of two cultivars (Albion and San Andreas). The ability of these preparations to reduce disease severity and to activate plant defenses were evaluated. AP, TAP and PAP reduced X. fragariae growth by up to 44.0%, 94.4% and 86.1%, respectively. In addition, T AP and P AP suppressed completely the symptoms in both cultivars. Increased activities of superoxide dismutase, dismutase, catalase and peroxidase were observed in the more susceptible cultivar (Albion) treated with the emulsions, while a higher concentration of total phenolic compounds was verified in the less susceptible cultivar (San Andreas). Thus, emulsions with EO and AP can be used to control angular leaf spot by activating latent defense mechanisms in strawberry.
Polysaccharides from fungal wastes were partially characterized and evaluated for their protective effects against bacterial spot caused by Xanthomonas gardneri on four tomato cultivars: Santa Cruz Kada, Natália, BRS Sena and Forty. The polysaccharides were extracted from spent mushroom substrate of Pleurotus ostreatus, residual brewery yeast (Saccharomyces cerevisiae), and basidiocarps discarded from Lentinula edodes production. These polysaccharides were characterized for total carbohydrates, phenolics and proteins content, pH, scatter intensity, conductivity, Zeta potential, DPPH scavenging assay and infrared spectroscopy. The effects of time interval between treatment and inoculation (4 or 7 days) and polysaccharide concentrations (0.5 or 1.5 mg.mL-1) were assessed for disease severity using a susceptible tomato cultivar. The polysaccharide action mode was investigated by determining the activity of peroxidases and phenylalanine ammonialyase and by quantifying flavonoids and total phenolics in the plants
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