Emulsions of essential oils and aloe polysaccharides: Antimicrobial activity and resistance inducer potential against Xanthomonas fragariae

Abstract

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, TAP and PAP 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.