Evaluation of Chemical and Natural Resistance Inducers against Downy Mildew (Plasmopara viticola) in Grapevine

Abstract

Chemical and natural resistance-inducing substances may be used to decrease the susceptibility of plants to various pathogens, thus reducing the application of pesticides in agriculture. This study evaluated the potential of biocontrol products and of plant extracts. The invoked mode of induced resistance was verified to control downy mildew on grapevine plants using leaf discs and potted vines. Induced resistance was determined by the increase of pathogenesis-related (PR) proteins, including peroxidase, polyphenol oxidase, β-1,3-glucanase, phenylalanine ammonia-lyase, stilbene synthase, β-1,3-glucanase, PR-1 protein, and caffeoyl-coenzyme A 3-O-methyltransferase. Candidate resistance inducers, including Solidago canadensis (CanG) extract, mycelium extract of Penicillium crysogenum (PEN), linoleic acid (LIN), and biocontrol agent Aureobasidium pullulans (Aureo), and chemical elicitors 3-dl-β-aminobutyric acid (BABA) and benzothiadiazole (BTH) were tested against Plasmopara viticola in potted vines grown outdoors. BABA, BTH, and CanG provided a protection of more than 80%, whereas PEN, LIN, and Aureo provided minimal protection. BABA and Aureo were not able to inhibit zoospores, whereas a concentration-dependent inhibition of zoospore mobility was observed for all other tested substances. BTH, CanG, PEN, and LIN induced the production of a broad spectrum of resistance-related metabolites, whereas Aureo did not cause any response. BABA provoked formation of necrotic spots and PR proteins immediately after inoculation. These results indicate the potential to partly induce natural resistance metabolites to enhance tolerance of grapevine plants to P. viticola, thus offering a synergistic effect when used with fungicides and aiding in reducing their ecological burden, even if they are not effective enough to replace them fully.