Beta-aminobutyric acid-induced resistance in grapevine against downy mildew: involvement of pterostilbene

BABA, a non-protein amino acid, was used to induce resistance in grapevine against downy mildew. BABA-induced resistance was observed in the susceptible cv. Chasselas as well as in the resistant cv. Solaris. Following BABA treatment, sporulation of <i>Plasmopara viticola</i> was strongly reduced and the accumulation of stilbenes increased with time following infection. Induction of <i>trans-piceide</i>, <i>trans-resveratrol</i> and, more importantly, of <i>trans-ɛ-</i> and <i>trans-δ-viniferin</i> and <i>trans-pterostilbene</i> was observed in BABA-primed Chasselas. On the other hand, induction of <i>trans-resveratrol</i>, <i>trans δ-viniferin</i> and <i>trans-pterostilbene</i> was observed in BABA-primed Solaris. The accumulation of stilbenes in BABA-primed Solaris was much higher than that found in BABA-primed Chasselas. Furthermore, BABA-treatment of Solaris led to a rapid increase in transcript levels of three genes involved in the phenylpropanoid pathway: phenylalanine ammonia lyase, cinnamate-4-hydroxylase and stilbene synthase. BABA-primed Chasselas showed increased transcript levels for cinnamate-4-hydroxylase and stilbene synthase. Here we show that pre-treatment of a susceptible grapevine cultivar with BABA prior to infection with <i>P. viticola</i> primed the accumulation of specific phytoalexins that are undetectable in non-BABA-primed plants. As a result, the susceptible cultivar became more resistant to downy mildew.