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 Plasmopara viticola was strongly reduced and the accumulation of stilbenes increased with time following infection. Induction of trans-piceide, trans-resveratrol and, more importantly, of trans-Sigma and trans-delta-viniferin and trans-pterostilbene was observed in BABA-primed Chasselas. On the other hand, induction of trans-resveratrol, trans delta-viniferin and trans-pterostilbene 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 P. viticola 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.