Leaves, shoots and flowers from two different economy-relevant grape cultivars, Merlot and Cabernet Sauvignon, were examined to assess the distribution of phytoalexins upon inoculation with Botrytis cinerea at pre-bloom, bloom, and post-bloom stages. Mass spectrometric analysis evidenced considerable levels of trans-resveratrol (3,5,4'-trihydroxystilbene), albeit higher in Cabernet Sauvignon, in leaves from both grape cultivars following fungal infection at all the examined stages of development. Although both these cultivars are reported to be sensitive against fungal infections, in Cabernet Sauvignon leaves and flowers, we were also able to measure relevant quantities of the resveratrol dehydrodimer delta-viniferin. While infection by B. cinerea occurs at bloom stage, high-sensitivity of the HPLC-mass spectrometric analytic method allowed detecting measurable levels of viniferins even in early pre-bloom stages in Cabernet Sauvignon flowers and to evidence even slight resveratrol differences between the cultivars. Concordingly, Cabernet Sauvignon better responded to fungal infection. This analysis allowed us to conclude that, even when analyzing fungal infection-sensitive cultivars, the HPLC-MS method holds the sensitivity to highlight the slightest differences in the concentrations of the two phytoalexins and correlate them to different anti-fungal response potential.
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