Susceptibility to downy mildew in grape clusters: New microscopical and biochemical insights

• Published in: Plant physiology and biochemistry 2012-03, Vol.52, p.140-146
• Main Authors: Gindro, Katia, Alonso-Villaverde, Virginia, Voinesco, Francine, Spring, Jean-Laurent, Viret, Olivier, Dubuis, Pierre-Henri
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Cluster; Disease Resistance; Disease Susceptibility; Downy mildew; Fundamental and applied biological sciences. Psychology; Genotype; Grapevine; Lenticels; Microscopy, Electron, Scanning; Ontogeny; Plant Diseases - immunology; Plant Diseases - parasitology; Plant physiology and development; Plant Stomata - anatomy & histology; Plasmopara viticola; Resistance; Seasons; Stilbenes; Stilbenes - analysis; Stilbenes - metabolism; Stomata; Vitaceae; Vitis; Vitis - anatomy & histology; Vitis - chemistry; Vitis - immunology; Vitis vinifera
• ISSN: 0981-9428; 1873-2690
• DOI: 10.1016/j.plaphy.2011.12.009

Grape clusters of different Vitis genotypes, including Vitis vinifera cvs Chasselas and Merlot, and two interspecific grape varieties, Solaris (cvs. Merzling* x (Saperavi severneyi x Muscat ottonel)) and 2091 (cvs. Gamaret x Bronner), are susceptible or resistant to downy mildew. These cultivars were inoculated with Plasmopara viticola at three developmental stages (BBCH stages 53, 69 and 75). Samples were examined by scanning electron microscopy and the synthesis of stilbenes was measured. Microscopical examinations of pedicels, rachis and calyptras showed important differences in stomatal structures within seasonal development. At BBCH 53, successful infections were observed on all tested cultivars and functional stomata were present, while no infections were observed after this stage. At BBCH 69 and 75, cracks were observed around the stomata and guard cells were unstructured or completely collapsed, leading to closed-like stomata. At BBCH 53, significant stilbene accumulation was quantified in 2091 and Solaris; pterostilbene and δ-viniferin were produced in large amounts. In the susceptible varieties, only piceid and resveratrol were induced. At the other two stages, the concentration of all measured stilbenes was undetectable. The critical roles of seasonal development and stilbenes in the resistance of grape clusters towards downy mildew are discussed. ► Stilbens are synthesized in grape clusters at early stages of bloom development. ► Grape clusters of resistant varieties produce toxic stilbens at BBCH 53. ► Toxic stilbens stop the development of downy mildew at BBCH 53. ► Functional stomata of grape clusters are transformed in lenticels after BBCH 53. ► After BBCH 53, resistance of grape clusters are not linked to stilben synthesis.