Dipartimento di Scienze Agrarie e Ambientali - Produzione, Territorio, Agroenergia (DiSAA), Università degli Studi di Milano, via Celoria 2, 20133, Milan, Italy.
BMC Plant Biol. 2012 Aug 1;12:124. doi: 10.1186/1471-2229-12-124.
Grapevine downy mildew, caused by Plasmopara viticola, is a very serious disease affecting mainly Vitis vinifera cultivated varieties around the world. Breeding for resistance through the crossing with less susceptible species is one of the possible means to reduce the disease incidence and the application of fungicides. The hybrid Bianca and some of its siblings are considered very promising but their resistance level can vary depending on the pathogen strain. Moreover, virulent strains characterized by high fitness can represent a potential threat to the hybrid cultivation.
The host response and the pathogen virulence were quantitatively assessed by artificially inoculating cv Chardonnay, cv Bianca and their siblings with P. viticola isolates derived from single germinating oospores collected in various Italian viticultural areas. The host phenotypes were classified as susceptible, intermediate and resistant, according to the Area Under the Disease Progress Curve caused by the inoculated strain. Host responses in cv Bianca and its siblings significantly varied depending on the P. viticola isolates, which in turn differed in their virulence levels. The fitness of the most virulent strain did not significantly vary on the different hybrids including Bianca in comparison with the susceptible cv Chardonnay, suggesting that no costs are associated with virulence. Among the individual fitness components, only sporangia production was significantly reduced in cv Bianca and in some hybrids. Comparative histological analysis revealed differences between susceptible and resistant plants in the pathogen diffusion and cytology from 48 h after inoculation onwards. Defence mechanisms included callose depositions in the infected stomata, increase in peroxidase activity, synthesis of phenolic compounds and flavonoids and the necrosis of stomata and cells immediately surrounding the point of invasion and determined alterations in the size of the infected areas and in the number of sporangia differentiated.
Some hybrids were able to maintain an intermediate-resistant behaviour even when inoculated with the most virulent strain. Such hybrids should be considered for further field trials.
由葡萄霜霉病菌引起的葡萄霜霉病是一种非常严重的疾病，主要影响世界各地的栽培葡萄品种。通过与较不易感的物种杂交进行抗性育种是降低发病率和使用杀菌剂的一种可能手段。杂种 Bianca 及其部分同系物被认为非常有前途，但它们的抗性水平可能因病原体菌株而异。此外，具有高适应性的毒力菌株可能对杂种的种植构成潜在威胁。
通过用从意大利各个葡萄种植区收集的单个游动孢子萌发的卵孢子分离物人工接种 cv Chardonnay、cv Bianca 及其同系物，定量评估了寄主的反应和病原体的毒力。根据接种菌株引起的病害进展曲线下面积，将寄主表型分为敏感、中间和抗性。cv Bianca 及其同系物的寄主反应因接种的卵孢子分离物而异，这些分离物在毒力水平上也有所不同。最毒力菌株的适应性在包括 Bianca 在内的不同杂种上与敏感 cv Chardonnay 相比没有显著差异，这表明毒力没有代价。在个体适应性成分中，只有在 cv Bianca 和一些杂种中，游动孢子的产生显著减少。比较组织学分析显示，在接种后 48 小时及以后，敏感和抗性植物在病原体扩散和细胞学方面存在差异。防御机制包括感染的气孔中胼胝质的沉积、过氧化物酶活性的增加、酚类化合物和类黄酮的合成以及气孔和入侵点周围细胞的坏死，这决定了受感染区域的大小和分化的游动孢子的数量的改变。
一些杂种即使接种最毒力的菌株也能保持中间抗性的行为。这些杂种应考虑进一步进行田间试验。
