Fröbel Sarah, Zyprian Eva
Julius Kühn-Institut, Institute for Grapevine Breeding Geilweilerhof, Siebeldingen, Germany.
Front Plant Sci. 2019 Jul 24;10:951. doi: 10.3389/fpls.2019.00951. eCollection 2019.
, the downy mildew pathogen, is one of the most important pathogens in European viticulture. This oomycete infects grapevine leaves via zoospores that encyst at stomata. A primary germ tube then enters the substomatal cavity and develops a tubular network of hyphae that proliferate intercellularly and parasitize the leaf mesophyll cells by haustoria. Leaf infections have thus been the primary object of multiple studies concerning the physiology of the pathogen and defense reactions of grapevines. Besides leaves, this oomycete pathogen is able to spread throughout the plant tissue. As shown here by microscopy, it colonizes leaf petioles, shoots, berries and seeds. Evidence is provided showing that this process is facilitated by formation of special fan-shaped hyphae that seem to be necessary to overcome physical barriers in plant tissues. Physical obstacles are mainly constituted by vascular tissue in leaf veins, leaf petioles and shoots. In grapevine shoots, the mycelium seems to extend along the cambial layer between xylem and phloem tissue. Infected young berries are completely colonized on the inside. Older infected "leather berries" show glossy appositions of the fan-shaped hyphae at the inner side of the berry skin. The seeds from that stage of infestation are devoid of endosperm and embryo and biologically dysfunctional. Furthermore, a classification system for infection based on the degree of infections in petioles and shoot tips is presented. This study contributes to a better understanding of downy mildew pathogenesis in grapevine, a prerequisite for efficient control measures.
霜霉病菌是欧洲葡萄栽培中最重要的病原菌之一。这种卵菌通过在气孔处形成包囊的游动孢子感染葡萄叶片。随后，一根初生芽管进入气孔下腔，并发育出一个管状菌丝网络，该网络在细胞间增殖，并通过吸器寄生叶肉细胞。因此，叶片感染一直是关于该病原菌生理学和葡萄防御反应的多项研究的主要对象。除了叶片，这种卵菌病原菌还能够在整个植物组织中传播。如显微镜观察所示，它定殖在叶柄、嫩梢、浆果和种子中。有证据表明，这一过程是由特殊扇形菌丝的形成所促进的，这些菌丝似乎是克服植物组织物理屏障所必需的。物理障碍主要由叶脉、叶柄和嫩梢中的维管组织构成。在葡萄嫩梢中，菌丝体似乎沿着木质部和韧皮部组织之间的形成层延伸。受感染的幼嫩浆果内部完全被定殖。受感染的老“皮浆果”在浆果表皮内侧显示出扇形菌丝的光滑附着。处于该侵染阶段的种子没有胚乳和胚，且生理功能失调。此外，还提出了一种基于叶柄和梢尖感染程度的感染分类系统。本研究有助于更好地理解葡萄霜霉病的发病机制，这是采取有效防治措施的前提条件。
