Term for cancerous, scabby and elongated deformities (tuberous = tumour-like), the formation of which is induced on the old (2 to 3-year-old) roots when attacked by phylloxera. They are much more dangerous than nodosities (tangles only on young roots). In the European grape varieties of the species Vitis vinifera (but also all other non-resistant species), the tuberosities penetrate through the medullary canals of the root to the central vascular system. Either already through this or through later invading secondary pathogens such as bacteria or fungi, the root is so severely damaged that it dies within one to two years from the point of infestation. The result is a considerable reduction of the root mass and consequently a reduced nutrient and water uptake. In the early stages, this leads to stunted growth and later to the death of the vine. Even a few grape aphids can cause dramatic damage to vineyards due to the devastating consequences of this infestation.
In rootstock varieties derived from the vine blight-tolerant American species Vitis cinerea var. helleri (Vitis berlandieri), Vitis riparia and Vitis rupestris, the tuberosities do not penetrate as deeply into the root due to a narrower arrangement of the medullary rays, they remain more superficial and are also completely sealed off by the plant by a protective cork tissue. Since the growths do not break through to the central vascular system, or at most only in exceptional cases, the roots survive such an infestation almost unscathed and there are no dramatic consequences as with the European Vitis vinifera varieties. Many American wild forms as well as crosses between them are in this way able to tolerate a phylloxera infestation very well. They are therefore preferred for breeding resistant rootstocks. Varieties derived from Vitis cinerea and Vitis rotundifolia even possess complete resistance to both types of phylloxera-induced root growth.
The left picture shows a microscopic section through a phylloxera attack on an older European grapevine root with resulting tuberosity with a hole-like depression penetrating far into the interior of the root. The right picture shows a microscopic section through a tuberosity on an American grapevine. The tuberosity has been sealed off by the formation of cork tissue. As a solution against phylloxera, grafting is practised worldwide today, in which a European scion is grafted onto an American rootstock. See also under vine enemies.
Source: Phylloxera - WIKIPEDIA German edition
Root phylloxera: By Joachim Schmid, Geisenheim, - Photographed by himself, CC BY 3.0 en, Link 1 and Link 2
European and American grapevine: J. Schmid, F. Manty, B. Lindner, ISBN 978-3-934742-56-7, GFDL 1.2, Link 1 and Link 2
Phylloxera: From unknown - Meyers, Public domain, Link
Tuberosities: LWG Bayern
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