The problem of phylloxera remains one of the most critical issues in global and domestic viticulture. Practitioners are well aware that the roots of certain grapevine species (such as the American rootstocks Vitis riparia, Vitis rupestris, etc.) suffer virtually no damage or are remarkably less affected by the pest. Conversely, the roots of the European vine (Vitis vinifera) rapidly degrade following the punctures of this insect, ultimately leading to the death of the vine.

Specialized investigations by prominent scientists (Millardet, Abesadze, Makarevskaya, Tskhakaya, and others) have proven that specific characteristics of the internal anatomical structure of the underground system form the basis of this variation (Fig. 11).

Anatomical Features of Resistant Grapevine Species

The high resistance of the roots of American grapevine species against phylloxera is determined by a comprehensive set of internal structural factors:

  • Tissue compactness: All internal cellular structures of the root are characterized by a high density of formation and considerable thickness of the cell walls.
  • Narrow medullary rays: Both primary and secondary medullary rays have a minimal width, which prevents the pest from easily reaching the deeper internal layers.
  • Small pith (medulla): The central part of the root is weakly developed and is devoid of excessive loose tissues.
  • Powerful phloem: The bast portion of the root is highly differentiated and provided with thick, strong layers of hard bast. Furthermore, these phloem elements lie very close to the surface, situated practically immediately beneath the outer suberized (cork) layer.
  • Double cork protection: A characteristic thickening of the cork layer forms over each medullary ray in resistant species. Concurrently, the old cortex, along with its cork cover, maintains a strong adhesion to the underlying tissues. Consequently, the root receives a double protective barrier of cork that is exceedingly difficult for the insect to pierce.

Anatomical Features of Susceptible European Varieties

In the roots of grapevines heavily infested by phylloxera (specifically within the European species Vitis vinifera), research has consistently demonstrated a diametrically opposite anatomical structure (Fig. 11):

  • Loose formation: The internal tissues of the root are characterized by large cell sizes and low structural density.
  • Wide pith and rays: The central portion of the root is highly developed, and the medullary rays (particularly within the phloem region) exhibit considerable width.
  • Weak phloem: The bast zone is poorly differentiated, and the layers of hard bast within it are thin and sparse. The phloem never approaches the outer protective layer closely. Instead, a very thick layer of large-celled cortical parenchyma always lies between them, serving as an easy target for the pest.
  • Deficient protection: The cork layer exhibits very weak adhesion to the underlying tissues of the cortical parenchyma, and cork thickenings over the medullary rays are completely absent. The overall thickness of the cork is not of decisive importance in this scenario, as the pest easily penetrates the non-dense tissues.

Wound Response and Tissue Maturation Rates

The anatomical character of the injuries and the cellular response to phylloxera punctures differ fundamentally among various grapevine species. In resistant American rootstocks, injuries from bites never penetrate deeply into the wood. The wound is always completely isolated from healthy areas due to the rapid development of a specialized layer of necrophylactic (protective) cork.

In susceptible European varieties, the protective cork within the wounds develops very slowly or fails to form entirely. Because of this, the insect's punctures induce deep and rapid destruction of all internal root tissues, extending to the very pith, which inevitably leads to the rotting and demise of the underground stem.

Furthermore, an important biological marker of endurance is the overall developmental rate of the underground organs. The roots of resistant grapevine species are characterized by a very early and rapid transition from the primary anatomical structure to the secondary one. In species susceptible to phylloxera, the development and maturation of tissues proceed in an extremely delayed manner, leaving the root defenseless against the pest for an extended period.