The Vitis vinifera x V. rotundifolia hybrids as phylloxera resistant rootstocks

In greenhouse and field tests of rooted vines and seedlings, a considerable number of vinifera X rotundifolia F1 hybrid clones exhibit high tolerance or immunity to the root form of phylloxera, as judged by the formatirm of lesions or the insects found lodged on the roots.The formation of root lesions is related to the anatomical structure, the more closely it resembles the rotundifolia, the fewer and smaller the lesions.Phylloxera samples from five different areas in California have not been found to differ in gross morphology or in their reaction to the VR hybrids.The species rotundifolia contributes genes exhibiting considerable dominance for resistance in the F1 generation.Unlike the rotundifolia parent, the VR hybrids can be successfully used as rootstocks for vinifera grapes, although observations are only for eight years and hence preliminary.Although the VR hybrids are less easy to propagate than many common rootstocks, the variation is great enough between clones to permit selection