Host Suitability ofVitis californicaBentham to Grape Phylloxera,Daktulosphaira vitifoliae(Fitch)

Abstract

The reportedly phylloxera-susceptible California native grape <i>Vitis californica</i> Bentham continues to be widely distributed despite the presence of grape phylloxera <i>Daktulosphaira vitifoliae</i> (Fitch). We collected roots of three <i>V. californica</i> plants from one Oregon and each of six California counties and evaluated them by laboratory bioassay for susceptibility to the two known California phylloxera biotypes, A and B. The two biotypes performed similarly to each other on all but two <i>V. californica</i> plants. Susceptibilities varied irrespective of collection site or proximity to known phylloxera infestations. In comparisons with standard resistant (the hybrid rootstock cultivar AxR#1) and susceptible (<i>Vitis vinifera</i> L. cultivar Cabernet Sauvignon) hosts, one <i>V. californica</i> plant was less suitable as a host than AxR#1, 11 plants were equal in host suitability to AxR#1, seven plants were intermediate or equal in host suitability to Cabernet Sauvignon, and three plants indicated mixed responses. The paucity of grape phylloxera on susceptible <i>V. californica</i>, even in regions where the insect is common in vineyards suggests that the resistance has not evolved in response to the introduction of phylloxera into the state.