HOST SUITABILITY OF VITIS-CALIFORNICA BENTHAM TO GRAPE PHYLLOXERA, DAKTULOSPHAIRA-VITIFOLIAE (FITCH)

The reportedly phylloxera-susceptible California native grape Vitis californica Bentham continues to be widely distributed despite the presence of grape phylloxera Daktulosphaira vitifoliae (Fitch). We collected roots of three V. californica 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 V. californica 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 (Vitis vinifera L. cultivar Cabernet Sauvignon) hosts, one V. californica 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 V. californica, 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.