NODOSITY POPULATIONS ON ROOTSTOCKS ARE NOT A CURRENT THREAT TO CALIFORNIAN VINEYARDS
Previous research in California suggested that nodosity phylloxera were increasing on pure American Vitis rootstocks, and were associated with vineyard decline. Bioassays showed that ability on nodosities was a genetic trait and not due to site conditions. Lack of virulence on V. vinifera and AXR#1 suggested that these phenotypes were not Biotype A or B. Hypotheses we tested were: 1) rootstocks select for single cultivar host races, 2) nodosities cause damage by producing phylloxera which spread soil borne fungal pathogens to mature roots via probing, and 3) high nodosity populations on rootstocks are not yet common, but are associated with vine decline. Bioassays of colonies from 1103 Paulsen, 101-14 Mgt. and Teleki 5C in a single vineyard block showed that host-of-origin for a colony was not correlated with elevated virulence in relation to other host-of-origin colonies. This suggests that these hosts-of-origin did not select differentially. Although nodosities are not conclusively associated with vine damage anywhere in the world, nodosity based damage appeared to occur in some field sites. A greenhouse test of phylloxera feeding, fungal infections and root health did not support expectations that nodosity phylloxera populations could spread fungal infections to mature roots through stylet probing. We surveyed for phylloxera on rootstocks in three California counties and found many nodosity populations. No phylloxera associated vine damage was seen suggesting that previous observations of nodosity based vine damage were due to other site related factors. Our research supported the idea that nodosity forming phylloxera have become common on many rootstocks, but do not cause direct vine damage. Because these phylloxera do not form damaging tuberosities, they do not directly threaten California viticulture.
Granett, J. and Walker, M.A. 2009. NODOSITY POPULATIONS ON ROOTSTOCKS ARE NOT A CURRENT THREAT TO CALIFORNIAN VINEYARDS. Acta Hort. (ISHS) 816:23-28
Vitis vinifera, grape phylloxera, nodosities, tuberosities, rootstocks, resistance