'Taking the strain' - Selecting the right rootstock to protect against endemic phylloxera strains

In Australia 83 genetically different endemic grapevine phylloxera strains have been characterised which vary in their geospatial distribution on both ungrafted and grafted Vitis vinifera under field conditions. Damage levels on V. vinifera also differed depending on which phylloxera strain was present. In order to understand the interactions which may influence phylloxera distribution and vine damage levels, and also develop sustainable rootstock resistance ratings, screening trials were conducted under controlled conditions. Bioassays where conducted under both laboratory and glasshouse conditions. Assessments were carried out using eleven Vitis rootstock types and six genetically diverse strains of grape phylloxera. These assessments were done using both excised roots (in vitro) and whole plant (in planta) bioassays, to allow quantification of both phylloxera development and mature lignified root response. Different phylloxera strains differed in population survival and development on both V. vinifera and grafted rootstock hybrids and in addition root physiological response differed between phylloxera genetic strains and rootstocks. Based on these assessments rootstocks were classed as resistant, tolerant or susceptible. A summary of 'genotype-specific' rootstock resistance ratings, based on laboratory and glasshouse screening conducted to-date, for phylloxera resistance are presented. These results highlight the need for further studies focusing on the genotype-specific interactions between the host plant and the insect pest, particularly under a range of experimental conditions.