Further evidence of phylloxera biotypes : variations in the tolerance of mature grapevine roots related to the geographical origin of the insect

In a previous paper evidence was shown that strain or biotype differences existed between a New Zealand and a German phylloxera population (King and Rilling 1985). While the study tested the resistance of leaves and rootlets to galling, the present investigation focussed on the tolerance of the woody roots to attack by these two phylloxera populations.