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

Abstract

Five rootstocks ( Vitis spp. hybrids) and a V. vinifera cultivar were phylloxera infested in standardized glasshouse trials in New Zealand and Germany. At the end of the second growing season the formation of tuberosities on the woody roots was evaluated. In both countries, highest frequency of tuberosities was found on roots of varieties ARG 1 and Muller-Thurgau. Tuberosities were rare on 3309 C infested by New Zealand phylloxera. Differences in the average degree of phylloxera tolerance, based on isolation of necroses by wound periderm, were small between the two countries, but significant in case of 420 A, SO 4, 1202 C and Muller-Thurgau. Phylloxera tolerance was scored as sufficient to good with varieties 420 A, SO 4 and 1202 C. 3309 C ranged medium, whereas ARG 1 and Muller-Thurgau were rated as sensitive. However, in ARG 1 infested by the New Zealand phylloxera necroses did not penetrate, even when wound periderm was lacking or incomplete. This rootstock is therefore assessed as having sufficient tolerance under New Zealand conditions, thus deviating from the numerical rating. 3309 C is, due to the low frequency of tuberosities, also considered as having practical tolerance to New Zealand phylloxera. The differences in tuberosity formation observed between the two experimental sites support further evidence of two different phylloxera biotypes between New Zealand and Germany.