Host Suitability ofVitisandVitis-MuscadiniaMaterial to the NematodeXiphinema indexover One to Four Years

Abstract

The dagger nematode <i>Xiphinema index</i> specifically transmits <i>Grapevine fanleaf virus</i> (GFLV), which causes progressive grape degeneration in vineyards worldwide. Nematode-resistant rootstocks are a promising alternative to the ban of nematicides. We report the evaluation, under controlled conditions in two independent experiments, of the host suitability (reproduction factor, RF) of 40 <i>Vitis</i> and <i>Vitis</i>-<i>Muscadinia</i> accessions to the isofemale line Fréjus of <i>X. index.</i> In the first experiment, 17 accessions, grown from either in vitro culture or cuttings, were evaluated after 1 and 3 years and, for four accessions, also after 4 years. The nematode multiplied early and late on reference rootstocks <i>V. rupestris</i> du Lot and <i>V. riparia</i> Gloire de Montpellier, respectively. Among <i>Vitis</i>-<i>Muscadinia</i> material, after 1 and 3 years, accession VRH 8624 had high RFs, while VRH 8771 and NC 35–50 had RFs close to 1. The nematode-resistant candidate rootstock accession RPG1 (=VRH 8771 x <i>Vitis</i> rootstock 140Ru) and the intergeneric hybrid VRH 97-99-79 had RFs significantly higher at 4 years than at 1 year, suggesting a progressive adaptation of the nematode to the plant resistance factors. Most <i>Vitis</i> botanic accessions had high RFs at both 1-year and 3-year durations. Low RFs, observed for the remaining accessions, were probably due to the poor root development and the subsequent difficult access of nematodes to feeding on this material. In the second experiment, 23 <i>Vitis</i> accessions, evaluated only at 3 years, had high RFs, except for a few accessions that expressed low RFs and poor development. Thus some muscadine-derived intergeneric hybrids are promising resistance sources that must be confirmed using nematode lines from other geographic origins.