Nematode-resistant rootstocks as a major component of the management alternative for grapevine fanleaf virus control in grape

The ectoparasitic dagger nematode Xiphinema index specifically transmits Grapevine fanleaf virus (GFLV) which is responsible for a progressive degeneration of grapevines occurring in most vineyards worldwide. Because of the ban on nematicides and of the economically unacceptable interval (>7 years) required for nematode eradication between two successive vines, alternative nematode management strategies must be developed. In this context, natural resistance appears a promising control alternative even though the long developmental cycle of the crop highly increases the risk for resistance breaking. A high resistance to X. index has been detected in the muscadine grape Muscadinia rotundifolia and attempts to introduce this resistance into rootstocks to obtain agronomically suitable candidate rootstocks have been difficult. A few M. rotundifolia × Vitis F1 hybrids and one BC1 individual (designated RPG1) were shown to express a good level of resistance. A range of X. index isofemale lines created from representative populations from the world nematode dispersal area are available for challenging the resistance of rootstock material. Significant pathogenicity differences between lines have been shown and data suggest no interactions between nematode lines and resistant accessions. RPG1 shows a delayed viral contamination under field conditions. Nevertheless, under controlled conditions, a progressive adaptation of the nematode to the plant resistance factors seems to occur in observations up to 4 years and better performing nematode-resistant hybrid material is being selected to cumulate muscadine resistance and partial Vitis resistance. In an integrated control strategy, this resistance strategy might be associated to the cultivation of non host or antagonistic crops between two vines.