Cloning and characterization of the dagger nematode resistance gene XiR1


The dagger nematode, Xiphinema index, feeds aggressively on grape roots and in the process vectors grapevine fanleaf virus (GFLV) leading to the severe viral disease known as fanleaf degeneration. Disease symptoms consist of disrupted fruit set caused by GFLV and depressed plant growth caused by root damage from X. index. The use of fumigants to control X. index in vineyards is no longer recommended because of their high cost, detrimental environmental effects and lack of effective soil penetration to control nematodes on a deep perennial root system. Therefore, resistance to X. index has been an important objective in grape rootstock breeding programs. We previously demonstrated that resistance to X. index derived from a Vitis arizonica/girdiana hybrid b42-26 was largely controlled by a major quantitative trait locus, XiR1 (X. index Resistance 1) located on chromosome 19. Genetic studies leading to the isolation and characterization of the genes conferring resistance to X. index would further our understanding of resistance and assist molecular and classical breeding efforts to control X. index. In this report, we present the development of high resolution genetic and physical maps in the XiR1 region as well as the isolation of the XiR1 locus by a positional cloning approach. This study has identified the first locus responsible for ectoparasitic nematode resistance. The markers developed from this study are being used to expedite the breeding of resistant grape rootstocks.


Environmental Plant Science and Natural Resources

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Acta Horticulturae