GENETIC ANALYSIS OF ROOT-KNOT NEMATODE RESISTANCE DERIVED FROM VITIS MUSTANGENSIS

Abstract

Root-knot (Meloidogyne species) are serious pests in grape production, especially in warm areas. Rootstocks resistant to root-knot are used to combat these pests. Nematode resistant rootstocks used in the United States include Freedom, Harmony, Dog Ridge, and Ramsey. The nematode resistance in these varieties is thought to be derived from Vitis mustangensis (all four rootstocks) or V. mustangensis and V. solonis (Freedom and Harmony). Dog Ridge and Ramsey are considered natural V. mustangensis hybrids, while Freedom and Harmony are complex hybrids that include Dog Ridge in their parentage. These rootstocks all apparently owe their resistance to the allele. Although these rootstocks are resistant to many M. incognita populations, M. arenaria and M. incognita populations have been identified in California that are virulent on these rootstocks, damaging them severely. These N virulent nematodes pose a new and significant threat to grape production in the United States. New rootstocks are needed with resistance to the virulent nematode populations. We have identified several Vitis species that provide resistance to virulent and are investigating the genetic control of the resistance. We examined progeny populations from crosses with V. mustangensis and V. mustangensis hybrids. Seedlings were grown in a greenhouse and inoculated with root-knot nematode juveniles once two true leaves were present. Resistance evaluation was by egg mass counting six weeks after inoculation. Resistance to virulent was inherited as a single dominant allele and appears to confer resistance both to the virulent Meloidogyne sp. and avirulent M. incognita nematodes. The V. mustangensis accessions used in this genetic study are sources of resistance superior to that found in Dog Ridge, Freedom, and Harmony. Vitis mustangensis promises to be a useful source of nematode resistance for use in rootstock breeding.