Daniel Pap, Summaira Riaz, Rebecca Wheeler-Dykes, Nina Romero, and M. Andrew Walker*
*Department of Viticulture and Enology, UC Davis, Davis, CA 95616 (awalker@ucdavis)

A rootstock carrying resistance to wide range of Phylloxera and root-knot nematode strains would be a useful tool to combat these soil-borne pests. The collapse of AxR1 in California identified a new biotype of Phylloxera and root-knot nematode strains have overcome the resistance of Harmony and Freedom rootstocks. The means by which these pests adapt to rootstocks is uncertain; however, the narrow genetic base of rootstocks may increase the chance that new, virulent pathotypes arise. The most commonly used rootstocks in California were developed ~100 years ago in Europe, and most have parentage that traces back to a single accession of V. berlandieri, V. rupestris or V. riparia. There is a need to widen the genetic base of resistance by thoroughly examining wild Vitis germplasm and breeding rootstocks from novel forms of resistance. Some resistance is specific and only manifests during infection in the form of a hypersensitive reaction, thus preventing pest feeding completely. Other types provide tolerance to feeding, but are tolerant of a wide range of pathotypes. In this ongoing study, we are discovering new and specific resistance sources, focusing on specific resistances to develop new breeding lines, and developing mapping populations capable of identifying genomic regions associated with specific resistance to optimize rootstock breeding with DNA-based marker assisted selection.

We gratefully acknowledge research funding from the California Grape Rootstock Improvement Commission.

Funding Support: California Grape Rootstock Improvement Commission