Bernadette Gagnier,* Maria Mireles, Inga Zasada, and Michelle Moyer
*Washington State University, 24106 North Bunn Road, Prosser, WA, 99350-8694 (bernadette.gagnier@wsu.edu)

The northern root-knot nematode (Meloidogyne hapla) is a prevalent plant-parasitic nematode in northern grapegrowing regions. This nematode induces small galls on roots that restrict water and nutrient uptake, resulting in poor vine establishment or exacerbated decline in stressed vines. Rootstocks can be a viable option for managing vine decline caused by M. hapla in commercial vineyards, but most screening efforts on grapevine rootstock tolerance to root-knot nematodes focus on Meloidogyne incognita, the southern root-knot nematode. This study reports the results of a greenhouse trial that screened nine Vitis spp. rootstocks (1616C, 99R, M4453, 140RU, Minotaur, SO4, SW, G3-5BB, and 1103P) and two Vitis vinifera controls (Chardonnay and Cabernet Sauvignon) against M. hapla. This experiment was conducted three times in two locations. Vines in 3.8-L pots were inoculated with 5000 M. hapla eggs, grown for three months, and then harvested destructively. M. hapla eggs were extracted from roots, counted, and the reproduction factor (Rf = final density/initial density) on each cultivar was calculated. An Rf > 1 indicates a susceptible host and an Rf = 0 indicates resistance (no reproduction). There was an impact of rootstock genotype on M. hapla Rf (p < 0.0001), driven by high Rf for V. vinifera Chardonnay (Rf = 56.5) and Cabernet Sauvignon (Rf = 30.9). M. hapla had lower Rf values on the non-vinifera rootstocks, although not all could be considered resistant. Rootstock M4453 is susceptible to M. hapla (Rf  = 13.03), while S04 (Rf = 0.96), G3-5BB (Rf = 0.03), 140RU (Rf = 0.17), 1616C (Rf = 0.013), SW (Rf =0.0086), Minotaur (Rf = 0.005), and 99R (Rf = 0.027) are poor hosts for M. hapla. M. hapla did not reproduce on 1103P (Rf = 0). These results provide a baseline for rootstock selection for commercial grapegrowers managing for M. hapla in their vineyards.

Funding Support: Washington State Grape and Wine Research Program; USDA National Institute of Food and Agriculture, Hatch project 1016563.