The purpose of this project is to identify selections from a USDA rootstock breeding program that might warrant release as commercial stocks, and to develop useful data on the performance of recently released rootstocks from other breeding programs to aid growers in selecting appropriate stocks for their vineyards. For the past several years Dr. Gan-Yuan Zhong, USDA-ARS, screened seedling selections for resistance to aggressive strains of root knot nematodes and shipped cuttings of resistant selections to the UC Kearney Agricultural Center in Parlier, CA, where they were rooted and planted into a vineyard for observation. Thirty selections were sent in 2016, 40 in 2017, and the remaining 112 selections in 2018. The vines will be grown at Kearney for three years before being screened for their potential as rootstock mother vines. Cuttings of vines with excellent traits will be challenged with a multi-species inoculum of plant parasitic nematodes, in collaboration with Dr. Andreas Westphal. Genotypes showing excellent mothervine traits and superior resistance to root knot nematode and/or broad resistance to multiple parasitic nematode species, will be advanced to replicated field trials as grafted vines. Stocks that show excellent potential as grafted vines will be referred to the USDA for consideration of release.
Currently five selections (PC0333-5, PC0349-11, PC0349-30, PC04153-4, and PC0597-13), have advanced to a replicated trial in a commercial table grape vineyard in Delano, and six selections (the same five from Delano plus PC0495-51) are in a replicated trial in a commercial winegrape vineyard in Merced. The vines in Delano were planted in summer, 2016, and grafted to Autumn King in 2017, but many of the PC selections failed after budding and were thus replanted in 2018 and are becoming established. The same rootstock selections were planted in Merced in September 2016, but will not be grafted until 2019. The replanting in Delano, and the grafting in Merced, should resolve questions about the potential, if any, of these selections as young grafted vines. The Merced trial is adjacent to another rootstock trial planted by former UCCE advisor Lindsay Jordan in 2016. The second Merced trial includes full rows of 1103P, and more recently released stocks including RS3, RS9, GRN2, GRN3, GRN4, and GRN5 grafted to Malbec, and replicated four times. However, most vines on GRN5 failed, so GRN5 was eliminated from the trial. Vine training in this trial was mostly completed in 2018, and petiole and nematode samples were collected. These preliminary data suggest the various stocks may affect vine nutrition and that they might differ with respect to nematode resistance. It is anticipated that the first fruit quality and yield data will be collected from the Merced trial in 2019.