Evaluation of Grapevine Rootstock Selections

The primary purpose of this project is to identify selections from a USDA rootstock breeding program that might warrant release as commercial stocks. Dr. Gan-Yuan Zhong screened seedling elections for resistance to aggressive strains of root knot nematode shipping 30 such selections to Kearney in 2016, 40 in 2017, with the remaining 100 selections to be shipped in 2018. Selections are  rooted and outplanted at Kearney and, when established, will be screened for their potential as rootstock mother vines. Those with excellent traits will be advanced to replicated field trials as grafted vines. Any 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. It is not clear whether the failures were due to the stocks per se, or for some other reason. Vines on Freedom and own rooted vines in that trial have done much better than the vines on PC stocks, but the vines on Freedom were planted at a different time, and not budded in the field. Therefore, the PC selections will be replaced in 2018, and more closely monitored. The same rootstock selections were planted in Merced in September 2016, but will not be grafted until 2018. 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 new rootstock trial planted by Lindsay Jordan in 2016. The second Merced trial includes full rows of 1103P, RS3, RS9, GRN2, GRN3, GRN4, and GRN5 grafted to Malbec, and replicated four times. Jordan’s resignation in 2017 could have led to the abandonment of the trial. We collected petiole data from those vines last year, as Jordan planned, and decided to include the trial in this proposal, at least for the 2018 season. If this additional objective is supported, it will provide an opportunity to acquaint Karl Lund, Jordan’s replacement, with the trial. It will be decided later if it should be separated from the others. Petiole analyses from the Malbec trial revealed that the stocks differed with respect to uptake of nitrate, phosphorus, potassium, boron, calcium, zinc, and magnesium. It was also observed that most vines on GRN5 failed, whereas most of the other vines are becoming established.  Therefore, GRN5 will be eliminated from the trial. It is anticipated that preliminary fruit quality and yield data may be collected from the second trial in Merced in 2018.