Development of next generation rootstocks for California vineyards

Since my last report (June 2019) Nina Romero has made excellent improvements to
our rootstock screening and is currently re-vamping our ring nematode resistance screening, and she has replaced three technicians who departed over the past year. There are 444 genotypes in testing for resistance to nematodes, salt or both. Our 2019 crosses again focused on using fertile and tetraploid VR hybrids to get rotundifolia forms of resistance into better rooting backgrounds, and mostly failed (due to the genetic distance between Vitis grape species and rotundifolia. We have been successful with crosses to two VR hybrids both of which resist phylloxera and combined with rootstocks. Seed from the 2018 crosses are mostly in storage for the next grape breeder, except for the 18113 (GRZN3 x V. acerifolia 9018. Chris Chen is working on his PhD with this population which brings excellent and broad nematode
resistance to our best form of salt tolerance (which also has strong root-knot resistance). We have improved our phylloxera screening in the greenhouse and have verified a number of fertile VR hybrids also have strong phylloxera resistance. A new post-doc (Erin Galarneau from the Baumgartner lab) was hired to direct examinations of phenolic compounds responsible for phylloxera and nematode resistance. They will also assist our efforts to determine how O39-16 induces fanleaf degeneration resistance. We are also making good progress on identifying the basis of red leaf virus tolerance. These efforts are being directed by a visiting scholar from China. We have rootstock examples of strong tolerance (St. George and AXR1) and very sensitive (Freedom and 101-14) and rapid tissue-culture and greenhouse-based
screens that are rapid and mimic field tests.