The 2013 crosses focused on developing rootstocks with deeper root systems, the genetics of root architecture traits, and introgressing the excellent soil pest resistance from rotundifolia into rootstocks using semi-fertile vinifera x rotundifolia (VR) hybrids (see Table 1). This may also be a way to incorporate fanleaf tolerance and allow improvement of O39-16. VR hybrids are normally sterile but a few were selected by Olmo to have some fertility. Unfortunately they are also crosses with vinifera so we must be assured of their phylloxera resistance (studies underway).
GRN Field Trials – This was the first year data was gathered from GRN rootstock trials; most of which are being overseen by farm advisers and Constellation. We took crop yields at a trial in Dunnigan with Franzia and another in Lodi with Gallo. This data will be combined with pruning weights (not yet taken) and presented with the next report and as a bulletin to nurseries and cooperators.
Nematode testing – We work closely with Howard Ferris and his technician to evaluate the nematode resistance of rootstock breeding populations. Nin Romero (my chief greenhouse and field technician) propagated and assisted with the nematode resistance screening of hundreds of seedlings this year. Nina and I first examined the populations and evaluated them for brushy growth, internode length, and vigor. Most were also evaluated for their ability to root from dormant cuttings. They were tested for resistance to the Harmony/Freedom aggressive root-knot strains (HarmA and HarmC) and Xiphinema index, and many were also screened for ring nematode resistance. The best 21 are shown in Table 2 and will be advanced to field testing on the UC Davis campus with 101-14 and 1103P comparison controls.
Fanleaf – We continue to make progress on identifying and verifying the function of the Xiphinema index resistance gene from V. arizonica b42-26, and it resistance locus XiR1. Two gene candidates are members of the NB-LRR (nucleotide binding-leucine rich repeat) resistance gene family that control recognition of pests and diseases and the triggering of a defense reaction. These two candidates were transformed into St. George and Thompson Seedless and they reduced susceptibility to X. index resistance, but the transformed plants were still susceptible. There are more lines to test and we are examining gene expression with qPCR and will pursue native promoters to determine if they can increase resistance.