2013 SOLANO COUNTY CLONAL PARADOX ROOTSTOCK TRIAL

The California walnut industry utilizes two seedling rootstocks for commercial production, Northern California Black (Juglans hindsii) and Paradox hybrid seedling (Juglans hindsii x Juglans regia). Both rootstocks are open pollinated resulting in genetic variability. This genetic variation leads to non-uniformity in the field related to size, vigor, compatibility, and disease susceptibility. Due to superior vigor, better adaptability to marginal soils and greater tolerance to Phytophthora crown and root rot, Paradox is the preferred rootstock for Northern California. Recent technology has resulted in micropagation and commercial availability of three new clonal walnut rootstocks, RX1, VX211 and Vlach. Clonal rootstocks have several horticultural advantages. First, they can be selected for desirable attributes such as disease resistance, nematode tolerance and vigor giving farmers the opportunity to match rootstock selection with planting sites. Second, they will impart less genetic variability and be more predictable in the orchard. Disadvantages include the loss of genetic diversity in orchard plantings and additional expertise is required to micropropagate, nursery culture and graft to produce a commercially viable product. A trial was planted in Solano County to evaluate Burbank, RX1, Vlach and VX211. Paradox seedling was also planted as the control. By 2013, there were no significant differences in scion circumference or yield among the clonal rootstocks. OBJECTIVES To evaluate the three newly released clonal paradox rootstocks and other test selections, a rootstock trial was planted in Solano County. The plot evaluates five rootstocks includes Burbank, RX1, Vlach and VX211 with Paradox seedling as the control comparison. The trial evaluates growth characteristics, yield potential and possible disease tolerance. PROCEDURES The rootstocks were clonal propagated by the UC Walnut Breeding Program and were grown for the first season at a commercial walnut rootstock nursery. The trial contains four clonal rootstocks; Burbank, RX1, Vlach, VX211 and Burbank with Paradox seedling used as the control comparison. Vlach was the only variety that was not grown all in the same nursery and the same clonal propagation. The portion of Vlach that was grown in the same environment as the other is labeled Vlach-1 and the Vlach from the other nursery is labeled Vlach-2. Vlach-2 was grown for two seasons in the nursery while Vlach-1 was only grown one season in the nursery.