2009 WALNUT CLONAL ROOTSTOCK TRIAL - SOLANO COUNTY

The walnut industry has used two seed propagated rootstock for the entirety of its existence, black walnut seedling and Paradox hybrid seedling. Both of these seedling rootstocks have their own problems and issues. Blackline disease attacks both rootstocks but is more severe in black walnut. Paradox rootstock is extremely susceptible to crown gall. Even with these problems associated with them there is an over laying problem that stems from the fact that they are seedlings and that every tree’s rootstock has a different genetic makeup. This genetic variation leads to non-uniformity in the field related to size, vigor, compatibility, and disease susceptibility. To create a uniform orchard, other tree crops use clonal rootstocks that are created by vegetative propagation. The walnut industry realizes the benefit in this approach and has moved forward in the last decade through the Paradox diversity study to identify certain individual rootstocks that show characteristics for disease tolerance and vigorous growth habit. OBJECTIVES The Paradox Diversity Study resulted in the selection of three promising clonal rootstocks: Vlach, RX1, and VX211. This trial will test these rootstocks and include another clonal rootstock, Burbank, in comparison to each other and to the standard Paradox seedling. The trial will evaluate their growing characteristics, yield capability and possible disease tolerance. PROCEDURES The rootstocks were clonally 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; Vlach, RX1, VX211 and Burbank with Paradox seedling used as a control comparison. Vlach was the only variety that was not all grown 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. The rootstocks were planted in the field on March 31, 2009 in a Solano County orchard. Planting space was 18.5 x 24 feet in an offset design. Experimental design was a randomized complete block design with 6 replications. Each plot contains 10 trees two rows wide with 5 trees in each row. Measurements of caliper were taken before planting and trees were randomly mixed for each plot with the same ratio of small and large trees. Data was collected for tree height on Aug 9 th . Rootstocks were budded in August with the Tulare variety by a professional crew.