2017 ASHS Annual Conference

UCB-1 is widely used in California as a pistachio rootstock because of its Verticillium resistance, salt and cold tolerance, and vigor. It can grow in most locations in California. However, significant variation exists in the phenotypic performance of trees grafted to seedling UCB-1 rootstocks. In July 2013, 961 UCB-1 seedlings were planted near Davis, CA to evaluate phenotypic and genotypic variation in this segregating population. This report focuses on growth performance and how the population’s phenotypic dynamics have changed over the first three years in the field. Annually, data were collected on tree height, trunk caliper, canopy height and diameter, and branching characteristics. The growth dynamics of the population changed as the trees aged, with the greatest uniformity during the first year, and increasing variation in the population in later years. First year growth performance is poorly correlated with that of subsequent years, especially for tree height, caliper, and branching. Therefore, selection for vigorous or weak phenotypes early is the life of the trees misses much of the subsequent variation and is less effective than desirable.