Phenotypic Variability in Non-grafted UCB-1 Pistachio Rootstock

Most pistachio rootstocks are currently F1 seedlings from controlled inter-specific crosses. These F1 seedlings are genetically variable because of the inherent heterozygosity of both parents. UCB-1 is a seedling rootstock that is widely used in commercial pistachio production. It’s parents are P. atlantica X P. integerrima. In 2013, 960 UCB-1 seedlings were planted near Davis, CA followed by an additional 264 seedlings one year later. This population is being used to investigate the UCB-1 phenotypic and genotypic variation and to look for superior UCB-1 individuals that might be used as clonal rootstock. Phenotypic measurements began after the first growing season, in January 2014. Data included, tree height, trunk caliper, and branching. There was high phenotypic variation in the planting. Tree height and caliper were weakly correlated during the first two growing seasons. The genomes of the parent trees and UCB-1 seedlings are being assembled and genotyping-by-sequencing of the whole population is underway. These genetic and phenotypic data will be combined to determine the genetic basis of stunting of some trees grafted onto UCB-1 rootstock.