Abstract
Crown gall of walnut (Juglans sp.), caused by the bacterium Agrobacterium tumefaciens, greatly impacts the CA walnut industry. To determine the genetic diversity of A. tumefaciens throughout the Central Valley of CA, we collected isolates from 12 walnut growing counties. A total of 340 A. tumefaciens biovar 1 isolates were collected and tested for the presence of the Ti plasmid by PCR; 267 isolates were Ti-plasmid positive or virulent. To assess genetic diversity, BOX PCR profiles were generated for the confirmed virulent isolates. Additionally, we tested the ability of the biocontrol agent A. rhizogenes K84 to inhibit the growth of virulent A. tumefaciens biovar 1 isolates. Further analysis of the genetic heterogeneity and K84 sensitivity of CA A. tumefaciens isolates will facilitate the design of effective crown gall management strategies, including more precise application of K84 depending on A. tumefaciens genotype present.