Susceptibility of Some L. Cultivars to pv. .

Bacterial blight of hazelnut ( L.) is caused by pv. (Xac). In the past, bacterial blight has been a key disease impacting the Oregon hazelnut industry where 99% of the United States hazelnut crop is grown. The disease is re-emerging in young orchards, as acreage of newly released hazelnut cultivars rapidly increases. This increase in hazelnut acreage is accompanied by renewed interest in developing control strategies for bacterial blight. Information on susceptibility of hazelnut cultivars to Xac is limited, partially due to lack of verified methods to quantify hazelnut cultivar response to artificial inoculation. In this research, Xac inoculation protocols were adapted to two hazelnut growing environments to evaluate cultivar susceptibility: tissue culture under sterile and controlled conditions, and potted tree conditions. Five hazelnut cultivars were evaluated using the inoculation protocol and seven hazelnut cultivars were evaluated using the inoculation protocol. Under conditions, there were severe bacterial blight symptoms on each cultivar consistent with those seen in the field, but no significant differences in the susceptibility of the newly released cultivars were observed compared to known Xac-susceptible cultivar ("Barcelona"). Under conditions, the proportion of necrotic buds were significantly higher in "Jefferson" and "Dorris" compared to all of the other tested cultivars, including "Barcelona." The symptom progression seen mirrored the timing and symptom progression of bacterial blight reported from field observations. The conditions significantly reduced the amount of time required to measure the inoculation efficiency compared to the environment and allowed for greater replication. Further studies on the effects of Xac can use the results of these experiments to establish a dose-response model for bacterial blight, a wider range of germplasm can be tested under conditions, and management strategies that can be evaluated on large populations of new cultivars using the methods.