Characterization of isolates of Xanthomonas arboricola pv. corylina, the causal agent of bacterial blight, from Oregon hazelnut orchards

Authors: WEBBER, JOHN - Oregon State University; PUTNAM, MELODIE - Oregon State University; SARDANI, MARYNA - Oregon State University; PSCHEIDT, JAY - Oregon State University; WIMAN, NIK - Oregon State University; Stockwell, Virginia

Submitted to: Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2020
Publication Date: N/A
Citation: N/A

Interpretive Summary: Hazelnuts are consumed in the US as roasted nut products and processed nut products, like hazelnut butter and Nutella. About 99% of commercial US hazelnuts are produced in Oregon. In the 1980's, a pathogen causing the devastating fungal disease of hazelnut called Eastern Filbert Blight was introduced in Oregon and threatened future production. The hazelnut breeding program at Oregon State University recently developed new cultivars resistant to Eastern Filbert Blight. Growers are planting over 8,000 acres of each year of the new resistant cultivars, bringing the total acreage of hazelnuts in Oregon to more than 80,000 acres. In five years, yields are expected to reach 90,000 tons annually. Unfortunately, in several areas of Oregon, young hazelnut trees are dying due to a re-emerging disease called bacterial blight of hazelnut. The bacterial pathogen is called Xanthomonas arboricola pv. corylina. The damaging disease was first described in Oregon in 1915, but bacterial blight of hazelnut in Oregon was rarely reported since the 1970s. We initiated a project to characterize the bacterial pathogen from this new outbreak, test sensitivity of the pathogen to copper, which is used for disease control, and to screen new cultivars and breeding stocks of hazelnut for resistance to this disease. This manuscript focuses on the characterization of the pathogen using genetic tests and physiological test, and the ability to cause disease. We found that there are two different genetic groups of the pathogen in Oregon, but there was no significant difference in the ability of either group to cause disease on hazelnut. This means that the isolates that we collected from Oregon hazelnut orchards represent the known diversity of the pathogen. The representative isolates of the pathogen are a valuable resource to screen hazelnut cultivars for tolerance to bacterial blight. We also found that the pathogen is sensitive to copper, so well-timed copper sprays may protect young trees from bacterial blight of hazelnut.

Technical Abstract: Bacterial blight (Xanthomonas arboricola pv. corylina (Xac)) of hazelnut (Corylus avellana L.) was described first in Oregon in 1915 and is now recognized as a damaging disease of young hazelnut trees worldwide. Thousands of hectares of new hazelnut cultivars that are resistant to eastern filbert blight (Anisogramma anomala) are being planted in the Willamette Valley of Oregon, where 99% of the US hazelnut crop is grown. Reports of bacterial blight on young hazelnut trees have increased, information about the pathogen that causes this disease is limited. We characterized bacterial isolates from tissues with bacterial blight symptoms for their ability to grow on semi-selective media, nutrient utilization profiles with Biolog GN2, quinate metabolism, copper tolerance, hypersensitive response on tobacco, and pathogenicity on hazelnut. Additionally, isolates were identified with a duplex PCR assay (ftsX and qumA), 16S rRNA sequence, and multi-locus sequence analysis using rpoD and gyrB. Pathogenic isolates were identified as Xac using morphological, biochemical, and molecular assays. With MLSA, Xac isolates separated into two clades, one clade with the type strain and a second clade described in isolates from Europe. Thus, the phylogenetic diversity of Xac observed in other countries also is present in Oregon.