|Woods, J -|
|Putnam, M -|
Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 30, 2012
Publication Date: N/A
Interpretive Summary: In 2006, an outbreak of the disease Verticillium wilt of hop was detected on a farm in Oregon, affecting several cultivars including Willamette and Nugget, which are the mostly planted cultivars in Oregon. The following year wilted plants of cultivar Willamette were detected on a second farm in Oregon. Verticillium wilt on hop can be caused by both two pathogens, and the appropriate management response depends on which pathogen attacks the crop and how much disease that pathogen can cause. In this research we found that the pathogen responsible for the new outbreaks of Verticillium wilt was the fungus Verticillium albo-atrum. Experiments to determine how virulent the strains of the pathogen were to hop indicated that the strains were not lethal. This finding was supported by observations of the pattern of diseased and dead plants in a hop yard in 2006 and 2007. The overall findings are consistent with previous reports of V. albo-atrum on hop in Oregon and suggest that lethal strains of V. albo-atrum are not yet present, or prevalent, in this state.
Technical Abstract: In 2006 and 2007, new outbreaks of Verticillium wilt on hop were detected on two farms in Oregon. Verticillium pathogens vary in their virulence to hop; some strains cause minor damage but others can kill susceptible cultivars. Studies were conducted to determine the identity of the Verticillium species associated with these outbreaks and their virulence to hop. Sixteen isolates were recovered from wilted plants in two yards, and were identified as V. albo-atrum based on morphological characters and sequence data of the ITS region. Pathogenicity assays conducted on a set of cultivars with differential susceptibility to Vertcillium wilt indicated all isolates had a low to intermediate level of virulence. Disease assessments in a hop yard indicated that 29.3% and 19.7% of plants had symptoms of Verticillium wilt in 2006 and 2007, respectively. However, the number of dead or missing plants did not increase from 2006 to 2007 (0.26% in both years). There was a clear directionality to the pattern of symptomatic plants among rows running north-south vs. east-west in 2006, although this directionality was less pronounced in 2007. The overall findings are consistent with previous reports of V. albo-atrum on hop in Oregon and suggest that lethal strains of V. albo-atrum are not yet present, or prevalent, in this state.