Hop Stunt Viroid: Effects on Vegetative Growth and Yield of Hop Cultivars, and Its Distribution in Central Washington State.

Hop stunt viroid (HSVd) is an economically important pathogen that reduces growth and yield of hops. Visual symptoms of infected hop are highly dependent on cultivar. A study was conducted using six cultivars of hop to determine the impact on yield. Average dry cone yields of infected 'Glacier', 'Cascade', and 'Willamette' were reduced by 62, 14, and 34%, respectively, relative to noninoculated healthy plants. No significant yield reduction was observed for 'Nugget', 'Columbus', and 'Galena'. The α-acid and β-acid contents showed a parallel pattern. Horticultural parameters of Willamette and Nugget were measured in the final year of the study. Internode length, shoot length, and side-arm length were reduced by 29, 26, and 73%, respectively, for infected Willamette bines relative to noninfected bines; no effects were observed resulting from infection of Nugget. To understand the current potential impact of HSVd, a survey was conducted to determine its distribution in central Washington. The survey revealed that 17% of hop plants tested are infected. Hop yield and hop plant longevity will be significantly affected by this level of infection.