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Poster: Biology & Disease Mgmt: Virology


Detection, Distribution and Effect of Hop stunt viroid on different hop cultivars
M. KAPPAGANTU (1), J. Bullock (1), S. Kenny (2), K. Eastwell (2) (1) Washington State University, U.S.A.; (2) IAREC-Washington State University, U.S.A.

Hop stunt disease caused by Hop stunt viroid (HSVd) is a growing threat to hop cultivation globally. It severely impacts growth and yield of certain hop cultivars. In 2004, HSVd was first detected in hop yards of Washington State, the major hop growing area in the United States. RT-PCR has been the major technique used for HSVd diagnosis; however, it is costly and sample handling is technically challenging. A more robust Reverse Transcription-Recombinant Polymerase Assay (RT-RPA) was developed to facilitate larger sample numbers. To understand the current distribution of HSVd in Washington, a survey was conducted and it revealed that 17% of hops grown in this region are infected with HSVd. Symptom expression is highly variable among different hop cultivars infected with HSVd. To understand the effect of HSVd, a 5 year study was conducted of six cultivars of hop to determine the impact on yield. Over the study period, the average cone yield of infected cultivars Glacier, Cascade and Willamette was reduced by 62%, 14% and 34%, respectively, compared to non-inoculated healthy plants. No significant yield reduction was observed in cultivars Nugget, Columbus and Galena cultivars. In the final year 2013, horticultural parameters of Willamette and Nugget were also measured.