Incidence and effects of viruses on production of two newly adopted hop (Humulus lupulus) cultivars in Australia

The incidence and spread of Hop latent virus (HpLV), Hop mosaic virus (HpMV), and Apple mosaic virus (ApMV) in nurseries and gardens established with elite material (certified free of HpLV, HpMV, and ApMV by serological testing), and the effect of these viruses on production of 2 newly adopted hop (Humulus lupulus) cultivars were assessed in Tasmania, Australia. Infection by HpLV in Agate was associated with significant losses in dry cone yield of 40-70% compared with the yield of elite plants. Infection by HpLV in Agate was also associated with a 44% reduction in alpha acid levels and the cohumulone proportion of the alpha acids. However, in the second year, no significant reductions in levels of alpha acid and beta acid contents, or in the ratio of alpha to beta acids were detected. Plants infected by HpLV were also significantly shorter than elite plants in both seasons. No significant effects on growth or yield were detected for HpMV in Agate or for any of the virus combinations tested in Super Pride. The incidences and spread of HpLV, HpMV, and ApMV were consistently higher in Agate than in Super Pride and the incidences of all these viruses were higher at Forrester River than at Bushy Park and Gunns Plains. The presence of viruses in nurseries containing material propagated from elite mother plants is also of concern and may be contributing to high levels of virus incidence found soon after establishment. When combined, this information can be used to design control strategies for the Australian hop industry for these cultivars.