Virus incidence in Australian hop (Humulus lupulus L.) gardens and cultivar differences in susceptibility to infection

Incidence of hop latent virus (HpLV), hop mosaic virus (HpMV), and Prunus n ecrotic ringspot virus [PNRSV (apple, A, and intermediate, I, serotypes)] w as assessed in 6 Australian-bred hop cultivars in Tasmania and Victoria, Au stralia. At Gunns Plains, Tasmania, virus incidence in 5 gardens of cv. 'Vi ctoria', initially established with elite material and 7-9 years old, was 8 9-98% for HpLV, 72-96% for HpMV, and 85-100% for PNRSV (A & I). Virus incid ence in 13 'Pride of Ringwood' gardens, 10-19 years old and initially estab lished from material of unknown virus status, was 0-49% for HpLV, 0-69% for HpMV, and 0-77% for PNRSV (A & I). In an 8-year-old trial, in which 3/4 cu ltivars were planted with elite material, incidence of HpLV in 'Victoria' ( 47%) was significantly (P < 0.001) greater than in `Opal' (8%). Incidence o f HpMV in 'Victoria' (52%) was significantly (P < 0.001) higher than in 'T1 1' (42%), which in turn was higher than in 'Opal' (24%). Incidence of PNRSV (A & I) in 'Victoria' (98%) was significantly higher than in 'T11' (58%), which was higher than 'Opal' (31%). Results suggested that 'Victoria' was m ore susceptible to infection by all 3 viruses than traditionally grown cult ivars and recently released or experimental cultivars. Planting with elite material and roguing of infected plants has been ineffective as a virus con trol strategy with this cultivar.