Coat protein (CP) sequences of 17 Ilarvirus isolates were obtained from hops at three farms in Tasmania, Australia. Phylogenetic analysis of these sequences and additional database sequences indicated several Apple mosaic virus (ApMV) isolate clusters distinct from Prunus necrotic ringspot virus (PNRSV): one containing isolates from apple; one containing a single isolate from almond; a third containing Australian hop isolates of the 'apple' serotype and a German isolate of unknown origin; and a fourth containing Australian hop isolates of the 'intermediate' serotype. Isolates from hop, pear and prune from the Czech Republic either formed a fifth grouping, or were divergent members of the 'intermediate' serotype group. Deduced amino acid (aa) residue differences between the coat proteins of the two hop isolate serotype groups were highlighted as possible regions of serological differentiation. No evidence for coinfection of plants with both serotypes was found. Tests of ApMV-infected hop buds using the Shirofugen flowering cherry assay revealed a possible differentiation of the two strains based on hypersensitivity. Because of serological similarities to PNRSV, these viruses have commonly been reported as strains of PNRSV. However, this study shows ilarviruses from Australian hops are strains of ApMV, but distinct from those infecting Malus spp.

Macrosiphum euphorbiae and Myzus persicae, polyphagous aphid species commonly found within hop gardens in Australia, were confirmed as vectors of hop latent virus (HpLV) and hop mosaic virus in glasshouse trials. Both vectors transmitted either virus with equivalent efficiency. This is the first record of HpLV transmission by an aphid other than Phorodon humuli. Furthermore, aphids feeding on single infected plants, sequentially on plants infected with one virus and then the other or on co-infected source plants did not influence transmission efficiency of either virus, nor was the frequency of co-transmission affected by the order of virus acquisition. The role of these vectors in carlavirus epidemics in Australian hop gardens is discussed. Materials and MethodsTwo clones of My. persicae (one from a hop garden, and the other from a residential garden) and one clone www.blackwell-synergy.com

Hop mosaic virus (HpMV), a member of the genus Carlavirus, is importance to hop production worldwide. We identified variation in nucleic and amino acid sequences among 23 HpMV isolates from Australia, the USA, the Czech Republic, South Africa and Japan using a 1,455-bp fragment covering the 3' end of the virus genome including ORFs 4, 5 and 6. Three clusters of two or more isolates were identified in phylogenies of the total nucleotide sequence and the coat protein (ORF5) amino acid sequence. Two of these clusters combined in analyses of ORF4 and ORF6 amino acid sequences. Isolates from within and outside of Australia were found in each cluster, indicating that sequence variation was not associated with geographic source. Monitoring of HpMV variants in the field and evaluation of the impact of variants on vector association, rate of spread, and hop yield and quality can now be undertaken.