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Sweet potato collusive virus (SPCV) is a member of the genus Cavemovirus, family Caulimoviridae, for which only one full-length genome sequence has been reported. SPCV was first detected in Australia in 2007 in two sweet potato accessions using the nitrocellulose membrane ELISA kit developed by the International Potato Centre (CIP). Infected plants were also shown to contain isometric virions of ~ 50 nm, typical of members of the genera Cavemovirus, Caulimovirus, Petuvirus and Soymovirus. We have now sequenced and characterised the complete genomes of the two SPCV isolates (designated SPCV-Aus1 and -Aus2) using a combination of next-generation sequencing and PCR/Sanger sequencing. The sequences of both isolates encode three major ORFs with a genome organisation typical of cavemoviruses. However, isolate SPCV-Aus2 possesses a considerably shorter genome length of 7275 bp compared to SPCV-Aus1 (7712 bp) and the only available full-length sequence from a Portuguese isolate (7723 bp; GenBank accession number NC_015328). Further, ORF 1 of SPCV-Aus2 is considerably shorter than the ORF 1 length of both SPCV-Aus1 and SPCV-Mad1. Phylogenetic and PASC analysis showed that SPCV-Aus1 is closely related to SPCV isolates from North and Central America, whereas SPCV-Aus2 clustered together with isolates from Portugal and Africa.

Yam is an important food staple in many Pacific Island countries, but its production is limited by several factors including virus infection. The presence of viruses also hinders the exploitation of the crop by restricting the international dissemination of yam germplasm due to quarantine concerns. In this study, a total of 224 yam accessions present in the Pacific germplasm collection at SPC-CePaCT, Fiji, were tested for the presence of badnaviruses using a combination of rolling circle amplification (RCA) and sequencing. Of these, 35 tested positive for either Dioscorea bacilliform AL virus (DBALV) or Dioscorea bacilliform AL virus 2 (DBALV2). DBALV was only detected in samples from Vanuatu and Tonga, while DBALV2 was restricted to Papua New Guinean samples. Ten complete genome sequences of DBALV and DBALV2 were obtained and pairwise comparison of the partial reverse transcriptase/ribonuclease H (RT/RNase H)-coding sequence revealed identities ranging from 89% to 100% and 92% to 100%, respectively. The results suggest that DBALV and DBALV2 are the prevalent badnavirus species infecting yams in the Pacific region.

Yam is an important food staple for millions of people globally, particularly those in the developing countries of West Africa and the Pacific Islands. To sustain the growing population, yam production must be increased amidst the many biotic and abiotic stresses. Plant viruses are among the most detrimental of plant pathogens and have caused great losses of crop yield and quality, including those of yam. Knowledge and understanding of virus biology and ecology are important for the development of diagnostic tools and disease management strategies to combat the spread of yam-infecting viruses. This review aims to highlight current knowledge on key yam-infecting viruses by examining their characteristics, genetic diversity, disease symptoms, diagnostics, and elimination to provide a synopsis for consideration in developing diagnostic strategy and disease management for yam.

Three tannia (Xanthosoma sp.) plants showing mosaic, mottling and vein chlorosis symptoms were observed in Buikwe district, Uganda. Next generation sequencing (NGS) of RNA extracted from the three plants revealed the presence of Cucumber mosaic virus (CMV). The complete genome sequence of this isolate, designated CMV-Xa, was assembled and sequence analyses based on the three genomic RNAs revealed that CMV–Xa belongs to subgroup IB. This is the first report of CMV infecting Xanthosoma sp. and also the first CMV isolate from subgroup IB detected from sub-Saharan Africa.

The complete genome sequences of three new badnaviruses associated with yam (Dioscorea spp.) originating from Fiji, Papua New Guinea and Samoa were determined following rolling circle amplification of the virus genomes. The full-length genomes consisted of a single molecule of circular double-stranded DNA of 8106 bp for isolate FJ14, 7871 bp for isolate PNG10 and 7426 bp for isolate SAM01. FJ14 and PNG10 contained three open reading frames while SAM01 had an additional open reading frame which partially overlapped the 3′ end of ORF 3. Amino acid sequence analysis of ORF 3 from the three isolates confirmed the presence of conserved motifs typical of other badnaviruses. Phylogenetic analysis revealed the sequences to be closely related to other Dioscorea–infecting badnaviruses. FJ14 and PNG10 appear to be new species, which we have tentatively named dioscorea bacilliform ES virus (DBESV) and dioscorea bacilliform AL virus 2 (DBALV2), respectively, while SAM01 represents a Pacific isolate of the recently published dioscorea bacilliform RT virus 2 and is described as dioscorea bacilliform RT virus 2-[4RT] (DBRTV2-[4RT]).

Little information exists on the type and incidence of viruses infecting garlic (Allium sativum L) in Ethiopia. Attempts were made to identify the viruses using molecular techniques from 95 composite leaf samples collected from 44 farmers’ fields and 51 germplasm accessions. Reverse transcription (RT-) PCR using genus and/or virus specific primers was used to amplify partial genome sequences of potyviruses, allexiviruses, carlaviruses and a tospovirus followed by sequencing of PCR products. Results indicated that ~73.7% of the samples are infected with at least one virus. Onion yellow dwarf virus (OYDV, genus Potyvirus, family Potyviridae) is the most common virus detected followed by Garlic virus C (genus Allexivirus) and Shallot latent virus (SLV, genus Carlavirus). Other viruses detected at lower frequency include Garlic virus X and Garlic virus D (genus Allexivirus), Leek yellow stripe virus (genus Potyvirus) and Iris yellow spot virus (IYSV, genus Tospovirus). Mixed infection of two or more viruses was detected in 65.7% of the samples. Phylogenetic analysis suggested that the different viruses may have been introduced to Ethiopia from Europe or Asia. This is the first report of Garlic virus X, Garlic virus D, IYSV and SLV in garlic in Ethiopia. The high incidence of OYDV and IYSV which cause severe yield loss alone or in mixed infection with allexiviruses and carlaviruses is a cause of concern to growers.

The complete genome of an Australian isolate of zantedeschia mild mosaic virus (ZaMMV) causing mosaic symptoms on Alocasia sp. (designated ZaMMV-AU) was cloned and sequenced. The genome comprises 9942 nucleotides (excluding the poly-A tail) and encodes a polyprotein of 3167 amino acids. The sequence is most closely related to a previously reported ZaMMV isolate from Taiwan (ZaMMV-TW), with 82 and 86 % identity at the nucleotide and amino acid level, respectively. Unlike the amino acid sequence of ZaMMV-TW, however, ZaMMV-AU does not contain a polyglutamine stretch at the N-terminus of the coat-protein-coding region upstream of the DAG motif. This is the first report of ZaMMV from Australia and from Alocasia sp.

The genus Badnavirus is characterized by members that are genetically and serologically heterogeneous which presents challenges for their detection and characterization. The presence of integrated badnavirus-like sequences in some host species further complicates detection using PCR-based protocols. To address these challenges, we have assessed and optimized various RCA protocols including random-primed RCA (RP-RCA), primer-spiked random-primed RCA (primer-spiked RP-RCA), directed RCA (D-RCA) and specific-primed RCA (SP-RCA). Using Dioscorea bacilliform AL virus (DBALV) as an example, we demonstrate that viral DNA amplified using the optimized D-RCA and SP-RCA protocols showed an 85-fold increase in badnavirus NGS reads compared with RP-RCA. The optimized RCA techniques described here were used to detect a range of badnaviruses infecting banana, sugar cane, taro and yam demonstrating the utility of RCA for detection of diverse badnaviruses infecting a variety of host plant species.

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The badnavirus taro bacilliform virus (TaBV) has been reported to infect taro (Colocasia esculenta L.) and other edible aroids in several South Pacific island countries, but there are no published reports from Australia. Using PCR and RCA, we identified and characterized an Australian TaBV isolate. A terminally redundant cloned copy of the TaBV genome was generated and shown to be infectious in taro following agro-inoculation. This is the first report of TaBV from Australia and also the first report of an infectious clone for this virus.

We have characterized the complete genome of a novel circular double-stranded DNA virus, tentatively named Dioscorea nummularia-associated virus (DNUaV), infecting Dioscorea nummularia originating from Samoa. The genome of DNUaV comprised 8139 bp and contained four putative open reading frames (ORFs). ORFs 1 and 2 had no identifiable conserved domains, while ORF 3 had conserved motifs typical of viruses within the family Caulimoviridae including coat protein, movement protein, aspartic protease, reverse transcriptase and ribonuclease H. A transactivator domain, similar to that present in members of several caulimoviridae genera, was also identified in the putative ORF 4. The genome size, organization, and presence of conserved amino acid domains are similar to other viruses in the family Caulimoviridae. However, based on nucleotide sequence similarity and phylogenetic analysis, DNUaV appears to be a distinct novel member of the family and may represent a new genus.