Amit C. Sukal

The Pacific Islands (Melanesia, Micronesia, Polynesia) were the last region in the world to be colonized by modern humans. In their migrations, they dispersed asexually propagated food plants that were first domesticated in Melanesia and exposed them to further selection in diverse insular environments. Later, staple food crops were introduced from South America. In our search for research on genetic resources characterization and breeding conducted between 1950 and 2022, we retrieved 338 references on 13 crop species. All studies were examined, and a review is presented here. Relatively few were on genetic improvement (92 references) compared to those on morphological diversity (246 references). The paradox is that the Pacific is considered a region exposed to the climatic crisis, perhaps more vulnerable than any other region in the world. This paradox is surprising when we consider that most people in the Pacific are growing staple food crops, for household use and/or for local markets, and occasionally for export. In some countries, it involves more than 75% of the population with a considerable contribution to gross domestic product (GDP). Plant breeding has not been considered a priority to mitigate against forthcoming changes in climate, which is likely to be detrimental to crops with a narrow genetic base. We suggest several possible reasons and that conventional plant breeding should be given high priority based on new approaches that include geographical distribution of allelic diversity.

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.

Next-generation sequencing of RNA extracted from a pumpkin plant with mosaic symptoms in Kenya identified the presence of a polerovirus sequence closely related to pepo aphid-borne yellows virus (PABYV). The near-complete polerovirus sequence comprised 5,810 nucleotides and contained seven putative open reading frames (ORFs) with a genome organisation typical of poleroviruses. BLASTp analysis of the translated sequences of ORFs 0, 1 and 2 revealed that their amino acid sequences differed by more than 10% from the corresponding protein sequences of other poleroviruses. These results suggest that this virus is a putative novel member of the genus Polerovirus, which has been provisionally named “pumpkin polerovirus” (PuPV).

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.

Taro ( Colocasia esculenta ) and tannia ( Xanthosoma sp.) are important root crops cultivated mainly by small‐scale farmers in sub‐Saharan Africa and the South Pacific. Viruses are known to be one of the most important constraints to production, with infections resulting in severe yield reduction. In 2014 and 2015, surveys were conducted in Ethiopia, Kenya, Tanzania and Uganda to determine the identity of viruses infecting taro in East Africa. Screening of 392 samples collected from the region using degenerate badnavirus primers revealed an incidence of 58–74% among the four countries surveyed, with sequence analysis identifying both Taro bacilliform virus (Ta BV ) and Taro bacilliform CH virus (Ta BCHV ). Ta BCHV was identified from all four countries while Ta BV was identified in all except Ethiopia. Full‐length sequences from representative Ta BV and Ta BCHV isolates showed that the genome organization of Ta BV isolates from East Africa was consistent with previous reports while Ta BCHV isolates from East Africa were found to encode only four ORF s, distinct from a previous report from China. Phylogenetic analysis showed that all East African Ta BV isolates form a single subgroup within known Ta BV isolates, while Ta BCHV isolates form at least two distinct subgroups. To the authors' knowledge, this is the first report describing the occurrence and genome organization of Ta BV and Ta BCHV isolates from East Africa and the first full‐length sequence of the two viruses from tannia.

Dasheen mosaic virus (DsMV) is member of the family Potyviridae, genus Potyvirus and infects taro and other aroids wherever they grow. DsMV infection results in characteristic feathery-mottle and mosaic symptoms on leaves and can cause up to 60% production losses on taro and other edible aroids (Lebot 2009; Reyes et al. 2006). In June 2012, taro plants showing mosaic, feathery-mottle and yellowing symptoms were observed in a germplasm collection at the Areka Agricultural Research Center, Wolayita Zone, in southern Ethiopia and leaf samples were collected. The samples were initially tested for potyviruses by antigen-coated plate (ACP) ELISA using the potyvirus group PathoScreen® kit (Agdia, U.S.A.) and all eight samples tested positive. Subsequently, the samples were screened for the presence of DsMV using double antibody sandwich (DAS) ELISA (Agdia, U.S.A.), with all eight samples again testing positive. Total RNA was then extracted from the samples using the ZR RNA MiniPrepTM kit (ZYMO, U.S.A.), cDNA was...

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.