Genetic Diversification and Dispersal of Taro (Colocasia esculenta (L.) Schott)

Transcriptome-based identification and validation of reference genes for corm growth stages, different tissues, and drought stress in Taro (Colocasia esculenta)

Taro is a widely utilized starch resource plant. It is essential to quantify the expression levels of functional genes associated with taro growth using real-time quantitative polymerase chain reaction (RT-qPCR). However, to obtain reliable RT-qPCR results, appropriate reference genes (RGs) are required for data normalization. In this study, we screened seven novel candidate RGs using transcriptome datasets from taro, encompassing data from growth corms and various tissues. The expression stability of these seven new RGs, along with the commonly used RGs Actin, EF1-α, and β-tubulin, was assessed using Delta Ct, BestKeeper, geNorm, and NormFinder algorithms. Furthermore, we conducted a comprehensive analysis using the RefFinder program and validated the results using the target gene, CeAGPL1. The findings revealed that ACY-1 and PIA2 were the optimal multiple RGs for normalization during corm growth, while COX10 and Armc8 were suitable for samples including various types of tissues. Furthermore, we found three RGs, Armc8, COX10 and CCX4L, were the optimal RGs for drought stress. This study assessed the suitability of RGs in taro for the first time. The identified RGs provide valuable resources for studying corm growth, diverse tissues, and drought stress. This study contributes to the advancement of our understanding of the underlying mechanisms that govern the growth of taro.

Assessment of ethnobotanical uses, household, and regional genetic diversity of aroid species grown in northeastern India

Aroids are an important group of indigenous tuber crops, grown widely for their leaves, petioles, stolons, corms, and cormels. A total of 53 genotypes were evaluated for their genetic diversity in northeastern region of India. At household level, a total of 16 landraces of Aroids were recorded having different ethnobotanical uses. Based on the population study under Jhum/Shifting farming, landrace Rengama was dominant in area with 47% of the total population followed by Tamachongkham and Tasakrek. However, Pugarkusu and Chigi occupied 33.0 and 24.0% of the population, respectively under backyard farming, and were considered as major landraces. Tamachongkham, high in acridity and total oxalate content (0.82%), was used for cooking with meat, while Tasakrek was used as a baby food due to high total sugar (>3.0%), low in acridity, and total oxalate content (<0.12%). The Simpson’s diversity index of the backyards was higher (0.80) as compared to Jhum field (0.63). The genotypes showed wider variability in growth and yield attributes like; plant height (89.4–206.1 cm), number of side shoots (1.84–5.92), corm weight (38.0–683.3 g), cormel weight (14.0–348.3 g), yield (0.24–1.83 kg plant−1). Similarly, wide variations were also observed for quality traits like total sugar (1.93–4.94%); starch (15.32–32.49%), total oxalate (0.10–0.82%), and dry matter (16.75–27.08%) content. Except for total oxalate, all the growth and yield attributes have shown high heritability and moderate to high genetic advance. Molecular analysis (33 polymorphic SSR markers) detected a total of 136 alleles, ranged 3 to 8 alleles per marker. The observed heterozygosity (0.24) was less than expected heterozygosity (0.69). The group-wise maximum genetic divergence was observed between Colocasia fallax (cv. Chigi) to C. esculenta var. aquatilis (cv. Tharsing); C. fallax (cv. Chigi) to C. gigantea (cv. Ganima) and C. gigantea (cv. Ganima) to Xanthosoma spp., while it was least between eddo and dasheen. The findings indicated, a wider diversity and distinct ethnobotanical uses of Aroid landraces at the house hold levels, which should be conserved and popularized to ensure nutritional security.

Detection of the local adaptive and genome-wide associated loci in southeast Nigerian taro (Colocasia esculenta (L.) Schott) populations

BACKGROUND

Taro has a long history of being consumed and remains orphan and on the hand Nigeria farmers. The role of farmer-driven artificial selection is not negligible to fit landraces to a particular ecological condition. Limited study has been conducted on genome-wide association and no study has been conducted on genome-environment association for clinal adaptation for taro. Therefore, the objective of this study was to detect loci that are associated with environmental variables and phenotype traits and forward input to breeders. The study used 92 geographical referred taro landraces collected from Southeast (SE) Nigeria.

RESULTS

The result indicates that SE Nigerian taro has untapped phenotype and genetic variability with low admixture. Redundancy analysis indicated that collinear explained SNP variation more than single climatic variable. Overall, the results indicated that no single method exclusively was able to capture population confounding effects better than the others for all six traits. Nevertheless, based on overall model performance, Blink seemed to provide slight advantage over other models and was selected for all subsequent assessment of genome-environment association (GEA) and genome-wide association study (GWAS) models. Genome scan and GEA identified local adapted loci and co-located genes. A total of nine SNP markers associated with environmental variables. Some of the SNP markers (such as S_101024366) co-located with genes which previously reported for climatic adaptation such as astringency, diaminopimelate decarboxylase and MYB transcription factor. Genome-wide association also identified 45, 40 and 34 significant SNP markers associated with studied traits in combined, year 1 and year 2 data sets, respectively. Out of these, five SNP markers (S1_18891752 S3_100795476, S1_100584471 S1_100896936 and S2_10058799) were consistent in two different data sets.

CONCLUSIONS

The findings from this study improve our understanding of the genetic control of adaptive and phenotypic traits in Nigerian taro. However, the study suggests further study on identification of local adaptive loci and GWAS through collection of more landraces throughout the country, and across different agro-ecologies.

Crop diversity: Breadfruit's checkered past bears fruit for food security

New interdisciplinary research on breadfruit helps reconcile cultivar names with genotypic and phenotypic diversity across time, continents, and cultures. The findings will advance breeding and conservation initiatives for this underutilized crop, but also highlight methodological challenges commonplace in crop evolutionary studies.

DNA Barcoding and ITS2 Secondary Structure Predictions in Taro (Colocasia esculenta L. Schott) from the North Eastern Hill Region of India

Taro (Colocasia esculenta L. Schott, Araceae), an ancient root and tuber crop, is highly polygenic, polyphyletic, and polygeographic in nature, which leads to its rapid genetic erosion. To prevent the perceived loss of taro diversity, species discrimination and genetic conservation of promising taro genotypes need special attention. Reports on genetic discrimination of taro at its center of origin are still untapped. We performed DNA barcoding of twenty promising genotypes of taro indigenous to the northeastern hill region of India, deploying two chloroplast-plastid genes, matK and rbcL, and the ribosomal nuclear gene ITS2. The secondary structure of ITS2 was determined and molecular phylogeny was performed to assess genetic discrimination among the taro genotypes. The matK and rbcL genes were highly efficient (>90%) in amplification and sequencing. However, the ITS2 barcode region achieved significant discrimination among the tested taro genotypes. All the taro genotypes displayed most similar sequences at the conserved matK and rbcL loci. However, distinct sequence lengths were observed in the ITS2 barcode region, revealing accurate discriminations among the genotypes. Multiple barcode markers are unrelated to one another and change independently, providing different estimations of heritable traits and genetic lineages; thus, they are advantageous over a single locus in genetic discrimination studies. A dynamic programming algorithm that used base-pairing interactions within a single nucleic acid polymer or between two polymers transformed the secondary structures into the symbol code data to predict seven different minimum free energy secondary structures. Our analysis strengthens the potential of the ITS2 gene as a potent DNA barcode candidate in the prediction of a valuable secondary structure that would help in genetic discrimination between the genotypes while augmenting future breeding strategies in taro.

DArTSeq SNP-based genetic diversity and population structure studies among taro [(Colocasia esculenta (L.) Schott] accessions sourced from Nigeria and Vanuatu

Taro is a valuable staple food crop among resource-poor rural people in countries such as Nigeria and Ghana, among others. Characterization of genetic diversity is a prerequisite for proper management of breeding programs and conservation of genetic resources. Two hundred seventy one taro accessions obtained from Nigeria and Vanuatu were genotyped using DArTseq-based SNP markers with the objectives of investigating the genetic diversity and population structure. In the analysis, 10,391 SNP markers were filtered from the sequence and used. The analysis revealed higher transition than transversion types of SNPs in the ratio of 1.43:1. The polymorphism ranged from 0.26 to 0.29 for the markers, indicating moderate genetic diversity. A model-based Bayesian clustering analysis of taro accessions yielded five subgroups and revealed the admixture situation in 19.19% of all accessions in the study. Vanuatu taro accessions exhibited more genetic diversity than Nigerian taro accessions. The population diversity estimate (PhiPt) was relatively higher (0.52) for accessions originating from Vanuatu than for Nigerian accessions. Analysis of molecular variance (AMOVA) revealed that most variation existed among individuals within a population at 52%. Nei’s genetic distance showed that relatedness is based on geographical proximity. Collection of taro genetic resources should give more emphasis to within regions to utilize diversity in taro breeding program. This study also demonstrated the efficiency of DArTseq-based SNP genotyping for large-scale genome analysis in taro. The genotypic markers provided in this study are useful for association mapping studies.

Complete chloroplast genome sequences of three aroideae species (Araceae): lights into selective pressure, marker development and phylogenetic relationships

Background

Colocasia gigantea, Caladium bicolor and Xanthosoma sagittifolium are three worldwide famous ornamental and/or vegetable plants in the Araceae family, these species in the subfamily Aroideae are phylogenetically perplexing due to shared interspecific morphological traits and variation.

Result

This study, for the first time ever, assembled and analyzed complete chloroplast genomes of C. gigantea, C. bicolor and X. sagittifolium with genome sizes of 165,906 bp, 153,149 bp and 165,169 bp in length, respectively. The genomes were composed of conserved quadripartite circular structures with a total of 131 annotated genes, including 8 rRNA, 37 tRNA and 86 protein-coding genes. A comparison within Aroideae showed seven protein-coding genes (accD, ndhF, ndhK, rbcL, rpoC1, rpoC2 and matK) linked to environmental adaptation. Phylogenetic analysis confirmed a close relationship of C. gigantea with C. esculenta and S. colocasiifolia, and the C. bicolor with X. sagittifolium. Furthermore, three DNA barcodes (atpH-atpI + psaC-ndhE, atpH-atpI + trnS-trnG, atpH-atpI + psaC-ndhE + trnS-trnG) harbored highly variable regions to distinguish species in Aroideae subfamily.

Conclusion

These results would be beneficial for species identification, phylogenetic relationship, genetic diversity, and potential of germplasm resources in Aroideae.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08400-3.

Genomic Screening to Identify Food Trees Potentially Dispersed by Precolonial Indigenous Peoples

Over millennia, Indigenous peoples have dispersed the propagules of non-crop plants through trade, seasonal migration or attending ceremonies; and potentially increased the geographic range or abundance of many food species around the world. Genomic data can be used to reconstruct these histories. However, it can be difficult to disentangle anthropogenic from non-anthropogenic dispersal in long-lived non-crop species. We developed a genomic workflow that can be used to screen out species that show patterns consistent with faunal dispersal or long-term isolation, and identify species that carry dispersal signals of putative human influence. We used genotyping-by-sequencing (DArTseq) and whole-plastid sequencing (SKIMseq) to identify nuclear and chloroplast Single Nucleotide Polymorphisms in east Australian rainforest trees (4 families, 7 genera, 15 species) with large (>30 mm) or small (<30 mm) edible fruit, either with or without a known history of use by Indigenous peoples. We employed standard population genetic analyses to test for four signals of dispersal using a limited and opportunistically acquired sample scheme. We expected different patterns for species that fall into one of three broadly described dispersal histories: (1) ongoing faunal dispersal, (2) post-megafauna isolation and (3) post-megafauna isolation followed by dispersal of putative human influence. We identified five large-fruited species that displayed strong population structure combined with signals of dispersal. We propose coalescent methods to investigate whether these genomic signals can be attributed to post-megafauna isolation and dispersal by Indigenous peoples.

Looking beyond history: tracing the dispersal of the Malaysian complex of crops to Africa

In his 1959 book, Africa: Its Peoples and Their Culture History, George P. Murdock suggested that a Malaysian complex of crops dispersed to Africa in ancient times across the Indian Ocean along the Sabaean Lane. The Malaysian complex comprised bananas, sugarcane, taro, three yam species, rice, Polynesian arrowroot, breadfruit, coconut, areca palm, and betel leaf. Except for rice, arrowroot, and potentially taro, most of these crops were domesticated in the Island Southeast Asia-New Guinea region, from where they dispersed to Africa. Our reassessment of agronomic, archaeological, classical, genetic, and historical sources shows that we need to go beneath standard historical narratives to recover a much more ancient and complex history of crop introductions to Africa. Despite considerable uncertainty and fragmented research, we were able to conclude that the Malaysian complex of crops did not arrive in Africa as a complete assemblage at one time or along one route. Multiple lines of evidence suggest that these crops arrived in Africa at different times and followed different pathways of introduction to the continent.

First report of dasheen mosaic virus infecting taro (Colocasia esculenta) in Louisiana

Taro [Colocasia esculenta (L.) Schott], also called dasheen or malanga is an important staple crop in many tropical and subtropical countries (Chaïr et al. 2016). In October 2020, taro plants showing foliar symptoms consisting of mosaic, feathery mottle, and vein clearing patterns were observed in the Hilltop Arboretum, the Bluebonnet Swamp Nature Center, the Louisiana State University Agricultural Center Botanic Gardens, and the University Lake, in Baton Rouge, Louisiana. Unidentified aphids were also observed infesting the plants showing the described symptoms. From each location, two foliar samples from symptomatic and two from asymptomatic plants were collected and tested by ELISA using antiserum for general potyvirus group (Agdia, Elkhart, IN). Seven of eight symptomatic samples tested positive while the asymptomatic samples were negative. The seven positive samples were used to perform an additional ELISA test using antiserum specific for dasheen mosaic virus (DsMV) (Agdia). All seven samples tested positive for DsMV. To confirm the identity of the virus, total RNA was extracted from the seven samples using the PureLink® Plant RNA Reagent Kit (Invitrogen, Carlsbad, CA). After DNA digestion with PerfeCta® DNase I (Qiagen, Beverly, MA), the RNA was used to perform reverse transcription polymerase chain reaction (RT-PCR) with primer set DMV 5708-5731-F/DMV 6131-6154-R which is specific for DsMV (Wang et al. 2017). RT-PCR was performed using the AccessQuickTM RT-PCR System (Promega, Madison, WI) following the reaction conditions described by Wang et al. PCR products of the expected size (~447 bp) were obtained with all seven samples and were Sanger-sequenced. A consensus sequence (MW284936) was obtained with the two sequences from samples collected at the University Lake and aligned with other sequences available in the GenBank using BLASTn. Our isolate of DsMV showed 90.6% nt identity to an isolate of DsMV from Ethiopia (MG602229). Mechanical inoculations to healthy taro plants were conducted using leaf tissue of symptomatic plants as source of inoculum. Inoculated plants exhibited mosaic symptoms three weeks after inoculation and were ELISA-positive for DsMV. Symptomatology, serological tests, RT-PCR testing, and DNA sequencing of RT-PCR products support that the symptomatic taro plants were infected with DsMV. Taro is a crop in Hawaii, but in the contiguous United States, it is mostly grown as an ornamental and is considered an invasive species. Its distribution is restricted to the southern continental states and Hawaii (Cozad et al. 2018). CABI, EPPO (1998) lists the presence of DsMV in several states of the United States, including Louisiana; however, there is no record in the literature of the identification of this virus in Louisiana. The potential impact of DsMV in taro and related ornamental species in southern United States is unknown. To the best of our knowledge, this is the first report documenting DsMV infecting taro in Louisiana.

Evolutionary origins of taro (Colocasia esculenta) in Southeast Asia

As an ancient clonal root and leaf crop, taro (Colocasia esculenta, Araceae) is highly polymorphic with uncertain genetic and geographic origins. We explored chloroplast DNA diversity in cultivated and wild taros, and closely related wild taxa, and found cultivated taro to be polyphyletic, with tropical and temperate clades that appear to originate in Southeast Asia sensu lato. A third clade was found exclusively in wild populations from Southeast Asia to Australia and Papua New Guinea. Our findings do not support the hypothesis of taro domestication in Papua New Guinea, despite archaeological evidence for early use or cultivation there, and the presence of apparently natural wild populations in the region (Australia and Papua New Guinea).

A high-quality genome of taro (Colocasia esculenta (L.) Schott), one of the world's oldest crops

Taro (Colocasia esculenta (L.), Schott), from the Araceae family, is one of the oldest crops with important edible, medicinal, nutritional and economic value. Taro is a highly polymorphic species including diverse genotypes adapted to a broad range of environments, but the taro genome has rarely been investigated. Here, a high-quality chromosome-level genome of C. esculenta was assembled using data sequenced by Illumina, PacBio and Nanopore platforms. The assembled genome size was 2,405 Mb with a contig N50 of 400.0 kb and a scaffold N50 of 159.4 Mb. In total, 2,311 Mb (96.09%) of the contig sequences was anchored onto 14 chromosomes to form pseudomolecules, and 2,126 Mb (88.43%) was annotated as repetitive sequences. Of the 28,695 predicted protein-coding genes, 26,215 genes (91.4%) could be functionally annotated. On the basis of phylogenetic analysis using 769 genes, C. esculenta and Spirodela polyrhiza were placed on one branch of the tree that diverged approximately 73.23 million years ago. The synteny analyses showed that there have been two whole-genome duplication events in C. esculenta separated by a relatively short gap. According to comparative genome analysis, a larger number (1,189) of distinct gene families and long terminal repeats were enriched in C. esculenta. Our high-quality taro genome will provide valuable resources for further genetic, ecological and evolutionary analyses of taro or other species in the Araceae.

Taro Genome Assembly and Linkage Map Reveal QTLs for Resistance to Taro Leaf Blight

Taro (Colocasia esculenta) is a food staple widely cultivated in the humid tropics of Asia, Africa, Pacific and the Caribbean. One of the greatest threats to taro production is Taro Leaf Blight caused by the oomycete pathogen Phytophthora colocasiae Here we describe a de novo taro genome assembly and use it to analyze sequence data from a Taro Leaf Blight resistant mapping population. The genome was assembled from linked-read sequences (10x Genomics; ∼60x coverage) and gap-filled and scaffolded with contigs assembled from Oxford Nanopore Technology long-reads and linkage map results. The haploid assembly was 2.45 Gb total, with a maximum contig length of 38 Mb and scaffold N50 of 317,420 bp. A comparison of family-level (Araceae) genome features reveals the repeat content of taro to be 82%, >3.5x greater than in great duckweed (Spirodela polyrhiza), 23%. Both genomes recovered a similar percent of Benchmarking Universal Single-copy Orthologs, 80% and 84%, based on a 3,236 gene database for monocot plants. A greater number of nucleotide-binding leucine-rich repeat disease resistance genes were present in genomes of taro than the duckweed, ∼391 vs. ∼70 (∼182 and ∼46 complete). The mapping population data revealed 16 major linkage groups with 520 markers, and 10 quantitative trait loci (QTL) significantly associated with Taro Leaf Blight disease resistance. The genome sequence of taro enhances our understanding of resistance to TLB, and provides markers that may accelerate breeding programs. This genome project may provide a template for developing genomic resources in other understudied plant species.

The domestication syndrome in vegetatively propagated field crops

BACKGROUND

Vegetatively propagated crops are globally significant in terms of current agricultural production, as well as for understanding the long-term history of early agriculture and plant domestication. Today, significant field crops include sugarcane (Saccharum officinarum), potato (Solanum tuberosum), manioc (Manihot esculenta), bananas and plantains (Musa cvs), sweet potato (Ipomoea batatas), yams (Dioscorea spp.) and taro (Colocasia esculenta). In comparison with sexually reproduced crops, especially cereals and legumes, the domestication syndrome in vegetatively propagated field crops is poorly defined.

AIMS AND SCOPE

Here, a range of phenotypic traits potentially comprising a syndrome associated with early domestication of vegetatively propagated field crops is proposed, including: mode of reproduction, yield of edible portion, ease of harvesting, defensive adaptations, timing of production and plant architecture. The archaeobotanical visibility of these syndrome traits is considered with a view to the reconstruction of the geographical and historical pathways of domestication for vegetatively propagated field crops in the past.

CONCLUSIONS

Although convergent phenotypic traits are identified, none of them are ubiquitous and some are divergent. In contrast to cereals and legumes, several traits seem to represent varying degrees of plastic response to growth environment and practices of cultivation, as opposed to solely morphogenetic 'fixation'.

Dry, rainfed or irrigated? Reevaluating the role and development of rice agriculture in Iron Age-Early Historic South India using archaeobotanical approaches

Domestic rice agriculture had spread across the mainland Indian subcontinent by c.500 BC. The initial spread of rice outside the core zone of the central Gangetic Plains is thought to have been limited by climatic constraints, particularly seasonal rainfall levels, and so the later spread of rice into the dry regions of South India is largely supposed to have relied on irrigation. This has been associated with the development of ritual water features in the Iron Age (c.1000-500 BC), and to the subsequent development of tanks (reservoirs) during the period of Early Historic state development (c.500 BC-500 AD). The identification of early irrigation systems within South Asia has largely relied on early historical texts, and not on direct archaeological evidence. This initial investigation attempts to identify irrigated rice cultivation in the Indian subcontinent by directly examining rice crop remains (phytolith and macrobotanical data) from four sites. The evidence presented here shows that, contrary to accepted narratives, rice agriculture in the Iron Age-Early Historic South India may not have been supported by irrigated paddy fields, but may have relied on seasonal rainfall as elsewhere in the subcontinent. More caution is urged, therefore, when using terms related to 'irrigation' and 'agricultural intensification' in discussions of the Iron Age and Early Historic South Asia and the related developments of urbanism and state polities.

Phylogenetic Relationships, Breeding Implications, and Cultivation History of Hawaiian Taro (Colocasia Esculenta) Through Genome-Wide SNP Genotyping

Taro, Colocasia esculenta, is one of the world’s oldest root crops and is of particular economic and cultural significance in Hawai’i, where historically more than 150 different landraces were grown. We developed a genome-wide set of more than 2400 high-quality single nucleotide polymorphism (SNP) markers from 70 taro accessions of Hawaiian, South Pacific, Palauan, and mainland Asian origins, with several objectives: 1) uncover the phylogenetic relationships between Hawaiian and other Pacific landraces, 2) shed light on the history of taro cultivation in Hawai’i, and 3) develop a tool to discriminate among Hawaiian and other taros. We found that almost all existing Hawaiian landraces fall into 5 monophyletic groups that are largely consistent with the traditional Hawaiian classification based on morphological characters, for example, leaf shape and petiole color. Genetic diversity was low within these clades but considerably higher between them. Population structure analyses further indicated that the diversification of taro in Hawai’i most likely occurred by a combination of frequent somatic mutation and occasional hybridization. Unexpectedly, the South Pacific accessions were found nested within the clades mainly composed of Hawaiian accessions, rather than paraphyletic to them. This suggests that the origin of clades identified here preceded the colonization of Hawai’i and that early Polynesian settlers brought taro landraces from different clades with them. In the absence of a sequenced genome, this marker set provides a valuable resource towards obtaining a genetic linkage map and to study the genetic basis of phenotypic traits of interest to taro breeding such as disease resistance.

Human mediated translocation of Pacific paper mulberry [Broussonetia papyrifera (L.) L'Hér. ex Vent. (Moraceae)]: Genetic evidence of dispersal routes in Remote Oceania

Paper mulberry, Broussonetia papyrifera (L.) L’Hér. ex Vent. (Moraceae), a dioecious species, was transported by humans from Taiwan to the islands of Remote Oceania. Its introduction and cultivation in Remote Oceania was intentional due to its cultural importance as a fiber source for barkcloth textiles. The aim of this study was to explore the genetic diversity and structure of paper mulberry populations within Remote Oceania in order to infer dispersal patterns that may reflect past human interaction among island groups. We present the integrated analysis of 380 samples (313 contemporary and 67 herbarium specimens) collected in Near and Remote Oceania. Genetic characterization was based on a set of ten microsatellites developed for B. papyrifera and complemented with the analysis of the ribosomal internal transcribed spacer ITS-1 sequence, a sex marker and the chloroplast ndhF–rpl32 intergenic spacer. Microsatellite data identify a total of 64 genotypes, despite this being a clonally propagated crop, and show three major dispersal hubs within Remote Oceania, centered on the islands of Fiji, Tonga, and Pitcairn. Of 64 genotypes identified, 55 correspond to genotypes associated to female-sexed plants that probably descend from plants introduced by the prehistoric Austronesian-speaking voyagers. The ratio of accessions to genotypes between herbarium and contemporary samples, suggests recent loss of genetic diversity. In addition to the chloroplast haplotypes described previously, we detected two new haplotypes within Remote Oceania both originating in Taiwan. This is the first study of a commensal species to show genetic structuring within Remote Oceania. In spite of the genetic bottleneck, the presence of only one sex, a timespan of less than 5000 years, and asexual propagation of this crop in Remote Oceania, we detect genetic diversity and regional structuring. These observations suggest specific migration routes between island groups within Remote Oceania.

Early tropical crop production in marginal subtropical and temperate Polynesia

Polynesians introduced the tropical crop taro (Colocasia esculenta) to temperate New Zealand after 1280 CE, but evidence for its cultivation is limited. This contrasts with the abundant evidence for big game hunting, raising longstanding questions of the initial economic and ecological importance of crop production. Here we compare fossil data from wetland sedimentary deposits indicative of taro and leaf vegetable (including Sonchus and Rorippa spp.) cultivation from Ahuahu, a northern New Zealand offshore island, with Raivavae and Rapa, both subtropical islands in French Polynesia. Preservation of taro pollen on all islands between 1300 CE and 1550 CE indicates perennial cultivation over multiple growing seasons, as plants rarely flower when frequently harvested. The pollen cooccurs with previously undetected fossil remains of extinct trees, as well as many weeds and commensal invertebrates common to tropical Polynesian gardens. Sedimentary charcoal and charred plant remains show that fire use rapidly reduced forest cover, particularly on Ahuahu. Fires were less frequent by 1500 CE on all islands as forest cover diminished, and short-lived plants increased, indicating higher-intensity production. The northern offshore islands of New Zealand were likely preferred sites for early gardens where taro production was briefly attempted, before being supplanted by sweet potato (Ipomoea batatas), a more temperate climate-adapted crop, which was later established in large-scale cultivation systems on the mainland after 1500 CE.

A Review on Viruses Infecting Taro (Colocasia esculenta (L.) Schott)

Taro is an important crop in parts of the world, especially in the Pacific Islands. Like all plants, it is also susceptible to virus infections that could result in diseases, which negatively affects the source of food and trade revenue. Understanding the biology of taro viruses could improve current knowledge regarding the relationship between viruses and taro, thus allowing for a better approach towards the management of the diseases that are associated with them. By compiling and discussing the research on taro and its four major viruses (Dasheen mosaic virus, Taro bacilliform virus, Colocasia bobone disease virus, and Taro vein chlorosis virus) and a relatively new one (Taro bacilliform CH virus), this paper explores the details of each virus by examining their characteristics and highlighting information that could be used to mitigate taro infections and disease management.

Literary evidence for taro in the ancient Mediterranean: A chronology of names and uses in a multilingual world

Taro, Colocasia esculenta (L.) Schott, is a vegetable and starchy root crop cultivated in Asia, Oceania, the Americas, Africa, and the Mediterranean. Very little is known about its early history in the Mediterranean, which previous authors have sought to trace through Classical (Greek and Latin) texts that record the name colocasia (including cognates) from the 3rd century BC onwards. In ancient literature, however, this name also refers to the sacred lotus, Nelumbo nucifera Gaertn. and its edible rhizome. Like taro, lotus is an alien introduction to the Mediterranean, and there has been considerable confusion regarding the true identity of plants referred to as colocasia in ancient literature. Another early name used to indicate taro was arum, a name already attested from the 4th century BC. Today, this name refers to Arum, an aroid genus native to West Asia, Europe, and the Mediterranean. Our aim is to explore historical references to taro in order to clarify when and through which routes this plant reached the Mediterranean. To investigate Greek and Latin texts, we performed a search using the Thesaurus Linguae Graecae (TLG) and the Thesaurus Linguae Latinae (TLL), plus commentaries and English and French translations of original texts. Results show that while in the early Greek and Latin literature the name kolokasia (Greek κολοκάσια) and its Latin equivalent colocasia refer to Nelumbo nucifera Gaertn., after the 4th century AD a poorly understood linguistic shift occurs, and colocasia becomes the name for taro. We also found that aron (Greek ἄρον) and its Latin equivalent arum are names used to indicate taro from the 3rd century BC and possibly earlier.

Population structure of elephant foot yams (Amorphophallus paeoniifolius (Dennst.) Nicolson) in Asia

The corms and leaves of elephant foot yams (Amorphophallus paeoniifolius (Dennst.) Nicolson) are important foods in the local diet in many Asian regions. The crop has high productivity and wide agroecological adaptation and exhibits suitability for the agroforestry system. Although the plant is assumed to reproduce via panmixia, a comprehensive study on the genetic background across regions to enhance wider consumer palatability is still lacking. Here, ten informative microsatellites were analyzed in 29 populations across regions in India, Indonesia and Thailand to understand the genetic diversity, population structure and distribution to improve breeding and conservation programs. The genetic diversity was high among and within regions. Some populations exhibited excess heterozygosity and bottlenecking. Pairwise FST indicated very high genetic differentiation across regions (FST = 0.274), and the Asian population was unlikely to be panmictic. Phylogenetic tree construction grouped the populations according to country of origin with the exception of the Medan population from Indonesia. The current gene flow was apparent within the regions but was restricted among the regions. The present study revealed that Indonesia and Thailand populations could be alternative centers of the gene pool, together with India. Consequently, regional action should be incorporated in genetic conservation and breeding efforts to develop new varieties with global acceptance.