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 ß-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.

Drought Stress Inhibits Starch Accumulation in Taro (Colocasia esculenta L. Schott).

BACKGROUND: Colocasia esculenta L. Schott is a main traditional root crop in China, serving as an important vegetable and staple food. Drought stress plays vital role on the growth and development of taro corm. METHODS: Two different varieties of taro in Jiangsu were selected: Xiangsha taro and Longxiang taro. The accumulation characteristics, morphological structure, and physicochemical properties of taro corm starch were studied by microscopic observation, particle size analysis, and X-ray diffractometer (XRD) analysis. Transcriptome analyses were used to identify the related genes of taro corm under drought stress. RESULTS: During the growth of taro, the number of amyloplasts showed an obvious increasing trend and shifted from being dispersed throughout the cells to being gathered on one side of the cells, and morphological observations showed that smaller granular distribution gradually changed to a larger lumpy distribution. The particle size of Longxiang taro is smaller than that of Xiangsha taro. Under drought stress conditions, the occurrence of starch grains and corm size were inhibited in Xiangsha taro. Transcriptome sequencing of drought-stressed taro corms showed that the enzymes related to starch synthesis were differentially expressed. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of drought-stressed taro corms showed that drought affected hormone signal transduction, material metabolism, drought stress tolerance, plant growth and development, and stress resistance, which triggered the plant drought adaptive response. CONCLUSIONS: Drought stress inhibits starch accumulation in taro.

Comparative Metabolome and Transcriptome Analyses Reveal the Regulatory Mechanism of Purple Leafstalk Production in Taro (Colocasia esculenta L. Schott).

Taro is a plant in the Araceae family, and its leafstalk possesses significant botanical and culinary value owing to its noteworthy medicinal and nutritional attributes. Leafstalk colour is an essential attribute that significantly influences its desirability and appeal to both breeders and consumers. However, limited information is available about the underlying mechanism responsible for the taro plant's colouration. Thus, the purpose of the current study was to elucidate the information on purple leafstalks in taro through comprehensive metabolome and transcriptome analysis. In total, 187 flavonoids, including 10 anthocyanins, were identified. Among the various compounds analysed, it was observed that the concentrations of five anthocyanins (keracyanin chloride (cyanidin 3-O-rutinoside chloride), cyanidin 3-O-glucoside, tulipanin (delphinidin 3-rutinoside chloride), idaein chloride (cyanidin 3-O-galactoside), and cyanidin chloride) were found to be higher in purple taro leafstalk compared to green taro leafstalk. Furthermore, a total of 3330 differentially expressed genes (DEGs) were identified by transcriptome analysis. Subsequently, the correlation network analysis was performed to investigate the relationship between the expression levels of these differentially expressed genes and the content of anthocyanin. There were 18 DEGs encoding nine enzymes detected as the fundamental structural genes contributing to anthocyanin biosynthesis, along with seven transcription factors (3 MYB and 4 bHLH) that may be promising candidate modulators of the anthocyanin biosynthesis process in purple taro leafstalk. The findings of the current investigation not only provide a comprehensive transcriptional code, but also give information on anthocyanin metabolites as well as beneficial insights into the colour mechanism of purple taro leafstalk.

Evaluation and phenotypic plasticity of taro [Colocasia esculenta (l.) Schott.] genotypes for nutrient and anti-nutrient composition.

The study was carried out to determine the nutritional and anti-nutritional composition of taro genotypes and also determine the phenotypic plasticity of the genotypes in two agro ecological zones in Ghana. The towns and zones were Bunso in the semi deciduous forest (an upland) and Tano Dumasi in the forest savannah transition agro-ecological (a waterlogged area) zone in the Eastern and Ashanti regions respectively.Two (2) freshly harvested corms of each genotype from each location were assessed for their nutritional (moisture, protein, carbohydrate, ash and fat) and anti-nutritional (phytate, oxalate and tannin) composition Data collected were subjected to analysis of variance and AMMI analysis using GenStat 12 edition to assess the effect of genotype, environment and their interaction on the traits studied. Phenotypic plasticity for the genotypes and the traits studied was also calculated. Pearson correlation was also conducted to assess the relationship between the traits studied. There were significant differences among the genotypes for nutrient and anti-nutrient composition except for percentage fat, indicating enough genetic variability among the genotypes, giving room for good selection progress for development of taro varieties. A higher magnitude of the environment over genotype and genotype by environment interaction observed indicates the influence of environment in the expression of the nutritional and anti-nutritional traits. Observed varied phenotypic plasticity among the genotypes for the nutrient and anti-nutrients composition also indicates varied adaptation of the genotypes to the environment. Genotypes BL/SM/115, CE/MAL/32 and CE/IND/16 and hybrids KAO19 × CE/MAL/32 and CE/IND/16×KAO19, CE/IND/16 × BL/SM/10, and CE/IND/16 × BL/SM/115 which recorded high nutrients and low anti-nutrients content and were stable across the environments can be released to farmers for cultivation. They could also be included in breeding programs for the development of enhanced nutritional quality of taro in Ghana.

Modulation of MRSA virulence gene expression by the wall teichoic acid enzyme TarO.

Phenol-soluble modulins (PSMs) and Staphylococcal protein A (SpA) are key virulence determinants for community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA), an important human pathogen that causes a wide range of diseases. Here, using chemical and genetic approaches, we show that inhibition of TarO, the first enzyme in the wall teichoic acid (WTA) biosynthetic pathway, decreases the expression of genes encoding PSMs and SpA in the prototypical CA-MRSA strain USA300 LAC. Mechanistically, these effects are linked to the activation of VraRS two-component system that directly represses the expression of accessory gene regulator (agr) locus and spa. The activation of VraRS was due in part to the loss of the functional integrity of penicillin-binding protein 2 (PBP2) in a PBP2a-dependent manner. TarO inhibition can also activate VraRS in a manner independent of PBP2a. We provide multiple lines of evidence that accumulation of lipid-linked peptidoglycan precursors is a trigger for the activation of VraRS. In sum, our results reveal that WTA biosynthesis plays an important role in the regulation of virulence gene expression in CA-MRSA, underlining TarO as an attractive target for anti-virulence therapy. Our data also suggest that acquisition of PBP2a-encoding mecA gene can impart an additional regulatory layer for the modulation of key signaling pathways in S. aureus.

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.

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.

Examination of the Virome of Taro Plants Affected by a Lethal Disease, the Alomae-Bobone Virus Complex, in Papua New Guinea.

Alomae-bobone virus complex (ABVC) is a lethal but still understudied disease that is limited to the Solomon Islands and Papua New Guinea. The only virus clearly associated to ABVC is Colocasia bobone disease-associated virus (CBDaV). Taro (Colocasia esculenta) plants with and without symptoms of ABVC disease were sampled from two locations in Papua New Guinea and examined for viruses using high-throughput sequencing (HTS). Similar to previous reports, isolates of CBDaV were present only in symptomatic plants, further supporting its role in the disease. The only other viruses consistently present in symptomatic plants were badnaviruses: taro bacilliform virus (TaBV) and/or taro bacilliform CH virus (TaBCHV). If ABVC requires co-infection by multiple viruses, CBDaV and badnavirus infection appears to be the most likely combination. The complete genomes of two isolates of CBDaV and TaBCHV, and single isolates of TaBV and dasheen mosaic virus, were obtained in this study, furthering our knowledge of the genetic diversity of these relatively understudied taro viruses. HTS data also provided evidence for an agent similar to umbra-like viruses that we are tentatively designating it as Colocasia umbra-like virus (CULV).

Screening of biocontrol bacteria against soft rot disease of Colocasia esculenta (L.) schott and its field application.

Soft rot disease is a major pathogenic bacteria of Fuding areca taro and has caused serious losses. This study aims to screen biocontrol bacterial against soft rot disease. A total of 53 bacterial strains were isolated from the rhizosphere soil, nine of which exhibited good biocontrol effect against the pathogenic bacteria of soft rot disease as seen in antagonistic screening of biocontrol bacteria from corm in vitro. Strains were selected by physical and chemical experiments, biocontrol effect tests in vivo, molecular sequencing, morphological observation and field tests. Four strains including CAB-L005, CAB-L012, CAB-L014, and CAB-L022 exhibited strong antagonistic effects. On the basis of the sequence homology of 16S rRNA genes, the similarity between strain CAB-L005 and Bacillus tropicus was 100%, that between strain CAB-L012 and Bacillus subtilis was 99%, and that between strain CAB-L014 and Bacillus tequilensis was 100%, and similarity between strain CAB-L022 and Bacillus cereus was 100%. The isolated bacteria demonstrated good biocontrol effects in field experiments. In this study, four strains with good biocontrol application value were isolated and identified, providing a foundation for biocontrol against soft rot disease in areca taro.

Genome Sequence Resource of Phytophthora colocasiae from China Using Nanopore Sequencing Technology.

Phytophthora colocasiae is a destructive oomycete pathogen of taro (Colocasia esculenta), which causes taro leaf blight. To date, only one highly fragmented Illumina short-read-based genome assembly is available for this species. To address this problem, we sequenced strain Lyd2019 from China using Oxford Nanopore Technologies long-read sequencing and Illumina short-read sequencing. We generated a 92.51-Mb genome assembly consisting of 105 contigs with an N50 of 1.70 Mb and a maximum length of 4.17 Mb. In the genome assembly, we identified 52.78% repeats and 18,322 protein-coding genes, of which 12,782 genes were annotated. We also identified 191 candidate RXLR effectors and 1 candidate crinkling and necrosis effector. The updated near-chromosome genome assembly and annotation resources will provide a better understanding of the infection mechanisms of P. colocasiae.

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.

Genetic Diversity and DNA Fingerprints of Three Important Aquatic Vegetables by EST-SSR Markers.

Twenty-two sacred lotus (Nelumbo nucifera), 46 taros (Colocasia esculenta) and 10 arrowheads (Sagittaria trifolia) were used as materials and combined with EST-SSR (expressed sequence tag-simple sequence repeats) primers developed by our laboratory. Core primers were screened from a large number of primers that were able to distinguish all materials with a high frequency of polymorphisms. Six pairs, twenty pairs and three pairs of core primers were screened from sacred lotus, taro, and arrowhead, respectively. The SSR fingerprints of these three important aquatic vegetables, producing 17-, 87- and 14-bit binary molecular identity cards, respectively, were separately determined by using the core primers. Since there were few core primers of sacred lotus and arrowhead, 3 and 9 primer pairs with higher polymorphic information content (PIC), respectively, were selected as candidate primers. These core and candidate primers were used to identify the purities of No.36 space lotus, Shandong 8502 taro and Wuhan arrowhead, which were 93.3% (84/90), 98.9% (89/90) and 100.0% (90/90), respectively. The fingerprints, displayed as binary molecular identification cards of three important aquatic vegetables, were obtained, and their purity was successfully determined with EST-SSR labeling technology. Phylogenetic trees were also constructed to analyze the genetic diversity of 22 sacred lotus, 46 taros and 10 arrowheads. This study classifies and identifies germplasm resources and is an important reference to test the authenticity and variety purity of other aquatic vegetables in the future.

Conserving and Sharing Taro Genetic Resources for the Benefit of Global Taro Cultivation: A Core Contribution of the Centre for Pacific Crops and Trees.

This review article gives an account of the origin, domestication, and dispersal of taro, a staple food crop in many countries in the humid tropics and subtropics. Genetic diversity studies indicated that distinct gene pools exist in all the regions where taro may be naturally distributed-the Indian subcontinent, China, Southeast Asia, and in Oceania. The Asian gene pool presented the highest genetic diversity. Diploid taro is prevalent in the Pacific Islands, while both diploids and triploids are found in mainland Asia. Triploids are thought to provide better adaptability and enhanced hardiness to higher altitudes and latitudes where sexual reproduction is not viable. The Centre for Pacific Crops and Trees (CePaCT) conserves in vitro close to 70% of the taro genetic resources held ex situ and is therefore considered the world center for taro genetic resources. Phytophthora colocasiae or taro leaf blight (TLB) is the most severe disease of taro' causing 25%-50% yield losses and postharvest decay of corms. The CePaCT genebank supported the participatory TLB breeding program in Samoa through the provision of diverse taro germplasm from the Asian gene pool. However, CePaCT not only serves taro producers in the Pacific but also shares new allelic diversity of taro globally. More recent distributions of taro genetic diversity to West and Central Africa were in response to an outbreak and spread of TLB in West Africa. Global dissemination of taro genetic diversity is assisting producer countries in the process of adaptation to emerging biotic and abiotic stresses, exacerbated by climate change.

Expression of Colocasia esculenta tuber agglutinin in Indian mustard provides resistance against Lipaphis erysimi and the expressed protein is non-allergenic.

KEY MESSAGE: Transgenic Brassica juncea plants expressing Colocasia esculenta tuber agglutinin (CEA) shows the non-allergenic nature of the expressed protein leading to enhanced mortality and reduced fecundity of mustard aphid-Lipaphis erysimi. Lipaphis erysimi (common name: mustard aphid) is the most devastating sucking insect pest of Indian mustard (Brassica juncea L.). Colocasia esculenta tuber agglutinin (CEA), a GNA (Galanthus nivalis agglutinin)-related lectin has previously been reported by the present group to be effective against a wide array of hemipteran insects in artificial diet-based bioassays. In the present study, efficacy of CEA in controlling L. erysimi has been established through the development of transgenic B. juncea expressing this novel lectin. Southern hybridization of the transgenic plants confirmed stable integration of cea gene. Expression of CEA in T0, T1 and T2 transgenic plants was confirmed through western blot analysis. Level of expression of CEA in the T2 transgenic B. juncea ranged from 0.2 to 0.47% of the total soluble protein. In the in planta insect bioassays, the CEA expressing B. juncea lines exhibited enhanced insect mortality of 70-81.67%, whereas fecundity of L. erysimi was reduced by 49.35-62.11% compared to the control plants. Biosafety assessment of the transgenic B. juncea protein containing CEA was carried out by weight of evidence approach following the recommendations by FAO/WHO (Evaluation of the allergenicity of genetically modified foods: report of a joint FAO/WHO expert consultation, 22-25 Jan, Rome, http://www.fao.org/docrep/007/y0820e/y0820e00.HTM , 2001), Codex (Codex principles and guidelines on foods derived from biotechnology, Food and Agriculture Organization of the United Nations, Rome; Codex, Codex principles and guidelines on foods derived from biotechnology, Food and Agriculture Organization of the United Nations, Rome, 2003) and ICMR (Indian Council of Medical Research, guidelines for safety assessment of food derived from genetically engineered plants, http://www.icmr.nic.in/guide/Guidelines%20for%20Genetically%20Engineered%20Plants.pdf , 2008). Bioinformatics analysis, pepsin digestibility, thermal stability assay, immuno-screening and allergenicity assessment in BALB/c mice model demonstrated that the expressed CEA protein from transgenic B. juncea does not incite any allergenic response. The present study establishes CEA as an efficient insecticidal and non-allergenic protein to be utilized for controlling mustard aphid and similar hemipteran insects through the development of genetically modified plants.

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.

Chromosome number and genome size variation in Colocasia (Araceae) from China.

Chromosome number and genome size are important cytological characters that significantly influence various organismal traits. We investigated chromosome number and genome size variation in 73 accessions belonging to four Colocasia species from China. Five different chromosome counts (2n = 26, 28, 38, 42, and 56) were found, the largest one representing a new record in Colocasia. The basic chromosome numbers are x = 13, 14, and 19, corresponding to 2x, 3x, and 4x cytotypes. Yunnan Province, China is considered the center of Colocasia polyploid origin. The 2C values in our accessions ranged from 3.29 pg in C. gigantea to 12.51 pg in C. esculenta. All species exhibit inter- and intraspecific chromosomal variation. Differences in DNA content among the Colocasia species seem to have occurred by chromosomal gain under similar habitats. Polyploidization also obviously contributes to 2C value variation.

Two-step identification of taro (Colocasia esculenta cv. Xinmaoyu) using specific psbE-petL and simple sequence repeat-sequence characterized amplified regions (SSR-SCAR) markers.

Colocasia esculenta cv. Xinmaoyu is an eddoe-type taro cultivar local to Taicang, Jiangsu Province, China; it is characterized by its pure flavor, glutinous texture, and high nutritional value. Due to its excellent qualities, the Trademark Office of the State Administration for Industry and Commerce of the People's Republic of China awarded Xinmaoyu, a geographical indication certification in 2014. Therefore, there is an urgent need to develop an efficient molecular marker for the specific identification of this cultivar, which would greatly facilitate the conservation and utilization of this unique germplasm resource. In the present study, amplifying the psbE-petL fragment from two dasheen-type and seven eddoe-type taro cultivars revealed three conserved insertions/deletions among sequences from the two taro types. Based on these sequence differences, a pair of site-specific primers was designed targeting the psbE-petL sequence from the dasheen-type taro, which specifically amplified a DNA band in all individuals from cultivars of this type, but not in those from the seven eddoe-type cultivars. To discriminate Xinmaoyu from the other eddoe-type taro cultivars, a pair of simple sequence repeat-sequence characterized amplified region (SSR-SCAR) primers was further developed to specifically amplify a DNA band from all Xinmaoyu individuals, but not from individuals of other eddoe-type taro cultivars. In conclusion, through a two-step-screening procedure using psbE-petL and SSR-SCAR markers, we developed a pair of primers that could specifically discriminate Xinmaoyu from nine taro cultivars commonly cultivated in Jiangsu Province and Fujian Province.

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

Taro (Colocasia esculenta (L.) Schott) is widely distributed in tropical and sub-tropical areas. However, its origin, diversification and dispersal remain unclear. While taro genetic diversity has been documented at the country and regional levels in Asia and the Pacific, few reports are available from Americas and Africa where it has been introduced through human migrations. We used eleven microsatellite markers to investigate the diversity and diversification of taro accessions from nineteen countries in Asia, the Pacific, Africa and America. The highest genetic diversity and number of private alleles were observed in Asian accessions, mainly from India. While taro has been diversified in Asia and the Pacific mostly via sexual reproduction, clonal reproduction with mutation appeared predominant in African and American countries investigated. Bayesian clustering revealed a first genetic group of diploids from the Asia-Pacific region and to a second diploid-triploid group mainly from India. Admixed cultivars between the two genetic pools were also found. In West Africa, most cultivars were found to have originated from India. Only one multi-locus lineage was assigned to the Asian pool, while cultivars in Madagascar originated from India and Indonesia. The South African cultivars shared lineages with Japan. The Caribbean Islands cultivars were found to have originated from the Pacific, while in Costa Rica they were from India or admixed between Indian and Asian groups. Taro dispersal in the different areas of Africa and America is thus discussed in the light of available records of voyages and settlements.