Mining and validation of novel genotyping-by-sequencing (GBS)-based simple sequence repeats (SSRs) and their application for the estimation of the genetic diversity and population structure of coconuts (Cocos nucifera L.) in Thailand

Genetic Analysis and Fingerprint Construction for Isatis indigotica Fort. Using SSR Markers

Isatis indigotica Fort. is a traditional medicinal plant, which has anti-inflammatory, antioxidant, and antiviral properties. Despite the development and licensing of several cultivars in recent years, morphological similarity among cultivars complicates their identification. The genetic diversity within I. indigotica significantly impacts the biosynthesis of bioactive substances. To elucidate genetic relationships and evaluate bioactive compounds, I. indigotica cultivars were analyzed using SSR markers. A total of 109 alleles were identified across 29 cultivars at 20 SSR loci, exhibiting a genetic diversity with an average polymorphic information content (PIC) of 0.46. Phylogenetic, principal coordinate analysis (PCoA), and Bayesian clustering revealed that genetic relationships were largely independent of geographic origin, potentially due to regional transplantations. Notably, some cultivars with distinct leaf sizes showed clear genetic differentiation, highlighting their potential as candidates for quality evaluation. A fingerprint was successfully constructed using five SSR markers. These findings provide technical support for cultivar identification, quality evaluation, and intellectual property protection of I. indigotica cultivars.

Genome-wide association analysis reveals regulatory genes for the metabolite synthesis of 2-acetyl-1-pyrroline in aromatic coconut (Cocos nucifera L.)

Coconut (Cocos nucifera L.) is a key tropical economic tree valued for its fruit flavor, particularly 2-acetyl-1-pyrroline (2AP), a vital aroma metabolite. To enhance high-aromatic coconut breeding efforts, it is essential to deeply understand the hereditary factors governing the production of 2AP. In this study, a genome-wide association analysis identifies 32 loci that exhibit significant associations with 2AP content based on single nucleotide polymorphism (SNP) variations from 168 aromatic coconut germplasm resources. Transcriptome analysis then pinpoints 22 candidate genes near significant loci involved in 2AP metabolism. Proteins encoded by these genes are involved in amino acid metabolism, glycolysis, and secondary metabolism. Among these, Asparagine synthetase coding gene ASN1, Gamma-glutamylcysteine synthetase coding gene GSH1, and UbiA prenyltransferase coding gene UBIA are enriched in the linkage region constructed by significant locus Chr04_61490504. In particular, the SNP mutation of CnASN1 leads to amino acid changes in the functional region of the coding protein, potentially resulting in differences in 2AP content among haplotype populations. Identifying variations in related candidate genes, particularly the gene CnASN1, provides molecular markers closely associated with 2AP synthesis for coconut breeding and offers further insights into the metabolic mechanisms of 2AP.

Evaluation and characteristic analysis of SSRs from the transcriptomic sequences of Perilla crop (Perilla frutescens L.)

Perilla crop is a self-fertilizing annual plant, cultivated and used mainly in East Asia. Perilla frutescens var. frutescens seeds are rich in unsaturated fatty acids, which have health benefits, and Perilla frutescens var. crispa leaves are rich in anthocyanins. However, genomic analysis such as whole genome sequencing or genetic mapping has not been performed on Perilla crop. This current study confirms the abundance and diversity of 15,991 simple sequence repeats (SSRs) classified in previous studies in the Perilla genome, selects and designs 1,538 SSR primer sets, and confirms which SSR primer sets exhibit high polymorphism. Of the 15,991 SSRs classified, there were 9,910 (62%) dinucleotide repeats, 5,652 (35.3%) trinucleotide repeats, and 429 (2.7%) tetranucleotide repeats. Among these, the most identified was (CT)n with a total of 4,817. The 15,991 SSRs had 4 to 26 repeats. Four repeats were the most frequent with 11,084 (69.3%). A total of 1,538 SSR primers were selected and designed to confirm polymorphism, of which 157 showed persistent and clear polymorphism. Among these 157 SSR primer sets, 98 (62.4%) were dinucleotide repeats, 39 (24.8%) were trinucleotide repeats, and 20 (12.7%) were tetranucleotide repeats. Among 549 SSR primers that showed polymorphism, trinucleotide repeats showed persistent polymorphism at a high rate. Therefore, when developing SSR primer sets for Perilla crop in the future, it is recommended that trinucleotide repeats be selected first. These research results will be helpful in future genomic analysis and development of SSR primers in Perilla crop.

Genetic Diversity and Fingerprinting of 231 Mango Germplasm Using Genome SSR Markers

Mango (Mangifera indica L.) (2n = 40) is an important perennial fruit tree in tropical and subtropical regions. The lack of information on genetic diversity at the molecular level hinders efforts in mango genetic improvement and molecular marker-assisted breeding. In this study, a genome-wide screening was conducted to develop simple sequence repeat (SSR) markers using the Alphonso reference genome. A total of 187 SSR primer pairs were designed based on SSR loci with consisting of tri- to hexa-nucleotide motifs, and 34 highly polymorphic primer pairs were selected to analyze the diversity of 231 germplasm resources. These primers amplified 219 alleles (Na) across 231 accessions, averaging of 6.441 alleles for per marker. The polymorphic information content (PIC) values ranged from 0.509 to 0.757 with a mean of 0.620. Genetic diversity varied among populations, with Southeast Asia showing the highest diversity, and Australia the lowest. Population structure analysis, divided the accessions into two groups, Group I (India) and Group II (Southeast Asia), containing 104 and 127 accessions, respectively, consistent with results from phylogenetic analysis and principal component analysis (PCA). Sixteen SSR primer pairs capable of distinguishing all tested accessions, were selected as core primers for constructing fingerprints of 229 mango accessions. These findings offer valuable resources for enhancing the utilization of mango germplasm in breeding programs.

Whole-Genome Resequencing Identifies SNPs in Sucrose Synthase and Sugar Transporter Genes Associated with Sweetness in Coconut

Coconut (Cocos nucifera L.) is an important agricultural commodity with substantial economic and nutritional value, widely used for various products, including coconut water. The sweetness is an important quality trait of coconut water, which is influenced by genetic and environmental factors. In this study, we utilized next-generation sequencing to identify genetic variations in the coconut genome associated with the sweetness of coconut water. Whole-genome resequencing of 49 coconut accessions, including diverse germplasm and an F2 population of 81 individuals, revealed ~27 M SNPs and ~1.5 M InDels. Sugar content measured by °Bx was highly variable across all accessions tested, with dwarf varieties generally sweeter. A comprehensive analysis of the sugar profiles revealed that sucrose was the major sugar contributing to sweetness. Allele mining of the 148 genes involved in sugar metabolism and transport and genotype-phenotype association tests revealed two significant SNPs in the hexose carrier protein (Cnu01G018720) and sucrose synthase (Cnu09G011120) genes associated with the higher sugar content in both the germplasm and F2 populations. This research provides valuable insights into the genetic basis of coconut sweetness and offers molecular markers for breeding programs aimed at improving coconut water quality. The identified variants can improve the selection process in breeding high-quality sweet coconut varieties and thus support the economic sustainability of coconut cultivation.

Genetic diversity, population structure, and genome-wide association analysis of ginkgo cultivars

Ginkgo biloba is an economically valuable tree worldwide. The species has nearly become extinct during the Quaternary, which has likely resulted in reduction of its genetic variability. The genetic variability is now conserved in few natural populations in China and a number of cultivars that are, however, derived from a few ancient trees, helping the species survive in China through medieval times. Despite the recent interest in ginkgo, however, detailed knowledge of its genetic diversity, conserved in cultivated trees and cultivars, has remained poor. This limits efficient conservation of its diversity as well as efficient use of the existing germplasm resources. Here we performed genotyping-by-sequencing (GBS) on 102 cultivated germplasms of ginkgo collected to explore their genetic structure, kinship, and inbreeding prediction. For the first time in ginkgo, a genome-wide association analysis study (GWAS) was used to attempt gene mapping of seed traits. The results showed that most of the germplasms did not show any obvious genetic relationship. The size of the ginkgo germplasm population expanded significantly around 1500 years ago during the Sui and Tang dynasties. Classification of seed cultivars based on a phylogenetic perspective does not support the current classification criteria based on phenotype. Twenty-four candidate genes were localized after performing GWAS on the seed traits. Overall, this study reveals the genetic basis of ginkgo seed traits and provides insights into its cultivation history. These findings will facilitate the conservation and utilization of the domesticated germplasms of this living fossil plant.

Improving Coconut Using Modern Breeding Technologies: Challenges and Opportunities

Coconut (Cocos nucifera L.) is a perennial palm with a wide range of distribution across tropical islands and coastlines. Multitude use of coconut by nature is important in the socio-economic fabric framework among rural smallholders in producing countries. It is a major source of income for 30 million farmers, while 60 million households rely on the coconut industry directly as farm workers and indirectly through the distribution, marketing, and processing of coconut and coconut-based products. Stagnant production, inadequate planting materials, the effects of climate change, as well as pests and diseases are among the key issues that need to be urgently addressed in the global coconut industry. Biotechnology has revolutionized conventional breeding approaches in creating genetic variation for trait improvement in a shorter period of time. In this review, we highlighted the challenges of current breeding strategies and the potential of biotechnological approaches, such as genomic-assisted breeding, next-generation sequencing (NGS)-based genotyping and genome editing tools in improving the coconut. Also, combining these technologies with high-throughput phenotyping approaches and speed breeding could speed up the rate of genetic gain in coconut breeding to solve problems that have been plaguing the industry for decades.

Morphological and Molecular Identification of Plant Pathogenic Fungi Associated with Dirty Panicle Disease in Coconuts (Cocos nucifera) in Thailand

Dirty panicle disease in coconuts (Cocos nucifera) was first observed in the KU-BEDO Coconut BioBank, Nakhon Pathom province, Thailand. The occurrence of the disease covers more than 30% of the total coconut plantation area. The symptoms include small brown to dark brown spots and discoloration of male flowers. Herein, three fungal strains were isolated from infected samples. Based on the morphological characteristics the fungal isolates, they were classified into two genera, namely, Alternaria (Al01) and Fusarium (FUO01 and FUP01). DNA sequences of internal transcribed spacer (ITS), glyceraldehyde 3-phosphate dehydrogenase (GAPDH), translation elongation factor 1-α (tef1-α), and RNA polymerase II second largest subunit (rpb2) revealed Al01 as Alternaria burnsii, whereas DNA sequences of ITS, rpb2, and tef1-α identified FUO01 and FUP01 as Fusarium clavum and F. tricinctum, respectively. A pathogenicity test by the agar plug method demonstrated that these pathogens cause dirty panicle disease similar to that observed in natural infections. To the best of our knowledge, this is the first report on the novel dirty panicle disease in coconuts in Thailand or elsewhere, demonstrating that it is associated with the plant pathogenic fungi A. burnsii, F. clavum, and F. tricinctum.

Genome-wide diversity analysis to infer population structure and linkage disequilibrium among Colombian coconut germplasm

Genetic diversity and relatedness of accessions for coconut growing in Colombia was unknown until this study. Here we develop single nucleotide polymorphisms (SNPs) along the coconut genome based on Genotyping by Sequencing (GBS) with the goal of analyze the genetic diversity, population structure, and linkage disequilibrium (LD) of a diverse coconut panel consisting of 112 coconut accessions from the Atlantic and Pacific coasts of Colombia. A comprehensive catalog of approximately 40,000 SNPs with a minor allele frequency (MAF) of > 0.05 is presented. A total of 40,614 SNPs were found but only 19,414 anchored to chromosomes. Of these, 10,338 and 4606 were exclusive to the Atlantic and Pacific gene pools, respectively, and 3432 SNPs could differentiate both gene pools. A filtered subset of unlinked and anchored SNPs (1271) showed a population structure at K = 4, separating accessions from the Pacific and Atlantic coasts that can also be distinguished by palm height, as found in previous studies. The Pacific groups had a slow LD decay, low Fixation Index (Fst) and low nucleotide diversity (π), while the Atlantic group had slightly higher genetic diversity and faster LD decay. Genome-wide diversity analyses are of importance to promote germplasm conservation and breeding programs aimed at developing new cultivars better adapted to the region.

Insights on Genetic Diversity, Population Structure, and Linkage Disequilibrium in Globally Diverse Coconut Accessions Using Genotyping-by-Sequencing

Genotyping-by-sequencing (GBS) has emerged as a cost-effective approach for genome-wide discovery of single-nucleotide polymorphism (SNP) markers and high-throughput genotyping. In this study, 96 coconut palms, representing 16 accessions from globally diverse origins, were genotyped using the GBS strategy. A total of 10,835 high-quality SNPs, which were identified after stringent filtering, were utilized to assess genetic diversity, population structure, and linkage disequilibrium (LD) analyses. The polymorphism information content (PIC) values of SNPs ranged from 0.1 to 0.4, with a large proportion of SNPs (8633 nos.; 79.7%) having a higher PIC in the range of 0.3-0.4. The genetic diversity analysis revealed the existence of a high level of variation in coconut accessions, with an average expected heterozygosity (H_e) value of 0.43. Unweighted neighbor-joining phylogenetic tree and Bayesian-based model population structure grouped coconut genotypes into four main clusters. The accessions are generally clustered based on their height (tall or dwarf), with a few accession clusterings based on geographical origins. Investigation of LD pattern in coconut indicated a relatively rapid LD decay with a short range (9 kb). The results obtained in this study will contribute to enhancing the capacity of coconut researchers to utilize genetic diversity for further genetic improvement. In addition, it would open up possibilities for performing genomic studies such as genome-wide association studies and genomic selection to accelerate the efficiency and speed of coconut genetic improvement.

Genome-wide simple sequence repeats (SSR) markers discovered from whole-genome sequence comparisons of multiple spinach accessions

The availability of well-assembled genome sequences and reduced sequencing costs have enabled the resequencing of many additional accessions in several crops, thus facilitating the rapid discovery and development of simple sequence repeat (SSR) markers. Although the genome sequence of inbred spinach line Sp75 is available, previous efforts have resulted in a limited number of useful SSR markers. Identification of additional polymorphic SSR markers will support genetics and breeding research in spinach. This study aimed to use the available genomic resources to mine and catalog a large number of polymorphic SSR markers. A search for SSR loci on six chromosome sequences of spinach line Sp75 using GMATA identified a total of 42,155 loci with repeat motifs of two to six nucleotides in the Sp75 reference genome. Whole-genome sequences (30x) of additional 21 accessions were aligned against the chromosome sequences of the reference genome and in silico genotyped using the HipSTR program by comparing and counting repeat numbers variation across the SSR loci among the accessions. The HipSTR program generated SSR genotype data were filtered for monomorphic and high missing loci, and a final set of the 5986 polymorphic SSR loci were identified. The polymorphic SSR loci were present at a density of 12.9 SSRs/Mb and were physically mapped. Out of 36 randomly selected SSR loci for validation, two failed to amplify, while the remaining were all polymorphic in a set of 48 spinach accessions from 34 countries. Genetic diversity analysis performed using the SSRs allele score data on the 48 spinach accessions showed three main population groups. This strategy to mine and develop polymorphic SSR markers by a comparative analysis of the genome sequences of multiple accessions and computational genotyping of the candidate SSR loci eliminates the need for laborious experimental screening. Our approach increased the efficiency of discovering a large set of novel polymorphic SSR markers, as demonstrated in this report.

Genome-wide simple sequence repeats (SSR) markers discovered from whole-genome sequence comparisons of multiple spinach accessions

The availability of well-assembled genome sequences and reduced sequencing costs have enabled the resequencing of many additional accessions in several crops, thus facilitating the rapid discovery and development of simple sequence repeat (SSR) markers. Although the genome sequence of inbred spinach line Sp75 is available, previous efforts have resulted in a limited number of useful SSR markers. Identification of additional polymorphic SSR markers will support genetics and breeding research in spinach. This study aimed to use the available genomic resources to mine and catalog a large number of polymorphic SSR markers. A search for SSR loci on six chromosome sequences of spinach line Sp75 using GMATA identified a total of 42,155 loci with repeat motifs of two to six nucleotides in the Sp75 reference genome. Whole-genome sequences (30x) of additional 21 accessions were aligned against the chromosome sequences of the reference genome and in silico genotyped using the HipSTR program by comparing and counting repeat numbers variation across the SSR loci among the accessions. The HipSTR program generated SSR genotype data were filtered for monomorphic and high missing loci, and a final set of the 5986 polymorphic SSR loci were identified. The polymorphic SSR loci were present at a density of 12.9 SSRs/Mb and were physically mapped. Out of 36 randomly selected SSR loci for validation, two failed to amplify, while the remaining were all polymorphic in a set of 48 spinach accessions from 34 countries. Genetic diversity analysis performed using the SSRs allele score data on the 48 spinach accessions showed three main population groups. This strategy to mine and develop polymorphic SSR markers by a comparative analysis of the genome sequences of multiple accessions and computational genotyping of the candidate SSR loci eliminates the need for laborious experimental screening. Our approach increased the efficiency of discovering a large set of novel polymorphic SSR markers, as demonstrated in this report.