Asia is where the mango began. India alone contributes nearly half of global production and serves as a major reservoir of genetic variability, while South and Southeast Asia harbour wild relatives, traditional landraces and farmer-selected cultivars that differ dramatically in flowering response, fruiting season, quality attributes and stress adaptation. The review emphasizes that this variation reflects a complex history of domestication, natural hybridization and long-term local adaptation. Mango is a highly heterozygous, predominantly cross-pollinated species, which drives extensive genetic recombination among seedling progenies. Polyembryony, present in several cultivars, adds another layer of complexity by allowing both sexual and nucellar reproduction, preserving maternal genotypes while still generating novel variation. Natural hybridization between cultivated and wild Mangifera species, particularly in Southeast Asia, has further shaped the crop’s genetic architecture.

For most of the past few decades, researchers probing this diversity relied on a succession of molecular marker systems, and the review offers a candid technical assessment of their trade-offs. Random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR) markers are inexpensive and technically simple, requiring no prior sequence information, but their dominant inheritance and sensitivity to reaction conditions limit reproducibility and preclude accurate estimates of heterozygosity. A direct comparison in mango cultivars found RAPD markers markedly less informative than microsatellites, with a mean polymorphism information content of 0.378 versus 0.735. Amplified fragment length polymorphism (AFLP) markers offer broader genome coverage and can uncover variation missed by other dominant systems, yet their technical complexity and cost have restricted large-scale adoption.

Simple sequence repeat (SSR) markers emerged as the workhorse of mango germplasm characterization, combining co-dominant inheritance, high polymorphism and cross-laboratory reproducibility. Their impact is illustrated by a genome-wide SSR analysis of 231 accessions that detected 219 alleles and identified a streamlined panel of just 16 core primers capable of discriminating nearly all tested cultivars. Such panels are invaluable for duplicate detection, varietal authentication and routine genebank curation. SSR-based population analyses have consistently separated Indian monoembryonic and Southeast Asian polyembryonic gene pools, a division that reflects both domestication history and reproductive biology. Microsatellite studies of Indian gene pools have reported population differentiation values as high as 0.248 between geographically distinct groups, underscoring how strongly shared ancestry structures the crop.

The real transformation, however, has come with next-generation sequencing. Single nucleotide polymorphism (SNP) platforms, genotyping-by-sequencing, whole-genome resequencing and transcriptomics now allow researchers to interrogate thousands to millions of loci across large germplasm panels. A SLAF-seq-based study in China evaluated 284 mango accessions from major producing regions including India, Pakistan, Thailand, Myanmar, Sri Lanka, Indonesia, the Philippines, Australia, the United States and China, and consistently recovered two major genetic groups corresponding to the Indian and Southeast Asian gene pools. The review argues that this recurring separation represents a genuine, deeply rooted domestication signal rather than a methodological artifact, pointing to independent domestication pathways and long-term geographical isolation between the lineages.

Reference genome assemblies have provided the scaffolding for this genomic era. A high-density consensus genetic map built from mapping populations spanning Florida, Queensland, Brazil and Israel integrated diverse breeding germplasm across major mango-growing regions. Whole-genome sequencing work in China using the Indian cultivar Alphonso delivered chromosome-scale resources and confirmed allelic admixture in several commercial cultivars, particularly those derived from Western breeding programmes. Transcriptome-derived SNP analyses in Israel revealed clear structuring among accessions from Southeast Asia, India and Floridian breeding programmes, while RNA-sequencing studies across multiple tissues and developmental stages have identified differentially expressed genes tied to fruit ripening, flavour biosynthesis, flowering regulation and stress responses. High-throughput genotyping has also begun linking genomic regions to agronomic traits including fruit size, peel colour, flowering behaviour and abiotic stress tolerance.

The review is equally attentive to the classical layers of diversity that genomics must ultimately explain. Morphological variation in tree growth habit, canopy architecture, leaf form, inflorescence structure and fruit characteristics such as size, shape, skin colour, pulp texture and seed type has traditionally underpinned cultivar identification and farmer selection, guided by standardized frameworks from Bioversity International, DUS testing guidelines and UPOV protocols. Biochemical diversity is equally striking, with substantial genotypic variation documented in total soluble solids, acidity, sugar-acid ratios, carotenoids, polyphenols and bioactive compounds such as mangiferin, which confer antioxidant, anti-inflammatory and anticancer properties. Physiological traits, including responses to temperature extremes, drought and photoperiod, along with the duration of the juvenile phase and polyembryony itself, round out a phenotype that genomics is only beginning to connect to sequence variation.

On the conservation front, the review maps a two-pronged strategy. In situ approaches preserve wild populations and traditional orchards in their natural habitats, including indigenous seedling populations in the forests of Tripura, Orissa, Chota Nagpur and the Western Ghats that exhibit primitive traits such as polyembryony, dwarfism and stress tolerance, as well as wild populations in northeastern India that retain ancestral characteristics without hybridization with commercial cultivars. Ex situ conservation relies heavily on field gene banks, which face pressures from land use, pests and disease but remain essential for elite and rare accessions. Community-based custodianship, through home gardens, sacred groves and diversity fairs, sustains locally adapted landraces often absent from institutional collections, and the authors argue that strengthening links between these community stewards and formal genebanks through joint documentation and benefit-sharing will be critical for long-term resilience.

Looking forward, the review identifies a suite of emerging technologies poised to accelerate mango improvement. Genomic selection, which predicts breeding values from genome-wide marker profiles, is particularly promising for a crop with a long juvenile period, because it could enable early, pre-flowering selection of superior seedlings and substantially shorten breeding cycles. Pangenomic approaches that capture structural variation across multiple reference genomes are expected to reveal variation missed by single-reference resequencing, while CRISPR/Cas-based genome editing offers potential for precise modification of ripening behaviour, disease susceptibility and postharvest quality, albeit constrained by mango’s long generation time and the technical challenges of transformation. High-throughput phenotyping using imaging and remote sensing could resolve a major bottleneck in linking genomic data to field performance.

The gaps that remain are as instructive as the findings. Comprehensive genome-wide characterization is concentrated in India and China, leaving germplasm from Myanmar, Cambodia, Laos and parts of Indonesia inadequately sampled, and studies from Bangladesh, Vietnam and the Philippines still rely predominantly on earlier-generation markers that likely underestimate true diversity. Inconsistent marker panels and reporting standards hamper cross-regional comparison, and the functional basis of key traits such as polyembryony, flowering periodicity and biotic stress resistance remains incompletely resolved. The authors call for harmonized phenotyping protocols, expanded genome-wide association studies across diverse Asian germplasm, and digital databases integrating passport, phenotypic and genomic data. For breeders, the practical message is to prioritize genetically distinct and underrepresented material in crossing programmes; for policymakers, to support cross-border germplasm exchange. The King of Fruits, it turns out, will need every tool modern biology can offer to keep its throne in a warming, more unpredictable century.

Subject of Research: Genetic diversity and characterization of mango (Mangifera indica L.) germplasm in Asia

Article Title: A comprehensive review of genetic diversity and characterization of mango (Mangifera indica L.) germplasm in Asia

Article References: Rozerto, K., Alila, P., Pienyu, K., Choudhary, J., Chotso, K., & Singh, S. K. (2026). A comprehensive review of genetic diversity and characterization of mango (Mangifera indica L.) germplasm in Asia. Discover Plants, 3(1), Article 433. https://doi.org/10.1007/s44372-026-00913-5

Image Credits: AI Generated

DOI: 10.1007/s44372-026-00913-5

Keywords: mango, Mangifera indica, genetic diversity, germplasm, molecular markers, SSR, SNP, genomics, conservation, plant breeding, Asia, polyembryony

Aquilaria malaccensis, a member of the family Thymelaeaceae, occupies a peculiar position at the intersection of commerce and conservation. The tree itself is unremarkable until it is wounded or infected by certain fungi, at which point it produces a defensive resin that saturates the wood and transforms it into agarwood, known in the trade as oudh. Demand for this resin across the Middle East and East Asia has driven centuries of harvest from wild populations, pushing the species into decline across its native Southeast Asian range and earning it a place on Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora. India, where the tree is cultivated most intensively in states such as Assam and Tripura, has become a focal point for both the industry and for scientific efforts to ensure that cultivation does not erode the genetic foundations of the resource it depends on.

The research, led by Ranjith Layola M. R. and Avishek Bhattacharjee of the Botanical Survey of India’s Central National Herbarium in Howrah, together with colleagues from the Botanical Survey of India headquarters in Kolkata, was conducted as part of two government-funded initiatives: a project on non-detriment findings for Aquilaria malaccensis in India financed by the Ministry of Environment, Forest and Climate Change, and an in-house action plan on the molecular and phytochemical identification of thirty CITES-listed plants in high international trade. The team’s fieldwork spanned the major agarwood-cultivating states, gathering leaf material from plantations and forest department holdings to build a sampling frame that captures the breadth of India’s cultivated agarwood population.

At the technical heart of the study lies a class of genetic markers known as Simple Sequence Repeats, or SSRs, sometimes called microsatellites. These are short stretches of DNA in which a motif of one to six base pairs is repeated many times in tandem, such as CACACACA. Because the number of repeats at a given locus mutates rapidly and is inherited in a codominant Mendelian fashion, SSRs act as highly polymorphic signposts scattered across the genome, allowing researchers to distinguish individuals, estimate heterozygosity, and infer patterns of relatedness and population structure. The authors screened sixty SSR primer pairs drawn from previously published literature on Aquilaria malaccensis, including markers developed through genome-wide mining and next-generation sequencing efforts, and identified fifteen polymorphic markers suitable for genotyping the full set of 195 accessions.

Once the genotyping was complete, the team applied a battery of frequency-based and genetic distance-based statistics, complemented by formal population structure analysis. The results were striking in several respects. The average values of observed heterozygosity and the Shannon diversity index were high, indicating that most individuals in the sampled collection carry substantial genetic variability. This is encouraging news for a species whose wild relatives have been depleted: high heterozygosity generally signals a healthy capacity for adaptation and a reduced risk of inbreeding depression in cultivated stands. For breeders, it also means that the raw material for selection and improvement remains rich within India’s existing plantation base.

Equally informative was what the analysis revealed about how that diversity is distributed across the landscape. The researchers observed overall low genetic differentiation among populations combined with high gene flow, a pattern suggesting that planting material has been moved extensively among regions, most likely through the trade in seedlings and seeds that accompanies the expansion of agarwood cultivation. The analysis of molecular variance, or AMOVA, reinforced this picture: the largest share of genetic variance was partitioned within populations rather than among them. In practical terms, a farmer’s plantation in one state is likely to contain nearly as much genetic variation as the pooled collection from all states, a signature of a crop whose genetic stock has been thoroughly mixed by human hands rather than shaped by local isolation.

The population structure analysis added a further layer of nuance. Using the Bayesian clustering software STRUCTURE, which assigns individuals to genetic clusters based on multilocus genotype data, the team found that all 195 accessions resolved into two genetic clusters. Crucially, these clusters did not correspond to geography. Trees from the same state frequently belonged to different clusters, and individuals showed high levels of admixture, meaning their genomes carry ancestry from both clusters in varying proportions. This decoupling of genetic structure from geographic origin is consistent with a crop that has been founded from mixed sources and repeatedly exchanged among growers, and it suggests that conservation and breeding decisions cannot rely on state boundaries as proxies for genetic distinctiveness.

Why does this matter beyond the laboratory? For a CITES-listed species, the answer lies in the machinery of international regulation. Non-detriment findings, the scientific assessments that determine whether trade in a listed species can proceed without harming wild populations, depend on credible data about the status and genetic health of the resource. By documenting high within-population diversity and quantifying gene flow across India’s cultivated agarwood estate, the study provides exactly the kind of evidence base that regulators and forest departments need to design sustainable harvest and trade policies. It also feeds directly into crop improvement: knowing which individuals and clusters harbor the greatest diversity allows breeders to design crosses that preserve variability while selecting for traits such as resin yield and quality, the economic lifeblood of the industry.

The findings also carry a cautionary dimension. High gene flow and admixture, while beneficial for genetic health, can homogenize locally adapted variation if unchecked, and the absence of clear geographic structure means that unique genetic lineages could be silently lost if planting programs favor a narrow set of commercially popular stock. The authors’ dataset, with allele fragment length matrices and primer details provided in the supplementary materials, offers a practical toolkit for future monitoring, enabling plantation managers and researchers to track whether diversity is being maintained as the industry expands. The work was supported by the Botanical Survey of India’s research facilities, and the authors acknowledge the cooperation of forest departments and plantation owners across the sampling regions.

Agarwood occupies a rare position among industrial crops: it is simultaneously a global luxury commodity, a livelihood for thousands of smallholder farmers, and a species whose trade is scrutinized under one of the world’s most stringent conservation treaties. The new study demonstrates that India’s cultivated agarwood trees still hold a deep reservoir of genetic diversity, but that this diversity is woven into a thoroughly mixed, human-mediated landscape rather than organized into neat geographic populations. As demand for oudh continues to rise and cultivation spreads, the genetic map drawn by this research will serve as a baseline against which the future health of the crop, and the sustainability of the trade built upon it, can be measured.

Subject of Research: Genetic diversity and population structure of the CITES-listed agarwood tree Aquilaria malaccensis in India assessed with microsatellite markers

Article Title: Genetic diversity analysis in Aquilaria malaccensis (Agarwood) in India, a CITES-listed industrial crop using microsatellite markers

Article References: Layola M. R., R., Kushwaha, P. S., Mallick, B., Chakraborty, S., Banu, F., Shaw, R., Chakraborty, O., Sengupta, S., Chakraborty, S., Bandyopadhyay, S., Sardar, S., Shil, T., Mao, A. A., & Bhattacharjee, A. (2026). Genetic diversity analysis in Aquilaria malaccensis (Agarwood) in India, a CITES-listed industrial crop using microsatellite markers. Indian Journal of Genetics and Plant Breeding, 86(2), 252-255. https://doi.org/10.1007/s44489-026-00019-y

Image Credits: AI Generated

DOI: 10.1007/s44489-026-00019-y

Keywords: Aquilaria malaccensis, agarwood, genetic diversity, microsatellite markers, SSR, CITES, population structure, heterozygosity, gene flow, India, crop improvement, conservation