Researchers at the National Horticultural Research Institute (NIHORT) in Ibadan set out to assess the genetic diversity of fifteen avocado accessions conserved in the institute’s genebank. The seeds behind these accessions were originally collected from smallholder farmers across four states in south-eastern Nigeria — Imo, Enugu, Anambra and Abia — during successive collection missions, and were registered with NIHORT accession numbers upon entry into the genebank. Because avocado is highly heterozygous and predominantly outcrossing, with a protogynous–protandrous flowering system that promotes cross-pollination, the seedlings raised from these seeds represent open-pollinated half-sib progenies rather than clones of the maternal trees, and were treated as independent accessions in the analysis.

The team, led by Omolara I. Akinyoola and published in the journal Discover Plants, employed two complementary DNA marker systems: inter-simple sequence repeats (ISSR) and start codon targeted (SCoT) markers. ISSR primers amplify DNA fragments lying between simple sequence repeats in the genome and require no prior knowledge of the species’ DNA sequence, making them accessible and inexpensive. SCoT markers, first developed in rice by Collard and Mackill, target regions surrounding the start codons of genes, giving them a functional bias that often makes them more informative. After a pilot screen of twenty ISSR and fifteen SCoT primers on three representative accessions, the researchers selected five primers of each type based on band clarity, polymorphism and reproducibility.

The laboratory work began with fresh young leaflets collected from the field and preserved in liquid nitrogen. Genomic DNA was extracted from approximately 100 milligrams of leaf tissue per accession using a modified CTAB protocol, in which polyvinylpyrrolidone and 2-mercaptoethanol were added to suppress polyphenols and oxidation, and the chloroform–isoamyl alcohol extraction step was repeated twice to remove residual protein and lipid. DNA was precipitated overnight with ice-cold isopropanol, washed with 70 percent ethanol and re-suspended in buffer containing RNase A. Quality checks on 1 percent agarose gels confirmed sharp, high-molecular-weight bands with no shearing, and Nanodrop spectrophotometry gave A260/A280 purity ratios between 1.80 and 2.00 before samples were diluted to a working concentration of 30 nanograms per microlitre.

Polymerase chain reactions were carried out in 25-microlitre volumes on an Applied Biosystems GeneAmp 9700 thermal cycler. ISSR amplification used a touchdown profile in which the annealing temperature dropped from 65 to 56 degrees Celsius over ten cycles before thirty standard cycles at 55 degrees, while SCoT amplification used thirty-five cycles with a 50-degree annealing temperature. Amplified fragments were separated on 2 percent agarose gels, visualised under ultraviolet transillumination and scored manually against a 50-base-pair ladder, with faint or ambiguous bands excluded. The convergence of results across two independent marker systems, and across multiple analysis platforms, provided a form of internal validation that strengthens confidence in the findings.

The results revealed a moderate but meaningful reservoir of variation. The ten loci detected a total of 41 polymorphic alleles, averaging 4.1 alleles per locus — higher than the 3.1 alleles per locus reported in a previous avocado study using EST-SSR primers. The polymorphism information content, a measure of a locus’s discriminating power, ranged from 0.509 to 0.825 with a mean of 0.654, and gene diversity averaged 0.708 across the ten loci. Genetic similarity coefficients between accessions ranged from 0.59 to 0.84. Notably, SCoT markers outperformed ISSR markers, generating a higher mean number of alleles per locus (4.4 versus 3.8) and higher mean PIC values (0.671 versus 0.637), leading the authors to recommend the combined use of both systems rather than either alone.

When the researchers clustered the accessions using the unweighted pair group method with arithmetic mean (UPGMA) on Jaccard dissimilarities, supported by 1000 bootstrap resamplings, the fifteen accessions split into two main clusters — one containing six accessions and the other nine — with membership broadly reflecting the south-eastern states of origin. A factorial coordinate analysis performed in DARwin software resolved four geographic groups along the first two factorial axes, with groups dominated respectively by accessions from Imo, Enugu and Anambra, while the single Abia accession stood apart. Some accessions, however, were interwoven between groups, a pattern the authors attribute to informal farmer-to-farmer seed exchange across state boundaries.

The most striking result came from the analysis of molecular variance. AMOVA partitioned 99.3 percent of the genetic variation within the UPGMA clusters and only 0.7 percent between them, with a Phi statistic of 0.007 that was statistically non-significant (P = 0.395, based on 9999 random permutations). Cross-validation in a second R package yielded an essentially identical result (P = 0.390), confirming the robustness of the partitioning. In other words, the two clusters represent dissimilarity gradients within a single, largely panmictic gene pool rather than genetically isolated subpopulations. The authors attribute this to two interacting forces: avocado’s strongly outcrossing reproductive biology, which maintains high heterozygosity within genotypes, and widespread informal seed exchange among smallholder farmers, which has homogenised allele frequencies across the sampled states.

The study is not without limitations, which the authors acknowledge candidly. The sample of fifteen accessions, while reflecting the current holdings of the NIHORT avocado germplasm at the time of sampling, is modest for inferring fine-scale population structure and limits the statistical power of subgroup analyses. Marker-trait associations were not pursued, and the dominant nature of ISSR and SCoT markers means each accession had to be treated as a single haploid genotype. Future work, the team suggests, should integrate SNP-based platforms such as genotyping-by-sequencing with phenotypic and biochemical fruit characterisation, to link the genetic variation documented here to agronomically relevant traits such as fruit quality, pest resistance and climate resilience.

Even so, the significance of the work extends well beyond a single genebank. Nigeria’s avocado industry is growing rapidly and holds considerable potential in the global market, but it faces threats from pests including the avocado lace bug, the Persea mite and the western avocado leaf roller, as well as diseases such as anthracnose and avocado black streak. The moderate diversity documented in the NIHORT collection provides a baseline molecular dataset for future curation, hybridisation and selection, and underscores a broader truth for crop science: genetic diversity is the raw currency of breeding, and knowing exactly what a genebank holds is the first step towards spending it wisely. The identified variation can now be deployed in breeding programmes aimed at developing better varieties with desirable traits, while the finding that most variation lies within rather than between geographic groupings offers a caution against assuming that provenance alone guarantees genetic distinctiveness in conserved germplasm.

Subject of Research: Genetic diversity assessment of avocado germplasm using ISSR and SCoT molecular markers

Article Title: Genetic diversity assessment of avocado (Persea americana Mill.) germplasm from NIHORT genebank

Article References: Akinyoola, O. I., Olagunju, Y. O., Matthew, J. O., Akin-Idowu, P. E., & Ajayi, E. O. (2026). Genetic diversity assessment of avocado (Persea americana Mill.) germplasm from NIHORT genebank. Discover Plants, 3(1), Article 414. https://doi.org/10.1007/s44372-026-00866-9

Image Credits: AI Generated

DOI: 10.1007/s44372-026-00866-9

Keywords: avocado, Persea americana, genetic diversity, ISSR markers, SCoT markers, germplasm, genebank, Nigeria, NIHORT, molecular markers, AMOVA, plant breeding

The research, conducted by an international team of scientists working at Pir Mehr Ali Shah Arid Agriculture University Rawalpindi in Pakistan, Nanjing Forestry University in China, and Purdue University in the United States, set out to answer three fundamental questions. First, where does S. maskeyi sit on the amphibian tree of life? Second, does the genetic makeup of its populations differ between natural and degraded habitats? And third, do the two recognized morphotypes of the species, known as the dotted form and the rusty form, represent genetically distinct lineages? To answer these questions, the team sequenced two widely used genetic markers: a segment of the mitochondrial 16S ribosomal RNA gene, which accumulates mutations quickly and is a workhorse for species-level identification, and a portion of the nuclear RAG-1 gene, which evolves more slowly and provides an independent check on mitochondrial results.

The phylogenetic analyses left little room for doubt about species identity. Using both maximum likelihood and Bayesian inference, two complementary statistical frameworks for reconstructing evolutionary trees, the researchers found that every sampled individual clustered firmly within the Sphaerotheca maskeyi clade, clearly separated from other species in the genus. This matters because cryptic morphology often hides cryptic species, and misidentification in the field can quietly corrupt decades of ecological data. By anchoring the species’ genetic identity with two independent markers, the study provides a reliable baseline for all future work on this frog, from population monitoring to taxonomic revision.

The habitat comparison revealed a pattern that is both encouraging and cautionary. Frogs captured in natural habitats showed numerically higher genetic diversity than those from degraded environments. For the mitochondrial 16S marker, natural-habitat populations displayed haplotype diversity of 0.963 and nucleotide diversity of 0.063, compared with 0.760 and 0.054 in degraded habitats. The nuclear RAG-1 gene told a similar story, with haplotype diversity of 0.9818 and nucleotide diversity of 0.0237 in natural settings versus 0.9556 and 0.0175 in degraded ones. Yet when the team ran formal statistical tests, these differences fell short of significance. The pattern is consistent with the idea that habitat degradation erodes genetic variation, a phenomenon documented in many amphibians, but the sample sizes in this study were not sufficient to prove it conclusively.

One of the most consequential findings came from the analysis of molecular variance, or AMOVA, a technique that partitions genetic variation into components occurring among populations versus within them. For both markers, the vast majority of variation was found within populations rather than between them. In practical terms, this means that individual populations of S. maskeyi are not sharply isolated from one another, at least across the geographic scale sampled. High within-population diversity combined with low among-population differentiation can indicate recent shared ancestry, ongoing or historical gene flow, or simply insufficient time for lineages to diverge. For a species whose global population is trending downward, this connectivity is good news in the short term, because it suggests that local extinctions might still be offset by recolonization from neighboring populations.

The comparison between the two morphotypes produced perhaps the most intriguing result of the study. The rusty form and the dotted form look different enough that researchers routinely sort them in the field, but the genetics suggest that appearance is not destiny. The rusty form showed numerically higher nucleotide diversity at both loci, with values of 0.00210 for 16S rRNA and 0.01258 for RAG-1, against 0.00059 and 0.00517 for the dotted form. Intriguingly, the two forms traded the top spot for haplotype diversity depending on the marker: the dotted form reached 1.000 at 16S while the rusty form hit 1.000 at RAG-1. The AMOVA between morphotypes yielded an FST of 0.09057 with a p-value of 0.058, a figure that sits tantalizingly close to the conventional significance threshold but does not cross it. The authors interpret this as weak genetic structuring with no strong evidence of pronounced divergence between the forms.

This near-miss raises a fascinating evolutionary question: if the two morphotypes are not genetically distinct species or deeply separated lineages, what maintains their visual differences? Color polymorphisms in frogs are often maintained by natural selection, sexual selection, or a balance of the two, and recent research has shown that such polymorphisms can persist for millions of years without accompanying genetic divergence across the rest of the genome. It is entirely possible that the dotted and rusty forms of S. maskeyi represent ecologically or reproductively relevant variants shaped by their environments rather than independently evolving lineages. Testing this hypothesis would require genome-wide markers, larger samples, and behavioral or ecological data linking the morphotypes to differences in survival, mating success, or habitat use.

The conservation stakes of this work are considerable. Genetic diversity is the raw material that allows populations to adapt to changing environments, and its loss often precedes, and predicts, demographic collapse. Species with low genetic diversity are more vulnerable to disease outbreaks, climate extremes, and inbreeding depression, threats that are particularly acute for amphibians, the most imperiled class of vertebrates on Earth. Although S. maskeyi is currently classified as Least Concern by the IUCN Red List, its global population trend is declining, and habitat loss across South Asia continues at a relentless pace. The finding that frogs in degraded habitats carry numerically reduced diversity, even if not yet statistically significant, is a warning sign that should not be ignored.

The study also underscores the value of combining mitochondrial and nuclear markers. Mitochondrial DNA, inherited only through mothers, can be swayed by historical demographic events and female-mediated gene flow, while nuclear genes like RAG-1 reflect the blending of ancestry from both sexes. When both markers agree, as they did here, confidence in the conclusions rises substantially. The sequence data from this study, deposited in GenBank under accession numbers PX645625 through PX645652 for 16S rRNA and PX657352 through PX657361 for RAG-1, will serve as a permanent genetic reference for the species and a foundation for future genomic studies.

For now, the message of this research is one of cautious reassurance paired with urgent vigilance. Sphaerotheca maskeyi still harbors substantial genetic diversity across its range, its populations remain genetically connected, and its two color forms are almost certainly variations on a single evolutionary theme rather than separate species. But declining populations and shrinking habitats are silently chipping away at that diversity, and the statistical trends detected in this study point in the same troubling direction as the species’ global trajectory. Preserving natural habitats, the study suggests, is not merely about saving scenic landscapes; it is about safeguarding the genetic library that this cryptic frog, and countless species like it, will need to survive the coming decades of environmental change.

Subject of Research: Genetic diversity patterns across habitats and morphotypes of the South Asian frog Sphaerotheca maskeyi

Article Title: Genetic diversity patterns across habitats and forms of a morphologically cryptic South Asian frog (Sphaerotheca maskeyi)

Article References: Ahmed, W., Amin, H., Rais, M., & DeWoody, J. A. (2026). Genetic diversity patterns across habitats and forms of a morphologically cryptic South Asian frog (Sphaerotheca maskeyi). Molecular Biology Reports, 53(1), Article 1568. https://doi.org/10.1007/s11033-026-12696-9

Image Credits: AI Generated

DOI: 10.1007/s11033-026-12696-9

Keywords: Sphaerotheca maskeyi, genetic diversity, cryptic species, 16S rRNA, RAG-1, phylogenetics, habitat degradation, color polymorphism, AMOVA, amphibian conservation, South Asia, molecular ecology