The research team, led by Mohamed R. Asaad of the Department of Agronomy at Minia University, evaluated nine mung bean genotypes under two contrasting irrigation regimes across two growing seasons. This created a matrix of genotype-by-environment combinations designed to expose how each line responded when water was plentiful and when it was deliberately withheld. The scale of the environmental influence was striking: environmental effects accounted for more than half of the total variation in both seed yield and biological yield. In practical terms, this means that more than half of what a breeder sees in the field is driven by where and when the plant is grown rather than by the plant’s own genetics, a sobering reminder of why single-location, single-season trials so often mislead selection decisions.

Drought stress, as expected, took a measurable toll. Across all nine genotypes, water limitation reduced seed yield by an average of 25.66 percent compared with well-irrigated controls. That figure is significant not only for what it reveals about the crop’s vulnerability but also because it establishes the baseline against which individual genotypes could be judged. A line that lost far less than a quarter of its yield under stress, while still maintaining respectable absolute production, would be a genuine candidate for drought-prone environments. The challenge was to separate those lines from the ones that simply performed well in the favorable treatment and then happened to decline less dramatically for reasons unrelated to true tolerance.

To do this, the researchers turned to a family of tools known as stress tolerance indices, mathematical transformations of yield data that compare a genotype’s performance under stress with its performance under normal conditions and with the average performance of the whole set. Three indices in particular stood out: the stress tolerance index, or STI, the geometric mean productivity, or GMP, and the mean productivity, or MP. All three were strongly associated with grain yield under drought conditions, meaning that genotypes scoring high on these indices were also the ones delivering the most seed when water was limited. This alignment matters because it gives breeders a single, easily calculated number that captures both the ability to yield under stress and the ability to yield when conditions are good, rather than forcing a trade-off between the two goals.

Heritability analysis added another layer of insight. Broad-sense heritability estimates the proportion of observed variation in a trait that is attributable to genetic rather than environmental causes, and when paired with expected genetic advance, it signals whether selection will actually move a population in the desired direction. In this study, three traits emerged as especially promising for breeders: green seed fresh weight per pod, green pod fresh weight, and thousand-seed weight. Each showed high broad-sense heritability coupled with high genetic advance, indicating that a large share of the variation in these traits is genetically controlled and that selecting the best-performing plants would produce meaningful improvement in the next generation. For a crop in which yield itself is notoriously difficult to select for directly, these traits offer reliable surrogate targets.

The multi-environment analysis then confronted the genotype-by-environment interaction, the statistical phenomenon in which genotypes rank differently across locations and seasons. The interaction was significant, confirming that the nine lines genuinely did not behave consistently across the four environment combinations. The researchers deployed the AMMI model, which combines analysis of variance for main effects with principal component analysis of the interaction term, and found that the first two interaction principal components together explained 95.04 percent of the interaction variance. In other words, nearly all of the complexity in how genotypes responded differently to environments could be compressed into two dimensions, making the patterns far easier to visualize and interpret. A complementary GGE biplot analysis, which plots both genotypes and environments in the same space to reveal which lines win where, reinforced the picture.

When the dust settled, two genotypes emerged with distinct but complementary virtues. G8 was identified as the highest-yielding genotype overall, the line that delivered the most seed across the trial. G6, by contrast, was the most stable across environments, maintaining its performance level regardless of whether it faced full irrigation or drought stress in either season. Stability statistics applied alongside the biplot analyses consistently supported this distinction, and the combined assessment showed that G8, G3, and G6 managed to pair superior productivity with favorable yield stability, a combination that is rarer than it might sound. Many high-yielding genotypes owe their numbers to one or two exceptional environment combinations, and their averages conceal poor performance elsewhere; the lines identified here avoided that trap.

What elevates the study beyond a conventional field trial is its molecular component. The team used SCoT markers, short for start codon targeted markers, a PCR-based fingerprinting technique that amplifies genomic regions flanking start codons and often targets gene-rich portions of the genome. The analysis generated 44 amplification products across the nine genotypes, of which 42 were polymorphic, a polymorphism rate of 95.45 percent. That figure confirms substantial genetic diversity within the evaluated material, which is exactly what a breeding program wants to see in its working collection, because diversity is the raw material from which new combinations of traits are assembled. Just as importantly, the molecular profiles supported the phenotypic differentiation of the superior genotypes, providing independent genetic evidence that the field-based groupings reflected real biological differences rather than environmental noise.

The molecular data proved especially illuminating for G6, a mutant-derived genotype. The SCoT analysis detected clear molecular differentiation between G6 and its parental genotype, G1, strengthening confidence that the mutation work had genuinely introduced novel genetic variation and that G6’s stability and broad adaptation were rooted in a distinct genetic makeup rather than residual similarity to its parent. This convergence of evidence, in which the yield trials, the stability statistics, and the DNA fingerprints all point toward the same conclusion, is precisely the kind of triangulation that modern plant breeding advocates have called for, and it demonstrates the advantage of combining phenotypic and molecular approaches when breeding decisions must be made under water-limited conditions.

The implications extend well beyond a single crop in a single country. Mung bean cultivation is expanding in arid and semi-arid regions where climate change is making water availability less predictable, and the framework assembled here, integrating drought tolerance indices, AMMI and GGE stability analyses, and SCoT marker screening, offers a transferable template for other crops facing the same challenge. The researchers, whose team included Hassan A. H. Soltan of the Agricultural Research Center, Hanaa S. H. Bakry and Bahaa Abugammie of Minia University’s Department of Genetics, and corresponding author Islam M. Y. Abdellatif of the Department of Horticulture, describe their identified genotypes as valuable genetic resources for developing climate-resilient cultivars. For farmers on the front lines of water scarcity, the arrival of a mung bean line that yields heavily and holds steady from season to season could translate directly into more reliable harvests, and for the scientific community, the study is a compelling demonstration that the answer to drought lies not in any single measurement but in the disciplined integration of field, statistics, and genome.

Subject of Research: Identification of drought-tolerant and stable mung bean genotypes using stress tolerance indices, multi-environment stability analysis, and SCoT molecular markers

Article Title: Identification of drought-tolerant and stable mung bean genotypes using stress tolerance indices

Article References: Identification of drought-tolerant and stable mung bean genotypes using stress tolerance indices. (n.d.). https://doi.org/10.1186/s12870-026-09706-0

Image Credits: AI Generated

DOI: 10.1186/s12870-026-09706-0

Keywords: mung bean, drought tolerance, stress tolerance index, genotype by environment interaction, AMMI, GGE biplot, SCoT markers, plant breeding, yield stability, broad-sense heritability, Vigna radiata, climate resilience