Gamma Rays Boost Sweet Potato Yield, Vitamin A and Virus Resistance in Mutation Breeding Trial

Sweet potato is one of the world’s most important staple crops, yet improving it through conventional breeding is notoriously difficult. The plant is highly heterozygous, meaning its genetic makeup is a mosaic of many different gene variants, and it is self-incompatible, so breeders cannot simply self-pollinate plants to fix desirable traits. It is also propagated vegetatively, from vine cuttings rather than seeds, which further complicates the recombination of traits. A new study from Ethiopia now shows that gamma irradiation can cut through these barriers, inducing valuable new variation in sweet potato lines and, at the right doses, simultaneously improving tuber yield, provitamin A content and resistance to viral disease.

The research, carried out at Hawassa University and published in BMC Plant Biology, was led by Alemu Bade Anchiwe and colleagues at Wolkite University and Hawassa University. The team exposed vine cuttings of three sweet potato genotypes to gamma radiation from a cobalt-60 source and then tracked how the first vegetative generation, designated M1V1, grew, photosynthesized, accumulated protective compounds and fared against virus infection over 150 days after planting. The work was conducted in a screen house using a randomized complete block design with 20 replications, a robust statistical layout that helps separate genuine treatment effects from environmental noise.

The three genotypes were chosen to represent different flesh colors and market profiles. Hawassa-83 is a white-fleshed variety, Alamura has orange flesh rich in beta-carotene, and Kabode carries a creamy yellow flesh color. Each was irradiated at four doses: zero as a control, and 15, 25 and 35 gray, the unit that measures absorbed radiation energy. The doses were deliberately low by industrial standards, because the goal was not to destroy the plants but to nudge their genomes into producing new combinations of traits while keeping enough of the population alive for selection.

A central question in any mutation breeding program is radiosensitivity: how much radiation a genotype can absorb before half of the individuals die or fail to grow. The researchers determined this threshold using probit analysis, a statistical technique that models dose-response relationships for binary outcomes such as survival. The results revealed striking genotype-dependent differences. Alamura proved the most radio-tolerant, with a median lethal dose, or LD50, of 39.51 gray and a dose producing 50 percent growth reduction, or GR50, of 37.56 gray. Kabode was the most sensitive, with an LD50 of 32.58 gray and a GR50 of 32.49 gray. These numbers matter practically, because they tell breeders the optimal irradiation window for each variety: too low and few mutations appear, too high and the population collapses before useful variants can be recovered.

Beyond survival, the study documented significant main effects and interactions between genotype and radiation dose across a suite of agronomic and physiological traits, all statistically significant at the five percent level. One of the most intriguing findings was evidence of hormesis, the phenomenon in which a stressor that is harmful at high doses produces a stimulatory effect at low doses. Tuber production followed this pattern clearly. Hawassa-83 reached its peak productivity at 25 gray, producing 6.94 tubers per plant, a 33 percent increase over the untreated control. Alamura also peaked at 25 gray with 6.35 tubers. In other words, a moderate blast of radiation actually made the plants more productive, not less.

The nutritional payoff was equally striking. At 25 gray, the beta-carotene content of Alamura tubers increased by 68.6 percent, reaching 11 milligrams per 100 grams. Beta-carotene is the pigment that gives orange-fleshed sweet potatoes their color and the precursor from which the human body synthesizes vitamin A. In regions where sweet potato is a dietary staple and vitamin A deficiency remains a serious public health problem, a mutation that boosts provitamin A content by more than two-thirds could have meaningful nutritional consequences, particularly for children and pregnant women who are most vulnerable to deficiency.

Virus disease posed the other major challenge the breeders set out to address. Sweet potato virus disease, caused by complexes of viruses that can devastate yields across Africa, was scored as virus disease severity, or VDS, across the growth stages. Untreated plants showed baseline severity scores between 3.2 and 3.6, indicating substantial infection. At the highest dose of 35 gray, however, severity dropped dramatically to 1.15 in Alamura and 1.37 in Hawassa-83, scores corresponding to highly resistant reactions. The suppression of viral symptoms correlated directly with the plants’ morpho-physiological condition, suggesting that radiation-induced changes in the plant’s internal state contributed to the resistance phenotype rather than the effect being a random artifact.

Two physiological measurements helped explain what was happening inside the irradiated plants. The first was chlorophyll fluorescence, specifically the Fv/Fm ratio, which quantifies the maximum quantum efficiency of photosystem II and is a standard indicator of photosynthetic health. Alamura maintained a high Fv/Fm value of 0.78 at 25 gray, close to the theoretical optimum for unstressed plants, before suffering severe photoinhibition at 35 gray. The second was proline, an amino acid that accumulates in plants under stress and acts as an osmoprotectant and antioxidant. Proline peaked at 25 gray in both Alamura, at 10.35 micromoles per gram, and Hawassa-83, at 8.3 micromoles per gram. The coincidence of peak proline accumulation, high photosynthetic efficiency and maximal virus suppression at the intermediate dose suggests a coherent physiological signature of the most beneficial treatment level.

To make sense of the many measured traits, the team turned to multivariate statistics. Correlation analysis, principal component analysis and hierarchical cluster analysis were applied to the full dataset, and these tools effectively isolated multi-trait putative mutant lines, plants that combined favorable changes across yield, nutrition and disease resistance rather than excelling in only one dimension. From the irradiated cohorts, the researchers identified three promising multi-trait putative M1V1 mutant clones: one each from the Alamura lines treated at 15 and 25 gray, and one from the Hawassa-83 cohort treated at 25 gray. Each showed concurrent enhancements in tuber yield, beta-carotene content and virus resistance, a combination that would be extremely difficult to achieve through conventional crossing in this crop.

The authors caution that these are putative mutants from the first vegetative generation, and further generational advancement will be needed to confirm that the enhanced traits are stable and heritable rather than transient physiological responses. Even so, the study establishes precise selection targets for sweet potato mutation breeding and demonstrates that the approach can deliver on all three fronts the breeders prioritized: resistance to viral disease, improved nutritional quality and high yield. The research was supported by the International Atomic Energy Agency through its Coordinated Research Project D24014, and the radiation source was provided by the Animal Health Institute’s Tsetsefly Efficiency Center. For a crop on which millions of smallholder farmers depend, the finding that a carefully calibrated dose of gamma radiation can push yield up by a third, provitamin A up by more than two-thirds and virus severity down to resistant levels offers a compelling, and remarkably efficient, new tool for food security breeding programs.

Subject of Research: Gamma irradiation-induced mutation breeding of sweet potato for yield, beta-carotene content and virus resistance

Article Title: Radiosensitivity and early-stage morpho-physiological profiling of M1V1 sweet potato (Ipomoea batatas L.) vine cuttings to different doses of gamma irradiation: breeding for mutants with virus resistance, nutritional quality, and high yield

Article References: Anchiwe, A. B., Buko, D. H., Terfa, M. T., & Roro, A. G. (2026). Radiosensitivity and early-stage morpho-physiological profiling of M1V1 sweet potato (Ipomoea batatas L.) vine cuttings to different doses of gamma irradiation: breeding for mutants with virus resistance, nutritional quality, and high yield. BMC Plant Biology. https://doi.org/10.1186/s12870-026-09919-3

Image Credits: AI Generated

DOI: 10.1186/s12870-026-09919-3

Keywords: sweet potato, gamma irradiation, mutation breeding, radiosensitivity, hormesis, beta-carotene, virus resistance, chlorophyll fluorescence, proline, Ipomoea batatas, M1V1 generation, multivariate analysis