The reclamation and sustainable use of post-mining lands have become an urgent priority due to accelerating soil degradation and ecosystem disruption caused by extractive industries(Sihombing et al., 2025). Gold mining, particularly in tropical regions such as Indonesia, has led to severe environmental problems, including the deterioration of soil structure, nutrient depletion, and heavy metal contamination(Kaba et al., 2025). These conditions restrict natural vegetation recovery and limit opportunities for agricultural and pastoral development(Sun et al., 2024). Identifying forage species that can tolerate such adverse environments while providing ecological and economic value is therefore essential for reclamation programs(Putra et al., 2025). Such efforts are expected to restore ecosystem services and support food and feed security in mining-affected landscapes.

Pennisetum purpureum Schumach., commonly referred to as Napier grass, is a perennial C₄ species valued for its high biomass production and strong adaptability to tropical environments(Aleme et al., 2024). The dwarf cultivar ‘Mott’ is widely used as forage because of its higher leaf-to-stem ratio and improved digestibility. However, its performance is markedly reduced under the harsh edaphic conditions of post-mining soils(Putra et al., 2022). Induced mutagenesis has emerged as a promising strategy to enhance its resilience and nutritional quality. Gamma irradiation, in particular, has been extensively applied in plant breeding and is reported to improve vigor, nutrient content, and stress tolerance(Al-Sayed et al., 2025);(Putra et al., 2025). Nevertheless, little attention has been given to its potential for improving forage crops cultivated on gold mine-degraded soils.

Despite the potential benefits of induced mutagenesis, there is a notable lack of research on its use to improve forage crops specifically for cultivation on post-mining land. Moreover, studies that integrate a comprehensive analysis of agronomic, nutritional, and anatomical properties, combined with multivariate analysis, to assess irradiated genotypes under these unique stress conditions are limited. The novelty of this study lies in being the first to integrate agronomic, nutritional, anatomical, and digestibility traits of gamma-irradiated P. purpureum cv. Mott cultivated on degraded gold mining soil, analyzed through a multivariate framework. This research fills that gap by providing a holistic evaluation of the effects of gamma irradiation on a promising forage cultivar grown on gold mine-degraded soil.

This study aims to evaluate the performance of gamma-irradiated Pennisetum purpureum cv. Mott cultivated on degraded gold mine soil. Specifically, it examines key growth traits, nutritional composition, fiber fractions, and digestibility parameters. By utilizing a comprehensive multivariate approach, this study seeks to identify mutant lines with superior adaptation and forage quality. The findings are expected to contribute to the development of improved forage cultivars suitable for land reclamation and sustainable livestock systems on degraded landscapes.

Gamma irradiation has emerged as a potent tool for inducing genetic variability in forage crops, with the ability to alter morphological, physiological, and biochemical traits(Raina et al., 2022). In this study, the application of gamma rays on Pennisetum purpureum cv. Mott produced a spectrum of variations that were functionally relevant to both plant productivity and forage quality. The mutants derived from low to moderate doses (particularly 10–20 Gy) exhibited marked improvements in plant height, number of tillers, leaf area, and both fresh and dry biomass yields. The positive response observed at moderate doses is consistent with the principle of hormesis, in which sublethal stress can stimulate physiological functions rather than suppress them(Cutler et al., 2022). At the cellular scale, low-dose irradiation often triggers a transient oxidative burst that activates antioxidant defense pathways, including superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX)(Rao et al., 2025). Strengthening these defense mechanisms enables plants to neutralize reactive oxygen species (ROS) more effectively and sustain cellular homeostasis, ultimately supporting improved metabolism and growth(Dumanović et al., 2021).

Gamma irradiation also promotes meristematic activity and modulates hormonal regulation, particularly through auxin, cytokinin, and gibberellin signaling, which govern cell division and elongation(Jan et al., 2012). As a result, plants exposed to moderate radiation exhibit greater vigor and higher biomass accumulation. This hormetic stimulation is reinforced by antioxidant protection that reduces oxidative damage and maintains metabolic efficiency(Franco et al., 2019). However, once the dose exceeds approximately 15 Gy, these advantages diminish. High irradiation levels compromise DNA integrity, lead to excessive ROS buildup, induce lipid peroxidation, and disrupt protein synthesis, collectively impairing growth. Under such stress, the repair systems are overwhelmed, hormonal balance is disturbed, and meristematic tissues are damaged, producing shorter internodes, fewer leaves, reduced cell division, and lower biomass yield(Wahab et al., 2022).

In addition to these morphological responses, gamma irradiation influenced nutritional traits. A notable effect was the increase in crude protein (CP) at moderate doses, which may be associated with improved nitrogen assimilation and shifts in metabolic flux toward amino acid and protein production. This outcome could involve the activation of key enzymes in nitrogen metabolism, such as nitrate reductase and glutamine synthetase, enabling more efficient conversion of inorganic nitrogen into organic compounds required for protein synthesis(Zayed et al., 2023). However, the differences in CP were not statistically significant across treatments, and other proximate components—crude fiber (CF), ether extract (EE), and ash—remained largely unchanged. This stability suggests that the core metabolic pathways regulating protein accumulation, structural fiber deposition, lipid synthesis, and mineral uptake were not markedly altered by the levels of irradiation applied. Crude fiber (CF) levels remained relatively constant among treatments, indicating that overall deposition of structural carbohydrates in the cell wall was stable, even though specific fiber components such as NDF, ADF, and lignin varied. Likewise, the absence of significant changes in ether extract (EE) suggests that lipid metabolism was largely unaffected by irradiation, while the consistent ash values point to an ability of the plants to maintain mineral acquisition and ion balance under both irradiated and non-irradiated conditions.

Shifts in fiber composition were evident at certain irradiation levels, with notable reductions in NDF, ADF, and ADL, indicating partial inhibition of lignification. Since lignin is a major barrier to forage digestibility due to its resistance to microbial degradation and its cross-linking with cellulose and hemicellulose, this decline provides clear benefits for nutrient availability in ruminants(Zhong et al., 2021). These changes are likely linked to gamma-induced alterations in the phenylpropanoid pathway, involving reduced activity or downregulation of key enzymes such as PAL, COMT, CAD, and related peroxidases, which collectively limit lignin monomer production and polymerization(Shad et al., 2024). As a result, lignin deposition in secondary cell walls decreases, while the structural arrangement of cellulose and hemicellulose is modified in ways that increase microbial access. In some cases, slight increases in cellulose or hemicellulose appeared as compensatory adjustments, but overall the outcome was greater cell wall porosity and flexibility(Wang et al., 2021). Taken together, these modifications improve cell wall degradability and enhance the digestible energy value of the forage.

As a result, irradiated plants demonstrated superior digestibility, with significant improvements in dry matter digestibility (DMD), organic matter digestibility (OMD), in vitro digestibility (IVD), and fiber digestibility (NDFD and ADFD). These enhancements point to increased availability of fermentable substrates and reduced structural barriers within the cell wall, both of which are critical for optimizing forage utilization in ruminant production systems(Tedeschi et al., 2023). Mechanistically, reduced lignin content together with altered cellulose and hemicellulose composition enlarges pore size and surface area of the cell wall, facilitating microbial colonization and enzymatic hydrolysis(Weimer, 2022). This improved accessibility leads to faster nutrient release and absorption, which can translate into higher feed intake and better animal performance(Reuben et al., 2022). Such outcomes underscore the functional integration between plant biochemical composition and its nutritional performance under digestive simulation.

The multivariate analysis also highlighted a crucial aspect: while biomass-related traits (e.g., shoot weight, leaf length, and dry weight) were crucial for yield, they did not always align positively with digestibility traits. This finding reinforces the importance of holistic breeding strategies that account for both yield and quality traits, rather than focusing on biomass alone(Khan et al., 2024). This suggests underlying trade-offs in metabolic allocation between structural growth and forage quality. Plants operate under finite resource allocation; thus, resources invested heavily into structural components for increased biomass (e.g., extensive lignification for mechanical support) might divert precursors and energy from processes that contribute to higher nutritional value or digestibility. This dynamic interplay between growth and defense/quality mechanisms is a key physiological response to environmental and genetic perturbations(Katam et al., 2022). The clustering dendrogram (Figure 2) further underscored this by segregating variables into distinct groups: one for morphological productivity traits and proximate contents, and another for digestibility traits and cell wall degradability indicators.

A particularly compelling aspect of this research lies in the environmental context—namely, the cultivation of plants on post-mining land, specifically former gold mine sites. These soils are typically characterized by poor soil fertility, heavy metal contamination, and damaged soil structure, including high acidity, low nutrient status, and low organic matter(Zine et al., 2024). These conditions represent a highly stressful environment that limits plant establishment and growth(Putra et al., 2022). That the gamma-rradiated mutants not only survived but outperformed controls under such marginal conditions (as shown by their advantageous positions in the biplot, Figure 4), indicates their improved adaptability(Riviello-Flores et al., 2022). This likely stems from enhanced root system architecture, allowing for greater nutrient acquisition efficiency in nutrient-poor soils, and possibly upregulation of antioxidant systems and phytochelatin production for metal detoxification(Ali et al., 2024).

Phytochelatins, small peptides, and metallothioneins, proteins, function by chelating heavy metal ions in the cytoplasm, sequestering them into vacuoles, thereby reducing their toxic effects and enhancing plant tolerance to contaminated soils(Faizan et al., 2024). Such resilience is vital for reclaiming degraded lands through phytoremediation-compatible forage systems. Functionally, these findings bridge plant productivity with ecosystem restoration. The selected mutants, by exhibiting high biomass, superior nutritional quality, and tolerance to abiotic stress, serve as dual-purpose genotypes—contributing to livestock feed security while also supporting ecological rehabilitation of degraded landscapes. The use of gamma irradiation has therefore shown promise not only in enhancing desirable agronomic traits but also in generating adaptive traits that permit successful cultivation in harsh and contaminated environments.

Gamma irradiation at moderate doses (10–15 Gy) effectively improved the growth, nutritional quality, and digestibility of Pennisetum purpureum cv. Mott. Mutants derived from these treatments performed well even on gold mine tailing soils, indicating strong adaptability. These findings demonstrate the potential of mutation breeding as a sustainable strategy for developing superior forage cultivars while contributing to land rehabilitation and livestock production.