Hui Wang

Foxtail millet (Setaria italica L.) is an important functional food crop with high photosynthetic efficiency and drought tolerance, and it plays a significant role in arid and semi-arid agricultural systems. However, germplasm resources from Xinjiang remain inadequately characterized, limiting their use in breeding programs. This study systematically evaluated 203 foxtail millet germplasm accessions using 8 qualitative traits and 13 quantitative traits across two growing seasons (2023–2024) in northern Xinjiang. Phenotypic variation and diversity, trait correlations, and phenotypic grouping were analyzed using the Shannon–Weaver diversity index (H′ = −Σ p_i ln p_i), coefficient of variation (CV), Pearson correlation, principal component analysis (PCA), and hierarchical cluster analysis. Among qualitative traits, leaf posture during flowering exhibited the highest phenotypic diversity index (H′ = 1.072), whereas leaf sheath color showed the lowest (H′ = 0.359). Predominant phenotypes included green seedling leaf color (77.83%), semi-erect seedling leaf posture (57.14%), drooping leaf posture during flowering (50.74%), curved panicle neck (74.88%), spindle-shaped panicle (83.25%), and yellow grain color (84.73%). Among quantitative traits, grain weight per panicle (GWE; CV = 38.91%), single panicle weight (SEW; CV = 37.65%), and yield (CV = 37.31%) showed the highest variability. Yield was strongly and positively correlated with SEW (r = 0.925, p < 0.001) and GWE (r = 0.925, p < 0.001), and SEW and GWE were almost collinear (r = 0.996). PCA of 12 standardized traits (SEW excluded to avoid redundancy with GWE) extracted five components explaining 65.55% of total phenotypic variation. Hierarchical clustering of the unstandardized trait means (yield in kg·mu⁻¹), in which yield contributed most strongly to group separation, divided the accessions into four groups: Group I (129 accessions, 63.55%) was intermediate (mean yield 3532 kg·ha⁻¹); Group II (37 accessions, 18.23%) had the lowest yield (1650 kg·ha⁻¹) and panicle weights; Group III (32 accessions, 15.76%) had high yield (5282 kg·ha⁻¹); and Group IV (5 accessions, 2.46%), all breeding lines, had the highest yield (6814 kg·ha⁻¹), the heaviest panicles, and the thickest stems. The evaluated foxtail millet germplasm showed substantial phenotypic diversity under irrigated conditions at a single site, providing candidate materials for yield improvement and for further evaluation of stress resistance and adaptation. Group III and Group IV accessions are candidate parents for high-yield breeding; however, this requires validation in multi-location trials because only one irrigated site was evaluated and lodging and drought responses were not measured. Entry-mean repeatability of accession means across the two seasons ranged from 72.1% to 99.99%, and these values are likely upper bounds because genotype × year interaction could not be separated from residual error. These findings provide a phenotypic baseline for germplasm utilization in Xinjiang foxtail millet improvement programs.

Drought limits the stability of foxtail millet production and the efficient use of germplasm resources, yet whether drought-tolerant and drought-sensitive accessions engage fundamentally distinct pathways or a shared, quantitatively reprogrammed network remains unclear. We generated 36 leaf transcriptomes from three drought-sensitive (DSEN) and three drought-tolerant (DTOL) accessions under well-watered (WW) and drought-stress (DS) conditions, retaining 25,099 genes for downstream analyses. Principal component analysis confirmed water treatment as the primary driver of global expression variation. DS-versus-WW comparisons identified 10,635 and 6215 drought-responsive DEGs in the DSEN and DTOL groups, respectively, with 5195 shared and a genome-wide response correlation of 0.791. Crucially, accession-level tests revealed no significant DEGs between groups under WW, only 22 under DS, and none for the group × drought-response interaction, underscoring the absence of qualitative pathway shifts. Functional enrichment analyses jointly indicated suppression of photosynthesis and translation, accompanied by reprogramming of carbohydrate metabolism, membrane lipid remodeling, phenylpropanoid and secondary metabolism, protein homeostasis, and stress signaling. WGCNA partitioned 10,000 highly variable genes into 16 modules. The blue module, which showed the strongest drought response in DSEN, was enriched for cell-wall and carbohydrate metabolism, membrane lipid processes, and stress-protection pathways, whereas the brown module, which responded most robustly in DTOL, was enriched for calcium signaling, protein phosphorylation/dephosphorylation, transcriptional regulation, proline biosynthesis, and dehydration protection. The yellow and cyan modules exhibited the largest between-group effect sizes under drought but failed multiple-testing correction, remaining candidate networks. Collectively, our results support a model of shared core response with divergent regulatory intensity, where sensitive accessions undergo broader transcriptional perturbation, while tolerant ones deploy more concentrated and coordinated modules. This study provides modular targets for drought-tolerance breeding and highlights the necessity of accession-level replication and conservative statistical inference in comparative transcriptomics.

Abiotic stresses caused by climate change pose a significant challenge to global food security, making it necessary to develop stress-resistant crops. Foxtail millet (Setaria italica (L.) P. Beauv.) is a drought-tolerant C₄ cereal and serves as a model crop for elucidating stress adaptation mechanisms and promoting climate-resilient agricultural solutions. This paper reviews the tolerance mechanisms of foxtail millet to abiotic stresses. Physiologically, the species exhibits excellent water-use efficiency, requiring 75% less irrigation than traditional cereals, achieved through enhanced osmotic adjustment via soluble substance accumulation and the maintenance of ion homeostasis. Morphological adaptations include reduced leaf area, adjusted stomatal density, well-developed root systems, and specialized anatomical features that optimize water conservation. At the molecular level, stress tolerance involves complex transcriptional networks mediated by multiple transcription factor family members, including those (NF-Y, DREB, NAC, WRKY, MYB) that coordinate stress-responsive gene expression, antioxidant defense systems, and osmotic adjustment pathways. Furthermore, this review summarizes multi-omics characteristics, including genomics (such as QTL mapping and GWAS), proteomics, transcriptomics, metabolomics, and regulatory networks, for foxtail millet under abiotic stress tolerance. Additionally, reproductive resilience is maintained through efficient mobilization of stem reserves to panicles, phenological plasticity in flowering timing, and preserved gametic viability under thermal stress. Combining advanced molecular breeding with the inherent tolerance of foxtail millet positions this crop as both a solution to climate change and a genetic resource for enhancing the stress resistance of other cereals. These findings establish foxtail millet as a valuable model for developing sustainable agricultural technologies essential for food security under projected climate scenarios.

Drought stress critically constrains agricultural productivity in arid and semi-arid regions, necessitating the development of drought-tolerant crop varieties for sustainable food security. This study evaluated drought tolerance in 222 foxtail millet (Setaria italica) germplasms from diverse Chinese agroecological zones from 2021–2023 at a specialized identification site in Xinjiang. Field experiments used a randomized complete block design comparing normal irrigation (3000 m³/ha) with drought stress (1800 m³/ha) across 12 morpho-agronomic traits including plant height, spike characteristics, biomass, and yield components. Drought stress significantly reduced all parameters, with yield exhibiting the highest sensitivity (drought tolerance coefficient = 0.58). Principal component analysis indicated that the first three components explained 82.70% of phenotypic variance, with yield-related parameters contributing the most to genotypic differentiation. Integrated evaluation using comprehensive drought tolerance coefficient (DTC), drought resistance index (DRI), and D-values classified germplasms into five categories: highly resistant (4.50%), resistant (11.71%), moderately resistant (57.21%), sensitive (16.22%), and highly sensitive (10.36%). Correlation and stepwise regression analyses identified five critical indicators: stem basal thickness, single plant biomass, spike weight, grain weight per spike, and yield. The predictive model demonstrated exceptional accuracy (R² = 0.9998), enabling efficient screening using the targeted traits. The elite germplasms T125 (92) and Baogu 23 (135) consistently ranked as the most drought-tolerant across all methods. These findings establish a robust methodological framework for evaluating drought tolerance in foxtail millet and provide practical selection criteria for developing climate-resilient cultivars. The identified germplasms and evaluation indices significantly contribute to agricultural sustainability in water-limited environments, supporting food security in regions that are increasingly affected by climate-induced drought stress.