Comparative analysis of agronomic, metabolic and nutritional functional properties of different sorghum (sorghum bicolor) genotypes exposed to striga hermonthica in Zimbabwe

Abstract

Striga hermonthica is a widespread parasitic weed that poses a major threat to sorghum production in many parts of sub-Saharan Africa, often leading to substantial yield losses in affected regions. This study investigated the agronomic performance, biochemical response, nutritional stability, and genetic variation of 74 sorghum genotypes from Zimbabwe and South Africa under varying levels of Striga infestation (0 mg, 2.5 mg, and 5 mg per pot), simulating densities of up to 40,000 plants per hectare. The research aimed to identify resistant genotypes and genetic markers associated with dual resilience—Striga tolerance and nutritional quality—to inform breeding strategies. Agronomic assessments showed significant (p < 0.05) reductions in plant height (up to 52%), chlorophyll content, panicle height, and grain yield in most genotypes under Striga stress. At the 5 mg infestation level, 75% of genotypes experienced severe biomass loss, while 41% recorded significant dry grain weight reductions at 2.5 mg. However, a subset of genotypes—including SCSHYB012150, SCSHYB017166, CHR20, SA2133, SA3028, SA1794, SA1617, and SA4186—demonstrated stable yield and biomass, forming part of the 24.3% of genotypes clustered as highly tolerant based on Principal Component Analysis (PCA), which accounted for 74.45% of phenotypic variation. Biochemical analysis revealed a clear differential accumulation of secondary metabolites in response to Striga. Resistant genotypes such as SCSHYB012150, SA2133, and SA3028 exhibited significantly elevated levels of ferulic acid, gallic acid, P-coumaric acid, syringic acid, and caffeic acid—with ferulic acid showing the highest association across 74 SNP loci. These phenolic compounds play critical roles in plant defence through antioxidant, allelopathic, and antimicrobial activities. Clustering analysis of metabolic profiles further confirmed these genotypes formed distinct groups with elevated antioxidant capacity under infestation. Nutritional profiling showed that susceptible genotypes suffered sharp declines in crude protein (by up to 3.2%) and fibre content (by 1.7%). In contrast, resistant lines—including SCSHYB012150, SA1794, and SA1617—retained nutritional stability. Notably, SA2133 exhibited consistent levels of protein (~9.3%), fibre (~2.8%), and total ash (~2.1%) even under infestation. These findings suggest the presence of metabolic resistance mechanisms and highlight the potential for breeding nutrient-dense, Striga-tolerant cultivars. Molecular analysis using Diversity Arrays Technology Sequencing (DArTSeq) identified 27,870 high-quality SNPs across the 74 genotypes. Population structure analysis revealed three main subpopulations, while AMOVA indicated that 82% of genetic variation occurred within populations. Unique alleles associated with resistance were identified in elite lines. GWAS, using both the FASTmrMLM and FarmCPU models, mapped significant SNPs linked to key traits across chromosomes 1, 2, 3, 4, 5, and 6. For instance, SNP SB00214.1 on chromosome 1 was linked to kernel hardness and explained up to 10% of phenotypic variance. Traits such as plant height (Chr 1, 2), chlorophyll content (Chr 2), panicle height (Chr 3), grain weight (Chr 4), and phenolic content (Chr 6) were all significantly associated with specific SNPs. Additionally, SNPs for nutritional traits—including protein (Chr 3), fibre (Chr 1, 3), fat (Chr 3), and carbohydrates (Chr 8, 9)—were identified, indicating the possibility of stacking resistance and quality traits in breeding pipelines. The co-localization of resistance and nutritional trait loci confirms the feasibility of developing dual-purpose sorghum varieties—combining yield, tolerance, and health-enhancing properties. The genotypes identified, particularly SCSHYB012150, SA2133, and SA1794, represent strong candidates for deployment in smallholder systems affected by Striga, as well as for use in commercial grain and brewing markets. These findings contribute to advancing marker-assisted selection (MAS), trait introgression, and the development of resilient, nutrient-rich sorghum suitable for both food and industrial uses. In conclusion, this study provides critical evidence that certain sorghum genotypes possess dual tolerance to Striga infestation and nutritional degradation, driven by both phenotypic resilience and favourable genetic architecture. The identification of key SNPs linked to both agronomic and nutritional traits lay the groundwork for marker-assisted selection (MAS) and genomic selection in future breeding programs. The dual-purpose genotypes—particularly SCSHYB012150, SA2133, and SA1794—are ideal candidates for developing climate-resilient, nutrient-dense sorghum cultivars. These findings have significant implications for enhancing food and nutritional security, especially for smallholder farmers in Striga-endemic regions. To ensure real-world impact, it is recommended that future work focuses on validating these markers through functional genomics, pyramiding resistance alleles, and integrating selected genotypes into national breeding pipelines. Additionally, participatory breeding approaches, inclusive policy support, and farmer-led adaptation strategies are essential to scale the adoption of these improved varieties. Ultimately, this study contributes a valuable genetic and phenotypic foundation to address one of the most pressing constraints in African dryland agriculture—securing high-yielding and nutritionally valuable sorghum under parasitic stress.