Nitrogen and water application differentially influence nutritional value and mineral content in grains of a genetically diverse sorghum germplasm collection

Abstract

Background: The nutritional profile of sorghum grains, such as antioxidant (AOX) status and mineral content, can be influenced by a number of environmental factors and agricultural practices, as well as by biotic and abiotic stresses. We investigated the impact of contrasting nitrogen (N) and water availability on 15 traits associated with sorghum nutritional value, including AOX capacity (AOX), total phenolics content (TPC), total protein, ash, moisture, and the concentration of 10 macronutrients [nitrogen in leaves (NCL) and grains (NCS), P, K, Mg, Ca] and micronutrients (Fe, Cu, Zn, Mn) in grains. To this end, we evaluated a broad and genetically diverse germplasm collection of 124 accessions over two years of field experiments conducted under optimal N and water availability (control, +N+FC100); under N restriction (-N+FC100); and under N and water restriction (-N+FC50).

Results: Significant effects for treatment, accession, year, and their interactions were found for most traits. In general, N and water restriction treatments were detrimental -as compared to controls- for most traits, as evidenced by decreases in mean values of 10-50% (for -N+FC100) and 8-58% (-N+FC50) consistently found for 11 traits. The most affected variables under -N+FC100 conditions were Zn, Mg, and Cu; and P, Zn, Mg under -N+FC50. In contrast, AOX and TPC levels showed increases in mean values of ~ 11-103% under -N+FC100 and -N+FC50 conditions. These two variables were moderately-to-strongly correlated (r = 0.53-0.96) across all environmental conditions and years, suggesting that phenolic compounds are the main drivers of AOX capacity in sorghum. Results from principal component analysis clearly depicted the strong effects of N-restricted and combined N plus water-restricted conditions on sorghum's nutritional and mineral contents. Genetically-stable accessions with the greatest and lowest performances for each trait and growing condition were selected for breeding purposes.

Conclusions: Nitrogen and water restrictions strongly -yet differentially- influence nutritional and mineral contents in sorghum, enhancing TPC and AOX while reducing mineral levels. This study characterized a large germplasm collection across various growing conditions and years, facilitating the selection of resilient genotypes for breeding programs aimed at improving nutritional value under changing climatic conditions.