Evaluation of nutritional and phytochemical variability of cowpea Recombinant Inbred Lines under contrasting soil moisture conditions in the Guinea and Sudan Savanna Agro-ecologies

Abstract

Plant breeders’ efforts in developing drought tolerant and high-yielding cowpea varieties may be in vain unless the developed varieties are evaluated to ascertain the influence of water stress on their nutritive value, antioxidants, and phenolic contents under contrasting moisture regimes. The study was set up to evaluate the nutritional value, phytochemical content and antioxidant activity of cowpea Recombinant Inbred Lines (RILs) under contrasting soil moisture in the Guinea and Sudan Savanna agro-ecologies of Ghana. Forty-eight cowpea RILs seed samples from well-watered and water stress experiment were pulverized. Distillation and titration was carried out and the organic samples extracted and various biochemical analyses were carried out using standard protocols and methodologies. The dried grain mineral contents were determined using an Atomic Absorption Spectrophotometer, while the protein content was determined by the combustion method. Correlation and regression analysis and principal component analysis were performed using STATA version 13. Biochemical analysis for seed related traits revealed that inbred lines responded differently to drought. Significant differences of watering regimes on various phytochemical traits were only observed in phosphorus and lead. Inbred line with family number 57 had the highest crude protein content of 46.90% under well-watered conditions. Inbred line 84 under water stress conditions had high levels of Mg and K. Inbred line 20 under well-watered conditions had the highest antioxidant content. For phenolic acid content, inbred line 255 scored the highest. Quercetin and rutin were most abundant in inbred line 186 for both water-stress and well-watered conditions. The indication is that moisture stress could affect seed yield but no effects on the phytochemical and nutritional variables. Genotypic differences could arise from parental combination used for developing the inbred lines for the study. 1. Introduction Cowpea [Vigna unguiculate (L.) Walp.] is an extensively cultivated legume food crop of the tropics and sub-tropics, used in the diets of humans and animals. Cowpea seeds are an excellent source of carbohydrate (50–60%) and an essential source of protein (18–35%) (Stancheva et al., 2017; Addo-Quaye et al., 2011). Cowpea also contains considerable amount of micronutrients such as vitamin A, iron, Zinc and calcium (Quaye et al., 2009; Prinyawiwatkul et al., 1996). The crude protein from the seeds and leaves ranges from 23 to 32% (Diouf, 2011). Since cowpea is an essential source of protein for all, the effects of moisture stress on protein and free amino acid concentrations in seeds cannot be over emphasized. Also, the leaves and stems have been noted for its high amounts of Ca, Mg, K and Zn and therefore may serve