Screening of Seed Soluble Sugar Content in Cowpea (Vigna unguiculata (L.) Walp)

Cowpea (Vigna unguiculata (L.) Walp) is a legume crop grown worldwide to provide protein, starch, soluble sugar, amino acids, fatty acids, minerals, and vitamins for human consumption and animal feed. Soluble sugar is an important physiological trait in cowpea seeds. It not only plays an important role in storability and abiotic stress tolerance in seeds, but also provides energy to the human body and improves cooking quality by giving a desirable taste and mouth feel. Therefore, this research aimed to evaluate variation of cowpea seed soluble sugar content, and assess the soluble sugar content of cowpea varieties with different seed coat colors for cowpea consumers. A total of 113 cowpea genotypes were used, including 89 USDA GRIN germplasm accessions and 24 advanced breeding lines developed from University of Arkansas, AR, USA. Seed soluble sugar content was measured using a Spectrophotometer by phenol-sulphuric acid method. The results showed that the seed soluble sugar contents among 113 cowpea genotypes exhibited a wide range varying from 32.6 mg/g to 86.1 mg/g with an average of 54.5 mg/g. The five highest soluble sugar contents in seeds were found in the Arkansas cultivar Empire (86.1 mg/g), USDA germplasm accession PI583202 (84.5 mg/g), Arkansas advanced breeding line 09-655 (82.1 mg/g), USDA accession PI601085 (81.6 mg/g), and Arkansas advanced breeding line 09-529 (80.9 mg/g), and they can be used in cowpea breeding programs to develop new cowpea cultivars with higher seed soluble sugar content. It was also observed that the soluble sugar contents in Arkansas commercial cultivars and advanced breeding lines were higher than those in USDA germplasm and the seeds with colorful coat may have soluble sugar levels desirable by consumers.