Does Selenium Application Increase the Yield of Cowpea Plants? Evidence from 29 Genotypes on Ureides and Sugar Index Affecting the Yield

Purpose: Cowpea (Vigna unguiculata L. Walp) is a low-cost source of protein in developing countries. Selenium (Se) is a micronutrient for humans and animals but is considered a beneficial element for plants. This study aimed to evaluate the effect of Se on the yield, sugar, and ureide concentration of cowpea. Methods: The experiment was comprised of 29 cowpea genotypes cultivated in a greenhouse fertilized with Se (control and 12.5 µg Se dm−3). The plants were cultivated until harvest to the following evaluations: grain yield, total sugar accumulation in grains, and total ureide concentration in shoots. The results were used to estimate Se influence in each variable by index production selenium (IPS), index sugar selenium (ISS), and index ureide selenium (IUS). The genotypes were divided into classes according to the respective indexes. Results: Selenium application provided an increase or decrease in yield, depending on genotypes. In genotypes with high IPS, Se application increases sugar in grains leading to greater yield, but no correlation between yield and ureides in shoots was observed. Conclusions: The class in which genotypes were allocated is important since some low-yield genotypes presented a significant increase in yield under Se application. On the other hand, Se provided a low-yield increase in some high-yield genotypes. This study shows valuable information for future cowpea breeding programs, to enhance the nutritional quality of grains and alleviate human malnutrition.