Identifying key contributing root system traits to genetic diversity in field-grown cowpea (Vigna unguiculata L. Walp.) genotypes

•Key traits that explain variation in field-grown cowpea genotypes are presented.•Root biomass-, tissue angle- and diameter-related traits contributed most to genotypic variation.•Root biomass correlated positively with count-, length- and diameter-related traits.•Soil and root tissue angles were positively correlated with each other.•Positive correlations among traits suggests multi-trait improvements are possible.