Root hair and rhizosheath traits contribute to genetic variation and phosphorus use efficiency in cowpea (Vigna unguiculata (L.) Walp)

Abstract

Rhizosheaths are soil particles that bind to the surface of plant roots after excavation. Rhizosheaths can indicate root hair length and are essential for the uptake of soil resources. Cowpea is a key legume crop for Africa's food security, livelihood, and agroecosystem sustainability. Still, genetic variation in rhizosheaths and root hair traits in cowpea and their impact on phosphorus (P) uptake have not been tested. Here, 60 cowpea genotypes were grown to assess genotypic variations in root hair, rhizosheath, and other root system traits. Subsequently, 20 genotypes were selected to evaluate variations in trait responses to varying rates of external P application ([P]ext). Root hair traits were positively related to rhizosheath dry weight, and this showed significant genotypic variation (p < 0.001), with more than 2.5-fold variation. Root hair length and density were 0.111 cm and 0.329 roots cm−2, respectively, with 54.3% and 59.1% differences between their lowest and highest values. Shoot biomass, specific rhizosheath weight, and root hair length were the top contributors to the genotypic variations. The main effect of [P]ext was highly significant, with plants producing more biomass at higher [P]ext but root hair length increased at low [P]ext. This paper contributes seminal information on variations in root hair and rhizosheath formation with P uptake and the potential for using this information in cowpea improvement for adaptation to rhizospheric stresses.