Abstract:
Cowpea (Vigna unguiculata (L) Walp) is an economically important legume
crop of vital importance to the livelihood of several millions of people. Even so,
cowpea yields on African farmers’ fields are still below the potential yield of
the crop. This is, largely, as a result of the use of unimproved genotypes and
farming on phosphorus (P)-poor soils, which are pervasive in the tropics. Plants
have evolved several strategies to obtain adequate P for their growth under P
limiting conditions. These strategies include modification of root system
architecture (RSA) and longer root hairs. Root hairs can be measured using
rhizosheath, sheet of soil retained on roots after excavation and shaking.
Breeding for cowpea genotypes with superior RSA, rhizosheath and root hair
traits will help in achieving food security. The variation in rhizosheath, RSA
and root hair were quantified among sixty (60) cowpea genotypes grown up to
21 d under greenhouse conditions. Twenty (20) genotypes were selected for
further screening on three (3) external P concentrations [P]ext (i.e.: 0, 250 and
500 mg P/kg soil). Analyses were conducted on rhizosheath, root hair, RSA and
biomass traits. The cowpea genotypes were also analysed for variation in P use
efficiency (PUE) parameters including agronomic P use efficiency (APE), P
uptake efficiency (PUpE), and P efficiency ratio (PER). There were genetic
variations among cowpea genotypes in almost all the traits examined.
Genotypes with longer root hairs produced larger rhizosheath mass compared
to genotypes with larger root hair density. Increasing [P]ext resulted in a
significant increase in rhizosheath mass, root hair density, biomass, shoot P
concentration and content except for root hair length, which was reduced with
increasing [P]ext. Substantial variation was observed for shoot-P, root-P and
various measures of PUE among the cowpea genotypes. Some genotypes,
including MU9, IT91, Sunshine and WC10*WC36 developed longer root hairs
under low P conditions and these were categorised as P-efficient genotypes.
Root system and root hair traits including root hair density, root hair length and
total root length correlated with PUE in cowpea. The results could be used to
select for cowpea -genotypes with improved PUE for use on P-poor soils and
provide potential materials and targets for breeding new cowpea cultivars better
adapted to P-poor soils in Ghana
