Abstract:
Background: Cowpea is a highly inbred crop. It is part of a crop-weed complex, whose origin and dynamics is
unknown, which is distributed across the African continent. This study examined outcrossing rates and genetic
structures in 35 wild cowpea (Vigna unguiculata ssp. unguiculata var. spontanea) populations from West Africa, using
21 isozyme loci, 9 of them showing polymorphism.
Results: Outcrossing rates ranged from 1% to 9.5% (mean 3.4%), which classifies the wild cowpea breeding system
as primarily selfing, though rare outcrossing events were detected in each population studied. Furthermore, the
analyses of both the genetic structure of populations and the relationships between the wild and domesticated
groups suggest possibilities of gene flow that are corroborated by field observations.
Conclusions: As expected in a predominantly inbred breeding system, wild cowpea shows high levels of genetic
differentiation and low levels of genetic diversity within populations. Gene flow from domesticated to wild cowpea
does occur, although the lack of strong genetic swamping and modified seed morphology in the wild populations
suggest that these introgressions should be rare.
