Magembe, EM.  2008.  Genetic diversity analysis among cowpea [vigna unguiculata (l.) walp] accessions from Sub-Saharan Africa using simple sequence repeats (ssr's). Abstract

Cowpea is one of the most important legumes in the world. 1t is the second most
important pulse crop in tropical Africa after common beans (Phaseolus vulgaris). Cowpea
is valued for the high protein content of its grains which is about 25%. In Africa, where
animal protein is not always freely available/ affordable, cowpea provides a valuable
source of proteins. Cowpea diversity and relatedness in Africa is poorly understood. This
lack of knowledge and information inhibits the use of novel germplasm and novel alleles
in breeding programs and results in potential crop improvement bottlenecks. A core set of
1430 accessions of cowpea landraces from Sub-Saharan Africa were identified from the
International Institute of Tropical Agriculture's (lIT A) global cowpea collection (15003
accessions). In this study sixteen SSR markers were used to evaluate the genetic diversity
cowpea landraces in Sub-Saharan Africa.
Within the core set a total of 125 alleles were detected with the mean number of alleles
per marker being 7.8. The number of alleles per SSR ranged from 2 to 18. The mean
polymorphism information content (PIC) was 0.4531 with the most informative marker
being VM70 with a PIC of 0.8636 while the least informative marker was VM54 with a
PIC of 0.0376. The overall level of genetic diversity, measured as heterozygosities was
medium to low, with an average gene diversity of 0.4988. The gene diversity (H) ranged
from 0.0383 for VM54 to 0.8760 for VM70. The genetic diversity in West Africa was
higher than North Africa indicated by H of 0.4987 and 0.4129 respectively. The mean
observed heterozygosity was low (0.0953) as expected from a predominantly inbreeding
species. Gene differentiation (FsT) among populations was low (0.095) suggesting free
gene flow between populations, a result confirmed by genetic distance (DA), and
phylogenetic analysis. In, contrast, FJS which can be taken variously as a measure of
heterozygote deficiency and departure from the Hardy-Weinberg equilibrium, but also as
a measure of inbreeding, was found to be extremely high at 0.797.

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