Development of a genetic linkage map and quantitative trait loci (QTL) analysis in cowpea (vigna unguiculata (L.) walp)
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Date
2010-06
Authors
Andargie, Mebeaselassie
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Abstract
Cowpea is a diploid plant species which contributes significantly to food security in developing
countries, especially in Africa. This research project was carried out in view of the upcoming
introduction of Bt cowpea in Africa which is likely to alter the equilibrium existing within the
cowpea taxa. The objectives of this study were to develop viable microsatellite markers and
construct the SSR based linkage map, identify quantitative trait loci that regulate yield,
domestication related traits as well as flower scent and identify the volatile compounds that
attract pollinators to cowpea flowers. In order to achieve these goals 159 F7 recombinant inbred
lines including the two parents and 206 markers (202 SSRs and 4 morphological) were used. The
first SSR based linkage map of cowpea was constructed that spans a genetic distance of2991cM.
QTL for seed weight (SW), domestication related traits (DRT), flower scent/aroma were mapped
in all 159 F7 plants and the two parents 524B x 219-01. Six QTL associated with 74 % of the
phenotypic variance were detected for SW on chromosomes 1, 2, 3 and 10. Both the 524B and
219-01 alleles increased SWat six of the QTL on chromosomes 1, 2, 3 and 10. For
domestication related traits, nine QTL (four for testa size and five for pod fiber thickness layer)
explaining 54.5 and 47.9 % of the phenotypic variance, respectively were on chromosomes 1,2,
4, 6, 7 and 10. The 524B allele increased DRTs at three-fourth of all QTL. QTL for SW and
DRTs were clustered on chromosomes 1 and 10. Association of SW and DRTs QTL may be the
cause of the significant phenotype and genotypic correlation detected between the two traits. The
test of linkage vs pleiotropy for SW and DRT QTL on chromosomes 1 and 10 suggested
pleiotropy. For flower scent/aroma, 63 QTL were detected on chromosomes 1,2,3,4, 5, 6, 7, 8,
and 10. In addition, a total of twenty-two different volatiles were identified by the GS-MS
technique. Clustering ofQTL were observed on chromosomes 1,2, and 4 mainly, suggesting that
it can occur either due to the presence of a single locus with pleiotropic effects on several volatiles or as a
result of tightly linked different loci. Such loci may encode transcription factors that co-ordinately
regulate genes, or they may encode enzymes that catalyse limiting steps in single pathways. It is
anticipated that this resource will have an important impact towards the development of marker
assisted selection systems for the cowpea breeding community, and for future genetic studies in cowpea.
Description
A thesis submitted in partial fulfillment of the requirements of the award of the degree of Doctor of Philosophy (Biotechnology) of Kenyatta University, Nairobi, Kenya, June 2010. QK 981.5 .M4