Identification of markers associated with bacterial blight resistance loci in cowpea (Vigna unguiculata (L.) Walp.)

Cowpea bacterial blight (CoBB), caused by Xanthomonas axonopodis pv. vignicola (Xav), is a worldwide major disease of cowpea [Vigna unguiculata (L.) Walp.]. Among different strategies to control the disease including cultural practices, intercropping, application of chemicals, and sowing pathogen-free seeds, planting of cowpea genotypes with resistance to the pathogen would be the most attractive option to the resource poor cowpea farmers in sub-Saharan Africa. Breeding resistance cultivars would be facilitated by marker-assisted selection (MAS). In order to identify loci with effects on resistance to this pathogen and map QTLs controlling resistance to CoBB, eleven cowpea genotypes were screened for resistance to bacterial blight using 2 virulent Xav18 and Xav19 strains isolated from Kano (Nigeria). Two cowpea genotypes Danila and Tvu7778 were identified to contrast in their responses to foliar disease expression following leaf infection with pathogen. A set of recombinant inbred lines (RILs) comprising 113 individuals derived from Danila (resistant parent) and Tvu7778 (susceptible parent) were infected with CoBB using leaf inoculation method. The experiments were conducted under greenhouse conditions (2007 and 2008) and disease severity was visually assessed using a scale where 0 = no disease and 4 = maximum susceptibility with leaf drop. A single nucleotide polymorphism (SNP) genetic map with 282 SNP markers constructed from the same RIL population was used to perform QTL analysis. Using Kruskall-Wallis and Multiple-QTL model of MapQTL 5, three QTLs, CoBB-1, CoBB-2 and CoBB-3 were identified on linkage group LG3, LG5 and LG9 respectively showing that potential resistance candidate genes cosegregated with CoBB resistance phenotypes. Two of the QTLs CoBB-1, CoBB-2 were consistently confirmed in the two experiments accounting for up to 22.1 and to 17.4% respectively for the first and second experiments. Whereas CoBB-3 was only discovered for the first experiment (2007) with less phenotypic variation explained of about 10%. Our results represent a resource for molecular marker development that can be used for marker assisted selection of bacterial blight resistance in cowpe

Lessons learned and ways forward on CGIAR capacity development: A discussion paper

This paper is a contribution to the establishment of a new capacity development (CD) strategy, a process that the Consortium Office will facilitate, with external input, during 2013. The paper explores the lessons learned from CGIAR’s experience with CD and reflects the findings of a working group that was brought together in late 2012

Gene pools and the genetic architecture of domesticated cowpea

Open Access JournalCowpea [Vigna unguiculata (L.) Walp.] is a major tropical legume crop grown in warm to hot areas throughout the world and especially important to the people of sub-Saharan Africa where the crop was domesticated. To date, relatively little is understood about its domestication origins and patterns of genetic variation. In this study, a worldwide collection of cowpea landraces and African ancestral wild cowpea was genotyped with more than 1200 single nucleotide polymorphism markers. Bayesian inference revealed the presence of two major gene pools in cultivated cowpea in Africa. Landraces from gene pool 1 are mostly distributed in western Africa while the majority of gene pool 2 are located in eastern Africa. Each gene pool is most closely related to wild cowpea in the same geographic region, indicating divergent domestication processes leading to the formation of two gene pools. The total genetic variation within landraces from countries outside Africa was slightly greater than within African landraces. Accessions from Asia and Europe were more related to those from western Africa while accessions from the Americas appeared more closely related to those from eastern Africa. This delineation of cowpea germplasm into groups of genetic relatedness will be valuable for guiding introgression efforts in breeding programs and for improving the efficiency of germplasm managemen

An improved consensus genetic linkage map of cowpea ( Vigna unguiculata L. Walp. )

Consensus genetic linkage maps are formed from merging individual linkage maps. They provide powerful tools for genetic analysis and a foundation for marker-assisted breeding, trait mapping, and positional cloning. In 2009, the first cowpea consensus map was developed. It included 928 markers spanning 11 linkage groups over a total map size of 680 centimorgans (cM), a 0.73 cM average marker distance. The map was the result of merging maps from 6 RIL populations genotyped with a 1536-SNP multiplexed assay developed from EST-derived genic SNPs. Here we report improvements to the consensus map for cowpea that result from merging genotype data from a total of 1070 lines composed of eight RIL and two F4 breeding populations. Individual maps were first constructed and then merged to develop a consensus map. The improved map is 680 cM in length and contains 1043 markers, which is an addition of 115 markers and an average 0.65 cm between markers. The map resolution is also increased with more marker bins, and there were some adjustments to marker order. The current SNP-based cowpea linkage map is included in a publicly available browser called HarvEST:Cowpea, which can be downloaded as a Windows software from http://harvest.ucr.edu or viewed through an online portal www.harvest-web.org

Modern approaches for cowpea breeding: how highthroughput genotyping and a highdensity map change everything

The genomics revolution has enabled rapid advances in genotyping capabilities and construction of high-density genetic linkage maps that enable new plant breeding strategies which have the potential to expedite delivery of improved crop varieties. These breeding strategies utilize molecular marker information at hundreds to thousands of points in the genome, encompassing selection for multiple traits and/or multigenic traits. This chapter summarizes the opportunities and challenges for the cowpea breeding community in adopting modern breeding given the recent development of enabling genomic resources. These resources include high-throughput SNP genotyping platforms, high-density consensus genetic map with more than 1000 markers, and QTL(s) linked to important biotic and abiotic resistance traits, including resistance to foliar and flower thrips, Fusarium wilt, root-knot nematode, bacterial blight, ashy stem blight (Macrophomina), Striga, and components of drought tolerance. Initial work in evaluating and optimizing marker-assisted backcross (MABC), marker-assisted pedigree breeding (MAPB), and marker-assisted recurrent selection (MARS) in cowpea breeding is described. We also report on the successful completion of tests evaluating the feasibility of outsourced SNP genotyping by African NARS breeders. Cost of genotyping, while much reduced compared to the recent past, is still a major constraint to widespread adoption of modern breeding by developing country NARS. High throughput precision phenotyping methods are needed to properly complement the recent advances in genomic resources. New resources and tools to help overcome these challenges have recently become available to breeders within the cowpea community, particularly in the areas of improving information management capability, decision making tools for marker-assisted breeding, and experimental design for precision phenotyping. Comprehensive training of breeders in the use of these tools is urgently needed

Modern approaches for cowpea breeding

The genomics revolution has enabled rapid advances in genotyping capabilities and construction of high-density genetic linkage maps that enable new plant breeding strategies which have the potential to expedite delivery of improved crop varieties. These breeding strategies utilize molecular marker information at hundreds to thousands of points in the genome, encompassing selection for multiple traits and/or multigenic traits. This chapter summarizes the opportunities and challenges for the cowpea breeding community in adopting modern breeding given the recent development of enabling genomic resources. These resources include high-throughput SNP genotyping platforms, high-density consensus genetic map with more than 1000 markers, and QTL(s) linked to important biotic and abiotic resistance traits, including resistance to foliar and flower thrips, Fusarium wilt, root-knot nematode, bacterial blight, ashy stem blight (Macrophomina), Striga, and components of drought tolerance. Initial work in evaluating and optimizing marker-assisted backcross (MABC), marker-assisted pedigree breeding (MAPB), and marker-assisted recurrent selection (MARS) in cowpea breeding is described. We also report on the successful completion of tests evaluating the feasibility of outsourced SNP genotyping by African NARS breeders. Cost of genotyping, while much reduced compared to the recent past, is still a major constraint to widespread adoption of modern breeding by developing country NARS. High throughput precision phenotyping methods are needed to properly complement the recent advances in genomic resources. New resources and tools to help overcome these challenges have recently become available to breeders within the cowpea community, particularly in the areas of improving information management capability, decision making tools for marker-assisted breeding, and experimental design for precision phenotyping. Comprehensive training of breeders in the use of these tools is urgently needed