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Making a mark for cowpea

Striga starves cowpea by attaching itself to the crop's root (Lucky Omoigui, Makurdi, Nigeria)
Striga starves cowpea by attaching itself to the crop's root
Lucky Omoigui, Makurdi, Nigeria

Cowpea, otherwise known as the black-eyed bean, provides the major source of dietary protein to millions of people across large swathes of northern sub-Saharan Africa. One of the most drought tolerant of all grain legume crops, its productivity is challenged by a number of environmental constraints but, until just recently, little investment has been dedicated to its improvement.

One of the most serious constraints to cowpea's productivity is the parasitic weed Striga gesneroides, which starves the cowpea host by attaching itself to the crop's root, and then proceeds to deposit millions of tiny seeds into the soil to await the next planting. With no chemical available either to kill the parasite or to disable the seed lying in the ground, the only feasible solution lies in breeding genes for resistance into the crop.

Paradoxically, one of the best known genes for resistance turned up in an unimproved variety from Botswana, where Striga does not occur. Establishing whether a particular plant carries the resistance gene using conventional testing is an experimental nightmare. However it represents a dream target for marker-assisted selection (MAS) technology, because a marker for tracking the resistance gene has already been developed. However, establishing and maintaining the necessary human and physical infrastructure needed to run a MAS laboratory is beyond the capacity of most breeding programmes in sub-Saharan Africa.

A decentralised approach

The top-down solution proposed by much of the donor community has been to create a central, technologically advanced hub, tasked to analyse plant materials provided by users, as exemplified by the Biosciences eastern and central Africa facility in Nairobi. However, a contrasting bottom-up approach is now being taken by The Kirkhouse Trust, a UK-based charity, which is engaged in helping to provide MAS technology directly to West African cowpea breeders. The Trust's conviction is that the requirements for MAS can be sufficiently simplified to allow the technology to be used even in a very remote location.

The Trust is helping to provide MAS technology directly to West African cowpea breeders (Kirkhouse Trust)
The Trust is helping to provide MAS technology directly to West African cowpea breeders
Kirkhouse Trust

The requirements for MAS boil down to a means of extracting DNA from the plant, and the equipment and reagents to then amplify the critical sequence in order to establish its presence or absence. The Trust's priority has been to source reagents which do not require constant refrigeration and are not hazardous. DNA extraction has become a matter of squashing a leaf segment onto a specially treated paper, and the amplification reaction is provided in dry form, to which the user needs only to add water, and the DNA in the form of a small disc of paper.

With support from the Trust, a consortium of cowpea breeders has been formed across the region. All have been provided with the same set of equipment, reagents and training; the initial group of four (Nigeria, Ghana, Burkina Faso and Cameroon) has grown to six (Mali, Togo and Senegal, with Ghana dropping out).

A beacon of success

While progress has been uneven, largely due to a lack of trained personnel, the group in Burkina has shown what can be achieved by a committed principal investigator, who has succeeded in setting up a functional laboratory, organising staffing, recruiting students and gaining the ear of the national Department of Agriculture. As a result, the Trust now uses this group as both a beacon and a training centre for more recent participants.

The Botswana resistance gene is effective over a large area, but it does not control all West African populations of Striga. Where the gene is ineffective, other resistance genes - which are known - will need to be marked and deployed. Beyond this are other productivity constraints, including aphid feeding and infection by various fungi and bacteria, for which resistance breeding could benefit from a marker-assisted leg-up.

The Trust's major focus has been to support national breeding programmes (IITA)
The Trust's major focus has been to support national breeding programmes

The Trust's major focus has been to support the breeding programmes in situ, but at the same time it has invested substantially in a cowpea genome sequencing programme, as this form of data is necessary for designing genetic markers. Training of senior and junior breeding staff has been conducted through a series of three-six month research visits to the University of Virginia (a Trust partner), the organisation of regional workshops, and by supporting a series of technicians' working visits to the Ougadougou laboratory. A similar programme is underway in East Africa, targeting common bean, which is the staple grain legume across the region.

The key to the whole effort is the search for sustainability; the Trust believes that this is much more likely to be achieved by putting the technology directly into the hands of the practitioners, rather than by gifting it from on high. This way, the breeders themselves are more likely to have a stake in proving its worth and to be prepared to generate the internal pressure to incorporate MAS into their own national programmes over the long term.

Note: The Kirkhouse Trust will be represented at the forthcoming Fifth World Cowpea Research Conference to be held in Senegal

Written by: Robert Koebner, CropGen International

Date published: August 2010


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