Breeding/Genetic Tranformation of Cowpeas

Breeding/Genetic Tranformation
of Cowpeas

Genetic Engineering - Advances in molecular 
and cellular biology have made it possible 
to move genes from one species of plant into 
another species.  The transferred gene can 
impart a needed trait in the recipient 
plant, and thereby enhance its vigor, 
health, or productivity.  For example, 
transfer of the gene encoding Bacillus 
thuringiensis delta-endotoxin from the 
bacterium into various crop plants has led 
to a high degree of resistance toward 
certain insect pests.  Genetically-
engineered insect-resistant cotton, maize, 
and potatoes are now grown widely in the 
USA, and the technology is spreading 
rapidly.  For genetically-modified plants in 
general, the total area planted to these 
crops reached 70 million acres in 1998.

Genetic engineering technology has a 
promising future.  Its special advantage is 
that it can be used to address problems that 
can't otherwise be easily solved.  This is 
the case with cowpea, where (1) the genome 
of the crop plant contains few or no useful 
insect resistance genes and (2) wide 
crossing, the only other avenue to bring 
resistance into cowpea cultivars, is stymied 
by high genetic species barriers.

Cowpea Transformation - The cornerstone 
of genetic engineering to introduce needed 
traits into any plant is a sound and 
efficient methodology for stable genetic 
transformation of the plant species.  The 
ideal methodology is effective with many 
different genotypes of the species, but 
even more importantly, it has high 
efficiency, i.e., a relatively high 
percentage of the plants subjected to the 
procedure are transformed.  According to 
recent reports from Jacob Mignouna, interim 
Coordinator of Biotechnology at IITA, some 
progress has been made toward genetic 
transformation of cowpea.  A good 
regeneration system is in hand, and some 
genetically-transformed cowpea plants have 
been produced.  However, more work is needed 
to make the method sufficiently efficient.  
In essence, the door to genetic 
transformation of cowpea has been opened a 
crack, but it needs to be opened more widely.

Genes for Insect Resistance - Once it 
is possible to genetically transform a plant 
species the question then becomes:  Which 
gene? Which gene will confer an insect-
resistance trait on cowpea?  Curently there 
are two promising candidates.  For 
lepidopterous pests of cowpea, principally 
the legume pod borer, Maruca testulalis, 
genes encoding Bacillus thuringiensis 
protoxin proteins - hereafter referred to 
as "Bt" have been shown to be effective in 
suppressing growth and development.  At a 
level of a few parts per millions these 
proteins stunt the insects' growth or kill 
them.  For cowpea weevil, for which only a 
single moderate natural source of resistance 
has been found after an extensive search of 
the cowpea world collection, the gene 
encoding alpha-amylase inhibitor from common 
bean holds promise.  This gene has already 
been used to transform garden pea, which is 
susceptible to cowpea weevil and azuki bean 
weevil.

Transformed seeds expressing the alpha-
amylase inhibitor gene at high level - the 
same level that occurs in common bean seeds, 
which incidentally are immune to cowpea 
weevil - proved to be highly resistant or 
immune to cowpea weevil and azuki bean 
weevil.  Moving the alpha-amylase 
inhibitor gene from common bean into 
cowpea would be tantamount to moving a 
gene expressed in one bean food into 
another bean food.

Genes for other insect pests of cowpea are 
not yet in hand, but the mechanism for 
discovery of genes for one important pest 
group, the pod sucking bugs, has recently 
become available.  A bioassay has been 
developed that allows candidate proteins 
(gene products) to be incorporated into 
artificial seeds and evaluated for potential 
anti-insect activity.

The Curretn Task is to develop or adapt 
existing methods to allow us to transform 
cowpeas with foreign genes.  Whether this 
can best be done with accelerated 
microparticles (the "gene gun"), with 
Agrobacterium tumifasciens transformation, 
or by some other method remains to be seen.

• Seed & Pod Resistance • Striga Resistance • Genetic Tranformation • New Cowpea Varieties • Screening Tools for Bruchid-Resistant Germplasm

• Seed & Pod Resistance • Striga Resistance • Genetic Tranformation
• New Cowpea Varieties • Screening Tools for Bruchid-Resistant Germplasm