The genus Vigna contains several species that are important
in world agriculture. Cowpeas (V. unguiculata),
mung beans (V. radiata), and urd beans (V. mungo)
are grown on more than 10 million ha annually, and provide a significant
portion of the dietary protein in many societies. Several other
species, i.e., adzuki beans (V. angularis), moth beans
(V. aconitifolia), rice beans (V. umbellata), and
Bambarra groundnut (V. subterranea) are important in the
diets of other societies. All of the cultivated Vigna species
can be grown over a wide range of environmental conditions and
all provide inexpensive protein available in several edible forms,
such as tender green shoots and leaves, immature pods, and green
and dry seeds. These species are also valued as fodder, cover,
and green manure crops. Two of the species, the cowpea and the
mung bean, are of economic importance in the United States.
The cowpea is one of the world's important legume food crops.
Available estimates of worldwide cowpea production indicate that
1.5 to 2.25 million metric tons of dry seed are harvested annually
from 5 to 7.5 million ha. In the United States, the cowpea is
grown on a relatively large scale as a processing vegetable crop
(southernpea), as a dry bean (blackeye pea, blackeye bean, field
pea), and as a market garden crop (field pea, crowder pea, purple
hull pea, etc.). Additionally, various types of cowpeas are popular
home garden items in all of the southern states from Texas through
the Carolinas and Virginia. Georgia, Arkansas and Tennessee are
the leading producers of processing peas, and California and Texas
are the leading producers of dry beans. It is estimated that 80,000
ha of cowpeas are grown in the United States each year.
The mung bean is widely grown in southern Asiatic countries. In
the United States, it is the bean that is commonly used for sprouting.
The Oriental restaurants and commercial processors in this country
sprout 9 million kilos of mung bean seed annually. About one-fourth
of these beans are grown domestically, primarily in Oklahoma.
Much of the present Vigna germplasm evaluation and enhancement
efforts in the United States is by horticultural plant breeders
working for public agencies. Except for a small mung bean breeding
program at Texas A & M University, virtually all of this work
is with cowpea. A recent search of more than 30,000 research resumes
in the USDA's Current Research Information System database (coverage
includes projects conducted primarily by the research agencies
of the U. S. Department of Agriculture, the state agricultural
experiment stations, the state land-grant colleges and universities,
Tuskegee University, and other cooperating institutions) identified
11 universities and one federal agency in the continental United
States with active or recently completed cowpea breeding or germplasm
evaluation projects. Cowpea breeding or germplasm evaluation research
is being conducted in 13 states.
Seven of the universities (Auburn University, Louisiana State
University, Purdue University, Texas A&M University, University
of Arkansas, University of California at Davis, and the University
of California at Riverside) and the Agricultural Research Service
of the USDA had clearly identifiable cowpea breeding objectives.
It should be noted, however, that the breeding program at Auburn
University is inactive at present. Two other universities (New
Mexico State University and University of Florida) have active
cowpea cultivar evaluation research projects.
A number of universities have active research projects to develop
improved technologies and methods that have possible application
to cowpea breeding programs. For example, these projects are addressing
such topics as the inheritance of economically important cowpea
traits; the identification of new sources of tolerances to herbicides,
seedling chilling, AL toxicity, CA deficiency, heat stress, and
drought stress; identification of new sources of resistances to
insects and nematodes; mechanisms of virus resistance; salt tolerance;
ways to improve protein quality; ways to improve photosynthetic
and nitrogen fixation efficiencies; and the development of improved
procedures to evaluate various cowpea traits.
In 1988, the University of California at Riverside (UCR) and the
USDA entered into the first of two Specific Cooperative Agreements
to increase a large number of new accessions (primarily from the
12,000+ accessions held by the International Institute of Tropical
Agriculture, Ibadan, Nigeria) for incorporation into the cowpea
germplasm collection located at the USDA Regional Plant Introduction
Station in Griffin, Georgia. The first agreement "Evaluation
and Multiplication of Cowpea (Vigna unguiculata) Germplasm"
was funded in the amount of $40,600.00 and was effective from
1 June 1988 through 30 September 1990. The second agreement "Characterization
and Multiplication of Cowpea (Vigna unguiculata) Accessions"
was funded in the amount of $46,000.00 and was effective 15 September
1991 through 30 September 1994. The end result of UCR/USDA
agreements was an approximately 200% increase in the size of the
USDA cowpea germplasm collection -- 4,595 unique accessions
were added. It should be noted that one of the objectives
of these agreements was the elimination of viruses based on symptomology.
Although successful for a large portion of the accessions, it
proved to be unsuccessful for the exotic viruses present in some
germplasm from Botswana, India, and Kenya.
Most cowpea breeding programs in the United States have short-term
goals, i.e. the quick development of cultivars to meet immediate
contingencies and industry requirements. Many of the general objectives
are the same. Such traits as increased yield, concentration of
pod set, superior plant habit, improved adaptation, and increased
tolerances to environmental stresses are important. Resistances
to fungal diseases (e.g., anthracnose, Cercospora leaf spot, Fusarium
wilt, root rots, and Verticillium wilt), bacterial diseases (e.g.,
bacterial blight and canker), viruses (e.g., bean yellow mosaic,
blackeye cowpea mosaic, cowpea chlorotic mottle, cowpea mottle,
cowpea yellow mosaic, cucumber mosaic, and southern bean mosaic),
root-knot nematodes (Meloidogyne spp.), and insects (e.g.,
cowpea curculio, aphids, and lygus bugs), particularly those that
cause significant yield reductions, are universally important.
Several U. S. breeding programs have stated long-term objectives,
e.g. improved breeding populations and conservation of genetic
variability.
Regional testing of advanced cowpea breeding lines is coordinated
by the Regional Southernpea Cooperative Trials. These trials are
a part of the Southern Cooperative Vegetable Trials sponsored
by the Southern Region of the American Society for Horticultural
Science. The cooperative trials, in which lines are tested in
many locations, provide breeders with as much information in a
single season as they could obtain at a single location over many
years. The southernpea trials are not intended to be a substitute
for ordinary cultivar trials, and only advanced breeding lines
are accepted for testing. The 1995 trials were grown at 10 sites
in 6 different states; there was 10 entries in the replicated
trial and 7 entries in the observational trial. The trials are
planned, coordinated and reported annually by a chairman.
There is one commodity-oriented organization that plays an important
role in coordinating U. S. cowpea germplasm evaluation and enhancement
programs. This organization is the National Cowpea Improvement
Association (formerly the Cowpea Improvement Committee), and it
is open to all scientists with an interest in cowpea improvement.
The organization, which is quite informal, meets annually, usually
in conjunction with the annual meeting of the Southern Region
of the American Society for Horticultural Science. The National
Cowpea Improvement Association is the "parent organization"
of the Vigna Crop Germplasm Committee.
The implementation of the Bean/Cowpea Collaborative Research Support
Program (CRSP) in October 1980 with funds provided by the U.S.
Agency for International Development under Title XII of the Foreign
Assistance Act has played an important role in bringing together
resources of institutions in the U.S. and those of institutions
in Africa and Latin American. The Bean/Cowpea CRSP researchers
have made many contributions toward resolving cowpea production
and utilization problems in those countries where the crop is
important in the human diet. As intended, many of these contributions
are applicable to the cowpea industry in the U.S.
Genetic vulnerability is not seen as a critical problem for the
Vigna species grown in the United States. In comparison
with many of the agronomic crops, cowpeas and mung beans are relatively
minor crops in the U. S. Neither crop is considered to be staple
food in U. S. society. The cowpea was once an important forage
crop in the U. S., but there is only limited use of the crop as
forage at present.
There is a broad range in the characteristics of cowpea cultivars
that are popular in the United States. There is a broad range
of genetic diversity among cultivars. It is not anticipated that
current breeding programs will have a significant impact on the
diversity. In fact, the availability of new cultivars might decrease
our dependence on some major cultivars that account for large
portions of the production in some areas. For example, 'California
Blackeye #46', a new blackeye cultivar with increased resistance
to Fusarium wilt, has greatly reduced our heavy dependence on
'California Blackeye #5' in the dry seed industry.
Collections
There are large and diverse Vigna collections held in several
international and national centers. The large numbers of unique
accessions that have been added to the USDA cowpea germplasm collection
since 1988 via the University of California at Riverside/USDA
Specific Cooperative Agreements discussed above has greatly enhanced
the adequacy of the USDA collection to meet U.S. cowpea germplasm
needs.
The International Institute of Tropical Agriculture (IITA) cowpea
base collection (12,000 - 13,000 accessions) is larger than the
current USDA collection. The IITA collection is a very important
collection, and a major effort needs to be made to store duplicate
samples in the U. S. We do not have easy access to IITA materials
at present, and the entire collection could be lost if there is
a civil war in Nigeria. Museum storage under cold conditions,
such as the National Seed Storage Laboratory (NSSL), would be
appropriate.
The University of California at Riverside has an appreciable collection
of cowpea germplasm (approximately 5,000 accessions) that was
obtained from the USDA, IITA, and different countries as part
of the Title XII Bean/Cowpea Collaborative Research Support Program.
Many of these lines have been evaluated and increased as part
of the UCR/USDA Specific Cooperative Agreements discussed above,
and are now included in the USDA working collection.
There is currently a large collection of mung bean germplasm stored
at the Asian Vegetable Research and Development Center. Consideration
should be given to storing duplicates of this collection at the
NSSL.
The National Bureau of Plant Genetic Resources (NBPGR), New Delhi,
India, maintains large collections of mung beans and urd beans
(V. mungo). The urd bean crosses quite readily with the
mung bean, and it should be considered part of the mung bean gene
pool. Consideration should be given to storing duplicates of both
collections in the U. S.
There is a problem of duplication in the U. S. collections, and
the problem will become more serious as duplicates of other collections
are accepted for storage. Effort are currently underway at the
Plant Introduction Station in Griffin, Georgia, to develop the
methodology needed to identify duplicates (synonyms).
The various Vigna collections described above represent
a broad sampling of much of the world's gene pools. However, their
are still centers of diversity that need sampling. The International
Board for Plant Genetic Resources (IBPGR) publication "Genetic
Resources of Vigna Species" (AGPG:IBPGR/81/82) assigned
the following crop priorities (each entry in order of need) for
exploration and collection:
The IBPGR publication also listed exploration and collection priorities
for the following species: V. umbellata, V. angularis, V. aconitifolia,
V. nervosa, and V. subterranea. These species are of
potential value to U. S. research programs, and they should be
included in any exploration effort to collect Vigna germplasm.
Evaluation
Much of the current Vigna germplasm evaluation work in
the U. S. is being carried out as adjunct projects to plant breeding
programs. Virtually all of this work is on cowpea. In general,
these programs are doing a creditable job of addressing the high
priority evaluation needs. An effort needs to be made to "educate"
plant breeders about the value of putting evaluation data into
the GRIN database. The two UCR/USDA Specific Cooperative Agreements
discussed above have generated a large amount of evaluation data
on the IITA and Title XII collections.
The USDA Vigna collection is currently located at the Plant
Introduction Station, Griffin, Georgia. This station's evaluation
work on Vigna germplasm has not been sufficiently active
in recent years, but the establishment of a curator in early 1994
has begun to address this problem.
Enhancement
As was the case with germplasm evaluation, much of the current
Vigna germplasm enhancement work in the U. S. is being
carried out as adjunct projects to plant breeding programs. Like
the germplasm evaluation work, virtually all of the Vigna
germplasm enhancement work is on cowpeas.
U. S. cowpea breeders face formidable challenges in developing
new cultivars suitable for modern, highly specialized production
and marketing systems. Cultivars are needed that exhibit increased
resistance to a wide array of diseases, insects, and nematodes,
better tolerances to environmental stresses, increased nitrogen-fixing
capacity, better seed qualities, and improved efficiency in the
utilization of limited soil nutrients. The plant breeder has an
obligation to improve the nutritional, flavor and aesthetic aspects
of cowpea products. The plant breeder can play an important role
in the development of improved production systems. For example,
cultivars with modified growth habits might be used to increase
production efficiency in intensely managed farming systems. Weed
problems might be solved by developing cultivars with tolerance
to existing herbicides. In comparison with many other crops, the
cowpea has received little attention from plant breeders, and
a large effort needs to be made to break yield barriers.
If American cowpea breeders are to be successful in addressing
the needs of modern agriculture, appreciable amounts of effort
will have to be directed to germplasm enhancement. The genes needed
to develop the truly revolutionary cultivars of tomorrow exist
now only in exotic genetic backgrounds (extensive cowpea germplasm
collections are held by various national and international agencies).
It is anticipated that much of the future germplasm and evaluation
work will continue to be adjunct projects of ongoing plant breeding
programs. For the most part, germplasm evaluation should be limited
to those traits of immediate concern to plant breeders. The individuals
evaluating germplasm can be expected to be charged with the responsibility
of directing developmental breeding programs (germplasm enhancement)
to transfer newly identified and potentially valuable genes into
cultivar materials. It is recommended that the bulk of the moneys
(70-85%) available for germplasm collection, evaluation and enhancement
be directed toward enhancement.
Development of a genetic map
Yield concentration (synchronous flowering; less insecticide needed
for controlling cowpea curculio)
Development of better techniques for evaluation and enhancement of germplasm for processing quality (especially seed stain)
Development of germplasm with wider maturity ranges (late maturing
cultivars are especially needed)
Bacterial blight resistance
Heat tolerance (needed for fall production)
Resistance to insects, e.g., cowpea curculio, lygus bug, leaf
miner, cowpea aphid
Resistance to Cowpea Severe Mosaic and Blackeye Cowpea Mosaic
Viruses
Combine resistance (resistance to seed damage)
Improved seed quality, e.g., splits and fish mouth
Preservation (storage)
The base USDA Vigna germplasm collections are held at the
National Seed Storage Laboratory (NSSL) in Fort Collins, Colorado,
and the USDA working collections are held at the Plant Introduction
Station in Griffin, Georgia. Storage conditions are adequate at
both locations. Procedures for preserving genetic diversity in
samples are adequate.
The working Vigna collections at Griffin contain a total
of 12,496 accessions, including 7,698 cowpea accessions, 3,890
mung bean accessions, 306 urd bean accessions, 498 Bambarra groundnut
accessions, and a small number of accessions (total = 104) for
each of several of the minor cultivated and wild species.
In 1995, The Vigna Crop Germplasm Committee established a core
subset of the USDA cowpea germplasm collection. The subset consists
of about 9% (700 accessions) of the 7,698 accessions currently
contained in the collection. The subset was selected on the basis
of country of origin, taxonomic characteristics, and known disease
and pest resistance characteristics.
Most of the accessions in the Vigna working collections
at Griffin are not backed up in the base collections at the NSSL,
but a major effort is currently being made to correct this problem.
There are now 1,300 cowpea accessions backed up, and 2,500 additional
cowpea accessions will be backed up by Spring 1996. Most of the
cowpea accessions increased in recent years by UCR, and now in
storage at Griffin, will also be backed up at NSSL in 1996.
Several of the nation's cowpea breeding programs (including some
inactive programs) maintain small working collections. There is
no good procedure in place to insure that the potentially valuable
materials in some of these collections are incorporated into the
base collection.
In many respects, the location of the USDA Vigna working
collection at Griffin, Georgia, is not a good location for cowpea
grow-outs and evaluation. Griffin is located just north a major
cowpea (southernpea) production area, and it is risky to produce
cowpea seed here because lines readily become reinfected by endemic
viruses. Also, Griffin is not adequate for increase of photoperiod-sensitive
lines. A site in southern California, e.g., Riverside, would be
a better location for grow-outs and evaluations of the working
collections. Such a location would provide a hot, dry, pest- and
disease-free growing environment, and a very low (negligible)
level of outcrossing. However, it should be noted the even Riverside
is not far enough south to adequately increase seed of some extremely
photoperiod-sensitive lines. Increase sites in Hawaii or the Virgin
Islands would probably have adequate photoperiods for these "hard-to-increase"
lines. (Note: University of California researchers have successfully
increased "very photosensitive" cowpea accessions by
using mid-August plantings at a low-elevation desert site 40 miles
south of Palm Springs, CA.)
Virus diseases pose the greatest threat to cowpea production in
the southern states. Special efforts need to be made to identify
sources of virus resistances and to transfer such resistances
into cultivar-type materials. This needs to be an ongoing effort
since new races/strains of each problem virus are likely to overcome
currently available sources of resistances.
Breeding cowpeas for resistance to the most destructive pathogens
has been an effective method of minimizing disease losses in the
U. S., but much more work is needed. Sources of resistance to
many fungal and bacterial diseases need to be identified, and
developmental breeding efforts need to be expanded to incorporate
new resistance genes into advanced breeding lines.
Insects (e.g., cowpea cucrulio, cowpea aphid, lygus bug, and leaf
miners) are major pests of the cowpea, and the problem has intensified
in recent years because of the withdrawal of pesticide registrations.
In fact, the unavailability of suitable pesticides has already
caused a major shift in the geographic areas where southernpeas
are grown for processing. Better sources of resistances to insects
are badly needed.
Breeding for all types of pest resistances (whether against insects,
nematodes, fungal pathogens, bacterial pathogens, viruses, or
weed pests) has a common environmental justification -- alternatives
are needed to pesticides. The southernpea and blackeye bean industries
are heavily dependent upon pesticides, and every effort needs
to be made to find alternatives!
Compared with many other crops, the cowpea has received little
attention from plant breeders, and a large effort needs to be
made to break yield barriers. Cowpea yields have never equaled
the yields that are expected of such food legume crops as lima
beans. If cowpea production is to keep pace with these crops,
its yield potential must be improved.
Updated June 24, 1996.