Agriculture Reference
In-Depth Information
including flowers. Its disadvantages are that it is not tolerant to waterlogging and yet
it needs a high rainfall. It is now cultivated worldwide and is a fashionable crop in the
United States and elsewhere, but it is fair to say that it has not been the miracle plant
for Africa for which it was hailed. More realistically cowpea,
V. unguiculata
, is a crop
that grows well in Africa, even in low rainfall areas, where it is often grown together
with maize (Plate 6.2). It is estimated that 200 million people in sub-saharan Africa
eat cowpeas when they are available (Anon, 2006). It has already been the subject of
considerable agronomic research and is being grown in South America and parts of
Asia, where it is usually known as black-eyed pea. Yields are still low and there are
major problems with insects, but the potential is great.
In the Indian sub-continent, other species of
Vigna
are in widespread use, including
green and black gram. However, perhaps the most interesting plants with potential
are those that produce both edible seed and tubers. Two of these are the African
and American yam beans (Table 6.1).Tubers are generally are both good to eat and
a way for the plant to survive adverse conditions such as drought, because they can
produce new shoots after rain. Plate 6.3 shows tubers of
Vigna vexillata
, which was
widely used as 'bush tucker' by Australian Aborigines and which is currently being
assessed for development (Grant et al., 2003). Most of the legumes listed in Table 5.3, but
especially species of
Vigna
, appear to nodulate freely (Plate 6.4). Normally nodulated by
bradyrhizobia, recent studies have found salt-tolerant strains of fast-growing rhizobia
from coastal sand dunes in India that perform well on cowpea and other legumes
(Arun & Sridhar, 2004).
6.1.2 Other phaseoloid legumes
There is certainly a move to capitalize on the wider use of legumes, especially when
they can be grown on marginal land. An example is the work of Sridhar & Bhagya
(2007) using
Canavalia maritima
growing on coastal sand dune vegetation in India. This
plant not only stabilises soil, it has edible pods, can be used for forage, as a green
manure and has bioactive compounds for potential medicinal use. As it is pan-tropical,
growing also in parts of Africa and Northern Australia, it is a good candidate for
further development.
Apios americana
has an interesting history. Its tubers were a staple food of native
Americans and it helped the early European settlers survive their first few winters
in North America. Following the Irish potato famine in 1845, it was introduced into
Europe and grew well. Now it has largely fallen out of fashion, but its potential, and
that of related species was raised recently by Vietmeyer (2008).
Pigeon pea,
Cajanus cajan
, has a long history of cultivation, but still needs developing
to achieve its full potential. It is one of the crops highlighted inAnon (2006). It is amulti-
purpose species that nodulates freely, a short-lived perennial though often grown as an
annual. It has a deep root system, can access poorly available soil phosphorus (Sprent,
1999), yields nutritious seed, can be browsed by animals and produces firewood. The
Internationational Institute of Tropical Agriculture (IITA) is developingmarkers for the
African yam bean (
Sphenostylis stenocarpa
), with a view to producing better cultivars
(Moyib et al., 2008). The tubers of this plant 'look like sweet potatoes, but taste more
