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African Crop Science Journal
African Crop Science Society
ISSN: 1021-9730 EISSN: 2072-6589
Vol. 3, Num. 2, 1995, pp. 135-142
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African Crop Science Journal, Vol. 3. No.2, pp. 135-142,
1995
Sorghum: one of the world's great cereals
L.R. HOUSE
Rt No. 2, Box 136A-1, Bakersville, N.C. 28705, USA
Code Number: CS95019
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ABSTRACT
Sorghum (Sorghum bicolor (L.) Moench) is a crop of
world-wide importance. It is unique in its ability to produce
under a wide array of harsh environmental conditions. The crop
has great genetic diversity, nmking selection for most traits of
economic importance possible. However, in spite of the
significant improvements in yield, isease and pest resistance and
utilization/quality traits, there is need to transfer these
technologies into farming and user communities.
Key Words: Crop improvement, genetic diversity, pest
resistance, Sorghum b:color, utilization
Resume
Le sorgho (Sorghum bicolor L.) est une culture
mondialement importante. Elle est unique quant a la capaci te de
prod uire sur une grande gamme de conditions drastiques de
l'environnement. La culture posse de une grande diversite
genetique, ce qui permet de rendre possible la selection des
traits d'importance economiques. Cependant, en depit
d'ameliorations significatiques en rendement, en resistance aux
maladies et insectes, et au point de vue de l'utilisation et de
la qualite des prodnits, ii s'avere necessaire de transferer ces
technologies aux communautes d'agriculteurs et de
consommateurs.
Mots Cids: Amelioration des plantes, diversite
genctique, resistance aux pestes, Sorghum bicolor,
utilisation
HISTORY
Sorghum (Sorghum bicolor (L.) Moench) belongs to the grass
family and was domesticated in different areas of Africa.
Recently, seeds of sorghum, several millets, legumes and other
edible plant remains were found at an ancient site, Nabta Playa,
in southern Egypt close to the border with the Sudan. These
remains were carbon dated to be approximately 8,000 years old.
Sorghum seeds were similar in size and structure to the modern
wild types, but infrared spectrographic results suggestthat they
arecloserto present day cultivated grains, particularly the
hexane extracts. This suggests the possibility of some
cultivation for food and selection that may have contributed to
domestication (Wendorf et al., 1992). This is the earliest
known archaeological record.
There are five basic races of sorghum: bicolor, guinea,
caudatum, durra, and kafir (Harlan and de Wet. 1972).
A major step in the process of domestication is the loss of the
seed shattering characteristic (Mann etal., 1983). Harlan
(1975) asserted that domestication of sorghum occurred 0 ver time
and in several areas where it was probably ennobled many times
over several years. He envisions that early domestication
occurred in an area extending from near the Ethiopian border,
west through Sudan and up to Lake Chad. There is great diversity
in this area as well as the presence of the primitive race
bicolor (Harlan and de Wet, 1972). It is likely that this
race arose from the
domestication of the aethiopicum verticilliflorum complex
some 3,000 to 5,000 years ago. The finding at Nabta Playa may
cause some rethinking of dates; however, it is not clear if these
8,000 year old seeds were from plants that did not shatter
grains, although altered chemical composition would indicate some
selection.
Bicolor sorghum has spread over much of the old sorghum growing
world, being found in India. and is the likely progenitor of the
kaoliongs of China (Mann et al., 1983L The race guinea
arose from bicolor with the possibility of interaction
with the wild race arundinaceum in the higher rainfall
areas of West Africa. The guinea are now the dominant
sorghum of West Africa but have spread and are found in Tanzania
and Malawi. The guinea race arose more than 2,000 years
ago. The race caudatum also likely arose from bicolor:
it is found in the same area. Today, the caudatums are most
abundant from east Nigeria to eastern Sudan and southward into
Uganda. The race durra was selected from early bicolor
that had moved into India some 3,000 years ago. With Arab
migration, the durras moved into Ethiopia around 615 A.D.; and
is today the dominant race in India, Ethiopia, the Nile Valley
of Sudan and Egypt. Race kafir was probably derived from
bicolor but there is also evidence of association with the
wild race verticilliflorum. The kafirs are found primarily
in eastern and southern Africa (Mann etal., 1983). Sorghum
found its way into the Americas after 1850.
Much of the agricultural history of sorghum has been for food,
beverage, feed and bui Iding material. It has been used as an
industrial crop during the last 100 years. Mechanization of its
cultivation and harvesting has occurred primarily in the last
60-70 years. Industrial uses of the crop have been for feed, some
for food, starch, the chemical industry. and for fuel alcohol.
ADAPTATION
Maize, sorghum and pearl millet are the most important dry land
summer cereals. Maize is generally cultivated where moisture is
adequate, without water-logging, and under moderate temperatures.
Sorghum is generally cultivated in dry, hot areas (38-40 C) with
an averge annual rainfall of 400-750 mm, though it can be grown
where rainfall is much higher. Sorghum also withstands water
logging. Pearl millet is frequently cultivated on lightly
textured, sandy soils with annual rainfall in the 300-500 mm
range. Under comparable moisture conditions, sorghum will do
better under cooler temperatures, while pearl millet does better
under warmer conditions.
PRODUCTION
For centuries, farmers selected seed from the best plants for
sowing the next seasoffs crop. They selected for traits ensuring
some production; i.e., avoidance of insect pests. grain moulding
from late rains, drought tolerance, etc. They also natrowed the
genetic base. thus restricting their opportunities for selection.
The consequence was varieties with a fairly reliable but low
production of grain. While there have been significant changes
from this base resulting in higher yields. there are still many
places where traditional cultivars are used in much the same way
as in the past. The advent of hybrids in the mid-l950's has been
an important factor contributing to the expanded use and higher
yields of the crop.
In terms of acreage. sorghum ranks fifth among the world's
cereals following wheat, maize, rice and barley- World production
at the beginning of the 1960's was about 40 million metric
tonnes. Production increased and, by the mid-1970's, was some 65
million metric tomes. It reached peak production of around 80
million metric tomes in the mid-1980's and then declined to 66
million metric tomes in 1992 (Dendy, 1995). The rate of increase
in production of sorghum has been relatively low (2.4% yr^-1)
while that of other important cereals has been better; i.e., 3.4
yr^-1 for wheat (Dendy, 1995).
On a world basis, sorghum represents 3.5% of total cereal
production. While this figure is small, there are countries where
it is of great importance: Burkina Faso (52.8%). Sudan (71.6%),
Chad 1.0%), Cameroon (39.9%), Botswana (84.4%), and Rwanda
(51.5%)- In Africa as a whole, the proportion is 17.6% (Dendy,
1995).
Where traditional agriculture predominates, average yields
have ranged between 200 to 1500 kg ha^-1 depending largely on
moisture availability. This average has remained relatively flat
over long periods of time. By contrast, in the USA. yields ranged
from 630-1260 kg ha^-1, prior to hybridization (belore 1960), to
3775-4400 kg by the 1980's (Maunder, 1990). However, in the USA,
there has been a decline in production in the 1992-94 period;
from 22.5 to 16.5 million metric tonnes. This is expected to
change in 1995 because export demand is up by 40% over last year
and, on average, production is projected to increase by 25 % over
the next four years (Maunder, personal communication). Prior to
the availability of hybrids in India Imid-l96ffs) average rainy
season yield was in the neighbourhood of 515 kg ha^-1, but this
has increased during the 1986-90 period to 878 kg ha^-1 (Murty,
1992). There is considerable variation in yield, with some
districts in India averaging over 2500kg ha^-1. Of concern in
much of the sorghum growing world has been the drop in increased
sorghum production below population growth. During the period
19721992, the average annual per capita growth rate for sorghum
production for sub-Saharan Africa was 1.04%, south Asia -2.07%,
and for Latin America -2.03%.
The use of grain as an animal feed has been an important
stimulus lot the global use of sorghum (Dendy, 1995). Feed use
was relatively minor until the mid-1960's when there was a rapid
expansion in this use. particularly in North America. Feed
utilization overtook food use for the first time in 1966. Over
the past 25 years. Feed use has risen from 15 to 40 million
tomes. Up to 97% of this use has been in developed countries, but
it has also been used in some higher income developing countries,
particularly in Latin America where it constitutes about 80% of
sorghum utilization. In several countries. there has been
interest in producing sorghum for feed and maize for food.
A number of factors have contributed to the recent decline
in sorghum production. Particularly in a number of developing
countries, programmes to develop and spread new sorghum cultivars
have been lacking, only recently initiated, and/or lower priority
than for other crops. There has been lack of high yielding
cultivars and appropriate management practices.
In countries with poorly developed infrastructure for the
dissemination of research accomplishments, scientists need to
participate in the production and marketing of seed, as well as
with the extension agency, to get new developments to farmers.
This is essential in generating interest among farmers and others
concerned with implementing the new technology. The approach is
becoming increasingly important as donors want clear indication
of accomplishment. Care must, however. be taken to ensure that
accomplishments do not get stalled at the research level.
Sorghum farmers are frequently distant from markets which
complicates the dispersal of development to them and their
produce to markets. Policies are needed which provide price
incentives as weII as stable prices to farmers.
Uncertainties in the supply of good quality grain have
contributed to a slow down in commercial use. For a number of
places, improvement in marketing grades and standards would be
helpful.
Urbanization and the availability of inexpensive wheat and
rice has contributed to discouraging production and marketing of
sorghum. As an indication. when Nigeria placed a ban on imports
of wheat and rice in 1985, production increased from 7.9 million
metric tomes on 7 million hectares in 1979-1981 to 11 million
metric tomes on 10 million hectares in 1989 (Dendy, 1995L Urban
people prefer wheat and rice partly because less energy is
required to prepare it for fbod compared to sorghum. There is
also lack 0f processed foods, such as flour, in markets compared
to othercereals. In southern Africa this is particularly true
where millimeal from maize is widespread.
In the USA, lack of flexibility in the farm programme where
a farmer's cotton acreage base is jeopardized if sorghum is
includ~d in the rotation the Conservation Reserve programme
providing a guaranteed price for hectares taken out of
production, and also advancesin d~;veloping maize for drier
areas. have contributed to reduced sorghum production (Maunder,
personal communication).
Sorghum will continue to be an important food crop in areas
where it is better adapted than other cereals, particularly in
drought prone areas and under high temperatures, and water
logging. Availability of varieties andhybrids with resistance to
yield limiting factors and good feed quality traits have
contributed to its production.
SORGHUM IMPROVEMENT
Important steps in the improvement of sorghum have been the
diversification of the genetic base, improved hybridization,
modification in plants so as to shorten their time to maturity,
shorter stature than locals (better grai n/straw ratio). control
of insects, diseases and weeds, better response to drought,
temperature and acidic soils, and improved grain and forage
qualities. We might give consideration to some aspects important
to improvement.
The genetic resource. One recognized contribution of
sorghum improvement has been the establishment of a world sorghum
collection. This collection is an outgrowth of an effort which
began in 1959. to collect the sorghums and several of the millets
in India, funded by the Rockefeller Foundation. The collection
was obtained by request from diflerent sorghum growing countries.
The International Crops Research Institute for the Semi-Arid
Tropical (ICRISAT) was responsible for this collection. and the
collecting programme continues to this day. The collection has
grown from about 10,000 accessions in 1972 to 33,766 in 1994
(Mengesha and Appa Rao. 1994). These are maintained at ICRISAT
Centre. at the long term storage facility of the USDA at Fort
Collins, Colorado, USA, and a set of every country collection
remains with the country.
These collections have been systematically evaluated at
ICRISAT and in as much as possible in the area of collection
using a set of descriptors that was recently revised (IBPGR and
ICRISAT, 1993). New accessions are catalogued using these
descriptors and are available from ICRISAT.
From the collection, ICRISAT has distributed 237,265 samples
of sorghum (Mengesha and Appa Rao, 1994). Besides the extensive
use of these accessions in breeding programmes to broaden the
genetic base for yield, resistance and quality traits, 21
accessions or selections from them have been released in nine
countries. ICRISAT is actively involved in germplasm enhancement
so that valuable accessions for yield, resistance and quality
traits are more usable to breeders around the world. The
conversion programme of Texas A&M University and USDA, initiated
in 1962, has been another valuable source of improved accessions
(this programme converts selected tropical lines to temperate
adaptation).
Several categories are maintained in the world collection:
accessions from farmer's landraces, wild types, sources of useful
traits, and released or elite varieties and parents of hybrids.
Concerned scientists in many countries have contributed their
collections to the world collection and have facilitated
collection in their country. Almost all sorghum breeding
programmes have benefited from introductions from the collection.
and from other breeders. in diversifying their germplasm base.
Hageen Durra-l. the first hybrid released in the Sudan, is from
introduced parents. Kuyuma and SIMA released in Zambia are from
introductions. as was SV-2 in Zimbabwe. The major proportion of
varieties and hybrids released in India since 1960 involve
introductions directly or from crosses with local varieties. The
tremendous source of variability available in the world
collection has made a significant contribution to the more than
three fold increase in yield during the past 45 years. and has
become one of the most environmentally friendly crops because of
its in-built resistance traits (Maunder. personal
communication).
Crop improvement. As mentioned earlier, traditional
sorghum cultivars have been farmerselected over long periods of
time, greatly narrowing the genetic base and leading to cultivars
that yield reliably. but at a low level. Traditional varieties
are usually tall, 2.5 to 4 m, and frequently long season,
requiring 120 to 180 days to mature. A common breeding objective
is to reduce plant height and select plants that mature 2 to 5
weeks earlier than locals. A general observation is that farmers
in dry conditions select for mid-season maturity (100-115 days)
and not for very shortseason types. Going to earlier types
brings problems, including changes in susceptibility to insect,
disease. and Striga pests, as well as grain quality for
the production of food and beverage.
Improvement by selection within traditional cultivars or by
selecting progeny from crosses between similar traditional
cultivars has generally not been promising in enhancing yield.
It is necessary to diversify the genetic base by introducing
exotic cultivars. Generally, these introductions include
breeding stocks, accessions from the world collection, and
converted lines from the Texas A&M - USDA conversion programme.
Selection in progeny from crosses of traditional x exotic or
exotic x exotic cultivars has been rewarding.
The opportunity to improve sorghum has not been the same in
all situations. For example, the All India Sorghum Improvement
Programme ratherquickly developed lines and hybrids superior to
locals for the rainy season; but have not had nearly the same
degree of success in the post rainy season. Direct use of
introductions was not helpful and crosses between locally adapted
and introduced cultivars frequently did not produce progeny from
which useful selections were forthcoming. It has been difficult
to make beneficial changes in the race guinea common in
West Africa. There has been little improvement of the tall late
sorghums found along the Ivory Coast across Africa into the high
rainfall zones of southern Sudan. Maize has replaced sorghum in
some of these areas. These are challenging situations in which
more imaginative, novel approaches may be required. For example,
(Cox et al., 1984) introduced a few genes from wild types
into cultivated sorghum. The phenotype of the cultivated type was
not greatly changed but the expression of some traits of interest
(yield) was enhanced.
On the other hand, substantial gains have been made in many
areas. Orrin Webster. years ago, introduced yellow endosperm
sorghums (Korgi and Kaura) into the USA from Nigeria. These were
developed into breeding stock from which came the pollinator
parent for CSH-I; the first hybrid released in India. From a
large nursery of yellow endosperm types came Karper 1597, the
pollinator parent of the first hybrid released in Sudan. These
yellow endosperm types contributed to drought resistance and
grain quality and have been extensively used in crosses in many
places in the world, to select new varieties and parents of
hybrids.
A landrace type, zera zera, found in the low lands
(Gambella area) of Ethiopia extending into a portion of central
Sudan, has been of great importance in providing a pearly white
grain of good food and feed quality with reasonable resistance
to grain weathering. Theavailability of this grain type has
virtually spread over the world and has, for example, contributed
much to the spread of white seeded hybrids in the USA.
The advent of hybrids from the pioneering work of Stevens and
Quinby at the Chillicothe Station in Texas, has provided breeders
with one of the most powerful tools for sorghum improvement.
Hybrid sorghum almost universally out-yields non-hybrid
varieties; and, as growing conditions become stressed, hybrids
out-yield varieties by an even greater margin. Most people
believe that hybrids require optimal growing conditions but, in
my experience, they are beuer than other varieties as growing
conditions become stressed. A concern with hybrids is the need
to provide farmers with hybrid seed each year - they should not
save seed. While this is a major undertaking, it will result in
amuch better situation to provide adequate quantities of good
quality seed on a timely basis. This can be a major contribution
in having a positive impact on the farming community.
I had the opportunity to initiate a sorghum improvement
programme for the Southern African Development Co-operation
(SADC) region under the auspices of ICRISAT. Approximately 5,500
breeding lines and accessions from the world collection were
introduced including 35 lines that had been introduced into India
some 25 years earlier. The difference in the performance of these
lines compared to introductions of current breeding stock from
25 stations, was obvious in demonstrating the significant gain
in the general performance of the crop.
There is a range of problems related to resistance and
quality considerations. too lengthy to go into here, and some
will be discussed in other papers at this meeting. I would like
to make several comments relevant to working with these
traits.
Crop improvement: Some considerations. Looking to the
future, it is going to be important to increase yield to keep
sorghum competitive w!th othercrops. However, the crop
improvement process also involves resistance to yield limiting
factors, end use and quality traits. A team approach is
recommended.
When dealing with resistance traits. it is necessary to know
what problems exist in a region and to prioritize research on
them. This sounds easy but in southern Africa. it took several
years including the evaluation of uniform nurseries grown in
select locations in the region. Today. many of these problems as
well as a reasonable idea of their importance are known. The
identification of sources of reststance generally begins with the
more elite breeding stock. then to germplasm collections to
broaden the genetic base of the trait. Procedures to evaluate the
trait need to be available. They should be simple. reliable.
affordable, repeatable and useful to evaluate a large number of
entries. Screemng nurseries are generally conducted in areas
where the trait is well expressed. and usually more than one
location is involved to be sure that satisfactory results can be
obtained. since there is risk of poor expression or over
expression of the problem of interest so that differences are not
obviously apparent.
Generally, techniques such as spreader rows. use of
irrigation or water with-holding, and artificial inoculauon are
used to ensure a uniform spread of infection over the nursery.
A standard, usually susceptible, cultivar is sown periodically
to help measure the degree of uniformity. Generally, it is more
difficult to realize unilormity in a nursery evaluating soil
borne prc, blcms. The nearest neighbout technique was used at
ICRISAT Centre to evaluate resistance to Striga asiatica.
Laboratory and greenhouse testing can be of help, and at
times the evaluation of more easily measured highly correlated
traits is helpful. This, generally, requires a good resource
base.
Collaboration with regional stations, international centres, and
universities can be helpful.
It is important for the research team to be vigilant after
a new cultivar reaches the fanner's fields. In spite of years of
testing, the first pearl millet hybrid released in India, while
high yielding, was extremely susceptible to downy mildew and
failed in some of the traditional high yield areas because of the
build up of inoculum. Striga asiatica increased following
the spread of the sorghum hybrid CSH-5 in India. Viruses are not
a serious problem in Zambia, but an exotic sorghum variety
released in 1982 was super susceptible to the virus and became
a potential spreader of the disease. It was quickly replaced.
These serve as examples of unexpected problems that the research
group should be able to respond to quickly and effectively.
The number of traits that a breeder can manage at one time
is generally considered to be 3 or 4. As the number of traits
increases, the gain per cycle of selection for each trait
decreases. This emphasizes the problem of prioritization of
traits. At ICRISAT, several years ago, consideration was given
to this concern. As the situation dictates, it is probably
expedient to first introduce simply inherited traits, such as
grain colour, plant colour, plant height, maturity, disease
resistance, etc. Breeding can then focus on more difficult traits
such as yield and insect resistance, where heritabilities are
lower and the traits polygenic in nature. In this process, care
must be taken to ensure that deterioration in other traits do not
occur. It is necessary to monitor traits of importance in the
region to ensure that newly developed cultivars are not more
susceptible than those already in farmer use. The role of
biotechnology in simplifying and hastening this process of trait
introduction is potentially of great value.
Some traits, such as resistance to stem borers and
S.triga. have components. For example, with stem borers,
eggs are laid usually on the underside of leaves. The adaxial
trichomes, when present, disorient the young larvae, slowing the
rate of migration down the leaf. The waxy cuticle can retard
their motion and the vertical angle of the leaf can contribute
to disorienting the larva. Rapidly elongating internodes
contribute to resistance. These traits help keep the young borer
subjected to a desiccating environment and exposed to predators.
Again at ICRISAT, resistance to Striga asiatica was found
to be associated with low seed germination stimulant from host
roots and a difference in the rate of thickening of root
endodermal cell walls, and deposition of silica crystals in those
cells interfering with haustorial penetration by this parasite
(Vasudeva Rao, 1985; Ramaiah et al., 1991). Ejeta et
al. (1992) at Purdue. USA, are actively searching for a
series of mechanisms that contribute resistance to Striga
so that they can be identified, selected, and combined. This
process of identifying component traits, their
characterization, selection, and breeding while retaining other
valuable traits in the cultivar is relatively tedious. As is
being done for Striga, the use of biotechnology may make
this type of study much more practical than it is now.
Sorghum has a number of traditional as well as commercial
uses. People become accustomed to a certain grain and it becomes
prelerred in terms of food. It is nearly impossible to develop
new varieties and hybrids with exactly the same characteristics.
Much can be done to select cultivars close enough to local
standards to be acceptable. In Africa, sorghum is frequently
made into a beer where malting and colour represent desirable
traits. In Southern Africa, the variety Red Swazi is not visually
impressive, but it withstands drought, has a satisfactory
diastatic power, and has a red coloured grain making a good local
opaque beer.
Sorghum flour is blended with that of wheat, maize, and grain
legumes. The flours of some varieties are better than those of
others for blending, and the characteristic is a selectable
trait, The range of uses led to consideration of the idea of
breeding for end use. When blending flours, a programme generally
considers only the crop that it is working with. Ideally. the
characteristics of both crops should be considered. For example.
adjustments might be made between the gelatinization temperatures
of the starch of both crops.
Sorghum is known to take more energy and time to cook than
wheat or rice. It has also been demonstrated to have a lower food
value. Traditionally, fermentation has been one technique used
to improve food value. Recently a highly digestible type has been
found, nearly as good as wheat (Haymaker, 1995). Tannins are
antimetabolites useful to reduce grain moulding and to repel
birds, but they also reduce food and feed value. A white seeded
sorghum was recently found that has resistance to bird
depredation without the tannins that would have adverse effects
on food quality. Details of its use are being studied (L.
Butler, personal communication). With forage, it is possible to
breed for higher protein, lower fiber and, via the brown mid-rib
gene, lower lignin content resulting in higher animal weight gain
(Cherney et al., 1986). Some traits such as resistance to
Striga asiatica (low stimulant production) and midge, as
well as many traits of the grain and brown mid-rib in the plant,
are simply inherited and effectively used in breeding. Other
traits such as resistance to stem borers and shootflies are
polygenic and. at best. only partially effective m pest control.
Little resistance has been found lotpests such as head bugs
(Calocoris angustatus) in India. When resistance has
limited contribution to pest control, it needs to be coupled with
other practices such as clean cultivation. destruction of crop
residue and use of chemicals. These practices are aspects of
Integrated Pest Management (IPM).
Shootfly is a serious problem in many of the sorghum growing
areas of India and West Africa. The maggot of the fly feeds on
and desti'oyb the growing point of seedlings. Some wild sorghums
are immune as well as some other crops such as sugarcane. Efforts
to bring this resistance into sorghum have not worked by
traditional techniques. Procedures from biotechnology might be
effective.
CONCLUSION
Sorghum is a crop of world-wide importance. Initially, the grain
was used primarily for food and still is in many developing
countries. Its use as a feed now exceeds its food use in
developed countries. There is great variability in sorghum,
making selection possible for most traits of economic importance.
Germplasm, in the form of breeding stock, collection accessions.
and converted tropical cultivars, now moves readily world wide
and has contributed significantly to the crop's improvement in
terms of yield, resistances and utilization/quality traits. In
recent years, there has been exciting research accomplishments
to which organizations such as INTSORMIL and ICRISAT have
contributed. A greater effort is needed to see these developments
from research into the farming and user communities. There are
still substantial areas using traditional cultivars with
traditional management. It is difficult for these farmers to res.
pond to market demands. There is, therefore, need for policy to
encourage market participation but also to resolve the problems
of extending technology where it can be used. For many
countries, financial resources are becoming increasingly
difficult to realize. Shared responsibility. with focus on
particular problems between countries of a region. with
international organizations and with universities. should make
research more efficient. Clearly sorghum is one of the world's
important crops and, while improvements have been significant,
there is a tremendous challenge for sorghum to continue to expand
in local and international importance.
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Copyright 1995 African Crop Science Society
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