Week 6 (Unit 12)

Sorghum (Sorghum bicolor L. Moench) & Millets

Sorghum
Sorghum taxonomy, morphology and reproduction
Crop requirements, adaptive traits, management practices
World production statistics
Genetic resources and sorghum breeding
Diseases and pests
Sorghum utilization and quality
Millets
Assignments
References

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Sorghum Taxonomy, Morphology and Reproduction

Sorghum (Sorghum bicolor L. Moench) is a tropical grass grown primarily in semiarid parts of the world, particularly in Africa, India, and Asia, where it is an important staple food crop. It is a member of the family Poaceae and the tribe Andropogoneae, of which there are three species: S. bicolor - diploid (2n=20) all annual and domesticated types, including stabilized weedy derivatives such as Sudangrass. Widely distributed. S. halepense - Johnsongrass. Tetraploid, native perennial of southern Eurasia, east to India. S. propinquum - Diploid, native perennial of Sri Lanka and southern India.

Photo courtesy Russ Karow, OSU

Sorghum bicolor is divided into three subspecies:

1. bicolor - cultivated sorghum
2. arundinaceum - wild sorghum (e.g. Sudangrass)
3. drummondii - hybrids between the above two subspecies

There are four races of the subspecies arundinaceum, all of which can cross with cultivated sorghum (race aethiopicum, arundinaceum, verticilliflorum, and virgatum).

Races of sorghum Cultivated sorghums are divided into 7 basic races (agronomic types): Kafir (S. Africa) - short plants Milo-Caudatums (E. Africa) Feterita-Guineas (Sudan) Durra (East Africa, Middle East and India) Sballu (India) Koaliang (China) Hegari (Sudan) Distinguishing features Growth habit panicle characteristics seed shape and color adaptation Additionally, hybrid races can be identified from crosses among the basic races. Very high levels of genetic diversity exist among and within races. Most US sorghums are derived from kafir x milo crosses.
	Distribution of wild and cultivated races of Sorghum (courtesy of J Hancock: Plant Evolution and the Origin of Crop Species; art work by Marlene Cameron)
	Photo courtesy ICRISAT

Domestication of sorghum

Sorghum was domesticated around 3,000 BC, in the savanna zone of Africa, south of the Sahara and north of the equator. From there it spread through Arabia around 1000 to 800 BC, through India (1st century AD) and China (3rd century, AD). It was introduced to the US with the slave trade.

Ethiopia can be considered to be one center of diversity for sorghum, but it is not the sole center of origin or diversity.

Several wild grasses belonging to the subspecies S. bicolor subsp. arundinaceum have been proposed by various research workers as possible progenitors of cultivated sorghum - these include the races verticilliflorum, aethiopicum, and arundinaceum.

Cultivation in the US became important as settlers moved to the western, drier states of Oklahoma and Texas. Acreage increased again during the 1950's with the introduction of commercial hybrids. Nearly all of the sorghum in the US is the dwarf type that can be readily harvested with a combine. It is used almost exclusively for animal feed, either as grain or as forage. In the developing world, nearly all of the crop is used for human food.

Sorghum inflorescence

The sorghum head is a panicle, consisting of a central rachis with secondary and tertiary branching. Spikelets usually have two florets, with one being sterile. Flowering and pollination occur shortly after the head emerges from the boot (leaf whorl).
	Photo courtesy Russ Karow, OSU

Sorghum is largely self-pollinating (~6% outcrossing). Some fodder sorghums and members of the guinea race may have up to 30% outcrossing. Hybrids are produced using a cytoplasmic male sterility system that prevents selfing.

The grain is partially covered by glumes, but the lemma and palea are removed during combining. The seeds are round, from 4 to 8 mm in diameter.

Crop Requirements, Adaptive Traits, Management Practices

Sorghum is a C4 species with wide adaptation, from temperate to tropical climates, under rainfed and irrigated conditions. It has a dense, deep root system and can tolerate high temperatures, low rainfall, and low soil fertility. Sorghum is a short-day species, but many cultivars are daylength insensitive.

Sorghum has a competitive advantage over maize on marginal lands in dry, hot areas. However, it is best adapted to slightly cooler, dry climates. Optimal growth occurs at 30 °C. In very hot, dry areas, pearl millet is a better alternative. About 17 to 25 inches of rainfall per year (450 to 1000 mm) are required to grow a sorghum crop.

Lack of cold tolerance limits adaptation and production of sorghum. Soil temperatures of 60-65 °F are required for good emergence. It is adapted to a wide range of soil types, from waterlogged to sandy soils, and low to high fertility.

Yield potential is similar to maize and wheat under many conditions, but somewhat less than maize and wheat in better environments (3-4 t/ha). When moisture is limiting, yields of 0.3 to 1 t/ha are typical. Highest yields reported are about 11 t/ha (246 bu/a).

Sorghum is a fast-maturing crop with high photosynthetic efficiency and a high rate of dry matter accumulation. Most varieties will mature within 90 to 140 days.

Sorghum has good drought tolerance and high water use efficiency. Sorghum has several mechanisms for drought tolerance:

• Dense, deep penetrating root system
• Ability to reduce transpiration through leaf rolling and stomatal closure under stress conditions
• Waxy leaves prevent water loss
• Ability to reduce metabolic processes to near dormancy under extreme drought

Sorghum varieties differ in their response to nitrogen. Some will respond to high fertility levels and produce higher yields and some will not.

Sorghum can be ‘ratooned’ like sugarcane. If the heads and stems are cut back, the plant can resprout from the roots. This is a useful characteristic both for subsistence farmers and for sorghum breeders.

Growth and development of sorghum is similar to maize. A plant will generally have a single stem, but may tiller profusely. Plant height may vary from 0.5 to 6 m, depending on the cultivar and growing conditions. Modern sorghums typically have 2-3 dwarfing genes, and are 2-4 ft in height.

Grain color of sorghum is variable and may be white, yellow, or brown. Brown-seeded types are generally high in tannins and lower in palatability.

Green plants contain a glucoside ‘dhurrin’, which converts to prussic acid (HCN), which is toxic to livestock. Grain sorghums are not suitable for pasturing. Forage types have been selected for lower HCN levels.

Where sorghum is grown as a subsistence crop, there are many locally selected and adapted varieties. These are Important in marginal areas in West Africa (Senegal to Chad) and East and southern Africa (Sudan to South Africa). Yields of local varieties average 700 kg/ha.   Photo courtesy ICRISAT

Traditional types have been selected for:

• Seedling emergence, strong early root development to compensate for irregular early rains
• Good tillering, to compensate for erratic rains during the growing season
• Long growing cycle to make best use of infertile soils
• Resistance to insect and molds
• Tolerance to bird pests and striga (parasitic plant)
• Suitable quality for local food preparations

There is a need to develop locally adapted varieties with improved yield and yield stability, disease resistance, drought tolerance and quality.

World Production Statistics

Sorghum is the fifth most important cereal crop, and is grown on about 42 million hectares worldwide. Average annual production from 1997-2001 was 59 million metric tons. About 90% of the world crop is grown in developing countries, where it is a dietary staple food for over 500 million people. It is estimated that 80% of the crop is produced by subsistence farmers, who often use local landraces that provide low, but stable yields under marginal conditions. Sorghum is the 2nd most important cereal crop in Africa, after maize. Thus, although the total production of sorghum and millet is far less than for wheat, rice and maize, these crops play a vital role for farmers in dry areas where little else can grow.

In 2000-2002, the USA was the leading country in terms of total sorghum production, due to relatively high yields. The US dominates international exchange of the crop, much of which is used for animal feed. India was the leading country in terms of area of production.

Mexico experienced a rapid increase in sorghum production from 1960 to 1980, and is currently the fourth leading country in terms of total production. Sorghum largely replaced maize because it required fewer irrigations than maize or wheat. A crop could be grown with two to four irrigations per year, whereas wheat required six to seven irrigations. Sorghum is also more heat tolerant than wheat.

In the USA, the area planted to sorghum depends a great deal on the corn/sorghum price differential and moisture conditions at planting time. Highest acreages are planted in the Central and Southern Plains States, with some irrigated areas in the Southwest. The trends in the US have been for decreased acreages of sorghum over the past several decades, while yields have increased due to adoption of hybrids.

Genetic Resources & Sorghum Breeding

Breeders have a wealth of diversity to work with in sorghum, and flexibility in choice of selection procedures. Sorghum can be improved as a self-pollinating crop, or using recurrent selection procedures for cross-pollinating crops, through the manipulation of male sterility systems. Photo courtesy ICRISAT

International agencies involved in sorghum breeding

ICRISAT, based in Hyberadad, India, is the CGIAR center with a mandate for sorghum improvement. The main target areas for their sorghum improvement effort are India, West and southern Africa. Priority areas for the ICRISAT sorghum program are: Breeding, management, disease resistance, germplasm enhancement Yield stability for resource poor farmers Collection and management of the world's germplasm and genetic stocks (>35,000 accessions) Photos courtesy ICRISAT

International Sorghum and Millet Collaborative Research Support Program
(INTSORMIL CRSP)

This is a USAID funded project involving seven US universities (University of Illinois, Kansas State University, Mississippi State University, University of Nebraska, Purdue University, Texas A&M University and West Texas A&M University) and the USDA/ARS, as well as research institutions in the U.S. and collaborating countries.

The focus of the organization is on education, mentoring, and collaboration with host country scientists in developing new technologies to improve sorghum and pearl millet production and utilization worldwide. The results of the research are of benefit to both the United States and collaborating countries.

Sorghum conversion project - Texas A&M

• Conversion of tropical types to short, early maturing forms
• Adapted to diverse regions, temperate zones
• Increased genetic diversity for breeding, selection
• Contributed to expansion in US, Mexico, Central S. America

Sorghum hybrids

First produced in 1957 in the US based on a cytomplasmic male sterility system. High levels of heterosis (similar to maize) can be attained in sorghum hybrids. Kafir types from S. Africa were crossed with milo-caudatum types from C. Africa. These represent complementary gene pools for expression of heterosis.

Within 4 years, all US sorghum growers had switched to hybrids. Mean yields were more than doubled; from 1.3 t/ha to 2.8 t/ha. Within 20 years, average US yield had increased to 4.2 t/ha.

Hybrids also contributed to quantum improvements internationally in India and Latin America. Adoption in Africa has not been as great - from 5 to 10% of the crop is hybrid.

U.S. hybrids were developed for feed, not food. Recently, food-quality hybrids have become available, but...

• They perform best under better production conditions
• Fresh seed must be purchased each year
• Male sterile plants are susceptible to ergot (due to milo-caudatum cytoplasm)

New sources of male sterility are being exploited to overcome these problems.

Male sterility systems have also been utilized extensively to facilitate crossing and apply recurrent selection programs in breeding, leading to the development of improved composite varieties. These varieties can be maintained by farmers, without the need to purchase new seed every year.

Diseases & Pests

Weeds

Striga Root parasite Single largest cause of yield loss in sorghum in Africa Landraces are tolerant, but Striga builds up in the soil Restricts use of foreign-developed sorghums in Africa Recently discovered striga-resistance gene Important breakthrough for subsistence farmers Will make US, China sorghum varieties available for Africa
	Striga hermonthica on sorghum Photo courtesy IITA

Shattercane

Shattercane (Sorghum bicolor ssp. drummondii) is a major weed problem in US maize and sorghum fields. It resembles forage types of maize and sorghum, and Johnsongrass. See the Extension Bulletin from West Virginia University for tips on how to distinguish these species. Shattercane is an annual plant that results from crosses between cultivated sorghum and johnsongrass or as a spontaneous appearance of "wild'' (ancestral) genes in cultivated sorghum through genetic recombination. It can cross readily with cultivated sorghum.

Jonsongrass

Johnsongrass (Sorghum halepense) is a tall, perennial weed of the Central and SE USA. It can be distinguished from cultivated sorghum by its large, loose panicle. It is a common weed in cultivated annual crop fields, along roadsides and in other disturbed sites. It spreads by thick rhizomes and can also reproduce by seed.

Diseases

Anthracnose

• major disease in semi-arid tropics
• Caused by species in genus Colletotrichum
• Effects leaves, stems, peduncles, panicles, and grain
• Yield losses of >50% in susceptible cultivars
• Chemical control not practical or economical
• Reduce inoculum – debris, susceptible weeds
• Host resistance breaks down through rapid evolution of new races
• Long term control - resistance gene management

Insects

Greenbug Greenbug (Schizaphis graminum) is a type of aphid that is particularly problematic in sorghum. The aphid injects a toxin into plants as it sucks the juices from them. Greenbugs also transmit maize dwarf mosaic virus. Small grains, primarily wheat, are the winter host. Where the growing season of wheat does not overlap that of sorghum, grasses such as johnsongrass, are interim hosts. Sorghum hybrids with genetic resistance to greenbug are available. However, greenbugs seem to be able to develop new biotypes that overcome the resistance.

Sorghum Utilization & Quality

Grain composition

• 84% endosperm
• 10% germ
• 6% seed coat
  
  
• 70% carbohydrate
• 12% protein
• 3% fat
• 2% fiber
• 1.5% ash
• moisture

The composition of sorghum is similar to maize or wheat. The grain has more protein and fat than maize, but lower vitamin A content (than yellow maize).

Major problems impacting nutritional quality

• Tannins – reduce body's ability to absorb protein, nutrients
  • Tannnins and phenolic compounds are important deterrents for birds
  • Especially characteristic of early sorghum cultivars with dark grain color
  • Newer hybrids are lower in tannin and have better feed quality
• Prussic acid (cyanide)
• Low protein quality
  • Low lysine (similar to maize)
  • Prolamines – relatively high proportion of the total protein; highly crosslinked, lower human digestibility
• Difficult to process grain - milling/grinding
• Must be crushed, cooked to improve digestibility
• Feeding value is 90% to 95% of maize (reflected in grain price)
  • Must be cracked or rolled to improve digestibility

Utilization of sorghum

Primary uses

• porridge
• dumplings
• flour blends
• couscous
• chapati (flat bread)

Others uses

• feed
• silage
• building material
• fuel
• molasses
• brooms
• popcorn
• wine
• beer - important component of African diet

Earlier maturing types have superior mold resistance and are best suited for beer. Cultivars with higher tannin levels have superior malting ability and hydrolyzable starch. Like barley, sorghum has some diastatic activity (capacity for enzymatic conversion of starch into sugar).

Beer production

1. Grain is malted, dried, ground, and mixed with water
2. Initial bacterial action on sugars forms lactic acid
3. Followed by yeast fermentation for 4-5 days
4. Milky consistency; suspended starch, protein, yeast, malt

Brewing raises nutritional value of sorghum:

• Adds vitamins
• Neutralizes tannins
• Hydrolyzes starch

Industrial uses

• Building materials, fuel, brooms
• Waxy sorghums for adhesives, paper, fabrics

Promise of specialty sorghums

• Popping sorghums
• Vegetable sorghum
• Panicle harvested at soft dough stage, roasted
• Vitamin A types – ‘yellow’ grain
• Tannin-free sorghums; combined with bird resistance
• Aromatic sorghums – aroma of basmati, ‘fragrant rice’
• Quality protein types from Ethiopian highlands
• Waxy starch types for cooking, pasting properties
• Sorgho – sweet stem like sugarcane
• Fuel and utility types, fiber uses
• Hybrids with Sudangrass are useful as fast-growing forage and green manure crops with heat and drought tolerance
  

Can sorghum remain competitive with maize?

Advantages of sorghum compared to maize

• Self-pollinated, produces head over longer time period
  • a drought of short duration is less damaging to sorghum at flowering
• Plasticity in response to environment
  • Head size and tillering vary in response to moisture conditions
  • Maize is more dependent on planting density
• Foliage resists drying
  • Waxy leaves
  • Less water loss than maize

Disadvantages of sorghum compared to maize

• Tannins, phenols in grain
• Need to process, crush and cook, for maximum benefit
• Outcrosses readily with shattercane and johnsongrass
• Lower economic return expected from lower value, subsistence crop

Future outlook for sorghum

Sorghum is uniquely suited to hot, dry conditions. It will remain a key food security crop in Africa. Investments in research and development contribute directly to alleviation of poverty.

There are limits for genetic improvement of drought tolerance in maize. Water constraints are likely to impact decisions regarding the relative acreage of sorghum and maize.

Sorghum is increasingly used as stockfeed.

Sorghum is not a ‘preferred target’ for biotech products.

Millets

"Millets" refer to the grain of a number of small-seeded grasses that are grown as cereal crops. The most important species is pearl millet.

Pearl Millet - Pennisetum glaucum L. Pearl Millet is the 6th most important cereal crop in the world. The 28 million ha of production are split equally between Africa and the Indian subcontinent. It is a staple and primary foodstuff for 90 million people. It is also used as animal fodder, fuel, and building materials. The common name for pearl millet in Hindi is 'Bajra'.
	Pearl millet Photo courtesy ICRISAT

Taxonomy and Biology

Pearl millet is an annual species, with 2n=14 chromosomes. Flowers are perfect, but are predominantly cross-pollinating (selfing is typically ~20%). Anthesis (pollen shed) occurs from 1-4 days after stigmas are exerted. This characteristic, called protogyny, helps to promote outcrossing. Plant height can vary from 50 cm to 4 m.

Pearl millet was domesticated in Africa 3000 to 5000 years ago, on the southern edge of the Sahara, west of the Nile.

The genus Pennisetum contains about 140 grassy tropical species. Wild relatives are problems for weed control and as crop contaminants.

Adaptation

Pearl millet is well adapted to areas of high temperatures, low and erratic rainfall, and poor soils. It is grown in areas with as little as 150 mm precipitation, but generally requires from 200 to 700 mm per year. It is the last crop for arable farming on the edge of the desert. It is tolerant of acid, sandy soils with very low organic matter. Time to maturity varies from about 60 days to 180 days, depending on the variety and the environment. Pearl millet has a faster growth rate than any other cereal crop, enabling it to respond to very brief periods of favorable conditions.   Photo courtesy IITA

Pearl millet can germinate at high soil temperatures, and tillers profusely, enabling it to compensate for irregular plant stands. Warm temperatures are required for the grain to mature, typically greater than 30 °C.

With concerns about global warming, erratic weather patterns, and water scarcities, pearl millet may well be the crop of the future. It offers some promise for the drier areas of the central US and Australia. Yields are generally low (500 to 600 kg/ha on average), but it is more reliable than maize or sorghum in marginal areas.

Pearl millet acreage has declined in many areas, especially in southern Africa. This is largely due to a preference and trend for increased maize production.

• Greater improvements in maize productivity have been achieved
• Governments offer incentives for maize production
• Easier processing and storage of maize

Breeding

Pearl millet possesses an enormous range of genetic variability, including genes for reduced height, early maturity, flowering and tillering synchrony, etc.

ICRISAT is the international center with a mandate for improvement of pearl millet. About 22,000 accessions of pearl millet are maintained in its genebank in Hyderabad, India.

Traditional cultivars are random-mating populations, which are highly variable. Modern varieties may be open-pollinated cultivars, synthetics, or hybrids.

Four cytoplasmic–genic systems for male sterility (CMS) are available. These male sterility systems are not stable in all environments.

Heterotic effects are large: good hybrids will yield 20 to 30% more than the best open-pollinated cultivar. Inbreeding depression is also large - there may be a 30% reduction in yield potential with one generation of selfing.

Photoperiod response is critical to adaptation and yield. Varieties may be

• Facultative (delayed flowering with long days)
• Obligate (only flower with short days)

Traditional varieties:

• Tall or semi-tall types with high biomass preferred
• Secondary use as forage or stover
• Harvest index (grain yield/plant biomass) is low (15-20%)

Harvest index is as high as 40% in modern cultivars, when grown under optimal management.

Standability is crucial; peduncle and stem lodging resistance are needed.

Diseases and pests

Pearl millet rust (Puccinia substraita) Blast (Piricularia setariae) – dominant resistance genes Downy mildew - major disease on Pearl Millet in Africa (not in US) Longevity of hybrids in India is only 3-5 years due to instability of resistance to downy mildew Ergot - related to protogyny mechanism
	Downy mildew Photo courtesy ICRISAT

Striga – most landraces are tolerant to this root parasite, but production of tolerant varieties leads to increased Striga seed bank in the soil. Striga seeds can persist and remain viable for many years.

Chinch Bug and False Chinch Bug are important insect pests of pearl millet in the USA. Damage may occur any time from the seedling stage to the soft dough stage.

Grain quality and end-use

The term ‘Pearl’ is derived from the glistening appearance of the grain. Composition 75% endosperm 17% germ 8% bran 12% protein 69% carbohydrate 5% lipid 2.5% fiber 2.5% ash moisture

Photo courtesy ICRISAT

Color

• creamy white
• light to dark brown
• blue/gray and purple

• Combination of color and thickness of pericarp
• Color is not related to condensed tannins, as in sorghum
• Differences are present in phenol content (impact flavor)
• Lighter color grain is generally preferred

Feed uses

• Equivalent to maize
• Superior to sorghum in protein content and quality
• Higher protein; larger proportion of germ
• Does not contain tannins, such as in sorghum, which reduce digestibility
• Deficient in essential amino acids, but 35% more lysine than sorghum
• Forage crop use in US, Australia, and southern Africa

Food uses

• Main uses
  • porridges
  • flat unleavened breads
• Others:
  • rice-like foods from pearled grain
  • couscous
  • blends with legumes flour
  • Malt and brewing for beer
• Flour
  • course or fine ground
  • usually with separation of bran coat
  • difficult to process
  • low flour yields

Flour deteriorates after a few days, so it must be ground frequently. This deterioration is associated with oxidation of lipids and ‘apigenin’, a flavanoid compound. The added need for food processing (frequent milling) is a disadvantage of millet as a crop.

Nutritional impact Generally better food source than sorghum or maize or rice Amino acid profile similar to small grains such as wheat, barley or rice Protein and some vitamins are deficient however, calories are the first consideration for most subsistence areas ICRISAT’s pearl millet genotypes with yellow endosperm (right) appear to have beta-carotene levels comparable to those of 'Golden Rice'. Yellow endosperm is a naturally occurring trait and is not genetically engineered like ‘golden rice’.   Photo courtesy ICRISAT

Trade-offs during selection

• Harder grain may provide better resistance to storage insects
• Softer grain is better for food products

Other millets

Finger millet (Eleusine coracania) - Major food crop in parts of Africa. It is adapted to more humid growing conditions. It stores well and accounts for 10% of global millet production Foxtail millet (Setavia italica) - Originated in China Proso millet (Panicum miliaceum) - Grown for Birdseed Finger millet Image courtesy ICRISAT

Assignments

Discussion

Review at least two of your classmates' group projects on the discussion board, and send them specific comments and suggestions that you think will improve their project.

Quiz

Take the quiz on this Unit on the Blackboard.

References

Andrews, D.J., J.F. Rajewski, and K.A. Kumar. 1993. Pearl millet: New feed grain crop. p. 198-208. In: J. Janick and J.E. Simon (eds.), New crops. Wiley, New York.
http://www.hort.purdue.edu/newcrop/proceedings1993/v2-198.html

Center for New Crops & Plant Products, Purdue University. 2002. Website on sorghum.
http://www.hort.purdue.edu/newcrop/crops/grain_sorghum.html

Dendy, DAV. 1995. Sorghum and millets: chemistry and technology. Amer. Assoc. Cereal Chemists, St. Paul, MN

ICRISAT. 2006. Sorghum.
http://www.icrisat.org/sorghum/sorghum.htm

ICRISAT. 2006. Pearl millet.
http://www.icrisat.org/PearlMillet/PearlMillet.htm

Lee, D., W. Hanna, G.D. Buntin, W. Dozier, P. Timper and J.P. Wilson. 2004. Pearl Millet for Grain. Bulletin 1216. Cooperative Extension Service, University of Georgia and USDA-ARS.
http://pubs.caes.uga.edu/caespubs/pubcd/B1216.htm

National Research Council. 1996. Lost Crops of Africa: Volume I, Grains. National Academy Press.
http://www.nap.edu/books/0309049903/html/