Sorghum bicolor (L.) Moench

Common names

Sorghum (En). Sorgo (Fr). Sorgho (Sp).

Description

Sorghum is a vigorous grass that varies between 0.5 – 5.0 m in height. It is usually an annual. It produces one or many tillers, which emerge initially from the base and later from stem nodes. The root system consists of fibrous adventitious roots that emerge from the lowest nodes of the stem, below and immediately above ground level. Roots are normally concentrated in the top 0.9 m of soil but may extend to twice that depth and can extend to 1.5 m in lateral spread. The stem is solid, usually erect. Its center can be dry or juicy, insipid or sweet to taste. The center of the stem can become pithy with spaces. Leaves vary in number from 7 – 24, depending on the cultivar. They are borne alternately in two ranks. Leaf sheaths vary in length between 15 – 35 cm and encircle the stem with their margins overlapping. The leaf sheath often has a waxy bloom. Leaves are from 30 – 135 cm long and 1.5 – 13 cm wide, with a flat or wavy margins. Midribs are white or yellow in dry pithy cultivars or green in juicy cultivars. The flower is a panicle, usually erect, but sometimes recurved to form a goose neck. The panicle has a central rachis, with short or long primary, secondary and sometimes tertiary branches, which bear groups of spikelets. The length and closeness of the panicle branches determine panicle shape, which varies from densely packed conical or oval to spreading and lax. Grain is usually partially covered by glumes. The seed is rounded and bluntly pointed, from 4 – 8 mm in diameter and varying in size, shape and color with cultivar.

Distribution

Sorghum originated in the north-eastern quadrant of Africa, where the greatest variability in wild and cultivated species is found to this day. It was probably domesticated in Ethiopia by selection from wild sorghum between 5,000 and 7,000 years ago. From this center of origin, it was distributed along trade and shipping routes throughout Africa, and through the Middle East to India at least 3,000 years ago. It reached China along the silk route. Sorghum was first taken to the Americas through the slave trade from West Africa. It was reintroduced in late 19th century for commercial cultivation and has subsequently been introduced into South America and Australia.

Sorghum is now widely found the drier areas of Africa, Asia, the Americas and Australia. Total annual production ranges from 40 – 45 million t from approximately 40 million ha, making sorghum the fifth most important cereal. The most important producers are the United States with annual production of 17 million t of grain from 4 million ha, India (11 million t from 12.5 million ha), Nigeria (6 million t from 5.7 million ha), China (5.5 million t from 1.5 million ha), Mexico (4.5 million t from 1.3 million ha), and Sudan (3 million t from 5 million ha).

Adaptation

Sorghum is adapted to a wide range of environmental conditions but is particularly adapted to drought. It has a number of morphological and physiological characteristics that contribute to its adaptation to dry conditions, including an extensive root system, waxy bloom on the leaves that reduces water loss, and the ability to stop growth in periods of drought and resume it again when conditions become favorable. It is also tolerant to waterlogging and can be grown in high rainfall areas. It is, however, primarily a crop of hot, semi-arid tropical environments with 400 – 600 mm rainfall that are too dry for maize. It is also widely grown in temperate regions and at altitudes of up to 2300 m in the tropics.

Sorghum can be grown successfully grown on a wide range of soil types. It is well suited to heavy Vertisols found commonly in the tropics, where its tolerance to waterlogging is often required, but is equally suited to light sandy soils. It tolerates a range of soil pH from 5.0 – 8.5 and is more tolerant to salinity than maize. It is adapted to poor soils and can produce grain on soils where many other crops would fail.

Crop improvement

ICRISAT attempts to address issues of national, regional and global concern for sorghum improvement through its programs in India, western and southern Africa. It is involved in development of finished cultivars for direct release to farmers in specific countries – for example, ICSV 111 and ICSV 400, sorghum varieties were released for cultivation in Nigeria late in 1996. ICRISAT is also involved in production of intermediate breeding products for use in other breeding programs – for example, it has bred a range of male-sterile lines that are widely used by private and public sector plant breeders in India and by a few public sector breeders in Africa as parents for production of hybrids cultivars. At the global level, ICRISAT is involved in diversification of sorghum breeding populations, and ultimately cultivars available to farmers, through the incorporation of traits and genetic materials that have not previously been used in crop improvement. For example, new random-mating populations have been produced using diverse germplasm selected for resistance to head and stem pests, earliness with high grain and biomass yield, tillering ability, large grain and resistance to grain molds.

Other major research topics

In addition to crop improvement, ICRISAT is engaged in a wide range of other sorghum research. For example, this includes biotechnological studies on the effects of antifungal proteins against grain molds, and the variability found in major pathogens, as aids to understanding how to identify resistant cultivars and control disease epidemics. Similarly, it includes studies using crop simulation models to match sorghum flowering and maturity patterns to available water, and studies of insect pest interactions with the crop. The underlying objective of all these studies is to identify crop management practices that will lead to higher and more stable sorghum yields for the resource-poor farmers of the semi-arid tropics.