Sorghum [Sorghum bicolor (L.) Moench] leads the dryland cereals in area sown (33.6 million hectares) and production in the developing world. It is a dietary staple of more than 500 million people in more than 30 countries. Sub-Saharan Africa is its primary center of genetic diversity.
Sorghum is genetically diverse, with five major races identified, several of them with subgroups. This reflects farmer selection pressure over millennia for adaptation to diverse production conditions. It is stress-hardy and produces under drought and poor soil fertility conditions that cause maize to fail. Sorghum is also more resistant to grain mold than maize and has a lower risk of contamination by mycotoxins. Diverse varieties of sorghum are adapted to a wide range of temperatures, including high elevations in East Africa. It can grow in sandy desert soils or in waterlogged inland valleys. It can be planted after the rains end on clayey soils, growing to maturity on residual soil moisture alone.
Sorghum is most extensively cultivated in zones of 600 to 1,000 mm rainfall. West and Central Africa leads the developing world regions in area cultivated, followed by Eastern and Southern Africa, then by South Asia.
Production has steadily increased over the past 25 years in West and Central Africa. Production increases until 1995 were mainly attributed to area expansion; after 1995, yield increases explain most of the rise in production. These gains may reflect increased use of improved varieties, better crop management practices and increased demand due to population growth and higher market prices.
Post-rainy season sorghum in India is much in demand for its superior grain and stover quality, and yields have steadily risen.
Sorghum grain is mostly used for human food, consumed as flatbreads and porridges (thick or thin, with or without fermentation). Sorghum grain has moderately high levels of iron (> 40 ppm) and zinc (> 30 ppm) with considerable variability among landraces (iron > 70 ppm and zinc > 50 ppm). Thus sorghum can complement food fortification strategies to reduce micronutrient malnutrition. In addition to food and feed, it is used for a wide range of industrial purposes, including starch for fermentation and bio-energy, construction material and fuel for cooking.
Increasing demand for livestock and livestock products as urban incomes rise is raising the importance of fodder and feed across the developing world. Sorghum stover is especially valuable as fodder for livestock because it matures after the rains end, when few other sources are available to smallholders. The value of sorghum stover in the Dryland Cereals target regions was estimated at about US$5.8 billion. A trend of increasing value of sorghum stover and other crop fodders is evident in Asia. Stover cash-sale markets are also emerging in more densely populated dryland areas of West Africa. Sweet sorghum is emerging as a multi-purpose crop that can provide food, feed, fodder and fuel (ethanol).
Constraints and opportunities
Major constraints to sorghum production include shoot fly, stem borer, head bug and aphid insect pests; grain mold and charcoal rot diseases; weed competition and the parasitic plant Striga (in Africa); and abiotic stresses such as drought (especially terminal drought), high temperatures, acid soils and low soil fertility.
Prime opportunities for sorghum improvement include:
- Gaining traction withhybrids in Africa;
- Improvedmultiple-purpose sorghum for grain, feed and fodder that would increase the total value of the crop while fostering crop–livestock mixed farming (mixed farming systems are more sustainable and remunerative for smallholders than sole-component farming/livestock rearing);
- Sequencing thesorghum genome and making use of new genetic and genomic tools to enable breeders to more efficiently utilize the crop’s rich genetic diversity to improve sorghum and to enhance learning in other cereals, particularly for difficult stress tolerance traits like phosphorus efficiency, aluminum toxicity and terminal drought and also for improving food, feed and fodder nutritional quality (micronutrient content, digestibility and industrial-use qualities); and
- Improving agronomic performance