Sorghum (Sorghum bicolor (L.) Moench) is one of the most important cereal crops in semi-arid and tropical regions. Belonging to the family Poaceae (Gramineae), sorghum is a drought- and heat-tolerant cereal often called the "camel of crops." The species is diploid with a chromosome number of 2n = 20.
Sorghum ranks among the top five cereals globally and is valued for food, fodder, and industrial uses (starch, syrup, bioethanol). Its genetic diversity, adaptation to marginal soils, and multi-purpose nature make it a crop of high importance for food security in water-limited regions.
The primary centre of origin of sorghum is Northeastern Africa (Ethiopian–Sudan region), where the greatest genetic diversity of the crop is observed. From here, sorghum dispersed to India, China, other parts of Africa, and later to the Americas. India and parts of West Africa serve as secondary centres of diversity due to long-standing cultivation and local adaptation.
Sorghum is cultivated in over 100 countries across tropical and subtropical regions because of its resilience to drought and heat. Key production regions include:
- Africa: Major producer and consumer—Nigeria, Sudan, Ethiopia among leaders.
- Asia: India (largest producer in Asia) and China grow sorghum for grain and industrial uses.
- Americas: United States, Mexico, Brazil—used for grain, feed, and forage.
- Australia: Important for fodder and grain in dry regions.
The genus Sorghum comprises ~25 species; however, only a few are widely cultivated. The most important cultivated taxa include:
The principal cultivated species (grain sorghum). It presents large variation in panicle type, grain color, maturity, and adaptation. It is classically grouped into races and their intermediates: durra, kafir, caudatum, guinea, and bicolor. Uses: human food, animal feed, industrial raw material.
Primarily a forage crop—rapid growth, high tillering, used as green fodder, silage, and for crop rotations.
Grown for long branching panicles used in broom and brush making. Economically important for non-food uses.
Characterized by juicy, sugar-rich stalks used for syrup, jaggery-like products, and bioethanol production.
Often derived from interspecific crosses (e.g., S. bicolor × S. sudanense) to increase biomass, nutritive value, and regrowth ability.
Wild relatives are reservoirs of traits for biotic and abiotic stress resistance and have been used in pre-breeding. Notable wild species include:
- Sorghum halepense (Johnsongrass) — perennial, useful for tolerance/resistance traits;
- Sorghum propinquum — contributes perenniality and tillering;
- Sorghum arundinaceum — source of disease resistance;
- Other species like S. versicolor and S. virgatum that add cytoplasmic and genetic diversity.
Sorghum is an annual grass with a fibrous root system that penetrates deeply (often up to 1.5–2 m). The shoot is a solid, pithy culm that varies widely in height (0.5 m to over 4 m depending on type).
- Leaves: Linear-lanceolate with a prominent midrib.
- Inflorescence: Terminal panicle, variable from compact to open and drooping.
- Spikelets: Two per node; usually one fertile and one sterile.
- Grain: Caryopsis; shapes range from rounded to oblong and colors vary widely (white, yellow, red, brown, black).
- Pollination: Largely self-pollinated but with notable outcrossing (5–30%), which allows exploitation of heterosis.
Sorghum’s multi-purpose nature underlines its economic significance:
- Food: Grain used for flatbreads, porridges, malt, and fermented products. Sorghum is gluten-free and nutritious.
- Fodder: Stover and forage support livestock—essential in dryland farming systems.
- Industry: Sweet sorghum for ethanol and syrup; broom corn for brooms; starch for food and industrial use.
- Environment: Suited to marginal lands and contributes to sustainable production under limited water.
Contemporary sorghum breeding targets a broad set of objectives to increase productivity, quality, and resilience:
- Yield: Increased grain and stover yield, higher harvest index.
- Adaptability & Stability: Photoperiod-insensitive and early-maturing cultivars for varied agro-ecologies.
- Abiotic stress tolerance: Drought, heat, salinity, and cold tolerance.
- Biotic stress resistance: Resistance to pests (shoot fly, stem borer, midge) and diseases (anthracnose, downy mildew, grain mold).
- Grain quality: Improved protein digestibility, low tannins, good cooking and malting qualities, biofortified levels of iron and zinc.
- Fodder quality: High biomass, stay-green trait, low HCN in forage types.
- Industrial traits: High sugar in sweet sorghums and traits for bioethanol/feedstock utility.
This section summarizes conventional and modern approaches used in sorghum improvement, including hybrid development strategies.
Introduction & selection: Germplasm introductions from centres of diversity followed by mass and pure-line selection established early improved cultivars.
Hybridization: Crossing between divergent parents using pedigree, bulk, and backcross methods to recombine desirable traits.
Hybrid breeding (CMS system): Sorghum hybrid breeding exploits cytoplasmic male sterility (CMS) with three-line system (A = male-sterile, B = maintainer, R = restorer). Commercial hybrids exhibit strong heterosis for grain and stover yield.
Population improvement: Recurrent selection and random mating populations are used to increase allele frequency for complex traits like drought tolerance and pest resistance.
Mutation breeding: Induced mutagenesis (gamma rays, chemicals) has produced beneficial variants such as dwarf stature, altered maturity, and disease resistance in some programs.
Marker-assisted selection (MAS): Molecular markers and QTL mapping accelerate selection for traits (drought tolerance QTLs, shoot fly resistance, grain mold resistance), enabling precise introgression.
Genomic selection: Genome-wide prediction models allow early selection of superior lines based on genomic estimated breeding values (GEBVs), reducing breeding cycle time.
Transgenics & biotech: Research into Bt sorghum and other transgenic approaches aims to provide durable pest resistance and improved nutritional traits (under regulatory scrutiny in many countries).
Genome editing: Targeted editing (e.g., CRISPR-Cas) offers precision modification of genes for height, starch composition, and stress-response pathways.
Participatory plant breeding (PPB): Farmer involvement in selection ensures developed varieties match local preferences and management practices.
Hybrid sorghums are key to boosting yields. Development involves:
- Selection of stable CMS sources (A1, A2, A3, A4, A5) to avoid vulnerability to diseases and to broaden the CMS base.
- Maintenance of B-lines (fertile maintainers) to propagate A-lines and identification of R-lines (restorers) carrying fertility restorer genes (Rf) to produce seed-setting hybrids.
- Testing hybrids across environments to assess heterosis, stability, and adaptability.
Examples: India’s CSH hybrid series (CSH-1 onward) and dozens of forage, sweet, and dual-purpose hybrids have driven productivity gains. Forage hybrids (e.g., multi-cut CSH types) and sweet-sorghum hybrids for ethanol are important product classes.
