Sorghum

• 1. Introduction

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  Sorghum has fed people for more than 5,000 years, and its story begins in the region between two rivers in Eastern Sudan, near what is now Kassala. Archaeologists have found the grain at a site there dating from 3500 to 3000 BCE, where it was part of the Neolithic Butana Group culture. Sorghum bread found in graves of Predynastic Egypt, roughly 5,100 years ago, is now displayed at the Egyptian Museum in Turin, Italy.

  Today sorghum is the fifth-most important cereal crop in the world, ranked behind only rice, wheat, maize, and barley. World production in 2023 reached 57 million tonnes. Yet despite those numbers, most people outside the regions where it grows have barely heard of it. How did a grass native to Africa and the Indian subcontinent become a global staple? How did it shape medieval kingdoms, fuel a 19th-century sugar trade, and now power ethanol facilities in the United States? And why do scientists today consider its genome key to the future of drought-resistant farming?

• 2. From Sudan to the World

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  S. bicolor was domesticated from a wild ancestor more than 5,000 years ago in Eastern Sudan, in the area of the Rivers Atbara and Gash. The first domesticated form was the bicolor subspecies, which had tight husks that had to be removed forcibly before the grain could be eaten. Around 4,000 years ago, sorghum made its way to the Indian subcontinent. Around 3,000 years ago it reached West Africa.

  Four other subspecies evolved through the practice of cultivation itself. Caudatum developed in the Sahel. Durra most likely emerged in India. Guinea took shape in West Africa and later reached India; from the guinea race, a variety called magentiferum gave rise to the sorghums of Southern Africa. Wetter conditions in parts of the Horn of Africa, roughly between 2,500 and 1,000 years ago, helped sorghum cultivation expand and supported the growth of complex agricultural societies, including Aksum.

  In the Middle Ages, the Arab Agricultural Revolution carried sorghum and other crops across the Arab world, reaching as far as Al-Andalus in Spain. Sorghum remained the staple food of the medieval kingdom of Alodia and most Sub-Saharan cultures prior to European colonialism. The name itself has a long linguistic trail: the English word traces back to Italian sorgo, which most likely comes from 12th-century Medieval Latin surgum or suricum, itself possibly from Latin syricum, meaning "grass of Syria".

• 3. Anatomy of a Survivor

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  Sorghum is a large, stout grass that can grow up to 2.4 metres tall, and some cultivars reach over 4 metres. Its flowerheads, called panicles, can hold up to 3,000 seeds each. Those seeds supply 329 calories per 100 grams, with a composition of 72% carbohydrates including 7% dietary fiber, 11% protein, and 3% fat.

  Most varieties are drought- and heat-tolerant, nitrogen-efficient, and suited to arid and semi-arid regions. Sorghum can tolerate high altitude, toxic soils, and a pH range from 5.0 to 8.5. It can recover growth after some drought. The growing season lasts roughly 115 to 140 days.

  One of its most useful traits as a crop plant is its ability to suppress competing weeds. Sorghum does this by producing a chemical compound called sorgoleone, an alkylresorcinol. This effect is strongest when the plant is grown in narrow rows. Sorghum requires an arable field left fallow for at least two years, or where crop rotation with legumes happened the previous year. A diversified two- or four-year rotation can improve its yield and make it more resilient to inconsistent growing conditions.

  There is also a caution built into the plant's biology. In the early stages of growth, some species can contain levels of hydrogen cyanide, hordenine, and nitrates lethal to grazing animals. Plants stressed by drought or heat can accumulate toxic cyanide and nitrates even later in their growth cycle.

• 4. Pests, Pathogens, and Defense

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  Over 150 insect species damage sorghum plants at different stages of development, causing significant biomass loss. Stored grain faces additional threats from insects such as the lesser grain borer beetle. The parasitic plant Striga hermonthica, known as purple witchweed, can establish itself on sorghum roots and reduce production.

  Fungal disease is another persistent pressure. The fungus Colletotrichum sublineolum causes anthracnose. Ergot, a toxic fungus, attacks the grain and risks harm to both humans and livestock. Sorghum produces defensive compounds called chitinases to resist fungal attack. Introducing additional chitinase genes through transgenesis has been shown to increase resistance to these diseases.

  Agrobacterium transformation, a standard technique for introducing new genes into plants, was demonstrated to work with sorghum in a 2018 report. The crop's genome was sequenced between 2005 and 2007. It is generally considered diploid, with 20 chromosomes, though evidence suggests a tetraploid origin. The genome size is approximately 800 megabases. A gene expression atlas published by Shakoor et al. in 2014 identified 27,577 genes, giving researchers a detailed map of the crop's biology as they work to improve its resistance and yield.

• 5. Sweet Sorghum and the Sugar Trade

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  Tall varieties of sorghum with a high sugar content are called sweet sorghum. In the 19th century they became economically significant as the price of sugar rose. Decreased production in the British West Indies, combined with growing demand for confectionery and fruit preserves, pushed the United States to search for a sugar plant that could be grown in the northern states. Sweet sorghum, sometimes called "Chinese sugar-cane," was seen as a candidate that could also be productive in the West Indies.

  Sweet sorghum's stalks, known as sorgo or sorgho, are taller than those grown for grain. In countries including the United States, those stalks are crushed in a cane juicer to extract a sweet, molasses-like juice. That juice is sold directly as syrup or used as a feedstock to produce biofuel.

  Sorghum juice can be concentrated into syrup for long-term storage, then fermented through a batch fermentation process to produce fuel ethanol. The energy ratio for sorghum-based ethanol production is similar to that of sugarcane and much higher than that of maize. As of 2018, production costs for sorghum ethanol were competitive with maize, while sorghum requires less nitrogen fertilizer. Residuals from processing contain enough energy to be burned and power the ethanol facilities themselves.

• 6. Food, Drink, and Cultural Life

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  Sorghum grain can be eaten raw when young and milky, but when mature it must be boiled or ground into flour. From that flour come couscous, porridge, and flatbreads such as the Indian jōḷada roṭṭi and tortillas. The grain can also be burst in hot oil to make a popcorn that is smaller than that produced from maize. Because sorghum contains no gluten, it fits naturally into gluten-free diets.

  In South Africa, a characteristically sour beer called malwa is made from sorghum or millet. The process starts by souring the mashed grain with lactic acid bacteria, then fermenting it with wild yeasts that were already present on the grain itself. In China and Taiwan, sorghum is one of the main materials in Kaoliang liquor, a colourless distilled drink of the baijiu family. In Uganda, sorghum is an ingredient in angodic, a traditional food of the Karamojong people.

  Beyond food, sorghum has other material uses across the world. In Nigeria, pulverized red leaf-sheaths are used to dye leather. In Algeria, sorghum has been used to dye wool. In India, the panicle stalks serve as bristles for brooms. Looking ahead, sorghum seeds and bagasse have shown potential to produce lactic acid through fermentation, which can then be used to make polylactic acid, a biodegradable thermoplastic resin.

  The plant also holds a place in oral tradition. In Korea, an origin tale sometimes called "The reason sorghum is red" tells of a tiger that chases a brother and sister into the sky. The tiger climbs a rotten rope after them, falls to its death, and impales itself on a sorghum stalk, which turns red with its blood. In Northeastern Italy in the early modern period, sorghum sticks were said to be the weapons of Maledanti, spirits who fought against Benandanti visionaries of the Friuli district and were believed to threaten crops and people.

• 7. Trade, Genetics, and Future Cultivation

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  In 2013, China began buying American sorghum as a livestock feed to complement its domestically grown maize, importing roughly one billion dollars' worth per year. In April 2018, China imposed retaliatory tariffs on American sorghum as part of a wider trade dispute, halting those purchases. By 2020 the tariffs had been waived, and trade volumes increased before falling again as China shifted to buying sorghum from other countries. As of 2020, China imports more sorghum than all other countries combined.

  The International Crops Research Institute for the Semi-Arid Tropics has worked to improve sorghum through traditional genetic improvement and integrated natural resource management. Around 194 improved cultivars are now planted worldwide. In India, yield gains from improved cultivars freed up 7 million hectares of land, allowing farmers to move into high-income cash crops.

  Genomics researchers have assembled the sorghum genome at 739 megabases, in work by Paterson et al. published in 2009. The most commonly used genome database was established by Luo et al. in 2016. A single-nucleotide polymorphism array for molecular breeding was created by Bekele et al. in 2013, a 3,000-SNP Infinium product from Illumina. These tools underpin a broader ambition: the Land Institute is working to develop a perennial sorghum cultivar capable of repeated, sufficient grain harvests without resowing, a goal that, if achieved, would change the economics of farming in the dry regions where sorghum matters most.