About crops

The plants that sustain the human race

Four of the five major crops by annual global production are members of the grass family. There are five grasses in the top ten globally productive crops. In decreasing order of production, these are: sugarcane, maize, wheat, rice and barley.

Grasses supply over half of the energy in human food through direct consumption and through products of grass-fed animals.

Global production of all cereal grains is around 2.8 x 109 tons per year; oilseed annual production is around 0.6 x 109 tons.

The story of why we have chosen to rely on such a limited range of, in some cases rather odd, food crop species is told in John Warren’s book The Nature of Crops.

Agriculture began with the domestication of wild grasses.

I explain the history of the relationship between humans and grasses in my 2017 book The War between Trees and Grasses.

Crop domestication selected variants with self-fertility, annual habit, hypertrophied grains and foliage, non-shattering seedheads, rapid establishment and growth, and high harvest index.

Wheat and barley originated in the pan-Mediterranean/Southwestern Asia region (sometimes called the Fertile Crescent).

The earliest cultivated forms of wheat were einkorn (Triticum monococcum) and emmer (T. dicoccum).

Modern bread wheat has a complex hexaploid genome as a result of interspecific hybridization between wild relatives.

The first hybridization event combined the genomes of T. urartu and a probably extinct close relative of Aegilops speltoides into the tetraploid T. turgidum subsp. dicoccoides. Then, during the early stages of human agriculture, about 10,000 years ago, a second hybridization introduced the genome of the diploid Aegilops tauschii.

Barley (Hordeum vulgare) is a diploid species and there is evidence of a history of much gene flow between wild and domesticated forms.

The ancestor of maize (Zea mays) is teosinte, a group of five species of large grasses native to Central America. Teosinte was domesticated around 8,000 years ago, probably in the area of present-day central Mexico whence agriculture based on maize spread south.

The earliest evidence of cultivated rice (Oryza spp.) comes from sites in the Yangtze River valley in China and dates from 10,000 years ago.

Sorghum (S. bicolor), a major crop of the semi-arid tropics of Asia and Africa, is believed to have originated in North-east Africa. It is considered likely that dryland-adapted sorghums arose during or after the dispersion from Africa to South-East Asia, about 4000 years ago.

The dawn of agriculture was a critical event in human civilization. As humans selected and refined the plants they rely on for food, feed, fibre, and fuel, so too did agriculture shape human physiology, psychology, and society.

The agricultural environment has a profound influence on the natural environment and the evolution of the organisms that interact with crop plants.

Certain grass weeds of cereals have evolved by acquiring domestication traits through co-selection. Some former weed species — notably oat and rye — have even become adopted as crops in their own right.

Other weeds, such as the poisonous ryegrass darnel (Lolium temulentum), persist as cereal mimics and in nonintensive agricultural systems.

The extraordinary story of darnel is told in Thomas (2019).

Such is the global scale of biotic and abiotic changes made by agricultural and subsequent industrialized civilizations that the present geological era is often called the Anthropocene (Thomas 2017).

How can we feed a world population that is increasing by about 81 million a year?

How is each person to be fed adequately when urbanisation, soil erosion and salinization is continuously decreasing the area of agricultural land available to sustain her from 0.45 hectares in 1961 to 0.21 hectares and falling today (FAO data)?

Plant breeders are among the largely unsung heroes that keep the food coming to our tables, against the odds.

Be nice to plant breeders and agronomists – they work ceaselessly to sustain crop yield, quality, resilience, and resistance to pests and diseases.

It takes up to 20 years to get a new crop variety from the start of a breeding program through to adoption and cultivation by farmers.

If you want to know the future, ask a crop breeder – the decisions he makes today have to be right decades hence.

To realize the ideal variety, many physiological and morphological traits have to be optimized.

My interest has been in the lifespan of the plant and its parts – discussed further in my 2016 book Senescence.

Technology (particularly biotechnology) has a bad name in some quarters, but without it, the job of keeping us fed would be impossible.

Essential technology includes the Haber-Bosch fertilizer process, farm machinery and integrated field-to-fork logistics systems.

Plant breeding is essentially applied genetics; the molecular revolution in genetics is increasingly central to the process of crop improvement.

The genomes of around 180 (to date) cultivated species have been sequenced, representing a source of genes and gene markers for precision plant breeding.

I suppose I have to mention “GM” (*sigh*). What is there left to say? One person in 200 of the population of the USA is a lawyer. If there were a hint of harm in cultivating or consuming GM crops, they would have been sued off the face of the planet. I could list twenty global biological issues to be worried about, and GMOs wouldn’t be among them.