Meet the Ancestors (of the past, present and future)

Crop Origins

The ancestors of wheat were small-grained, wild grasses of the Fertile Crescent in the Middle East. There is evidence that hunter-gatherers had been collecting grain from wild wheat populations for thousands of years before they were introduced into cultivation. The first step in the development of modern wheat was a natural hybridisation that occurred at least 10,000, and up to 40,000, years ago between a wild einkorn wheat (Triticum urartu) and a wild goat grass related to Aegilops speltoides (the original ancestor no longer exists). The new species created by this hybridisation was Triticum diccocoides, wild emmer wheat. Emmer, and to a lesser extent einkorn, were the first cultivated wheats. Emmer wheat (T. diccocoides) is the ancestor of modern durum wheat (Triticum durum) whose rather coarse granular flour is used in making pasta.

A second hybridisation occurred in prehistoric times between emmer (T. diccocoides) and another species of goat grass (Aegilops tauschii). This hybrid gave rise to the new species Triticum aestivum, the ancestor of modern bread-making wheats.

One of the major changes in the cereal plants that were brought into cultivation was the development of non-shattering ears, which reduced the loss of grain prior to, and during, harvesting. The grains themselves also increased in size as farmers selected plants with larger grains. Less obvious were the changes in the chemical make up of the flour. The emmer x goat grass hybridisation introduced 2 or 3 genes into the new species (T. aestivum) that account for the production of higher levels of specific proteins that create an elastic dough when the flour is mixed with water. This is essential to producing an acceptable loaf.

Wild pecies of brassicas are commonly found on sea cliffs and in arid areas on poor soils. Many of our vegetable brassicas (cabbage, broccoli, kale, cauliflower, brussels sprouts) belong to the same species (Brassica oleracea). Turnips are a closely related species (Brassica rapa). The familiar modern vegetables are quite unlike the wild species that are their ancestors. In the case of the B. oleracea family we can see how thousands of years of selecting for particular plant types has modified the species in very remarkable ways. Selection from the same starting material has resulted in cauliflowers and broccoli - plants that proliferate masses of flower buds that are slow to flower; cabbages - plants that have delayed flowering and shortened internodes between their large leaves; brussels sprouts - plants with much enlarged axillary buds in the axils between the stem and leafstalks.

A hybrid formed between B. oleracea and B. rapa gave rise to a new species, Brassica napus. This was the ancestor of modern oilseed rape, which was introduced into agriculture relatively recently (perhaps 2,000 years ago) and cultivated for its oil, which has been used for cooking and for fuelling lamps. During the industrial revolution rape oil was found to be a very good lubricant for steam engines. Since the 1950s new varieties of rape have been bred that are low in naturally occurring toxic chemicals, making the oil more suitable for human food use.

The potato (Solanum tuberosum) is the fourth most important food crop in the world, after maize, rice and wheat. It seems potato was domesticated on the high plateau of Bolivia and Peru, near Lake Titicaca. Wild potato tubers are bitter, and many carry toxic quantities of alkaloids, but about 7,000 years ago several low alkaloid species were selected, (including S. brevicaule, S. sparsipilum. S. leptophyes and S. canasense). Because of the close similarities between species the origin of the immediate ancestor of modern potatoes is not clear. However the majority are believed to have originated via the edible, ancient cultivated type S. tuberosum ssp. andigena.

The first potatoes were brought to Spain in 1570, and independently introduced in to the UK in 1590. Potatoes from the central Andes are adapted to short days, and will form tubers very late (or not at all) if grown in the long days of the north European summer. By the end of the 18th century European clones, adapted to long days, had been selected and by the end of the 19th century modern varieties (S. tuberosum ssp tuberosum) had emerged. These had different daylength requirement for tuberisation, fewer flowers, larger leaves, shorter stolons, fewer, larger and smoother tubers, less pigment, and enhanced disease resistance compared to the semi-wild Solanum tuberosum ssp. andigena.

It is thought that the cultivated tomato (Lycopersicon esculentum) was originally domesticated in Mexico, from a vine-like plant that would have resembled the wild species Lycopersicon esculentum and Lycopersicon pimpinellifolium. These wild ancestors are widespread in Central America. Tomato is one of 9 closely related species in the genus Lycopersicon that are all native to western South America. Most cross species hybrids between L. esculentum and its relatives are fertile and this has enabled breeders to use related species as rich sources of genes, particularly for disease resistance. Tomato was first introduced into Europe in the Mediterranean region, where because of its resemblance to poisonous nightshades, it was initially viewed with suspicion.

The familiar pea (Pisum sativum) is a domesticated form of the wild species Pisum elatius. However, there is good evidence that some genetic material from another wild species (Pisum fulvum) has been introduced into Pisum elatius by cross-pollination (whether in a wild or cultivated environment is unknown). So the modern pea is actually a mixture of genes from P. elatus and P. fulvum. Pisum species cross-pollinate freely so there are good opportunities to use other wild species as sources of interesting genes in breeding programmes. In order to produce good cultivated types of pea it was necessary for early farmers to select for non-shattering pods, thin seed coats, large seeds and erect plant growth. Recently, semi-leafless pea varieties have been introduced into agriculture to ease harvesting.

Coriander is familiar as a spice (produced from ground seeds) or a fresh leaf used to flavour salads or garnish dishes. Coriander is an oilseed, although it has been selected for use as a spice and therefore its seeds have a relatively low oil content (about 18% of the seed weight is oil). The oil is rich in a particular chemical - petroselinic acid - that is a potential substitute for a chemical currently manufactured from fossil fuels and used as a starting material for manufacturing high quality engineering nylon.

The pretty inflorescences of the marigold (Calendula officinalis) eventually develop into seed heads covered in unusually shaped seeds. These contain oil with chemical properties that make it particularly suitable as a 'drying' oil, that is a chemical suitable for use in paints, inks and varnishes. As such it is a potential substitute for non-renewable mineral oils.

Eruca vescaria ssp. sativa or 'wild rocket' is grown as a salad leaf. The oil in its mature seed is rich in a chemical (erucic acid) that can be used to manufacture plastics. As such it is a potentially valuable renewable substitute for similar chemicals that are manufactured from non-renewable mineral oil.