26 July 2016

Taming the savage cabbage

Researchers from Kew’s Plant Resources team ponder the transformation of wild plants into crops – the process of domestication that enabled the rise of civilisation.

Mark Lee

By Dr Mark Lee and Dr Matthew Nelson

Kitchen Garden, RBG Kew

What is plant domestication?

Domestication is essentially the taming of wild plants and animals to make them more useful and productive to humans. Increased food production freed up a significant proportion of the population to specialise in diverse professions and trades, enabling the rise of increasingly complex and interdependent societies.

The early stages of plant domestication were most likely unintentional. For example, wild wheats shed their seeds at maturity – a characteristic that aids natural seed dispersal but makes harvesting very difficult and time-consuming. Rare mutations that prevent seed shedding occur naturally in wild wheats, making seed gathering by humans much more efficient. Seed spillage or deliberate sowing of these seeds around early human settlements served to increase the frequency of these more useful forms of wheat. Domestication involved the gradual accumulation of several such useful traits and eventually transformed wild plants into productive crops.

Modern day plant breeders are continuing the process of domestication that our ancestors started more than 10,000 years ago, making plants more useful and productive to humans.

'Taming the Savage Cabbage'

Some of the most impressive transformations achieved by domestication and breeding come from vegetable crops. For the upcoming Kew Science Festival, Kew’s Plant Resources team has developed an exhibit called 'Taming the savage cabbage – how science feeds the world'. Here, visitors can come and compare crop plants with their wild ancestors and see how they have changed through domestication. 

One of the great examples on display will be the amazing transformation of wild cabbage (Brassica oleracea). Selection by farmers, gardeners and breeders over many centuries has produced leafy crops of all shapes, colours and sizes (cabbages, kales, collards); variants in flower development (broccoli, cauliflower, Romanesco broccoli, broccoflower); enlarged side buds (Brussels sprouts); and enlarged stems (kohlrabi). Most of these transformations probably occurred gradually, involving the selection of many genes. Conversely, some transformations would have been quite rapid, involving just one or two gene changes, such as the changes in flower development that gave rise to cauliflower and broccoli. 

Someone picnicking on a British beach could be forgiven for not making the connection between their lunch and the sea beet or wild cabbage plants growing nearby; yet at a microscopic level there remain more similarities than differences. In our science exhibit, we reveal the similarities and differences between crops and their wild ancestors, using microscopes to uncover the plants' finer details. We also encourage visitors to notice the amazing diversity of edible plants growing at Kew, such as those that provide us with coffee and chocolate, fruits, vegetables, herbs and spices.

Domestic bliss?

While early farmers and modern plant breeders brought about tremendous improvements in the usefulness and productivity of plants, it was not all domestic bliss. Perhaps the most serious threat to long-term sustainability of crop improvement is the loss of genetic diversity caused by population bottlenecks. These bottlenecks were most acute at the initial stages of domestication where very few individual plants with suitable domestication traits were selected (such as the rare wheat plant that did not shed its seed).

In a similar way to many modern dog breeds, repeated crossing of closely-related individuals has reduced the genetic resilience of many crops. This makes these crops vulnerable to changes in the environment, such as increased temperature, drought stresses, or changes in pest and disease pressures.

There is no doubt that agricultural productivity must continue to increase in order to feed the growing human population. However, increased crop productivity can only be achieved if plant breeders have the genetic diversity needed to select higher yielding, more nutritious and more climate-resilient crops.

What are we doing about it at Kew?

Kew’s Plant Resources team led by Dr Aaron Davis is taking various research approaches to develop the knowledge and tools needed to support this urgent task. For example, we are improving our basic understanding of the genetic causes and effects of plant domestication and adaptation, and developing efficient methods to tap into the wealth of genetic diversity in crop wild relatives (by Dr Matthew Nelson and Dr Michael Chester). This includes identifying the most nutritious pasture species to feed our livestock (by Dr Mark Lee) and conserving and protecting endangered tree species (by Dr Peter Gasson).

We are developing predictive tools to understand how climate change will influence key crops such as coffee, and to determine which wild resources can be brought into modern usage (by Dr Aaron Davis). These projects require collaboration across many scientific disciplines and across society, from the farmers who grow our food to us – the consumers who buy and eat their produce.

The future

The human population and its food requirements continue to grow; our population is projected to soar to around 11 billion by the end of this century. We will need to overcome a wide range of environmental challenges including the reality of climate change and ever-increasing need for land – both of which put huge pressure on our natural environment. Paradoxically, it is the world’s wild places that provide us with the plant resources we need for future crop development. Can our current domesticated species continue to sustain human civilisation? At Kew, we are building on a 10,000 year enterprise of plant domestication to help ensure plants can continue to feed the world.


'Taming the savage cabbage' was developed by Kew’s Plant Resources team including additional input by Dr Michael Chester, Dr Peter Gasson and Dr Aaron Davis.


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