The beauty (and wonder) of diversity

June 1815. British and allied troops muster in Brussels (then part of the United Netherlands) as the Duke of Wellington prepares to meet Napoleon at the Battle of Waterloo.

The troops are in good spirits, the social life of high society thrives, even as troops march to the front, with officers being called away to their regiments from the Duchess of Richmond’s Ball on the eve of the battle. The weather is fine, although it would deteriorate dramatically over the course of the battle in the next day or so.

Arriving in Belgium, one soldier commented on the productivity of  the local agriculture: I could not help remarking the cornfields today . . . they had (as I thought) a much finer appearance than I had seen in England, the rye in particular, it stood from six to seven feet high, and nearly all fields had high banks around them as if intended to let water in and out, or to keep water out altogether – but the rich appearance of the country cannot fail to attract attention.

Another cavalry officer wrote: I never saw such corn [probably referring to wheat] 9 or 10 feet high in some fields, and such quantities of it. I only wonder how half of it is ever consumed.

These are among the many contemporary commentaries in Nick Foulkes’ entertaining account of the social build-up to Waterloo. So what does all this have to do with the beauty (and wonder) of diversity?

Landrace varieties
Well, they are actual descriptions, almost 200 years old, of the cereal varieties being grown in the vicinity of Brussels.  Once upon a time, not too long ago before plant breeding started to stir up genetic pools, all our crops were like those described by soldiers off to fight Boney. We often refer to them as farmer, traditional or landrace varieties which have not been subjected to any formal plant breeding. You also hear the terms ‘heritage’ or ‘heirloom’ varieties, especially for vegetables and the like. Landrace varieties are highly valued in farming systems around the world – and the basis of food security for many farmers who grow them. However, in many others they have been replaced by highly-bred and higher yielding varieties that respond to inorganic fertilizers. The Green Revolution varieties released from the 1970s onwards, such as the dwarf wheat and rice varieties championed by pioneers such as Dr Norman Borlaug, bought time when the world faced starvation in some countries.

Now I’ve been in the business of studying the diversity of crops and their wild relatives almost all my professional life: describing it; assessing its genetic value and potential; and making sure that all this genetic treasure is available for future generations through conservation in genebanks.

The nature of diversity
But it wasn’t until the early 20th century – with the work of  Nikolai Vavilov and his Russian colleagues, and others that followed in their footsteps – that we really began to understand the nature and geographical distribution of diversity in crops. Today, we’ve gone the next step, by unraveling the secrets of diversity at the molecular level.

This diversity has its genetic basis of course, but there is an environmental component, as well as the important interaction of genes and environment. And I’m using a wide definition of ‘environment’ – not just the physical environment (which we think of in terms of growing conditions governed by geography, altitude, soil and climate) but also the pest and disease environment in which crops (and their wild relatives) evolved and were selected by farmers over centuries to better fit their farming systems. Landrace varieties that are still grown today in some parts of the world (or conserved in genetic resources collections) are extremely important sources of genes for adaptation to a changing climate for instance, or resistance to pests and diseases, as we have highlighted in our forthcoming book.

My own work on potatoes, rice and different grain legumes aimed to understand their patterns and origins of diversity, as well as the breeding systems which molded and released that diversity. I’ve been fortunate to have the great opportunity of working with or meeting many of the pioneers of the genetic resources movement, as I have described in other posts in this blog. But at the beginning of my career I became interested in studying crop diversity after reading the scientific papers of a group of botanists, Jens Clausen, David Keck and William Hiesey at Stanford University  (and others in Europe) who undertook research to understand patterns of variation in different plant species and its genetic and physiological underpinning.

These Californian pioneers studied several plant species found across California (including Achillea spp. and Potentilla spp.), from the coast to the high sierra, and planted seeds from each of the populations in different experiment stations or ‘experimental gardens’ as they came to be known. They described and determined the physiological and climatic responses in these species – and the genetic basis – of their adaptation to the different environments. The same species even had recognizable morphological variants typical of different habitats.

Experimental gardens established by Clausen Keck and Hiesey at three sites across California to study variation in plant species.

Interesting research has also been carried out in the UK on the tolerance of grasses to heavy metals on mine spoil heaps. Population differentiation occurs within very short distances even though there may be no morphological differences between tolerant and non-tolerant forms. Researchers from Aberystwyth have collected grasses all over Europe and have found locally-adapted forms in rye grass (Lolium) for example, which have been used to improve pasture grasses for British agriculture. But such differences in these and many other crops can often only be identified following cultivation in field trials where the variation patterns can be compared under the same growing conditions (following the principles and methods established by Clausen and his co-workers), and the data analysed using the appropriate statistical tests.

I began my work on genetic resources in 1970. I quickly realized that this was the area of plant science that was going to suit me. If I wasn’t already hooked before I moved to Peru, my work there at CIP on potato landrace varieties in the Andes (where the potato originated) convinced me I’d made the right decision. The obvious differences between crop varieties are most often seen in those parts of the plant which we eat – the tubers, seeds and the like, the parts which have probably undergone most selection by humans, for the biggest, the tastiest, the sweetest, the best yielder. Other traits that adapt a variety to its environment are more subject to natural selection.

Patterns of diversity are so different from one crop species to another. In potatoes it’s as though a peacock were showing off for its mate – you can hardly miss it, with the colorful range of tuber shapes but also including differences in the color of the tuber flesh. Modern varieties are positively boring in comparison. Who wouldn’t enjoy a plate of purple french fries, or a yellow potato in a typical Peruvian dish like papa a la huancaina. Such exuberant diversity is also seen in maize cobs, in beans, and the squashes beloved of Americans for their Halloween and Thanksgiving displays.

Many of the other cereals, such as wheat, barley, and rice are much more subdued in their diversity. It’s much more subtle – it doesn’t hit you between the eyes like potatoes – such as the arrangement of the individual grains, bearded or not, and color, of course. When I first started work with rice landraces in 1991, I was a little disappointed about the variation patterns of this important crop. Little did I know or realize. Comparing just a small sample of the 110,000 varieties in the IRRI genebank collection side-by-side it was much easier to appreciate the breadth of their diversity, in growing period, in height, in form and color, as I have shown in the video included in another post. Just check the field plantings of rice landrace varieties from minute 02:45 in the video. Now there are color differences between the various grains, which most people never see because they purchase their rice after it has been milled.

From a crop improvement point of view, this easily observable diversity is less important. It’s the diversity for yield, for resistance to pests and diseases, and the ability to grow under a wide range of conditions – drought, submergence, increased salinity – that plant breeders seek to use. And that’s why the worldwide efforts to collect and conserve this diversity – the genetic resources being both crop varieties and their related wild species – is so important. I was privileged to lead one of the major genetic resources programs at the International Rice Research Institute in the Philippines for 10 years. But the diversity programs of the other centers of the CGIAR collectively represent one of the world’s most important genetic resources initiatives. Now the Global Crop Diversity Trust (which has recently moved its headquarters from Rome to Bonn in Germany) is not only providing some global leadership and involving many countries that are depositing germplasm in the Svalbard Global Seed Vault, but also providing financial support to place germplasm conservation on a sustainable basis.

Crop diversity is wonderful to admire, but it’s so much more important to study and use it for the benefit of society. I spent almost 40 years doing this, and I don’t have any regrets at all that my career moved in this direction. Not only did I get to do something I really enjoyed, I met some incredible scientists all over the world.