The increased use of diversity in cereal cropping requires more descriptive precision

Until 100 years ago, cereals were grown only as populations with varying amounts of genetic diversity both within and among different crops. However, since the nineteenth century, methods for isolating and reproducing monocultural varieties have become universal, particularly among larger producers, leading to widespread within-field genetic monotony. A range of approaches is now being used to increase genetic diversity within and among crops including bringing back into cultivation a range of populations using a variety of different names, such as old varieties, landraces, ancient grains, heritage varieties, heirloom varieties, and mixtures. The objective of this paper, which is the result of the First International Conference on Landraces (Bologna, July 2018), is to contribute to the more precise definition of the names that are used more frequently.

One early approach to increasing diversity among such monocultures was the use of variety mixtures, initially using static mixtures, meaning mixtures that were re-constituted from their original component varieties for each growing season. Some farmers, however, preferred to re-grow static mixtures from the harvested, and therefore selected, seed, thus converting them to what can be termed dynamic mixtures. Consequent natural inter-crossing within such dynamic mixtures means that, within a few seasons, following natural segregation, recombination and selection, they become populations. There is a wide body of literature on both static and dynamic mixtures, the discussion of which is beyond the scope of this paper. More recently, interest has been increasing in modern forms of evolutionary breeding of populations through direct hybridization of monocultural varieties followed by segregation and, commonly, natural selection, often in target production areas. As expected from evolutionary theory, such populations exhibit considerable resilience under variable environmental conditions, which is increasingly important in relation to the complexity of climate change.

To help identify different approaches, and communicate information, definitions can be based on the approximate known historical age of the plant material in question and its genetic structure. © 2019 Society of Chemical Industry.