Abstract

It is only in the last hundred years or so that crop monoculture has become predominant in industrialized agriculture for field and plantation crops. The reasons were for simplicity of planting, harvesting and other operations, which could all be mechanized, and for uniform quality of the crop product. However, monoculture produced severe disadvantages, such as vulnerability to diseases, pests and weeds, and yield instability, which necessitated, for example, the large-scale use of pesticides, fertilizers and growth regulators. To avoid or reduce some of the problems of monoculture, we need to introduce and manage diversity in better ways. At the highest level, species monoculture is difficult to change, at least in the short term. At the variety level, diversification is easy to manage, in the form of variety mixtures within the field. The idea of purposely blending different varieties of wheat is more than 50 years old and was first proposed and tested to reduce the impact of stem and leaf rust. More recently, this concept has also been expanded to look whether blends improved grain yield and/or grain quality. This article reviews the current knowledge about the mechanisms that account for disease reduction and yield increase in a variety of mixtures. It discusses the various determinants in the adoption of a variety of mixtures and the prospects for and challenges in using a variety of mixtures as a functional diversification strategy.

Key words: Disease reduction, diversity, sustainable agriculture, wheat variety mixtures, yield stability.