On-farm breeding of local rice varieties in the Philippines：many farms are going back to producing and using their own seed. Photo：Masipag

Plant breeding has existed since crop domestication. For more than 10，000 years farmers have been selecting plants to develop varieties that produce higher yields，are less susceptible to diseases，and that show a certain degree of uniformity in germination and ripening，which makes harvesting easier. Through this selection of crop plants and by cultivating them under various，in some cases harsh environmental conditions，over the millennia a rich diversity of agricultural crop species has developed. In India，for instance，until a few decades ago up to 30，000 rice cultivars were grown.

During the past 150 years this trend has reversed. The biological diversity of crop plants has since been dwindling. Fewer and fewer species are being used for agriculture，and no more than three of them（rice，maize and wheat）supply 60 percent of the world’s food. Not only are fewer and fewer plant species used for agriculture，but genetic diversity within species is also declining. Plant breeding and commercial seed production have contributed substantially to the reduction of genetic diversity within individual species. The number of varieties of any given crop is constantly decreasing and the varieties are becoming increasingly uniform，while certain characteristics are being lost during the process. In view of the necessity of adapting to climate change and of ensuring global food security，this “genetic erosion” threatens the existence of the global population. In order to meet these and future challenges，some of which are still unknown，humanity needs whatever genetic diversity still exists. At the same time，conservation of biological diversity must be reconciled with agricultural intensification. Plant breeding plays a key role in this endeavour.