Agriculture depends on relatively few crops – only about 150 are cultivated on any significant scale worldwide - however, each comes in a vast range of different forms. They may vary, for example, in height, flower colour, branching pattern, fruiting time, seed size, or flavour. They may also vary in less obvious characteristics such as their response to cold, heat or drought, or their ability to tolerate specific pests and diseases. In fact it is possible to find variation in almost every conceivable trait, including cooking and nutritional qualities, and of course taste. And if a trait cannot be found in the crop itself, it can often be found in a wild relative of the crop. This multitude of different traits can be combined in an almost infinite number of ways.
Diversity in a crop can result from different growing conditions: a crop growing in poor soil is likely to be shorter than a crop growing in fertile soil. It can also be the result of genetic differences: a crop may have genes conferring early maturity or disease resistance. It is these heritable traits that are of special interest as they are passed on from generation to generation and collectively determine a crop’s overall characteristics and future potential. Through combining genes for different traits in desired combinations, plant breeders are able to develop new crop varieties to meet specific conditions. A new variety might, for example, be higher yielding, more disease resistant and have a longer shelf life than the varieties from which it was bred.
Put simply, crop diversity is the biological base of all agriculture. Its use goes back to the origins of farming, and farmers and scientists must continually draw on this irreplaceable resource to ensure productive harvests.