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Wild plants, crops, and genebanks: the nature of the resource
Of the estimated 250,000 species of flowering plants in existence today, human beings cultivate around 3000 for food, and many more for fibres and medicines and other purposes. Many of the domesticated species have wild relatives that could also be of value, or contain genes that could be valuable. Many useful plants exist in the wild in several or many different forms, known as races or subspecies. Some crops exist only in cultivation: either because the wild ancestors have disappeared (or can no longer be identified) or because they arose in domestication (as the swede or rutabaga did). Some food plants, like the bread wheats, were bred or arose spontaneously from combinations (hybrids) of several different wild species. Many have taken on a wide variety of forms during their long years and centuries of domestication. Often farmers in different parts of the world (or different fields or hillsides in the same part of the world) develop their own variations, especially suited to their own conditions, and these are known as ‘landraces’. Most important crops have been subjected to more formal breeding programmes, and this has given rise to different ‘varieties’ or ‘cultivars.’ For species such as rice and wheat there may be tens or even hundreds of thousands of different recognized types. Breeders also maintain special ‘lines’ that may not by themselves be suitable as commercial crops, but contain particular genes that are worth incorporating into commercial varieties.
Thus crop plants are subdivided into species, subspecies, landraces, varieties (or cultivars), and breeding or genetic "lines": each of which contains a unique combination of genes, and some of which contain individual genes that are contained in no other. The total range of genes within each species or landrace or variety or line is called its ‘gene pool’. The totality of all the gene pools represents the world’s total supply of plant genetic resources.

To ensure that they will be on hand when needed, scientists collect representative samples of existing landraces, varieties, and lines, and of the wild ancestors and their relatives, hoping that between them they will contain all or most of the genes in each gene pool. Collecting can take place in farmers’ fields – with permission of course; in local markets; remote places where the crops’ wild ancestors and relatives grow; and in gardens and other scientific and commercial institutions where botanists and breeders have built up their own resources.

The collected material (seeds or tubers or whatever) is then maintained for the future through a number of possible approaches. Sometimes, by the way, it is not so much a matter of collecting genetic resources but of encouraging farmers who grow traditional varieties to go on doing so, or conserving wild habitats. Many genetically valuable plants are now grown in situ, either on farm or in nature reserves. In many cases, however, it is necessary to remove a sample of the genetic resources from the site and to place it in specialist centres called genebanks for storage. Conservation away from the place where the plant originally grew – such as in a botanic gardens or a genebank - is called ex situ.

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