Screening Existing Populations

It is possible to select the best plants in an existing mixed population, and to propagate them as improved pure lines or clones. This provides a very rapid but somewhat limited improvement, which is often useful as a stop-gap pending the results of a more sophisticated breeding program. This approach is most useful with subsistence crops and forest trees.

John Chapman, who was known as "Johnny Appleseed", travelled westward, in the early 1800s, into Ohio, Indiana, and Illinois. As he went, he planted orchards containing hundreds of apple seeds that he had obtained from cider presses in Pennsylvania. These seeds produced variable seedlings known as 'pippins', and the fruit was good enough to make cider which was then fermented and frozen in the snow to produce 'applejack'. This was the only alcohol available to those early settlers and his trees were in great demand. Most of his seedlings would have produced aberrant types, but some were undoubtedly useful. His activities helped to make the Ohio Valley a major apple producing area. In a similar fashion, there was an English aristocrat who always had a pocket full of acorns and, whenever he saw a promising site for an oak tree, he would plant an acorn.

In Canada, many old railway tracks have been converted into hiking trails, often by an organisation called "Rails to Trails". Passengers in the old trains would often eat an apple, and then throw the core out of the window. Some of the seeds in those cores would germinate and survive. These trails now have feral apple trees growing along their boundaries, and these might make a useful screening population. This triviality is mentioned only to demonstrate that screening populations can occur in the most unexpected places.

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