genetic erosion The loss of genetic information that occurs when highly adaptable cultivars are developed and threaten the survival of their more locally adapted ancestors, which form the genetic base of the crop. For example, a new hybrid strain of maize (Zea mays), developed largely by Donald F. Jones from a variety discovered in 1917, had yields 25 per cent greater than standard maize. By the 1960s it was economically very favourable to use this single hybrid type, and more traditional varieties rapidly receded in distribution. The widespread adoption of this hybrid led to the narrowing of the genetic base (i.e. genetic erosion). In 1962 workers in the Philippines noticed that the fungus Helminthosporium maydis (southern corn leaf blight) was highly virulent on this hybrid. By 1970, 80 per cent of the US crop was vulnerable to H. maydis, because of the heavy dependence on the one hybrid, and during the wet summer of 1970 around 20 per cent of the US crop was lost to the blight. Fortunately, in this case the genetic resources needed to produce a resistant strain had not become completely obsolete and so a recovery could be made.

genetic erosion The loss of genetic information that occurs when highly adaptable cultivars are developed and threaten the survival of their more locally adapted ancestors, which form the genetic base of the crop. For example, a new hybrid strain of maize (Zea mays), developed largely by Donald F. Jones from a variety discovered in 1917, had yields 25 per cent greater than standard maize. By the 1960s it was economically very favourable to use this single hybrid type, and more traditional varieties rapidly receded in distribution. The widespread adoption of this hybrid led to the narrowing of the genetic base (i.e. genetic erosion). In 1962 workers in the Philippines noticed that the fungus Helminthosporium maydis (southern corn leaf blight) was highly virulent on this hybrid. By 1970, 80 per cent of the US crop was vulnerable to H. maydis, because of the heavy dependence on one hybrid, and, during the wet summer of 1970, around 20 per cent of the US crop was lost to the blight. Fortunately, in this case the genetic resources needed to produce a resistant strain had not become completely obsolete and so a recovery could be made.