Consequences of reduced diversity

In the early 1970's crop scientists began to worry that the genetic diversity plant and animal breeders was rapidly being lost. The corn leaf blight brought home to crop breeders in North America the extent to which genetic diversity in crop plants was being eroded.⁵

• By 1970 roughly three-quarters of the corn acreage was planted in ``Texas T cytoplasm'' corn.
  • The Texas T cytoplasm results in individuals that are male-sterile. This makes production of hybrid corn far less labor intensive than when seed companies had to hire young, midwestern farm boys to de-tassel corn plants in the field.

  • Individuals with this cytoplasm are susceptible to a leaf blight caused by Helminthosporium maydis. In 1970 this blight swept through fields of ``Texas T cytoplasm'' corn.

  • Yield was reduced by approximately 710 billion bushels. The cost to farmers was about $1 billion.

• Although the corn leaf blight is a recent example of the reduction in genetic diversity in crop plants, it is by no means the first.
  • In 1916 a rust fungus destroyed about 3 million bushels of wheat in the United States, roughly one-third of the crop.

  • In the 1840's an infestation of Phytophora infestans was precipitated by extensive planting of a single, genetically uniform potato in Ireland.⁶The reduction in the potato harvest associated with the potato blight was at least partially responsible for
    • the death of 1-2 million people and

    • the emigration of 2 million more.