Plant breeding: Induced mutation technology for crop improvement

present forms of life are the product of three factors: • mutation, the fundamental source of heritable variation, • environmental factors, which influence the selection of those mutations that survive and reproduce, and • time, during which the genotype and environment constantly interact and evolutionary change is realized. Genetic variation found in nature does not represent the original spectrum of spontaneous mutations. Rather, this is the result of genotypes recombining in populations and continuously interacting with environmental forces. Green plants are the ultimate source of resources required for human life, food, clothing, and energy requirements. Prehistoric people, who depended on their skills as hunters, drew upon abundant natural vegetation to collect nutritious and nonpoisonous fruits, seeds, tubers, and other foods. As human populations increased, greater and safer supplies of food had to be found, and gradually production systems based on plant domestication were developed. The domestication of crops historically has been influenced by ecological and agricultural conditions, as well as by food gathering preferences. Genotypes that have adapted to a wide range of climatic and edaphic conditions typically have been selected for cultivation. The achievement of higher yielding crops facilitated population growth, sedentary settlements, and further development. Which crops were domesticated depended not only on the number of seeds or the size of fruits, but also on taste, palatability, and other factors. Only a small fraction of the world's approximately 200 000 plant species have been