plant breeding, science of altering the genetic pattern of plants in order to increase their value. Increased crop yield is the primary aim of most plant-breeding programs; advantages of the hybrids and new varieties developed include adaptation to new agricultural areas, greater resistance to disease and insects, greater yield of useful parts, better nutritional content of edible parts, and greater physiological efficiency. Other goals are adaptation of crops to modern production techniques such as mechanical harvesting and improvement in the market quality of the product. Traditionally, plant breeders have made genetic changes in crops by using various crossing and selection methods; attempts have also been made to introduce favorable mutations by the use of ultraviolet or gamma rays. Increasingly, desirable traits (i.e., genes) are being introduced into cultivated plants via genetic engineering.