4.Contribution of plant breeding Most of the cultivated species of crop plants have been modified by plant breeding to increase their usefulness as food ,feed,and industrial products.Older varieties are replaced by newer combinations on continued basis.The net result is the development of higher yielding types better adapted to the environment of the area of their culture. The improvements effected by the plant breeder are gradual and progressive in that any single new variety represents but a small advance over its predecessor. Improved crop varieties give the grower an opportunity for greater profits and consequently lead to innovation and the adoption of new agricultural technology. Sometimes the advance is spectacular and can transform the importance of a crop in an area.Plant breeding thus has contributed immensely towards greater food security, productivity and improved quality of the economic product.The major achievement has been in developing varieties resistant to various diseases,insects and abiotic stresses. 5.Plant Breeding in the Twenty-First Century Plant breeding is as old as domesticated plants.When our forebears nurtured and selected desirable plants from a few favored wild species and eventually formed the first landraces,they practiced crop breeding identical in its fundamentals to today's "scientific"crop breeding.During the past 10,000years,farmer-breeders have developed untold numbers of landraces(farmer varieties),and thousands of them are still on hand,although the numbers are shrinking rapidly as professionally bred varieties answering the demands of the marketplace replace the landraces in many parts of the world. Our only record of changes in plant breeding procedures during the past 10,000years has occurred during the past couple of centuries.We imagine,without evidence,that chance outcrossing provided heterozygous new materials from which new varieties could be selected.But we do know that discovery of the nature of sexuality in plants in the eighteenth century fostered deliberate outcrossing as a basis for new variety formation.And we know that rediscovery of Mendel's principles of genetics at the end of the nineteenth century gave great impetus to development of plant breeding as a science,eventually providing full-time work to professional plant breeders. Other discoveries,inventions,and technological advances also increased the power and speed of plant breeding.Statistical theory helped breeders create efficient field plot designs and methods for precise data analysis,thereby greatly improving the accuracy of selection procedures.Statistical theory,including quantitative genetics, also provided great assistance in the design of breeding programs,giving them better precision,speed,and direction.Mechanization of planting and harvesting machinery greatly increased the quantity of yield trial data that a breeder could generate.Even though the odds for success might not be increased,breeders operated on a numerical base that was many times greater than when all trials were conducted by hand.3 4. Contribution of plant breeding Most of the cultivated species of crop plants have been modified by plant breeding to increase their usefulness as food ,feed, and industrial products. Older varieties are replaced by newer combinations on continued basis. The net result is the development of higher yielding types better adapted to the environment of the area of their culture. The improvements effected by the plant breeder are gradual and progressive in that any single new variety represents but a small advance over its predecessor. Improved crop varieties give the grower an opportunity for greater profits and consequently lead to innovation and the adoption of new agricultural technology. Sometimes the advance is spectacular and can transform the importance of a crop in an area. Plant breeding thus has contributed immensely towards greater food security, productivity and improved quality of the economic product. The major achievement has been in developing varieties resistant to various diseases, insects and abiotic stresses. 5. Plant Breeding in the Twenty-First Century Plant breeding is as old as domesticated plants. When our forebears nurtured and selected desirable plants from a few favored wild species and eventually formed the first landraces, they practiced crop breeding identical in its fundamentals to today’s “scientific” crop breeding. During the past 10,000years, farmer-breeders have developed untold numbers of landraces (farmer varieties), and thousands of them are still on hand, although the numbers are shrinking rapidly as professionally bred varieties answering the demands of the marketplace replace the landraces in many parts of the world. Our only record of changes in plant breeding procedures during the past 10,000years has occurred during the past couple of centuries. We imagine, without evidence, that chance outcrossing provided heterozygous new materials from which new varieties could be selected. But we do know that discovery of the nature of sexuality in plants in the eighteenth century fostered deliberate outcrossing as a basis for new variety formation. And we know that rediscovery of Mendel’s principles of genetics at the end of the nineteenth century gave great impetus to development of plant breeding as a science, eventually providing full-time work to professional plant breeders. Other discoveries, inventions, and technological advances also increased the power and speed of plant breeding. Statistical theory helped breeders create efficient field plot designs and methods for precise data analysis, thereby greatly improving the accuracy of selection procedures. Statistical theory, including quantitative genetics, also provided great assistance in the design of breeding programs, giving them better precision, speed, and direction. Mechanization of planting and harvesting machinery greatly increased the quantity of yield trial data that a breeder could generate. Even though the odds for success might not be increased, breeders operated on a numerical base that was many times greater than when all trials were conducted by hand