Human began to modify the characteristics of plants used for food and fiber approximately ten to twenty thousand years ago. Even primitive seeding,cultivating,harvesting and storing practices would have exerted selection pressures on those plant species which became domesticated that were different form the pressures their progenitors encountered in the wild. Over time,but particularly in the last 150 years,plant breeding has developed into a complex discipline that now incorporates information form many branches of science and mathematics. The most recent development is the utilization of biotechnology for plant improvement (Ratner,1989)
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