Improvements in adaptation and maturity leading to greater yield are the most important criteria for the acceptance of a new crop cultivar, since it is the yield which dictates the economic value of the crop. Therefore, yield improvement is one goal of virtually every crop breeding program. Many such programs have tended to concentrate on identifying the genetic traits responsible for higher yield and selecting each of them in the later stages of the breeding cycle. However, selection for yield per se is still the most effective method, since it is a combination of traits, operating within...