Читать книгу Principles of Plant Genetics and Breeding - George Acquaah - Страница 184

Apart from relative importance, the traits the plant breeder targets vary in other ways. Some are readily evaluated by visual examination (e.g. shape color, size), whereas others require a laboratory assay (e.g. oil content) or mechanical measurement (e.g. fiber characteristics of cotton). Special provisions (e.g. greenhouse, isolation block) may be required in disease breeding, whereas yield evaluations are most reliable when conducted over seasons and locations in the field.

In addition to choosing the target traits, the breeder will have to decide on the level of expression of each one, below which a plant material would be declared worthless. The acceptability level of expression of a trait may be narrowly defined (stringent selection) or broadly defined (loose selection). In industrial crops (e.g. cotton), the product quality may be strictly defined (e.g. a certain specific gravity, optimum length). In disease resistance breeding, there may not be a significant advantage of selecting for extreme resistance over selecting for less than complete resistance. On the other hand, in breeding nutritional quality, there may be legal guidelines as to threshold expression for toxic substances.