General Introdruction
1995
Dippenbrock, W. | Becker, H.C. (Halle Univ., Halle-Wittenberg (Germany). Inst. fuer Acker- und Pflanzenbau)
A better knowledge of yield physiology can be helpful in the choice of parental material or during the selection of superior genotypes. From a practical point of view, these two stages of breeding are characterized by the different amounts of material that have to be handled. Usually, only a rather limited number of parents is used, whereas the selection of superior genotypes starts with many thousands of plants. The usefulness of many physiological traits characterising yield structure, photosynthesis or root growth is limited by the fact that their investigation is very expensive and laborious. Consideration of such traits is only interesting for the choice of parental material. At this stage, the number of genotypes is comparatively low and expensive investigations can be justified if they improve the source material for the subsequent long and costly breeding process. During the second phase of cultivar development, when selecting superior genotypes, the interest of breeders will be concentrated on traits that can easily be determined, such as plant height, flowering time or leaf angle. Such traits can be monitored without much additional cost and thus they are always of interest, even if their correlation with yield is not very high. Many of these traits have a high heritability and they can improve visual selection during early generations where direct yield measurements are not feasible. When considering physiological traits closely related with yield formation, a selection for such traits usually requires special experiments in addition to the standard field trials. Such extra effort is only justified for traits that have a high genotypic correlation with yield and that are easier to determine than yield itself or have a higher heritability.
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