A plant generation is generally considered to be the life span starting from seed and extending to the next production of seed. Some annual plants produce up to five generations per year. At the other extreme, some trees require many decades to complete a single generation. In plant breeding, one breeding cycle may embrace several plant generations, such as a multiplication generation, and selfing generations for single seed descent and late selection. Genetic advance
The increase in the level of a quantitative variable that results from recurrent mass selection . For example, after one screening generation, there might be a 5% increase in the yield, or in the level of horizontal resistance to a particular species of parasite. Genetic base
The totality of polygenes at the start of a population breeding program. Consider a simplified model. Ten parents each possess 10% of the polygenes controlling horizontal resistance. Each parent is thus very susceptible, and the parent population is also very susceptible. But each parent possesses polygenes that no other parent possesses. This means that the genetic base contains 100% of the polygenes controlling horizontal resistance. The purpose of the population breeding is to bring all these polygenes together in one individual by recurrent mass selection and transgressive segregation.
In practice, some 10-20 different parents, consisting of modern cultivar, preferably originating from independent breeding programs, will normally provide an adequate genetic base for a horizontal resistance breeding program. If the base proves to be inadequate, it can always be widened at a later stage by adding new parents to it.
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