The main feature of recurrent mass selection is that it deals with quantitative variables, such as horizontal resistances. And it raises the level of many desired variables simultaneously, including all the horizontal resistances to all the locally important parasites.
The method of recurrent mass selection is to grow a large screening population of seedlings which all genetically different. The best 10-20 individuals in that population are selected, and they become the parents of the next screening generation. Each generation (or breeding cycle) exhibits transgressive segregation, and the desired variables increase accordingly. This increase is usually 10-20% in the early breeding cycles, and the rate of increase gradually declines until no further progress is possible. This 'ceiling' is normally reached after 10-15 breeding cycles and, with horizontal resistances, it should provide a complete control of all locally important parasites without any use of crop protection chemicals.
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