Marker assisted recurrent selection for cumulating QTLs for bread-making related traits

We used a computer program to manage marker data in a recombinant inbred line population. The objective was to select pairs of inbred lines to be intercrossed, in order to cumulate all favourable alleles, either with additive effects or with interactive effects. The population size required to have 95% chance of obtaining the best line from a given cross is computed, taking into account the number of QTLs and the probability that no recombination event occurs in any QTL confidence intervals. It is shown that the accuracy of QTL location greatly affects selection efficiency and that a recurrent selection scheme is highly preferable for pyramiding many QTLs. Dough strength (W) was chosen to illustrate the use of this method. In a population of 187 DH lines from the cross Courtot x Chinese Spring, W was found to be controlled by 8 additive QTLs and two pairs of interactive QTLs. None of the 187 DH lines possess all favourable alleles or combination of alleles. The best possible line could be produced by a single cycle of crossing followed by line extraction, but several thousand lines needed to be produced to achieve this goal. Alternatively, a recurrent crossing scheme allows to obtain the best line in two generations, and requires less than 150 lines per cycle.