Quantitative trait loci mapping and mushroom breeding

In the last decades, progress has been made in the generation of genetic linkage maps and quantitative trait loci (QTL) analyses for edible mushrooms. However, the low number of papers on QTL analyses and the fact these have not been used to generate new varieties, indicate that mushroom breeding is still in its infancy compared to plant and animal breeding. An overview of QTL for diverse agronomic traits shows that these explain in most cases 5-25% of the phenotypic variation and cover relatively large genomic regions. This hampers the introduction of new traits into varieties. In addition, introducing new/improved traits by repeated backcrossing to acceptor lines is hindered by inbreeding depression. We have, therefore, evaluated each step in mushroom breeding and make suggestions for improvement. An efficient breeding program should start with the identification of suitable acceptor and donor lines, by evaluating a broad selection of lines on the trait of interest. Next, the breeding value of a selection of these lines should be examined. That can be done by recovering all constituent nuclei of the selected parental lines, crossing these in all possible combinations, and evaluating these for the trait of interest. This will identify homokaryons which are suitable acceptor or donor lines for QTL analysis useful for a breeding program. By genotyping more haploid individuals than will be used to generate a linkage map, a selection of individuals can be made with a maximal number of crossovers that are evenly distributed over the genome which will benefit the resolution of QTL. Finally, to avoid inbreeding depression we propose to use two acceptor lines for the introduction of new/improved traits from donor lines.