Mapping QTL for Day-neutrality in Strawberry

Abstract

While it is important for strawberry breeders to know the genetics of day-neutrality, evidence for inheritance of the trait is still contradictory. It is not known how many genes govern the trait, to what extent each gene affects phenotype and how the environment influences gene expression. Several recent studies point toward a polygenic threshold model and a rejection of the single gene model. A linkage mapping approach is being used to determine if day neutrality can be mapped to several different quantitative trait loci (QTL) that may represent different genes. To confirm that a linkage mapping approach is the method of choice for QTL detection, a small population of the cross `Honeoye' x `Tribute' consisting of 57 progeny segregating for the trait was genotyped with single dose restriction fragment (SDRF) markers and a preliminary genetic map was created using Join Map 3.0. Results separated the molecular markers into at least 24 linkage groups and several putative QTL for day neutrality were identified indicating that the technique will be successful. However, due to the complexity of the octoploid genome of strawberry, over 200 progeny need to be genotyped to build a complete map that includes the 56 linkage groups of the genome. Furthermore, for determining QTL, an accurate phenotypic evaluation is critical. Individuals of the population above were phenotyped under field conditions (East Lansing, Mich.) in 2002 and 2003, and are now being analyzed under controlled temperature and photoperiod conditions for confirmation of the QTL detected for the trait. A larger population of the same cross with over 200 progeny has also been generated and will be mapped using molecular markers after determining their phenotype under the same environmental conditions.