AFLP mapping and QTL identification for day neutrality in the octoploid strawberry (Fragaria x ananassa).

摘要

Day-neutrality in strawberry is a highly desirable trait to increase productivity. Day neutral (DN) cultivars developed in California have not been successful in continental regions of the US, because they are poorly adapted to high summer temperatures. Studies on the inheritance of this trait are also contradictory and support a number of models from single gene to quantitative inheritance. A linkage mapping approach was used to determine if day neutrality is qualitatively or quantitatively inherited. Amplified Fragment Length Polymorphic (AFLP) markers were used to build a genetic linkage map from a segregating population created from a cross between the DN cultivar, 'Tribute' and the short day (SD) cultivar, 'Honeoye'. One hundred and twenty seven progeny were genotyped and 387 single dose restriction fragments (SDRFs) were mapped to obtain a consensus map of 1310.7 cM with 42 linkage groups and an average marker density of 0.3 markers/cM. Individuals of the mapping population were observed for their flowering habit throughout the growing season in Michigan (MI), Minnesota (MN), Maryland (MD), Oregon (OR) and California (CA), and quantitative trait loci (QTL) for day-neutrality were identified from the phenotypic data collected at each of the locations. A number of QTL were identified which were either shared or were location specific, but none of these QTL explained over 40% of the phenotypic variation, indicating that inheritance of day-neutrality is not regulated by a single, major gene. Of the QTL identified for the eastern states (MI, MN, MD), one on linkage group 17 was found in all eastern states, suggesting that a gene or genes regulating day neutrality is found in this linkage group. However, only one significant QTL was identified in the two western states (OR and CA) and it was located on another linkage group (LG 7) in California. These results suggest that different genes may be responsible for regulating day-neutrality in eastern and western climates. The western climates of OR and CA, have much milder temperatures than the eastern ones of MI, MN and MD during the production season and generated higher percentages of DN progeny. This could be one reason why DN cultivars developed in California do not perform as well in the eastern climates.