Genetic mapping of day-neutrality in cultivated strawberry

Day-neutrality is a highly desirable trait in strawberry (Fragaria L.)-breeding programs worldwide due to its importance in extending the harvest season in commercial production. Day-neutral genotypes are photoperiod insensitive and will initiate flowers under any photoperiod conditions as long as temperatures are moderate (below 30/26 degrees C day/night). In the current study, the inheritance of dayneutrality was investigated using an F-1 population derived from the cross 'Tribute' 9 'Honeoye'. The day-neutral trait was scored qualitatively [day-neutral (DN) or short-day (SD)], and quantitatively (number of weeks of flowering). When qualitatively scored in five locations, the DN trait fit a 1: 1 segregation ratio in the hot summers of Maryland (MD), Minnesota (MN) and Michigan (MI). Segregation was skewed toward additional DN progeny in the cooler summers of California (CA) and Oregon (OR). Regardless of evaluation location, the trait was mapped on linkage group IV-T-1 of the 'Tribute' map near the markers ChFaM148-184T and ChFaM011-163T. Quantitative-trait loci (QTL) for number of weeks of flowering in MD and CA and for stolon or 'runner' production in MN, MI and OR also were identified on linkage group IV-T-1 of the 'Tribute' map. These QTL were significantly associated with the qualitatively scored trait and its closely linked molecular markers. The marker ChFaM148-184T explained 63.8 % of the total phenotypic variation for the number of weeks of flowering for MD and 32.4 % of the total phenotypic variation for runner production in MN. Consequently, it was hypothesized that a single major gene or tightly linked cluster of genes in coupling control day-neutrality in this population. The results found in the current study suggest that day-neutrality can be qualitatively scored at least in the locations where the temperatures do not allow SD plants to behave as DN.