| Flower initiation in strawberry genotypes is primarily determined by two environmental factors: photoperiod and temperature. Commercially grown strawberries are generally classified as remontant (repeat flowering) or short day types based on their photoperiod requirement for flower initiation. However, both types will flower in any photoperiod when temperatures are sufficiently cool and flower initiation is inhibited beyond a temperature threshold. The currently available remontant genotypes do not perform well in the extreme heat of midwestern summers. Therefore it is necessary to develop remontant cultivars tailored to the midwestern environmental growing conditions by incorporating heat tolerance and/or other sources of remontancy. This research was designed to identify the regions of the genome that regulate heat tolerance and remontancy in a population developed from 'Honeoye' x 'Tribute', where 'Tribute' is a remontant parent and as a result the progeny segregated for remontancy. A SSR-based linkage map was generated and the QTL associated with remontancy and duration of flowering were identified using phenotypic data collected in multiple environmental conditions (MI, MN, MD, OR, CA) and multiple years (2005, 2006, 2011). In addition, the same population was grown under different temperatures in the greenhouse to observe segregation of heat tolerance in the progeny. Flowering phenotypic data collected from the different temperature environments were used to identify QTL associated with heat tolerance.;The 'Honeoye' x 'Tribute' linkage map consisted of 34 linkage groups (LG) and heat tolerance QTL were identified on 8 linkage groups. Five of the heat tolerance QTL co-located with remontancy QTL indicating that the commonly observed photoperiodic response in the field may actually be due to differences in heat tolerance. Remontancy QTL from all 5 field locations overlapped at 8 chromosomal locations. QTL associated with remontancy in the cooler western states (CA and OR) co-located in three LG regions and QTL for remontancy in the warmer states (MI, MN, MD) co-located in two LG regions. Duration of flowering QTL co-located with several remontancy QTL indicating that our way of phenotypic categorization of remontant vs non-remontant trait was able to identify regions of the genome that determine extended flowering season. Duration of flowering QTL co-located with heat tolerance QTL suggesting that the ability of a plant to have an extended flowering season is dependent on its ability to tolerate extreme summer temperatures. Five markers associated with the heat tolerance trait were identified and several progeny that were both heat tolerant and remontant were identified. These markers associated with heat tolerance should be validated on a larger panel before their use in marker-assisted breeding. However, the most heat tolerant, remontant progeny may be used in further crosses to develop cultivars better suited to the hot, midwestern climate. |
