Abstract
BACKGROUND: Flower initiation in strawberry is often classified by photoperiod sensitivity; however, temperature also plays a major role in determining flower initiation. OBJECTIVE: Our goal was to determine the role heat tolerance plays in regulating remontant flowering in a segregating population of strawberry, Fragaria×ananassa. METHODS: Non-remontant (short day) ‘Honeoye’ and remontant ‘Tribute’ were crossed and 54 progeny were grown in three temperature regimes (17, 20, and 23°C) under a long photoperiod in the greenhouse and differences in flower and runner formation among the progeny were compared. In addition, clonally replicated individuals of the same family were grown in the field in Michigan and Oregon, so that the extent of heat tolerance observed for each genotype in the greenhouse studies could be compared to their phenotype in the field (remontant vs. non-remontant). RESULTS: A significant Genotype x Environment interaction was observed in the greenhouse studies, indicating that there was a strong genetic component regulating the response of the individuals to increasing temperature. The level of heat tolerance, as defined as the difference in flower numbers at 23°C vs. 17°C, showed a continuous distribution among the progeny, indicating polygenic control. The majority of the genotypes that were remontant in the field produced more flowers at 23°C than at 17°C in the greenhouse trials. Flower initiation in both the parents was reduced at 23°C, but ‘Tribute’ produced significantly more flowers than ‘Honeoye’ at 23°C (48.0 vs. 11.3). Most remontant progeny had few runners, although there were some notable exceptions. CONCLUSIONS: Temperature tolerance plays an important role in the flower and runner initiation of remontant genotypes. Genotypes with high heat tolerance can be selected that will more dependably flower in environments with highly variable levels of summer heat.