Temperature Tolerance, Not Photoperiod Insensitivity, Is the Primary Factor Controlling Repeat Flowering (Remontancy) In Strawberry

Fragaria ×ananassa Duch. ex Rozier (strawberry) cultivars are traditionally classified as short-day (Junebearing), day-neutral, or long-day (everbearing) plants based on when and how often flowering occurs during the growing season.  Temperature is also known to influence flowering in strawberry.  To more clearly define the roles of temperature and day length in flowering control of strawberry, the short-day cultivar ‘Honeoye’, and two repeat flowering genotypes, ‘Tribute’ and an elite clone of Fragaria virginiana Mill. ssp. virginiana, RH 30, were grown at 14 ,17, 20, 23, 26, or 29 °C, under a short (9 hr; SD) or long (16 hr; LD) photoperiod.  All three genotypes produced more flowers under LD than SD at 14 and 17 ºC.  ‘Tribute’ produced more flowers under LD than SD, regardless of temperature.   ‘Honeoye’ produced more flowers under SD than LD under temperatures of 20 to 26 ºC, but did not flower under either photoperiod at 29 ºC.  ‘Honeoye’ and RH 30 exhibited similar flowering patterns in response to temperature, with RH 30 producing flowers at temperatures 3 ºC warmer than the threshold temperature for flowering in ‘Honeoye’, regardless of photoperiod.  ‘Tribute’ continued to produce flowers under all treatments except 29 ºC under SD.  Runner production was photoperiod and temperature sensitive.  ‘Honeoye’ and ‘Tribute’ only produced runners under LD, with most runner formation occurring at ≥23 ºC for all genotypes.  Our results suggest that the term day-neutral does not accurately describe repeat flowering of strawberry.  We propose that the term remontant replace day-neutral to describe strawberry genotypes producing multiple flowering cycles in a season and that this response is primarily regulated by temperature.