Responses of dayneutral and Junebearing strawberries to temperature and daylength

Abstract

SummaryModified environments enable out-of-season strawberry fruit production, but factors that regulate growth and flowering need to be understood to obtain optimum production. Phytotron and controlled temperature glasshouse studies compared the responses of two shortday (SD, Junebearing) cultivars (Redgauntlet and Torrey) and three dayneutral (DN) cultivars (Aptos, Brighton and Hecker) of strawberry (Fragaria 3 ananassa) to various daylength and temperature regimes. The responses were determined independently for inflorescence initiation and the development of inflorescences and fruit. Daylength (9 or 15.h) and day/night temperature regime (18/13, 21/16 or 30/258C), during inflorescence initiation had major effects on yield parameters in the SD cultivars. Floral initiation was repressed in long days, with poor fruit set and development compared with flowers initiated under short-day conditions. The day-neutral cultivars were less affected by daylength, but each had specific temperature/daylength combinations during floral bud initiation for optimum fruit development. During floral initiation, exposure to short days and a 25/208C temperature regime resulted in poor fruit development for all three DN cultivars, but SD cultivars were less affected. Daylength during the development of organs ± runners, inflorescences, flowers and fruit ± affected only vegetative characteristics, with long days promoting the number of runners and the length of petiole, peduncle and pedicel. For all cultivars, low temperatures (18/138C) during the development of organs enhanced the number of flowers per inflorescence, fruit set and fruit size, but reduced runner production. Additional experiments were carried out using wider temperature ranges (15/10, 18/13, 21/16, 24/19, 27/22, 30/258C). The optimum temperature during floral initiation for the reproductive development of all cultivars was between 18/138C and 21/168C, with sharp decreases in flower number, fruit set and fruit weight at lower or higher temperatures. Although daylength does not limit floral initiation in day-neutral cultivars, all five cultivars tested had poor floral and fruit development outside a relatively restricted temperature range, 18/138C (mean 15.58C) to 21/168C (mean 18.58C), and this remains a key limit to their productivity.