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Possible role of non-structural carbohydrates in flower induction in strawberry

Summary Flower-induction is the event that initiates the transition of a vegetative apex into a floral apex in response to an environmental or developmental cue. Under flower-inducing conditions, biochemical or physiological changes can be recognised. One possible change that could occur is in sugar content. In this study, levels of non-structural carbohydrates (e.g., sucrose, glucose, fructose and starch) were measured in shoot tips, leaves and roots of strawberry (Fragaria ananassa cv. ‘Kordestan’) under flower bud-inducing conditions, and compared with non-induced plants. Runner plants were potted and grown for 4 weeks under non-inducing conditions (31º/25°C day/night; 16 h daylength). Half of the plants were then put under flower-inducing conditions (25°/15°C day/night; 8 h daylength) for 3 weeks. Samples for carbohydrate analysis were taken from induced and non-induced plants every 3 d over 3 weeks, and sucrose, glucose and fructose contents were determined by HPLC, and starch concentrations by the anthrone method. The most abundant soluble sugar, in all organs tested, was sucrose. Sucrose levels in shoot tips and leaves decreased at the beginning of the induction treatment, but soon increased to the levels recorded in non-induced plants. Fructose increased markedly in shoot tips of induced plants 3 d after the start of the short-day treatment, and declined thereafter. Starch contents in shoot tips, leaves and roots of non-induced strawberry plants were higher than those in induced plants on most sampling dates. From the results of this study, it appears that soluble carbohydrate contents in different organs of June-bearing strawberry may have a decisive role on flower-bud induction.