SUGAR CHANGES IN THE SHOOT APEX OF STRAWBERRY UNDER FLOWER BUD INDUCTIVE CONDITIONS

Abstract

Soluble sugar (sucrose, glucose, and fructose) content in the shoot apex of strawberry (Fragaria x ananassa cv. Nyoho) under flower bud inductive conditions was measured and compared with non-induced plants. Runner plants were rooted in June and grown under a canopy with natural daylength and ventilation over 25 °C. For flower bud induction, plants were transferred into a growth cabinet set at 25/15°C (day/night) with 8 h daylength at the beginning of August until flower initiation was observed by microscopic inspection. Control plants were kept under the canopy. With about three weeks of induction treatment, flower initiation was recognized. Ethanolic extracts of shoot apices including some leaf primordia were collected every three days. Sucrose, glucose and fructose were measured enzymatically. The most abundant sugar was sucrose (50-58% of total) followed by glucose (34-42% of total); fructose content was much less than sucrose and glucose (5-10% of total). Glucose content in the shoot apex decreased after the plants were transferred to the inductive condition, then increased gradually, similar to control plants. Sucrose content decreased at the beginning of induction treatment, but it increased soon to the level of control plants. Fructose was higher in induced than control plants just before initiation was recognised. The results indicated that accumulation of sugar in the shoot apex had no direct relation to flower induction of June-bearing strawberry.