FLOWER BUD INITIATION OF A DECAPLOID STRAWBERRY 'TOKUN' BY NIGHT CHILLING AND SHORT DAY TREATMENT

‘Tokun’ was developed from a cross between synthetic decaploids K58N7-21 (‘Karen berry’ × Fragaria nilgerrensis) as the seed parent and ‘Kurume IH No. 1’ (‘Toyonoka’ × F. nilgerrensis) as the pollen parent at the NIVTS, Japan. The pale yellowish-orange fruit of ‘Tokun’ is a short cone with excellent skin gloss and a superior overall appearance. The fruit has aroma components of caramel, coconuts, and peach. Although the total yield per plant is higher than that of ‘Toyonoka’, the harvest starts in the end of January under forcing culture. This late maturity is a major drawback in Japan. Examination therefore was carried out to confirm the effect of night chilling and short day treatment on flower bud initiation of ‘Tokun’. Plants in pot (10.5 cm) were grown under short day conditions (8 h) with low night temperature (12°C), starting on 4, 19 Aug., 1, 15 Sept. ‘Tokun’ differentiated the flower bud approximately on 10 Oct. under conventionally condition. In the trial, flower buds were differentiated after 49 days when the treatment started on 4 Aug. while flower bud differentiation was already observed after 21 days when the treatment started on 15 Sept. Early treatments require the longest period to differentiate flower bud. Flowering and harvesting were accelerated by treatments. Harvesting of plants treated at 4 Aug. was 33 days earlier than those of conventionally grown plants. Yields of fruits were increased by the treatments. The highest yields were obtained from plants treated at 4 Aug.