Effects and Interaction of Pre-chilling History and Daylength on Successive Floral Formation in Everbearing and Non-everbearing Strawberry Cultivars

Abstract

1. Three experiments were conducted to determine the effects and interaction of pre-chilling history and daylength on successive floral formation in everbearing and non-everbearing strawberry cultivars.
2. The previously non-chilled plant material of five strawberry cultivars; everbearer of ′Rabunda′, and non-everbearers of ′Fukuba′, ′Hokowase′, ′Aiko′ and ′Kletter Erdbeere Hummi′, were grown in the growth chamber at a constant 20°C under 16 hour (16-LD) or 8 hour (8-SD) daylength for 30 days. The floral formation of ′Rabunda′, ′Aiko′ and ′Kletter′ was induced under 16-LD and 8-SD, whereas that of ′Fukuba′ and ′Hokowase′ was inhibited by 16-LD, and prmoted by 8-SD.
3. Plants of ′Rabunda′, ′Kletter′ and ′Hokowase′ were stored at 1°C for 4.5 months till 5 April 1987, then transferred to growth chamber and grown at 20°C under 16-LD from 5 April to 18 June. Among these cultivars, only the ′Rabunda′ of everbearer continually formed flower buds during this experiment.
4. ′Rabunda′ plants that had been stored at 1°C for 2 months till 29 January 1988 were grow at 20°C under 16-LD or 8-SD from 29 January to 29 March. At the end of photoperiodic treatment, the floral initiation of 16-LD plant had occured at an average of 2.2-node intervals in the terminal bud; 8-SD induced flower bud at an average of 3.6-node intervals in the terminal bud.
5. The above mentioned results indicated that the non-chilled plant of ′Aiko′ and ′Kletter′ showed the similar photoperiodic response to the non-chilled plant of ′Rabunda′. On the contrary, pre-chilled plant of ′Kletter′ showed a different photoperiodic response from pre-chilled plant of ′Rabunda′. Therefore, it is apparent that everbearing strawberry exhibited successive floral formation due to its insensitivity to pre-chilling history and daylength.