The study of floral bud initiation and development of ‘Merton Thornless’ blackberry in Taipei

Blackberry (Rubus subgenus Rubus Watson) is a perennial small fruit crop with biennial canes. In general, flower initiation of most brambles is induced by short day and cool temperature, but the timing varies among cultivars and local climates. There is no report on the flowering phenology of blackberries in Taipei. Many blackberries commence flower initiation in the autumn of temperate zone. Because the temperature and day length of winter in Taipei are similar to autumn in temperate zone, flower initiation of blackberries may be induced by the short day and cool temperature in the winter of Taipei. In the first part of this thesis, axillary buds of potted ‘Merton Thornless’ blackberries were sampled monthly from different sections of primocanes, and the timing of flower initiation and flower differentiation were determined. The natural phenology was recorded. In the second part of this thesis, dormant buds were forced in January and February 2015. The effects of bud forcing on the formation of inflorescence and phenology were investigated. The shoot apex surface area of axillary buds gradually increased in December 2013, indicating that axillary buds had been induced from vegetative state to reproductive state. However, by May 2014, most axillary buds had yet commenced flower initiation. The mode of flower bud formation is similar to the ‘Hull Thornless’ blackberry in West Virginia in which the axillary buds were induced to transform to reproductive state before winter, but flower initiation had not commenced until budbreak in the next spring. Cool temperature (15-24°C) is required for reproductive growth of blackberries. Therefore, after bud forcing in January and February 2015, the axillary buds that broke dormancy in February and March generated laterals and formed inflorescences. On the other hand, those broke dormancy after April developed into laterals but failed to form inflorescences. The phenology of ‘Merton Thornless’ blackberries under natural condition of Taipei was described. Primocanes grow from the crown buds and continue growing until December. Axillary buds are induced by short day and cool temperature to reproductive state between December and January. Axillary buds resume growth in the following April and then commence flower differentiation and inflorescence development. Flowering and fruiting take place in May and July, respectively. After bud forcing in January or February, flowering and fruiting were advanced to April and June, respectively.