Flowering phenology and the interrelations between phenological stages in apple trees (Malus domesticaBorkh.) as influenced by the Nordic climate

Temperature control of shoot growth and floral initiation in apple (Malus × domestica Borkh.)

“…Association of floral initiation with growth cessation in apple as demonstrated in the present experiments (Tables 2, 3; Fig. 4) concurs with the conclusions of Luckwill (1970) and Hanke et al (2007), and supports the suggestion by Rivero et al (2017) that a late-summer drop in temperature may be involved in floral initiation in apple under field conditions. Likewise, in warm apple production areas, where floral initiation in apple is late (Gur 1985), a late-season drop in temperature was reported to be crucial for next year's apple crop (Zatyko 1974).…”

“…These are processes that are known to interfere with FBF (Fulford Fulford 1966a, 1966bChan and Cain 1967). Finally, only a fraction of the buds of an apple tree becomes floral, and buds on dwarf shoots (spur buds) and buds on vigorously growing extension shoots have different seasonal timing of FBF (Zeller 1960;Jonkers 1979;Rivero et al 2017). In addition, because of its size, the apple tree does not lend itself readily for experimentation in controlled environments.…”

“…Tromp (1976Tromp ( , 1980 concluded that under controlled environment conditions, temperature during the first 4-5 weeks after full bloom appeared to be especially important for FBF, while Zhu et al (1997) found that the period 6-7 weeks after full bloom had the greatest effect although temperature conditions during the entire growing season affected FBF. Dissection of buds collected in the field (Singh 1948;Jonkers 1979;Rivero et al 2017) revealed that in spur buds, floral initiation takes place 6-8 weeks after full bloom, while in buds on extension shoots, it takes place at least 2-3 weeks later. Foster et al (2003) found that broadening of the shoot apex, which they considered the first visible sign of floral commitment, occurs between 39 and 53 days after full bloom.…”

“…In 2017, all spur buds (0-20 per tree) on three randomly selected trees were likewise dissected in each treatment, while for reduction of the workload, only 5 lateral buds from the mid zone of each of the three longest current season extension shoots of the same three selected trees were dissected and examined (total of 15 buds per tree). The sampled buds were either dissected fresh or fixed and stored on 70% ethanol until dissection and determination of their flowering stage under a stereo microscope according to the 7-stage scale of morphological changes used by Foster et al (2003) and Rivero et al (2017). Scanning electron microscopy images as presented by Rivero et al (2017) were used for assessment of the floral stages (see Fig.…”

“…The sampled buds were either dissected fresh or fixed and stored on 70% ethanol until dissection and determination of their flowering stage under a stereo microscope according to the 7-stage scale of morphological changes used by Foster et al (2003) and Rivero et al (2017). Scanning electron microscopy images as presented by Rivero et al (2017) were used for assessment of the floral stages (see Fig. 2).…”