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Table 3 The influence of constant and changing temperatures on the percentage of reproductive buds and the mean floral development stage of dissected buds of spurs and extension shoots of the apple cultivars ‘Summerred’ and ‘Discovery’ after completion of 12 weeks of exposure to the indicated temperatures (2017 experiment)

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

Cultivar Temperature (°C) Spurs Extension shoots
Generative buds (%) Mean floral development stage (1–7)a Generative buds (%) Mean floral development stage (1–7)
‘Summerred’ 12 °C cont. 3.7 eb 1.1 d 0.0 d 1.0 b
18 °C cont. 97.6 a 6.5 a 41.1 a 5.0 a
24° C cont. 73.6 b 4.8 b 39.6 a 4.5 a
27 °C cont. 21.0 d 1.6 cd 18.5 b 1.8 b
Ambient 48.0 c 2.3 c 4.8 c 1.3 b
  1224 °C 49.8 B 2.4 B 27.6 C 2.9 B
1827 °C 31.3 C 1.9 B 15.0 D 3.0 B
2412 °C 64.6 A 4.6 A 50.8 B 4.0 A
2718 °C 66.4 A 4.6 A 62.2 A 3.7 A
‘Discovery’ 12° C cont. 3.7 c 1.1 c 0.0 c 1.0 c
18 °C cont. 100 a 5.6 a 26.5 b 2.6 a
24 °C cont. 82.7 b 4.4 b 33.1 a 1.7 b
27 °C cont. 2.3 c 1.1 c 0.0 c 1.0 c
Ambient 0.0 d 1.0 c 0.0 c 1.0 c
  1224 °C 0.0 C 1.0 C 0.0 B 1.0 B
1827 °C 0.0 C 1.0 C 0.0 B 1.1 B
2412 °C 56.6 B 3.7 B 22.7 A 2.0 A
2718 °C 86.9 A 4.9 A 23.8 A 2.1 A
Probability level of significance by ANOVA
 Source of variation
  Cultivar (A)   < 0.001 < 0.001 0.001 0.001
  Temperature (B)   < 0.001 < 0.001 < 0.001 < 0.001
  A × B   < 0.001 < 0.001 < 0.001 < 0.001
  1. The data are means of all spur buds from each of three replicate trees and of 15 lateral buds from the middle part of 3 extension shoots from each tree
  2. aStage 1 denotes entirely vegetative buds, and stage 7 denotes fully differentiated primary flowers
  3. bFor separation of means, Tukey’s multiple comparison test was performed separately for the two cultivars (lower case letters), and likewise for constant and changing temperatures (capital letters)