This document discusses factors that influence apple flowering and fruit quality. It covers the multi-step process of floral initiation through fruit development. Flowering is initiated months in advance through bud differentiation and is influenced by genotype, crop load, growth regulators, and other environmental and horticultural factors. Pollination requires compatible cultivars with overlapping bloom periods. Fruit quality can vary two-fold or more depending on factors like location within the tree canopy. Later-blooming flowers tend to produce lower quality fruit. Precision pollination techniques may help address challenges with traditional bee pollination.

1. Matthew Whiting Washington State University
APPLE FLOWERING &
FRUIT QUALITY

2. Flowering & quality:
• Broad topic
– Genotype
– Environment
– Management
1. Initiation
2. Pollination
3. Fruit quality

3. Floral initiation to fruit harvest
Initiation Differentiation Dormancy Flowering Fertilization Fruit growth

4. Floral initiation
• First step in processes of flowering and
fruit development
• Evolutionary mechanism through which
plant distributes seed
• Manipulated by growers for profit
– Sequence of events
– When, where, why

5. Floral initiation
• Flower initials formed within buds
– Summer and Fall
– A 15-month process
• Buds either vegetative or mixed

6. Floral initiation
• Floral buds typically borne on spurs
– 2-year-old and older wood
• Lateral buds on current season shoot
– Cultivar-dependent
• Terminal buds on shoots

7. Initiation of flowering
• Transformation of vegetative apex to
reproductive apex
• Can occur on same tree at widely varying
times
– Not triggered by specific temp or daylength

8. Initiation of flowering
• Key factors interfering:
– Hormonal balance
– Availability of nutrients (CH2O in particular)
– Interaction of these
– Others…..

9. Floralinitiation Scanning
Electron
Microscopy
Foster et al., 2003
Annals of Bot. 92:199-206
V: Narrow, flat
V: Broad, flat
R: Domed

10. Foster et al., 2003
Annals of Bot. 92:199-206
FM – floral meristem
B – bract
tFM – terminal FM
S – sepal

11. Factors affecting flowering
• Fruit load
– Heavy cropping will inhibit FBI
– Creates biennial/alternate bearing
– Excessive crop ‘on’ year leads to light crop ‘off’
year
– Effect is local
• Half trees can be ‘on’ or ‘off’
• Effect may be more localized – spur only
– Thought to be GAs produced in seeded fruit +
nutritional

12. Factors affecting flowering
• Light

13. Uniform flowering in UFO system

14. Factors affecting flowering
• Genotype
• Both cultivar and rootstock have great effect
Growth regulators
– GAs inhibit FBI (GA3 and GA7)
– Cytokinins promote FBI
• Pruning
– High vigor = lower FBI
– Summer pruning can improve FBI (ca. 12 lvs)

15. Dormant hedging
“Setting the box” to be followed with summer pruning

16. Dormant cut
made first
Summer cut
summer cut
(see next floral bud)
Summer cut
Mechanical pruning in summer (10-12 lvs)

17. Dormant cut
Summer cut
Floral bud

18. Floral initiation
• Critical first step to productivity
• Controlled by developmental processes,
endogenous and exogenous factors
• May be manipulated for profit
– Goal: consistent, balanced floral initiation

19. Fruit set/fertilization
• Pollination
• Mediated by Apis
mellifera
• Pollenizers +
pollinators
• Fertilization
– 5 locules
– 10 ovules
– Seed set

20. Pollenizer + pollinator model
• Apple requires cross-pollination
• Gametophytic incompatibility
– Know your S-alleles and bloom timing…...

21. Fruit set
• Trees produce 10-15x more flowers than
desirable fruit number/tree
• Cell division reduced if too many fruit =
small fruit
• Critical to adjust fruit numbers early
– Benefits fruit size, current season
– Benefits bloom, subsequent season

22. • Insufficient density/distribution
• Lack of overlapping bloom
• Distribution of pollen born viruses
• Harboring pests/diseases
No bloom overlap
Pollenizers
Challenges with P+P model:

23. • Colony collapse disorder
• Increasing cost
• Variable colony performance
• Distribution & density
• Variable environmental conditions
Pollinators
Challenges with P+P model:

24. Proposed solution:
1. Collect pollen
2. Suspend pollen
3. Apply pollen via sprayer
No pollenizers nor pollinators

25. Precision pollination
‘Tieton’/ ‘Gisela 5’: 8 years old trained to UFO

26. Future pollination system?

27. Fruit quality variability

28. Fruit Value/Consumer Appeal
Genetic Potential
Ideal management
NumberofFruit
Conventional
management
The ultimate goal:

29. • Three key questions:
1. By how much does fruit quality vary?
2. What are sources of this variability?
3. How can variability be reduced/improved?

30. 3rd leaf Fuji – 0.8 x 3 m
Defoliated trees
Mapped fruit position
Mapped wood

32. 15 yr old Fuji
2.5 x 4 m

33. 0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
10 12 14 16 18 20
tree1
tree2
tree3
bigtree
1. By how much does quality vary?
Fruit soluble solids (obrix)
2-fold variability - 10 to 20 brix

34. 0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
50%
50 150 250 350 450
big tree
tree1
tree2
tree3
Fruit weight (grams)
1. By how much does quality vary?
>4-fold variability - 90 to 400 g

35. 0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
0 20 40 60 80 100
tree1
tree2
tree3
BigTree
Fruit color (% red)
1. By how much does quality vary?
Tremendous variability - 0 to 100%

36. Relationship with fruit position?

37. Fruit position vs. quality
3D canopy models
• Defoliate
• Map fruit position
• Analyze each fruit
• Create 3D quality maps

38. Fruit size and color
3rd leaf Fuji
29 fruit
No clear positional effects

39. Fruit size and color
15-yr old Fuji
384 fruit

40. Defoliation to improve harvest efficiency & fruit quality

41. Harvest efficiency +25% 100% colour

42. Causes of variability?

43. Which flower has the greatest quality potential?

44. Treatment Fruit
weight (g)
Firmness
(lb)
Soluble
solids
(%)
Hand-thinned control 230 a 17.5 a 12.0 a
Thinned to KING
flower
203 b 17.3 a 10.7 b
Thinned to SIDE flower 230 a 17.5 a 10.6 b
Table 1. Effect of hand-thinning every cluster throughout entire trees to either
the king or a side flower on fruit quality attributes of Buckeye Gala. Thinning
treatments are compared to normal commercial practice (hand-thinned control).

45. Quality potential similar for king & side flowers

46. Timing of flowering on fruit quality

47. y= -4.3517x + 232.75
R²= 0.13
0
50
100
150
200
250
300
350
g
Bloom Date
'Buckeye Gala' Fruit Weight 2010
y= -0.5374x + 79.038
R²= 0.14
0
10
20
30
40
50
60
70
80
90
100
mm
Bloom Date
'Buckeye Gala' Fruit Diameter 2010
y = -8.947x + 266.37
R² = 0.23
0
50
100
150
200
250
300
350
Weight(g)
Bloom Date
'Buckeye Gala' Fruit Weight 2009
y = -0.99x + 82.23
R² = 0.26
60
65
70
75
80
85
90
95
100
Diameter(mm)
Bloom Date
'Buckeye Gala' Fruit Diameter 2009
Last-opening flowers appear to have lower quality potential

48. QUESTIONS?
mdwhiting@wsu.eduFB: WSUStoneFruitPhysiology