Physiology of flowering in temperate fruit crops

1. Physiology of
flowering in
temperate
fruit crops
Presented by:
Mandeep Kaur
Presented to:
Dr J S Brar
Senior Horticulturist

2. The switching from vegetative growth to reproductive growth is called
"flowering". The shoot meristem is reduced to develop sepals, petals, stamens,
carpals in place of leaves.
Flowering

3. Physiology of flowering
• The process until plants come to flower is classified into three stages, that is:
1. Differentiation of flower buds
2. Development of flower bud
3. Opening of flower

4. Events in the bud leading to flowering
a. Induction:
-flowering stimulus is generated.
-Influenced by water stress, chilling temperature or photoperiod.
b. Evocation:
-shoot apical has received floral stimulus and irreversibly committed
to form flower bud primordia.
c. Initiation:
-evoked bud becomes recognizable as a flower bud and is thus
committed to reproductive development.
-broadening and flattening of the growing points.

5. 2. Differentiation of the growing points:
 Increase in synthesis of DNA and RNA.
 Frequency of cell division within the central zone of shoot
apical meristems is increased.
 Shoot meristem is induced to develop sepals, petals,
stamens and carpals in case of leaves.
 The flat apical meristem becomes domed.
 The meristem becomes a block like structure.
 The subsequent development of flower meristem is
relatively rapid.

8. • Plants switch to reproductive growth after a certain period of vegetative
growth.
• The switch from vegetative to reproductive growth – flowering – is critical
to plant development, because the proper timing of flowering ensures the
success of the next generation and the continuity of the species.
• Flowering is regulated autonomously or by environmental factors.
• The primary environmental factors are the duration of the day and night
periods, which regulate photoperiodic flowering, and low temperatures
near the freezing point, which regulate vernalization.
Regulation of flowering

9. Flower Production
Four genetically regulated pathways to flowering have been identified.
1. The light - dependent pathway
2. The temperature - dependent pathway
3. The gibberellin - dependent pathway
4. The autonomous pathway.
Plants can rely primarily on one pathway, but all four pathways can be
present.

11. Fig. In apple, flower buds are formed mainly in the terminal position of shoots
(A) and on spurs of older shoots (B).

12. Three-year growth of an apple fruit branch from the year 2012 to the year 2014.

15. Seasonal changes in the development of
terminal spur buds in apple
Abbott (1977)

16. Dormancy breaking of reproductive buds and flowering in almond referenced to the phenological stages

21. Chilling Hours Models
▪ Chilling requirement is defined as the number of effective chilling
hours needed to restore bud growth potential in spring.
▪ The chilling requirement is typically measured in terms of numbers of
hours, during which temperature remains at or below 7°C during the
winter season.
▪ The Chilling Hours Model is the oldest method to quantify winter chill
(Perez et al, 2008).
▪ According to this model, temperatures between 0°C and 7.2°C are
assumed to have a chilling effect, with each hour at temperatures
between these thresholds contributing one chilling hour.
▪ Chilling hours are accumulated throughout the dormant season and
then summed up .

22. Utah Model
▪ The Utah Model developed in Utah, USA.
▪ It contains a weight function assigning different chilling efficiencies to
different temperature ranges, including negative contributions by high
temperatures.
▪ This model defines a CU as the permanence of the buds for a period of
1 hour in a temperature range considered optimum (2.5-12.5°C) to
accumulate chill.
▪ The model presumes that chill accumulation occurs within a
temperature range of 2.5 and 12.5°C, outside of which, the
accumulation is nil or negative.
▪ Provides good results in cool temperate climates.
▪ It is not accurate in areas with high winter day temperature (over 20°C)
as it yields a large quantity of negative chill.

24. Dynamic Model
▪ The Dynamic Model was developed in Israel.
▪ Based on hypothesis, chill accumulation occurs in the form of portions or
quantum of chill, that takes place in two step processes.
▪ An intermediate product is first formed in a process promoted by cold
temperatures. It transforms into a chill portion which can no longer be
destroyed. A certain chill portion accumulation indicates fulfilment of chilling
requirement.
▪ Warm temperatures can destroy this intermediate product.
▪ Better results in warm temperate and sub-tropical climate.
▪ Dynamic Model is relatively accurate in different climates as compared to
other commonly used Chilling Hours approach.

26. Stress-induced flowering
▪ Stress-induced flowering can be now considered as the third
category of flowering response in addition to photoperiodic
flowering and vernalization.
▪ Plants inhibit the processes of growth and development when they
are stressed but they have evolved the ability to resist, endure, avoid,
or adapt to stress such that they can protect themselves from harmful
environmental conditions.
▪ Stress-induced flowering is one response to stress and is the ultimate
stress adaptation, because plants can survive as a species if they
flower and produce seeds even when they cannot survive as
individuals under severe stress.
▪ Many types of stress factors have been reported to induce flowering.
▪ These include high or low light intensity, UV light, high or low
temperature, poor nutrition, nitrogen deficiency, drought, low
oxygen, crowding, root removal, and mechanical stimulation.

27. Flowering physiology of
temperate fruit crops under
increased temperature

28. ▪ The physiology of flowering in temperate fruit crops is triggered by several
factors like photoperiodism, phytochrome, growth hormones, florigin,
temperature, vernalization etc. operated through genetic factors. They
have major impact on flowering.
▪ In the past 20 years, the average mean temperature in hill states has risen
from 1⁰C to 2⁰C. Increased temperature has inhibited general growth and
development such as abnormality in leaf development and
underdevelopment of reproductive organs.
0
1
2
J&K
UK
HP
1.89
1.51
1.37
Rise
in
annual
mean
temperature
by
(oC)

29. ▪ The flowering depends on the chilling hours (early, medium and late flowering).
▪ Due to increased temperature, the chill units for temperate fruit production
have exhibited a decreasing trend. It has become very critical and showing
impact on blooming.
▪ It effected vernalization of high chill requiring fruits like apple, walnut, apricot,
almond and cherries.
 Harmful effects of insufficient chilling:
1. Changes in flowering phenology
2. Delay in flower bud bursting
3. Lack of synchronized bud-break
4. Early flowering
5. Flower drop
6. Poor fruit set
7. Increased incidence of pest and diseases
8. Negative effect on pollination
9. Changes in quality

30. ▪ Trend analysis indicated that snowfall is decreasing at the rate of 82.7
mm/annum in the entire region of HP.
▪ Overall, decrease of about 2-3% in yield has been reported in Shimla,
Kullu, Lahul and Spiti districts in mid 2000s and the maximum decline
of about 4% was witnessed in marginal farms.
▪ Apple growing areas in low altitudes like Solan have been reduced by
77% between 1981-2007. So, under low altitudes, there is complete
crop failure of high chill fruit crops.
▪ NO FLOWER NO FRUIT.
▪ Majority of the apple orchards in UK have become unproductive over
the year – low chilling.
▪ Consequently, the apple cultivation area is moving further up in higher
altitude and cold arid areas.
▪ Overall, shift in ecological zones, cropping pattern and suitability areas.
https://www.slideshare.net/mahenslides/climate-change-impact-on-productivity-and-quality-of-temperate-fruits-and-its-mitigation-strategies

31. Apple production in Ladakh
(Future potential area)
Unproductiveorchards in lower altitudes in U.K.
Fruit bearing peach trees in U.K.
https://www.slideshare.net/mahenslides/climate-change-impact-on-productivity-and-quality-of-temperate-fruits-and-its-mitigation-strategies

32. Climate warming enhances earliness of
blooming of deciduous fruit trees
• Climate change advances the date of full bloom in apple and pear.
Woznickia et al (2019)
Norwegian University of Life Sciences, Ås, Norway

33. Fig. Earlier flowering coincides with the time of spring frost during February and
March in Kashmir, resulting in increasing risk of frost damage to apple flowers.
https://www.slideshare.net/mahenslides/climate-change-impact-on-productivity-and-quality-of-temperate-fruits-and-its-mitigation-strategies

34. Occurrence of late snowfall coincided
with full bloom – causes heavy damage
to almonds.
Apricot in bloom - coincided with late
winter snow fall
https://www.slideshare.net/mahenslides/climate-change-impact-on-productivity-and-quality-of-temperate-fruits-and-its-mitigation-strategies

35. Flowering physiology of
temperate fruit crops under
low temperature

37. Nature of frost damage to deciduous
flowers & fruitlets
▪ Extremely cold temperatures (below -18°F) kill flower buds, particularly those on
cherry, plum, apricot, and peach trees.
▪ Following a cold winter, some or all of the flower buds may be dead even though
the rest of the tree survived.
▪ At temperatures of 5-10 0C pollen tube growth is very slow & not all of the
germinating pollen grains reach the base of the style.
▪ When opening, these flowers appeared undamaged but internal studies showed
arrested or abnormal ovule development. At freezing temperatures, cells are
destroyed in the flower.
▪ Usually the ovule and style are more susceptible to freezing damage than the
pollen (Lommel and Greene, 1931).
▪ Also, temperatures just above freezing inhibit the fusion of the nuclei in the embryo
sac, resulting in only the egg and not the endosperm being fertilised (Konstantinov,
1960).
▪ All these factors leads to an inability to set fruits.

38. Frost damage to Apple & Pears
*Source: https://www.canr.msu.edu/news/assessing_frost_and_freeze_damage_to_flowers_and_buds_of_fruit_trees
A B C

39. Frost damage to Stone fruits
A B
*Source: https://www.canr.msu.edu/news/assessing_frost_and_freeze_damage_to_flowers_and_buds_of_fruit_trees

40. Nectarine buds, cut longitudinally to show the pistil, one live and one dead.
Frost damage to Nectarine
https://www.intermountainfruit.org/cold-effects/cold-damage

41. Frost damage to peach
https://www.intermountainfruit.org/cold-effects/cold-damage

42. • Young peach fruit damaged by the frost. The small developing fruit are
more vulnerable to frost damage than the blooms.
• A brown peach is a dead peach, and these will eventually fall off the tree
before maturing.
https://growingsmallfarms.ces.ncsu.edu/2016/04/freeze-damage-to-local-fruit-crops/
Frost damage to peach fruits

43. Frost damage to Apricot buds
https://www.intermountainfruit.org/cold-effects/cold-damage

44. Frost damage to Sweet cherry buds & flowers
https://www.intermountainfruit.org/cold-effects/cold-damage

45. ▪ Research conducted at Long Ashton Research Station in the
1960s (Williams, 1970b) showed that pre-blossoming frosts could have a
very damaging influence upon potential fruit set of Cox apples.
▪ Poor weather conditions shortly before, during and shortly after flowering
of apples can cause significant reductions in fruit set and harvestable
yield.
▪ Hail, although unusual at flowering time, can also, if severe, damage
blossoms and young fruitlets.

46. Hail is a form of solid precipitation.
It consists of balls or irregular lumps of ice,
each of which is called a hailstone.

47. Evaluation of susceptibility of pear and plum
cultivars to winter frost
Khorshidi et al (2014)
Ferdowsi University Of Mashhad, Mashhad, Iran
• During the bloom stage, a single event with temperatures going a few degrees
below zero is sufficient to damage flower buds or even kill them.
• Objective: To investigate winter frost damage to pear and plum buds in Mashhad,
after a period of unusually warm weather for a few days in March 2013 followed by
a sudden drop in temperature to -12°C.

48. • Vegetative bud of ‘Ghodumi’ suffered the most damage.
• Whereas its Reproductive bud suffered the least damage.
• The EC and proline content of ‘Dare Gazi’ were the highest despite it did not show
high resistance. (Reason: Proline increase doesn’t increase cold resistance).
Twelve cultivars of pear
William’s, Bell de june, Ida, Spadona, Koshia, Domkaj, Dare Gazi,
Mohamad Ali, Boheme, Asian pear, Shekari and Ghodumi.

49. • ‘Computi’ had the most resistant reproductive bud and no damage was observed in
the other parts. It had the lowest proline content.
• Conclusion: Proline index is not appropriate for evaluating frost damage.
Eight plum cultivars
(European: Prunus domestica L. Stanley, Early Santa Rosa, Late Santa Rosa, Shablon,
Black Diamond; Japanese: P. salicina L. Shiro, Shams, Computi)

50. Percentage of frost damage of pistil and male organs of some plum cultivars
• In all plum cultivars the pistil suffered more damage than the male part.
• Cold hardiness of pistil was weaker than stamen.

51. Cold Hardiness of Southern Highbush Blueberry
Smith (2019)
University of Georgia, Tifton Campus, Tifton, USA
• Cold tolerance decreased as growth proceed from tight bud to petal fall.
• Tight bud (stage 1) & Bud swell (stage 2) : Can tolerate cold temp. of −12 to −9 °C.
• Bud break (stage 3): More sensitive to cold, where at −7 °C, damage can occur.
• Full bloom (stage 8): Cold tolerant to −2.2 °C
• Petal fall (stage 9): Cold tolerant 0 °C, freeze damage will occur & even small green
fruit is sensitive to 0 °C.

52. Comparative metabolic profiling of Vitis
amurensis & Vitis vinifera during cold
acclimation
▪ Plantlets of V. amurensis and V. vinifera cv. Muscat of Hamburg were
treated at 4 °C for 24 and 72 h, and changes of metabolites in leaves were
detected.
▪ Metabolites, including carbohydrates, amino acids, and organic acids,
accumulated in V. amurensis was responsible for the excellent cold
tolerance.
▪ The expression levels of the genes encoding β-amylase (BAMY), galactinol
synthase (GolS), and raffinose synthase (RafS) were evaluated by qRT-PCR.
Chai et al (2019)
Chinese Academy of Sciences, Wuhan, P.R. China

53. qRT-PCR results for BAMY gene family members in V. amurensis and V. vinifera cv. Muscat Hamburg.
The expression BAMY (VIT_02s0012 g00170) was primarily responsible
for the accumulation of maltose.

54. qRT-PCR results for GolS gene family members in V. amurensis and V. vinifera cv. Muscat Hamburg.
The expression GoIS (VIT_14s0060g00760) was primarily responsible
for the accumulation of galactinol.

55. qRT-PCR results for RafS gene family members in V. amurensis and V. vinifera cv. Muscat Hamburg.
The expression RafS (VIT_05s0077 g00840) was primarily responsible
for the accumulation of raffinose.

56. Transcriptome analysis provides insights into the
stress response crosstalk in apple subjected to
drought, cold and high salinity
A. Total number of upregulated and downregulated genes.
B,C. Venn diagram of upregulated & downregulated genes in the three samples vs. control.
Li et al (2019)
Beijing Academy of Forestry and Pomology Sciences, Beijing, China

57. How flowering physiology of temperate fruit
crops is affected by lack of sunlight
▪ Failure to form flowers: Fruit trees need full sunlight, and will
fail to produce flowers if planted in full shade. Lack of sunlight
and severe disease are additional reasons why fruit trees fail to
form flowers.

58. How flowering physiology of temperate fruit
crops is affected by deficit irrigation
▪ Deficit irrigation (DI) at phenological stages less sensitive to
water stress (pit hardening and post-harvest stage) influenced
fruit quality & plant growth.
▪ There is also some evidence that water stress can lead to
flowering soon after the plants are rewatered.

59. Deficit Irrigation in Nectarine: Fruit Quality, Return
Bloom and Incidence of Double Fruits
▪ Irrigation treatmets were applied in ‘Spring Bright’ and ‘Summer Bright’
nectarines during pit hardening and post-harvest stages.
▪ DI 58 and DI 33 treatments increased flower density in ‘Spring Bright’
▪ DI 58 and DI 33 treatments resulted in development of intense red fruit
colour and early maturity in ‘Spring Bright’.
Thakur and Singh (2013)
Four irrigation levels
DI 75 (75 % of CI)
DI 58 (58 % of CI)
DI 33 (33 % of CI)
Control irrigation (CI)

60. Effects of regulated deficit irrigation practices on flower
quality & floral characteristics of Braeburn Apple
▪ To determine effects of regulated deficit irrigation practices on flower dry weight,
anther number, pollen quantity, pollen viability and pollen germination.
▪ Two consecutive years. Ten years old Braeburn apple trees on M9 rootstock under
drip irrigation systems.
▪ Results showed that lowest flower dry weight was obtained deficit irrigation
between the 40th and 70th days after full bloom (I3).
▪ During the experiment, anther number, pollen quantity and pollen viability were not
affected by any irrigation practices.
Kacal et al (2014)
Turkey
5 Irrigation treatments
None deficit irrigation (I1)
Deficit irrigation between the 40th and 70th days after full bloom, DAFB (I2)
Deficit irrigation between the 70th and 100th DAFB (I3)
Deficit irrigation between the 100th and 130th DAFB (I4)
Deficit irrigation between the 130th and 160th DAFB (I5)

61. A moderate regulated deficit irrigation does not
negatively affect flowering, fruit-set and return-
bloom in a late apple cultivar
▪ Two different water regimes were considered: Control, i.e., well-watered
(WW) corresponding to grower irrigation based on 100% of estimated crop
evapotranspiration (ETc) throughout the irrigation season.
▪ RDI treatment equal to 50% water deficit in July (50% of WW, water-stressed,
WS)
▪ Fig: Effects of the 2013-water regime on the number of flowers in terminal
inflorescence for each 2013-shoot size category.
Atay et al (2019)
France

62. Physiological and biochemical responses of young
olive trees to water stress during flowering
▪ Three different water regimes:
▪ T0 (severe water stress ): No irrigation.
▪ T50 (moderate water stress ): Irrigated half the water needed to maintain the soil at
field capacity.
▪ T100 (control; Well watered plants): Irrigated twice a week to field capacity (≈800 mL).
Yamani et al (2018)
Sidi Mohamed Ben Abdellah University, Morocco
Fig. Leaf relative water content (RWC), water potential (Ψw), transpiration rate (E),
stomatal conductance (gs), total chlorophyll content (TCC), maximum quantum
efficiency of PSII (Fv/Fm), proline content (ProC) and soluble sugars content (SSC).
Severe
Mod
Control

63. “Honey bees”
Pollination primers in apple orchards
• In temperate fruit orchards, pollination depends on bees to transfer pollen
from one flower to another.
• Temperature
• Most of the insects work well at or near 4 0C.
• When the temp is either very low or high, they don’t take flight, which affects
pollination and thereby the fruit set.
• Consequently, there may be fewer fruit when bad weather occurs at bloom.
• Rainfall: Rainfall during flowering time affects the activity of pollen carrying
insects.
• Wind: Pollen carrying insects work more effectively in a still atmosphere. Strong
wind inhibits bee activity (>10 mph) during the bloom period.
• Relative Humidity: Activity of bees and other pollen carrying insects is
hindered under lowor very high relative humidity.

65. How flowering physiology of deciduous temperate
fruit crops is affected by biotic stress
▪ Biotic stress: Severe outbreaks of disease, such as apple scab,
cause defoliation, and without leaves, the tree does not have
enough energy to form flowers. Damage to the leaves and
defoliation leads to poor flowering the following spring.

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