Buds Flowers Pollination Fruit Set Principles of Fruit & Nut Tree Growth, Cropping and Management UC Davis, Feb. 26, 2013
Buds Types of Buds Bud Positions Spurs
Pollination and Fertilization Pollen Pollination Vectors Effective Pollination Period
Flowering Flower Differentiation Prunus: A Case Study Ovary Development Sex Expression
Outbreeding Mechanisms Self Incompatibility Managing Incompatibility Dichogamy
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Buds Types of Buds Bud Positions Spurs
Pollination and Fertilization Pollen Pollination Vectors Effective Pollination Period
Flowering Flower Differentiation Prunus: A Case Study Ovary Development Sex Expression
Outbreeding Mechanisms Self Incompatibility Managing Incompatibility Dichogamy
Buds • Apples and Pears Mixed buds with leaves and several flowers. Buds terminal on the shoot.
• Stone Fruits (Prunus spp.) Flower buds lateral on shoots with one (Peach, Nectarine) or several (Plum, Cherry) flowers.
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Buds
• Peaches and Nectarines bear flower buds laterally, on one-year old wood. • Apples, Pears, Cherries bear on spurs, short shoots on older wood. Note that flowers form on the current year’s growth of the spur, but the spur itself is located on older portions of the long shoot.
Buds
Peach buds on one-year old wood.
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Peach Flowering
Almond Spur
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Cherry Spur
Pears and apples bear mainly on spurs.
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Apple Spur Shoot
Bourse Shoot
Mixed Terminal Bud Basal leaves. Terminal flower subtended by 4 lateral flowers. Bourse shoot originates in the axil of a leaf to continue growth of the spur.
Newer apple cultivars are tip-bearing as well as spur-bearing.
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Buds Types of Buds Bud Positions Spurs
Pollination and Fertilization Pollen Pollination Vectors Effective Pollination Period
Flowering Flower Differentiation Prunus: A Case Study Ovary Development Sex Expression
Outbreeding Mechanisms Self Incompatibility Managing Incompatibility Dichogamy
Flower Structure Stone Fruit Species (Prunus) have flowers with 5 sepals, 5 petals, many stamens one pistil The sepals, petals and stamen bases are united to form the floral tube (jacket) which secretes nectar.
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Apple Flower Structure Pears and Apples have flowers with 5 sepals, 5 petals, many stamens and a compound pistil that is embedded in accessory tissue.
Flower Bud Differentiation For deciduous tree species, flowers form in the buds during the growing season prior to bloom. All the parts of the flower are fully formed as the tree enters the dormant season. For evergreen species (e.g. olive, citrus) flower differentiation occurs during the weeks prior to bloom, not the previous season. Timing of the events involved varies among species and locations. Many of the stone and pome fruit species have not been investigated in California.
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Flower Bud Differentiation Inside the developing buds, all growth comes from a terminal cluster of cells called the apical meristem. Vegetative apical meristems produce bud scales, and leaves.
Flower Bud Differentiation A Case Study: Prunus
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Flower Bud Differentiation
Scanning Electron Microscope View of the Apical Meristem of Sweet Cherry
Flower Bud Differentiation
Sometime in mid-summer the shoot apex of a flower bud begins to produce primoridal flowers.
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Flower Bud Differentiation
As the flowers develop, sepal primordia initiate at the flanks of the floral meristems.
Flower Bud Differentiation
About a week after the sepals are initiated, petal primordia form inside the sepals.
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Flower Bud Differentiation
Stamens are initiated next, leaving a broad base of undifferentiated meristem where the pistil forms.
Almond Flower Bud Differentiation Simulation
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Ovary Development The pistil forms from that base of undifferentiated cells usually consuming all of the meristem. If the base is excessively large, or if the primordial pistil fails to consume all of it as it develops, aberrant fruit types can result. Note that the pistil is initiated as an open structure that grows at its margins, not as an enclosed unit.
Ovary Development
Eventually the margins grow together to form a closed locule that defines the ovary.
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Ovary Development
When the margins come into contact, they fuse together, forming a suture. Here again, failure of development leads to aberrant fruits.
Aberrant Fruits from Abnormal Ovary Development Spurred, sutured and doubled cherry fruits result from abnormal ovary development, differentiation or suture sealing. Doubled or spurred peaches occur similarly, often when trees are stressed during these stages of flower development.
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Sex Expression: Unisexual Flowers Flowers may have the organs of only one sex.
Walnuts and pecans have male flowers arranged in clusters, called catkins (l).
When male and female flowers occur separately on the same plant, the species is monoecious.
The female flowers are borne in pairs (walnut) or small groups (pecan).
Walnut and pecan are monoecious species.
Both male and female flowers lack petals.
Sex Expression: Unisexual Flowers of Monoecious Walnut
Male
Female
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Sex Expression: Unisexual Flowers When male and female flowers occur on separate male and female plants, the species is dioecious. Pistachio and kiwifruit are dioecious species.
Sex Expression: Unisexual Flowers
Inflorescences (top) and flowers (bottom) of dioecious pistachio.
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Buds Types of Buds Bud Positions Spurs
Pollination and Fertilization Pollen Pollination Vectors Effective Pollination Period
Flowering Flower Differentiation Prunus: A Case Study Ovary Development Sex Expression
Outbreeding Mechanisms Self Incompatibility Managing Incompatibility Dichogamy
Pollen and Pollination Pollen grains form in the stamens of the flowers. When the pollen is released it is carried to the stigmas.
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Insect Pollination
Insect pollinated species have showy flowers that are usually fragrant and and produce nectar.
Wind Pollination Wind pollinated species include walnut, pecan, olive, pistachio. The flowers of wind pollinated species usually lack petals or have small, insignificant petals. They often lack scent and do not produce nectar. The stigmas are usually large and feathery, adapted to catching pollen from the air flow.
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Wind Pollination Experiments using microscale wind tunnels show that pollen capture in wind-pollinated species is not simply chance capture of pollen moving in the air. The shape and form of the flower structures create air flow patterns that direct the pollen to the stigma surfaces.
Pollination
Pollen is released as a dehydrated cell. When it lands on the stigma it rapidly hydrates in the fluid that is secreted by the stigma surface cells.
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Stigma Receptivity Stigma will support pollen hydration and germination for a limited period of receptivity. Some species have wet stigmas with a liquid exudate that marks the period of receptivity. As receptivity passes, the stigma dries and turns brown. Others have dry stigmas. Here, the period of receptivity is sometimes more difficult to determine.
Stigma Receptivity in Walnut
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Pollen Germination When pollen becomes hydrated on the stigma it germinates to form a tube that penetrates between stigma cells.
Pollen Tube Growth
stigma
style
The pollen tubes grow through the stigma, the style and into the ovary. The pollen tubes carry male germ cells (sperms) to the ovary.
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Ovules
Within the flowers’ ovaries are ovules. Stone fruits have two ovules. Apples and pears have ten, two in each of the five ovaries.
Female Germ Cell
The ovules are potential seeds. They contain the female germ cells, eggs. There is one egg cell in each ovule.
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Fertilization Pollen tubes grow to the ovules. The first pollen tube to arrive enters the ovule and releases it contents. One sperm cell fuses with the egg. A second sperm cells fuses with two other female cells to form endosperm. Fertilization triggers fruit set.
Effective Pollination Period (EPP)
EPP integrates three factors. 1. Stigma receptivity: the ability of the stigma to support pollen germination. 2. Pollen tube growth rate: the time required for the pollen tubes to grow through the style to the ovule. 3. Ovule viability: the time that the ovule is capable of being fertilized. Each of these is temperature dependent.
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Effective Pollination Period Stigma Receptivity The stigma will support pollen germination
Pollen Tube Growth
Effective Pollination Period The ovule is capable of being fertilized
Ovule Viability
0
1
2
3
4 Time
5
6
7
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Temperature Pollen germination and pollen tube growth responses to temperature for almond and peach.
55 68 55
68
80 F
80 F
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Prune Pollen Temperature Responses
Cultivar
Optimum
Pollen Germination
‘Improved French’
73 ºF
Pollen Germination
‘Muir Beauty’
72 ºF
Pollen Tube Growth
‘Improved French’
75 ºF
Pollen Tube Growth
‘Muir Beauty’
76 ºF
Buds Types of Buds Bud Positions Spurs
Pollination and Fertilization Pollen Pollination Vectors Effective Pollination Period
Flowering Flower Differentiation Prunus: A Case Study Ovary Development Sex Expression
Outbreeding Mechanisms Self Incompatibility Managing Incompatibility Dichogamy
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Self Incompatibility Self-incompatibility (or self-unfruitfulness) refers to the inability of a flower to support growth of pollen from the same tree or cultivar. Self-incompatible species set little or no fruit without being pollinated by a compatible cultivar.
Incompatibility groups comprise cultivars that are incompatible with each other. The response to pollen of a cultivar from the same incompatibility group is the same as that to self pollen.
Self Incompatibility Peach, nectarine, apricot are self compatible. There is no requirement for a pollinizer cultivar. Sweet cherry, almond and some plum cultivars are selfincompatible.
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Self Incompatibility Apples are partially self-incompatible. Apple fruit size is positively correlated with seed number, so compatible pollinizers are needed to assure full seed set and optimum fruit size. Bartlett pears will, under some California conditions, set parthenocarpic fruit. Pollination and fertilization are not necessary for fruit set where parthenocarpy occurs. Other pears are self-incompatible. Olives are partially self-incompatible. Self-incompatibility in olive is temperature dependent. The relationship is poorly understood, but self-incompatibility is greater under higher temperature conditions.
Gametophytic Self-Incompatibility (GSI) Compatible pollen tubes grow straight down the style. Incompatible pollen tubes branch, swell and grow irregularly, never reaching the ovary.
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Genetics of Gametophytic Self Incompatibility GSI in Solanaceae and Rosaceae is determined by multiple alleles at a single locus, the S locus. Compatible pollinations occur when the S allele carried by the male gametophyte is different for either of the alleles carried by the diploid sporophyte (style). Incompatible pollinations occur when the S allele carried by the male gametophyte is the same as either of the alleles carried by the diploid sporophyte (style).
Genetics of Gametophytic Self Incompatibility
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Genetics of Gametophytic Self Incompatibility
Possible Progeny: None
S1S3, S2S3
S1S3, S1S4, S2S3, S2S4
Almond Compatibility Groups
I II III IV V VI VII
(Sc,d) (Sa,b) (Sa,c) (Sb,c) (Sa,d) (Sb,d) (S?,d) (S?,d) (S?,?)
Nonpareil, IXL, Long IXL, Profuse, Tardy Nonpareil Mission, Languedoc, Ballico Thompson, Robson, Harvey, Mono, Sauret No. 2, Granada Merced, Ne Plus Ultra, Ripon, Norman, Price Cluster, Rosetta Carmel, Carrion, Sauret No. 1, Livingston, Monarch Monterey Solano, Sonora, Vesta Kapareil Butte, Grace Aldrich, Dottie Won, Fritz, Pearl, Ruby, Padre, Tokyo
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Cherry Incompatibility Groups I (S1,2) Black Eagle, Black Tartarian, Early Rivers, Sparkle II (S1,3) Abundance, Black Heart, Sodus, Van, Venus, Waterloo III (S3,4) Bing, Compact Lambert, Emperor Francis, Lambert, Merton Marvel, Napoleon (Queen Anne), Vernon IV (S2,3) Kassin, Merton Premier, Sue, Velvet, Victory, Yellow Spanish VI (S3,6) Elton, Gold, Governon Wood, Merton Heart VII (S4,5) Black Republican, Hedelfinger VIII(S2,5) Schmidt IX (S1,4) Chinook, Giant, Hudson, Merton Late, Merton Reward, Prosser 1-585, Prosser 1-638, Rainier, Yellow Glass
Incompatibility in Plums Compatible Cultivars Casselman Grand Rosa July Santa Rosa Nubiana Roysum Santa Rosa Simka
Self-Incompatible Cultivars Angeleno Blackamber Black Beaut El Dorado Kelsey Laroda
Red Beaut Queen Ann Royal Diamond Royal Red Spring Beaut Wickson
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Incompatibility in Plums Compatibility may vary. ‘Santa Rosa’ is considered self-fruitful in the southern San Joaquin, but in some Northern California production areas it may require cross pollination.
Managing Incompatibility • Compatible pollinizer cultivars must be present in the orchard. • Bloom timing between compatible cultivars must overlap sufficiently. • Honeybees are usually required to effect movement of pollen between and among compatible cultivars. • Orchard layout must facilitate pollen flow. Honeybees typically fly up and down rows, not across.
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Managing Incompatibility Almond Orchard Layout
Main Variety
Compatible Variety 1
Compatible Variety 2
Managing Incompatibility
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Managing Incompatibility
Pollen-gathering bees are more efficient pollinators than nectar-gathering bees.
Managing Incompatibility Pollinizer row in plum orchard trained to upright single trunk. Useful where minimum number of pollinizer trees are required.
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Managing Incompatibility
Pollinizer cultivar grafted to the center of plum tree. Used for pollensterile cultivars (‘Red Beaut’) where honeybees would not work the tree otherwise.
Partial Self Incompatibility Olives and some cultivars of apples are partially self incompatible. Some fruit set occurs with self pollination, but it is reduced relative to compatible cross pollination. Self incompatibility in olives is temperature dependent. The same cultivar is highly selfincompatible in the hot, southern San Joaquin Valley, but largely self compatible in the cooler growing areas of the northern Sacramento Valley. For some apple cultivars, the flowers behave as self incompatible during the first few days of bloom. For the final day of receptive bloom the flowers become self compatible.
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Self-Incompatibility of Olive Fruit Set of ‘Manzanillo’ after self and cross pollinations
Pollen Source
1994
1995
Self
0.122 a
0.100 a
Mission
0.094 a
0.147 a
Ascolano
---
0.245 a
Sevillano
0.506 b
0.463 b
Sev:Mis Mixture
0.575 b
---
Managing Self-Incompatibility: Supplemental Pollen Application
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Managing Self-Incompatibility: Supplemental Pollen Application
0.60
1989
0.50
1990
0.40 0.30 0.20 0.10 0.00
0
30
60
90
120 150
Distance from Pollen Application (ft)
Shotberries Shotberries per Inflorescence
Fruit per Inflorescence
Normal Fruit 0.40
1989 1990
0.30 0.20 0.10 0.00
0
30
60
90
120 150
Distance from Pollen Application (ft)
Sound Fruit & Shotberries vs. Distance from Pollen Application
Supplemental Pollination: Electrostatic Pollination
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Supplemental Pollination: Electrostatic Pollination
Dichogamy Dichogamy is an outcrossing mechanism that depends on the temporal separation of male and female function to discourage self fertilization. Walnut and pecan, monoecious species, are dichogamous. For some cultivars, the male flowers bloom before the female flowers (protandry). For others, the females bloom first (protogyny). Dichogamy in walnut is usually incomplete, so there some self pollination does occur, but for optimal set, growers usually plant one or more pollinizer cultivars that have a bloom period overlapping that of their main cultivar.
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Dichogamy in Walnut Protandrous Cultivars Have Male Bloom Before Female Bloom
Terminal Bud (with pistillate flowers) Catkin (staminate flowers)
Dichogamy in Walnut Protogynous Cultivars Have Female Bloom Before Male Bloom
Terminal pistillate flowers
Catkin (staminate flowers)
Walnut Protogyny
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Dichogamy in Walnut: Bloom Patterns of Some Walnut Cultivars
Dichogamy in Avocado Avocado has hermaphrodite flowers. The flowers open twice: first as females with receptive stigmas, then as males shedding pollen. There are Type A and Type B cultivars of avocado. Type A cultivars open first in the morning as females, close, then open again in the late afternoon as males. Type B cultivars open as females in the afternoon, close, then open as males the following morning.
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Dichogamy in Avocado
Avocado flower in the female stage (top) and the male stage (bottom).
Dichogamy in Avocado
Open as female
Reopen as male Close
Bloom Over
Bloom Pattern of Each Individual Flower
Type A
Type B
Day 1
Day 1
Day 2
Day 2
Day 3
Morning
Afternoon
Morning
Afternoon
Morning
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Dichogamy in Avocado In its native habitat in the Central American highlands, dichogamy is complete, effectively preventing self fertilization. Under the cooler conditions in California, Florida and the Mediterranean areas of southern Europe, avocado orchards, the system breaks down and there is sufficient overlap to permit selfing and compatible types are not needed.
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