Anthesis & Pollination

Anthesis & Pollination

Biology of Bloom and Flower Development

In the spring flowers develop largely in response to temperature.

Threshold of 45ºF In all fruit there are specific stages that the flowers go through

A. flower development hastens

B. Floral structures complete their development

C. All floral structures grow through cell enlargement

D. Microgametophytes undergo final meiosis and produce pollen grains

Flower development terminology

Apples:

Silver tip	Open cluster	Full bloom
1/2 inch green	Full pink	Petal fall
Tight cluster	King bloom

Peaches

First swelling	Calyx red	First bloom	Post bloom
Calyx green	First pink	Full bloom

A. Beginning of bloom: 12-15% of flowers open

B. End of bloom: 95-100% of flowers open

C. Petal fall: When all petals have fallen

Anthesis: the opening of flowers

Apple flowers typically consists of

5 to 6 flowers /cluster

king blossom.

Cyme type of inflorescence

Distinctive opening pattern

Pear and cherry inflorescences are

Referred to as racemes.

The terminal flower is the last formed.

Basal flowers produce the larger fruit.

Other fruit species are solitary lateral flowers

Pollination Sequence of Events

A. As the flowers open and the petals fold open exposing the pistil, the stigma becomes receptive to pollen.

B. When receptive, the stigma is coated with stigmatic fluid.

C. If a pollen grain lands on a receptive stigmatic surface it can germinate

D. Many pollen grains must be deposited on a stigma for successful germination and fertilization.

Pollination is the transfer of pollen grains from the anther to the stigmatic surface. In some cases this is enough to stimulate the fruit to begin to grow

V. Effective Pollination Period (EPP)

The Effective Pollination Period is the difference between the period of time for pollen tube growth and that of ovule longevity.

Pollination must occur within 2-4 days after the flowers open

Pears have a much longer EPP

- up to 6 or 7 days

Factors Influencing Pollination

Temperature
Low

Affects pollinator flight - below 55º little flight

Affects pollen grain germination and pollen tube growth

Affects viability of embryo - frost damage

High

Degeneration of embryo sac

Drying of stigmatic surface

Reduced flowering time

Increased bee flight

Temperature	Condition for Pollen
70 - 80º F	Ideal
60 - 70º F	Good, but slower growth
< 50º F	No pollen germination
> 90º F	Moves quickly, but desiccation may occur, ovule degenerates faster

VI. Compatibility

A. Apricot, peach, nectarine and sour cherry are mostly self compatible (+Stella, Lapins)

B. Apple, pear, European plums, and Japanese plums require cross-pollination

C. Cross-incompatibility also occurs

1. Triploid apples - pollen is not viable

2. Sweet cherries incompatibility is caused by a genetic factor "S allelle". Incompatibility groups

D. Flowering time must also overlap for cross compatible cultivars

Summary of Pollination Situation – General conditions for several fruit crops. Those fruits listed are self-fertile and will set fruit with their own pollen.

Apple: Cross pollination always needed to produce adequate fruit crop.

Apricot: All varieties are self-fruitful but cross pollination is helpful.

Cherry: (1) Sweet--all varieties, except Stella, and a few new ones are self-unfruitful.

(2) Red tart--the commercial varieties are self-fruitful.

(3) Duke--must be cross pollinated.

Nectarine: Most varieties are self-fruitful; however, those having J. H. Hale in the parentage will require cross pollination.

Peach: All commercial varieties, except J. H. Hale are self-fruitful.

Pear: All varieties are self-fruitful. But a pollinator will improve crop.

Plum: A wide diversity occurs in the plums:--about half of the varieties are self-fruitful and half are not. To be on the safe side pollinators should be provided.

Quince: All varieties are self-fruitful.

VII Cultivar & Pollinizer Relationships

A. Pollinators = honeybee

1. For most fruit crops honeybees are preferred.

2. Hives are rented from commercial beekeepers. Rate is 1 hive per acre.

3. Bumblebees work when weather is colder

4. Several new solitary bees, Mason, Bluefaced

5. Other insects such as flies, beetles may also spread pollen.

B. Pollinizer = pollen source.

1. Mixtures of cultivars:

2. Crabapples or pollinizer plants

3. Hive inserts

4. Bouquets of flowering branches from a compatible cultivar

5. Commercially viable cultivar

6. Physically different from main cultivar to prevent confusion at harvest

C. Pollinizer - Orchard Design

1. Diamond patterns - every third tree in every third row

2. Alternating rows in groups of 2's & 4's

3. In new high density plantings that are hedgerows, bees tend to fly up and down rows and not as much across rows.

Terms

Parthenocarpic requiring no pollination; seedless. Bartlett pear in Sacramento Valley in CA, Sultanina grape, banana

Self-fruitful Capable of setting a commercial crop following self pollination. Montmorency cherry, Stanley plum, most peach cultivars

Self-unfruitful Requiring cross pollination for a commercial crop. Most sweet cherry, apple and pear cultivars.

Triploid Lacking viable pollen, therefore must be cross pollinated. Mutsu, Winesap, Jonagold

Incompatible Having viable pollen, but incapable of setting fruit when cross pollinated.

The last condition is called cross unfruitful in this condition different cultivars will not cross pollinate to set fruit

VIII. Incompatibility

A. Pollen sterility.

B. Genetic incompatibility keeps pollen germ tubes from growing correctly

C. Non viable pollen.

D. Poor embryo sac development.

E. Dichogamy.

F. Environmental conditions

IX. Germination & fertilization

A. Once the pollen has been transferred the potential exists for fruit to set.

B. Pollen grains are released from the anther and are carried by honeybees to the stigmatic surface.

C. Germinate and produce germ tubes that grow through the style to the ovary.

D. Each pollen tube has 3 nuclei

1. Tube nucleus that directs growth of the germ tube

2. 2 sperm nuclei

E. At the same time that the pollen is germinating and germ tubes are growing the ovules mature and prepare for fertilization.

F. Double fertilization is required

1. One sperm combines with the egg to form a zygote

2. The other sperm nucleus combines with the two polar nuclei to form the endosperm (3n) X. Embryo growth

G. Once the egg is fertilized the embryo begins to grow quickly.

X. Fruit Set

Triploid cultivars usually set heavier than diploids because of a longer stigma receptivity and longer ovule longevity. In diploids that have a biennial tendency in the "on" year the EPP is sometimes twice as long as it is in the "off" year.

Seed development stimulates the apple tissue to grow int the immediate vicinity

In general adequate fruit size is achieved when there are a minimum of 6-7 seeds.

The number of seeds present also help determine whether that fruit will remain on the tree.

Myths

Pollen does not influence the typiness of the fruit.

Pollen does not influence the color of a fruit

Location http://hortweb.cas.psu.edu/courses/hort432/lecturenotes/anthesispollination.html