Written by Jenny Bolivar, WSU Extension ITT, Jun 4, 2021.
For a formatted printable inforgraphic pdf download. Floral biology and pollination in WA38
En Espanol download Biologia floral y polinizacion en WA38
Floral Biology
- In general, there are 6 blossoms per bud: a king flower (central)
surrounded by 5 Lateral flowers. WA38 King flowers bloom 48-72
hours earlier than lateral flowers. - In 2020, WA38 king flowers bloom starts by the third week of April
(Rock Island, Wenatchee).
![floral biology graphic](https://s3.us-west-2.amazonaws.com/treefruit.wsu.edu/wp-content/uploads/2021/06/04103423/apple-flower-labeled.jpg)
Pollination (results from 2019 study)
- Apple flower requires cross-pollination from two different compatible cultivars to set fruit.
- Effective pollination period (EPP) is the time window when a pollination results into a successful flower fertilization and fruit set. In WA38, preliminary data shows an EPP of 2 days for king flowers.
EPP is influenced by stigmatic receptivity, pollen tube growth and ovule longevity. - Stigmatic receptivity is the time when stigma is receptive (sticky) and support adhesion of the pollen grain and the subsequent pollen germination. The stigmatic receptivity in WA38 was 9 days.
- Pollen tube growth rate is the length of time for a pollen tube to grow and reach the ovule. In WA38, Granny Smith pollen tubes reach the ovules 7 days after pollination.
- Ovule longevity is the duration of ovule’s viability. In WA38, ovule longevity started to declined after 9 days.
- Overall, it was found that the first 2 days after the flower opens (anthesis) are critical for a successful pollination in WA38.
![cross pollination Granny Smith and WA38 graphic](https://s3.us-west-2.amazonaws.com/treefruit.wsu.edu/wp-content/uploads/2021/06/04104358/WA38-Pollination-cartoon.png)
Pollinizer
- Is a tree with pollen that is compatible with a commercially interesting apple cultivar (in this case WA38), and therefore, used as a source of pollen.
- A good pollinizer has a fast pollen tube growth rate inside WA38 flower and good fruit set.
- Effective pollinizers evaluated for WA38 are Snowdrift, Indian Summer, Granny Smith, and Everest. Snowdrift pollen tube growth was faster in 2019, but there were no difference in pollinizers in 2020.
![graphic representation of pollinizer tree](https://s3.us-west-2.amazonaws.com/treefruit.wsu.edu/wp-content/uploads/2021/06/04104615/Pollinizer-and-flower.jpg)
Fruit Development and Quality
- WA38 is a self-thinning variety, meaning it will only retain 1-2 fruits per cluster.
- Flower and fruitlet drop occurred from 3 days to 8 weeks after bloom.
Fruit quality is not affected by the pollen source (pollinizers mentioned above). - Good size and shape fruit was correlated with 9-10 seeds per apple.
- WA38 king fruit tends to be more spherical, heavier and numerous in seeds than the lateral fruit.
![fruitlet and fruit graphic](https://s3.us-west-2.amazonaws.com/treefruit.wsu.edu/wp-content/uploads/2021/06/04105049/Apple-dvlp.png.jpg)
Source
Serra, S., and Musacchi, E. (2021). Pollination, Flower Biology and Fruit Development in ‘WA38’ apples. Final Project
Report. https://treefruitresearch.org/report/pollination-flower-biology-and-fruit-development-in-wa38-apples/
Contact
Jenny L. Bolivar-Medina
ITT Tree Fruit Horticulture Extension-WSU
j.bolivarmedina@wsu.edu
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