MONDAY IN THE VINEYARD SERIES
Understanding the Critical Phases of Flowering, Pollination, and Fruit Set and the Factors Influencing them.
You might find this article useful if you are a curious wine enthusiast or if you are currently preparing for your WSET Diploma D1 or WSET 3 examination. In that case, don't forget to check out our FLASHCARDS as well.
When do Flowering, Pollination, and Fruit Set happen?
Northern Hemisphere: Between May and June
Southern Hemisphere: Between November and December
Defining Flowering, Pollination, and Fruit Set
FLOWERING: indicates the opening of individual grapevine flowers, revealing the pollen-laden stamens with anthers and filaments.
POLLINATION: Pollination occurs when pollen grains from the stamens are released and land on the moistened stigma surface. Each pollen grain germinates, producing a pollen tube that penetrates the stigma and then the ovule within the ovary, which contains the female reproductive cells. The pollen tube delivers sperm cells that fertilize the eggs in the ovule, leading to the development of a grape berry. Research indicates that cultivated vine varieties are typically self-pollinating, meaning that the pollen from one flower's stamens is transferred to the stigma of the same flower or a different flower on the same plant. Insects and wind play a minor role in the pollination of grapevines.
FRUITSET: is the term used to indicate transformation from flower to grape. The fertilized ovules form seeds, with up to four per grape, while the ovary wall enlarges to create the grape's skin and pulp.
Ideal Conditions for Flowering, Pollination, and Fruit Set
Flowering is highly dependent on temperatures. In ideal conditions, minimum temperature of 17°C (63°F), flowering usually happens around eight weeks after budburst. During such temperatures, individual inflorescences can rapidly begin and complete their flowering process within a few days. On the contrary, low temperatures have the opposite effect, prolonging the flowering period, sometimes spanning several weeks from start to end. Unfortunately, this extended duration negatively impacts the evenness of grape ripening, leading to potential issues with the crop's overall quality and consistency.
Pollen germination requires warm temperatures, with the optimal range being 26–32°C / 79–90°F. The percentage of flowers that become grapes can vary significantly, typically ranging from zero to 60%, with around 30% being the average. In hot, dry, and windy conditions, water stress in the vine can negatively impact pollen tube growth, leading to irregular fruit set and reduced yields. Conversely, cold, rainy, and/or windy weather also hampers pollen tube growth, becoming a key cause of poor yields in cooler climates.
Two common forms of irregular fruit set exist, Coulure and Millerandage. Read the respective articles if you want to know more about them.
I hope you found this article both useful and insightful. If you enjoyed it, make sure to stay tuned for my next article. Join me next Monday for more fascinating insights!
Have a happy week and happy studying,
Nicky
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