Grapevine Inflorescence Formation---Parts 1 and 2

Trying to talk about the formation of inflorescence is a little like the question, "Which came first, the shoot or the bud?" This topic is fraught with the unknown and the unknowable. A little illustration can help clarify this question and breaking up the cycle into 4 parts can also be helpful in the discussion.¹

In this blog, I'm going to limit myself to what is going on in (1) and (2) of the cycle. If we begin at the top of this illustration (1) in spring of this year, bud break results in the growth of the shoot. Something that I learned recently when I read Markus Keller's book² is that this shoot growth can be divided into two phases. The first is the fixed growth which results in the formation of the first 6 to 10 nodes and the second phase is the free growth which is the subsequent growth of the shoot. (This will become important later.)
As the shoot is growing, the dormant or winter bud is being formed directly above the leaf petiole and the shoot. The prompt or lateral bud can also grow in the leaf axil and result in the growth of the summer lateral shoot.³

(2) The dormant bud is formed in the spring from their own shoot apical meristem. In the following illustration, the shoot apical meristem is labeled A.²

The apical meristem of the primary bud generates two types of lateral meristems (labeled L in the illustration above): (1) is responsible for leaf production and (2) the other is responsible for inflorescence and tendril production.
Got all that? So, a lot is happening right now at the nodes of the growing shoots. More information to come in future blogs.
Reference:
1. For the illustration the grape inflorescence growth cycle was taken from:
Wine Science - Third Edition, Ronald Jackson
The grape bud was taken from:
YouTube: The Grapevine Bud
The was taken from:
Jennifer Hashim-Maguire, Managing the vegetative canopy and its effects on bud fruitfulness and fruit quality.
2. Markus Keller, The Science of Grapevines Anatomy and Physiology, 2010, Academic Press.
3. Charlotte Pratt, Vegetative anatomy in cultivated grapes, A review, American Journal of Enology and Viticulture, 1974, 25:131-150.
4. Devin Carroll, What Causes a Bud to Produce a Bunch or Not, Practical Winery and Vineyard, November/December 2009.
5. Markus Keller, Chapter 1
6. Larry Williams, Bud Development and Fruitfulness of Grapevines.