11-09-2006
Here's some more information about bud fruitfulness in grapes.
The central link to the development of bud tissue is truly regulated by plant hormone IAA and cytokinins and these ratios can change annually from the events of root development (where the cytokinins first come up from) as well as sunlight (remember auxins move downward and are greater on the shady side of the plant) and properly or improper amounts of nutrients which regulate the increase, decrease or prolonged nature of these hormones.
In the first of differentiation, where the ratio of cytokinins coming up from the roots are greater then IAA coming down from the apical tissue and leaves, this is where you get your fruit bud formations in the shoots. When GA comes up from the roots you and meets up with IAA you get elongation between these buds.
So without exogenous applications of growth regulators....the environment, cultural/chemical practices and the fruit load (seeded or non-seeded varieties) are largely responsible for the development of those hormones that give you good or poor bud formation.
Think about this....Grape Fan Leaf Virus prevents the downward movement of IAA.....from the shoot tips....this causes short internodes, leaves that look deficient in zinc (zinc plus tryptophan makes IAA in the canopy of the plant)....and bascially the leaves and shoots look like 2,4-D injury with that parachute looking leaf. This is because IAA is not moving down to meet the cytokinins coming up. Same with GA.
20 years of working with plant hormones and growth regulators.....I can say....its still an area most of us don't truly understand well, but with the use of micronutrients, ag chemicals and/or correct pruning practices we can do a good job of creating better bud tissue in our annual practices.
Best Regards,
Lance Beem
Beem Consulting