Acrotony in Grapevines: Understanding Its Causes and Effects

The world of viticulture is as fascinating as it is complex, encompassing a myriad of processes that are crucial for the cultivation of high-quality grapes. One such process, often overlooked yet vitally important, is acrotony or apical dominance in grapevines. This phenomenon, which involves the preferential growth and development of buds located at the apex of a vine shoot over those in the middle and lower sections, plays a significant role in the life cycle and productivity of a vineyard. In this article, we delve deep into the concept of acrotony, exploring its implications, causes, and the factors influencing it.

The Essence of Buds in Grapevines

Buds are critical organs in a grapevine, pivotal in fruit production and overall plant health. They are formed at the junction of the leaf and the shoot, taking on a bulging conical shape and located at a node on the shoot. Each bud is a complex structure comprising a primary bud at the center and two secondary buds on either side. These secondary buds can either remain dormant, springing to life in case of damage to the primary bud, or they can grow simultaneously with the primary bud, forming "double shoots" that may require removal due to their competitive nature.

Another type of bud, known as the 'prompt' bud, is smaller and grows in the same year it forms, leading to a shoot termed a "feminela."

Vine Anatomy 101

Understanding acrotony in grapevines also requires a basic grasp of vine anatomy:

• Roots: These structures anchor the vine and absorb essential nutrients and water. They also store carbohydrates to help the vine survive winter.
• Shoots: New growths produced each year, featuring nodes where leaves, flowers, or tendrils will develop.
• Leaves: The powerhouses of the vine, responsible for photosynthesis.
• Tendrils: These aid the vine in support, as it cannot hold itself upright.
• Flowers and Berries: The reproductive organs, with each pollinated flower turning into a berry, eventually forming grape clusters.

The Problematic Nature of Acrotony

Acrotony can be problematic for vineyard management, potentially leading to uneven grape maturation and complicating vineyard operations, thus increasing cultivation costs. This phenomenon is largely attributed to the inhibitory effect of the apical bud on adjacent buds, weakening as it moves down the shoot.

When vines are unpruned, growth tends to concentrate at the shoot tips, far from the trunk and arms. This can lead to overly large and leafy plants. Excessively long pruning elements can inhibit the growth of lower and middle buds, reducing overall yield.

The Causes Behind Acrotony

Acrotony in grapevines is primarily a physiological process influenced by two main factors:

• Vascular Connection and Sap Pressure: The early-budding apical buds have a more robust connection to the vine's vascular system, coupled with higher sap pressure towards the shoot's tip. This results in weaker growth of mid and lower buds.
• Pruning Practices and Climatic Conditions: These factors, along with the production of growth hormones (auxins), lead to the correlated inhibition of lower buds.

Factors Influencing Acrotony

• Pruning Position: The angle and shape of pruned elements can affect bud growth, with certain positions leading to more homogeneous budding.
• Vine Vigor: Weaker vines tend to exhibit more pronounced acrotony, a reflection of the plant's self-regulatory mechanisms under adverse conditions.
• Varietal Differences: Some grape varieties exhibit more acrotony than others. For instance, Cabernet Sauvignon tends to have stronger acrotony, while Malbec is more uniform in its budding.
• Winter Severity: Mild winters can encourage acrotony.

In conclusion, acrotony in grapevines is a critical aspect of viticulture, impacting grape growth, vineyard management, and ultimately, the quality of wine produced. Understanding and managing acrotony effectively is key for vintners aiming to achieve optimal vine health and grape yield.