Which of the following is NOT a system of pruning?

The correct answer is rooted in understanding the various pruning systems used in viticulture. Pruning systems are essential for managing grapevine growth and optimizing fruit production. Head, cordon, and cane are all recognized methods of pruning that dictate how the vine is shaped and how many buds are retained for future growth.

The head pruning system involves cutting the vine just above a certain point, leading to new growth from the head of the vine. Cordon pruning, on the other hand, establishes a horizontal framework for the vine, encouraging fruiting canes to develop off a persistent cordon (or branch). Cane pruning involves choosing one-year-old canes from which new growth will emerge, allowing for a more manageable vine structure.

In contrast, trunk is not a recognized system of pruning. While the trunk is a critical part of the grapevine as it supports the entire structure and transports nutrients, it does not represent a method or system used for pruning. Pruning systems all involve strategic decisions about how to cut and shape the vine to promote healthy growth and fruit production, which does not include "trunk" as a category.