Canopy growth and development processes in apples and grapevines: Responses to temperature

An understanding of the physiology of canopies in temperate horticultural trees and vines is important to determining the relationships between productivity, performance, and climate. This is especially so with regard to the production of fruit because of the strong demand for metabolites that are required to maximize production. Another important feature that strongly influences production is the two-season nature of the reproductive system, where floral induction occurs and reproductive primordia are laid down in buds in one season to varying degrees of development before overwintering, and the subsequent morphogenetic development that occurs in the following spring. Therefore, the climate in both seasons can impact on reproductive systems. In addition, as the majority of temperate perennial fruit crops are deciduous, they require extensive carbohydrate reserves to be mobilized in spring to support tree and vine growth. This chapter describes the various processes from prior to budbreak through to the harvest of the fruit, and specifically compares apple trees with grapevines. Although phenology is generally similar between trees and vines, the development of flowers in the dormant buds is dramatically different, with flowers almost fully formed in the apple trees at budbreak, but where flowering is delayed by up to 40 days after budbreak in grapevines. Thus, leaf area development of vines and the size of the leaves are important attributes to ensure that a rapid acquisition of carbon occurs to meet the demands of reproductive sinks. However, apple fruit are a much bigger size, and thus the development of these fruit is also highly dependent on the acquisition of carbon; fruit size is also intrinsically more sensitive to crop load than is apparent with grapevines. As part of this chapter, the responses of the various processes to temperature are evaluated so as to provide the background to assess likely impacts of climate change-induced temperature increases on the various processes, but particularly on phenology. The consensus for both apple trees and grapevines is that budbreak has become earlier, and in some cases the harvest date has also been advanced with increased global temperatures. It is possible, that some cultivars may not be as productive in a changed climate in certain regions. An understanding of canopy physiology will be critical to making such decisions.