Assessment of fruit growth response to water stress in a super-high-density olive orchard: monitoring, physiological mechanisms and potential use to schedule irrigation.

Abstract

Olive fruit growth has an important effect on the final yield, and thus, it is important to study its response to water stress, and to know how olive fruits grow under no water restriction. The present PhD. Thesis centered on the fruit growth, and the factors that influence it, such as the root system distribution, the leaf gas exchange and the water relations between fruits and leaves as well as on the utility of continuous measurements of fruit diameter variations. Therefore, in Chapter 2 we assessed the influence of the increment of drip lines (from one to two drip lines per tree row) on the belowground and aboveground vegetative and on the fruit growth, during two irrigation seasons. We also estimated leaf stomatal conductance from sap flux measurements, and simulated photosynthesis (Chapter 3). From the simulated photosynthesis, we compared its accumulated values with growth, both vegetative growth (leaf area and number of internodes in current-year stems) and fruit growth (fruit dry weight and oil content). As fruit growth is not only influenced by photosynthesis, but also by the water relations, we assessed the influence of water stress on the water relations between fruits and leaves, and its influence on fruit growth (Chapter 4). Additionally, we performed pressure-volume curves with olive fruits from well irrigated and deficit irrigated treatments. Finally, we evaluated the usefulness of fruit dendrometers, and the indexes derived from its measurements, to assess tree water status and to schedule irrigation (Chapter 5). The results presented in this PhD. Thesis improve the knowledge on the factors involved in fruit growth and present a first step towards the use of fruit dendrometers in olive trees. Additionally, these results are important for the development of future studies on the olive fruit growth physiology.