Olive-tree physiological response to biotic and abiotic stress fruit yield, oil quality and tolerance to Anthracnose

Doctoral thesis abstract

Abstract

The olive tree is highly tolerant to water deficit and in humid climate regions, such as Uruguay, the need to irrigation is questioned. However, Uruguay's climate is characterized by high interannual variability, resulting in periods of water deficit. In the event of a water deficit, plants trigger a series of defense mechanisms to maintain cellular homeostasis, including increased antioxidant enzyme activity and cuticle thickening to prevent transpiration. These responses are common during abiotic stress and biotic stress caused by pathogen infections. Anthracnose, caused by the Colletotrichum complex, is a major disease in olive trees, leading to reduced fruit yield and oil quality. Mild drought stress has been found to activate the basal defense response, enhancing plant tolerance to pathogen infections. Therefore, the hypothesis was that exposing olive plants to moderate water deficit during the lipogenesis stage would trigger the basal defense response, increasing fruit tolerance to biotic stress caused by Colletotrichum acutatum. The study also examined whether this response was sustained under moderate water deficit. Results showed that water deficit induced anatomical and biochemical changes in olive fruits, promoting anthracnose tolerance with reduced incidence and severity of C. acutatum infection both in vitro and in vivo. Fruit weight and pulp/pit ratio decreased in response to water deficit, while cuticle thickness and fruit polyphenol content increased. An induction of enzymes related to hydrogen peroxide scavenging were observed, in particular PER and CAT. This enzymatic activity was induced by the pathogen inoculation treatment and was higher in the non-irrigated treatment. Severe water deficit resulted in significant reductions in fruit weight and oil content, but the fruits exhibited enhanced tolerance to anthracnose infection.