Metabolomics of plant-pathogen interaction in walnuts: a multi-aspect approach to the effect of Walnut bacterial blight and Walnut husk fly on fruits and oil.

Diseases and pests have always been one of the main concerns of growers as they can greatly affect fruit yield and quality. Deep comprehension of the plant-pathogen mechanisms is of the utmost importance as it helps to understand the extent of the damage on the fruit quality and development, as well as constitutes the base on which new control methods can be developed. This postdoctoral project focuses on the plant-pathogen interaction of Walnut bacterial blight (WBB) and Walnut husk fly (WHF), the two main problems that cause severe damage in walnut production. Their symptoms are similar, comprising necrotic black spots on the fruit husk. In late infections, the effect remains limited to the husk, while in early infections the whole fruit is affected. In the first part of this project, we aim to address different aspects of the plant-pathogen interaction. First, to analyze the pathogen’s performance during the season from the point of view of the host susceptibility and in correlation with environmental conditions and plant metabolites. Second, we address the coordination of the plant defense system between the affected spot and the s tissue, as well as between different parts of the fruit, focusing particularly on the kernel. In the second part of the project, the aim is to find value in affected kernels, which are now discarded as waste, by describing how the use of kernels with mild pathogen damage effect walnut oil quality and storage through the analysis of primary and secondary metabolites, as well as their antioxidant and oxidation capacity. The description of this interaction and the consequent impact on fruit and product quality will be addressed through comparative metabolomics, which comprises sugars, organic acids, phenolic compounds, vitamins, carotenoids, ethylene, volatile organic compounds, and fatty acids. It also includes the analysis of the activity of key enzymes of different metabolic and antioxidant pathways (PAL, POX, PPO, GS).