The role of the oomycete Phytopythium vexans as a biotic stress component of Kiwifruit Vine Decline Syndrome in Italy.

Several soilborne oomycetes belonging to the genus Phytopythium have been associated to kiwifruit vine decline syndrome (KVDS) which is defined as a multifactorial syndrome where both abiotic and biotic stressors are involved. Phytopythium vexans is one of the main species isolated in affected orchards also revealing several interactions with other taxonomic groups composing the microbiome associated to the syndrome. Microbiome network analysis between taxa revealed strain-specific interactions, requiring further studies on the genomics of involved oomycetes. Furthermore, plant response to the presence Phytopythium vexans in Actinidia deliciosa roots, characterized through gene expression analysis approach, revealed an upregulation of ROS scavenging pathways and hormonal stress signaling in response to the pathogen presence and flooding at specific time points. Further transcriptomic studies on Actinidia roots will reveal a major understanding of all the involved pathways in oomycete pathogenesis on fruit trees. The model of KVDS as a multifactorial syndrome, where climate change plays an important role in defining the onset of the syndrome, requires the application and combination of different omics techniques for reaching a wider comprehension of oomycete pathogenesis in complex systems.