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.