The key role of the biotic component in kiwifruit vine decline syndrome (KVDS) in Italy, an emerging multifactorial syndrome

Kiwifruit vine decline syndrome (KVDS) is considered a multifactorial syndrome where abiotic and biotic stressors are involved. In this study, the microbial communities of kiwifruit soil, rhizosphere and root were characterized together with their associations with abiotic stressors. Several soilborne oomycetes belonging to the genus Phytopythium were previously associated to the syndrome onset. Association networks unveiled the correlation of Phytopythium spp. with the diseased status of orchard soils, whereas in the rhizosphere the oomycete ASVs were negatively associated with growth promoting fungal genera and AM fungi found in kiwifruit. Network analyses conducted for the rhizosphere communities mainly showed that associations were established between different P. vexans ASVs, thus revealing strain specific characteristics which require further investigation. The dynamic emerging from the analysis of the ecological processes driving rhizosphere community assembly, highlights the possibility of a dysbiosis phenomenon in the rhizosphere, driven by deterministic processes in the oomycete community. Differently, fungal and bacterial microbiotas showed mainly stochastic processes. The study highlights the importance of considering multifactorial aspects and their interactions in emerging pathosystems, where climate change plays a role in syndrome onset. The combination of different omics techniques is needed for a wider comprehension of oomycete pathogenesis in complex systems.