Bacterial and Fungal Communities in Old Vines and Their Progeny: Insights into Microbial Inheritance Through Mass Selection.

Mass selection is increasingly promoted in viticulture to enhance resilience by restoring intra-varietal diversity, yet its effects on the structure and inheritance of plant-associated microbiomes remain poorly understood. Here, we investigated bacterial and fungal communities associated with old grapevine mother plants and their progeny across four Bordeaux estates practicing mass selection, using a fully in situ experimental design. Root and leaf microbiomes were characterized by metabarcoding and analyzed using multivariate ordination, hierarchical clustering, and assembly-process metrics (βNTI and NST). Microbial community composition and structure were primarily shaped by plant compartment and vineyard origin, whereas generation effects were significant but weak. Microbial resemblance between mother vines and their offspring was limited and highly context-dependent, occurring mainly under comparable environmental conditions. Assembly-process analyses revealed heterogeneous deterministic signals, particularly in root-associated bacterial communities, but did not consistently result in phylogenetic similarity between generations. Although inheritance signals were generally weak, their recurrence across multiple vineyards and contrasted field conditions highlights their ecological relevance. By integrating environmental variability, this in situ approach mitigates the adaptive bias in plant-microbiome interactions and shows that mass selection does not rely on systematic microbial transmission but rather operates within a nuanced framework of environmentally mediated interactions.