From Root to Fruit: A Root-Fruit Quality Axis Linking Rhizosphere Microbiomes with Fruit Quality

Abstract

Whether rhizosphere microbiomes can influence fruit quality remains an emerging question in plant-microbiome research. Current mechanistic evidence is concentrated in tomato and related Solanaceae. Two independent intervention studies provide the clearest causal evidence that root-associated microbial treatments can alter selected fruit traits, including vitamin and carotenoid accumulation. A further study from the same research group supports microbiome-mediated community effects in tomato, whereas recent citrus studies are primarily correlational and hypothesis-generating. Together, these findings motivate a Root-Fruit Quality Axis (RFA), defined here as a working framework linking rhizosphere microbiome activity with systemic plant responses and fruit metabolic regulation. We distinguish two non-exclusive routes. In the Relay Track, microbial cues or microbiome-induced host responses may be integrated into root-to-fruit communication through vascular and source-sink networks. In the proposed Direct Delivery Track, root-associated endophytes may migrate towards distal tissues and produce microbial effectors locally; this route has not yet been demonstrated for quality-promoting strains. We discuss how these processes may influence selected fruit traits, including vitamins, carotenoids, sugar-acid balance and flavour-related metabolism, while emphasising environmental dependence and possible trade-offs. Finally, we outline design criteria and field barriers for quality-oriented synthetic communities (Quality-SynComs).