Root-root communication within Solanaceae and its effects on root exudate composition

The ability of plants to distinguish between self and non-self roots significantly influences competitive dynamics and resource allocation. However, the mechanisms underlying these discriminatory responses remain largely elusive. This study investigated the responses of cherry tomato (Solanum lycopersicum L.) and bell pepper (Capsicum annuum L.) grown as self by using a polypropylene separator for the roots (C, B) and in non-self-pairings, without a separator (CC, BB and CB) in a semi-commercial greenhouse experiment. Root respiration increased in non-self-pairings and awas highest in low degrees of relatedness pairings (L-DOR). Cherry tomato exhibited enhanced morphology, physiology, fruit quality, and quantity, and root thickening when paired with bell pepper, whereas bell pepper showed reductions in these parameters. Root exudate carbon and nitrogen concentrations were highest in non-self-combinations and highest in CB pairings. Distinct metabolic profiles were observed in root exudates and root tissues depending on the existence and identity of the neighbor. Upregulation of TCA cycle intermediates, specifically citric acid, was associated with enhanced root respiration in L-DOR pairing, suggesting a metabolic cost associated with neighbor recognition. Auxin analogue indole-3-lactic acid was significantly upregulated in cherry tomato when paired with bell pepper, coinciding with improved morphological traits, while being downregulated in bell pepper under the same conditions. Amino acid profiles further differed between species in L-DOR pairings, reflecting species-specific metabolic regulation. These findings suggest that exudate composition may serve as a specific communication language between individuals that can change in response to the existence and identity of a neighbor.