Influence of scion cultivar on the rhizosphere microbiome and root exudates of Phaseolus vulgaris in grafting system

Purpose: Grafting is a commonly used technique in horticulture and agriculture. The rhizosphere microbiome is critical for plant growth and performance, however, knowledge of the effect of grafting on rhizosphere microbial assemblages is still limited. Here, we use grafting systems of common beans (Phaseolus vulgaris) to study the effects of scion cultivar and grafting on rhizomicrobiome and root exudates. Methods: Grafting systems were constructed by using two cultivars of common bean. The rhizomicrobiome of intercultivar grafts (wherein different cultivars used as the scion and the rootstock) and intracultivar grafts (wherein same cultivar used as the scion and the rootstock) were analyzed by high-throughput sequencing of the bacterial 16S rRNA gene and fungal internal transcribed spacer region. Root exudates of intercultivar and intracultivar grafts were analyzed by ultra-high performance liquid chromatography-mass spectrometry analyses. Results: The rhizomicrobiome and root exudate profiles of common bean were significantly different between two cultivars. Scion cultivar significantly influenced the composition of rhizomicrobiome and root exudate profiles. Intercultivar grafts narrowed the differences of rhizomicrobiome between two cultivars. Pseudomonas and Talaromyces were highly accumulated in intercultivar grafts relative to those in intracultivar grafts. m-Coumaric acid, methyl jasmonate, and sebacic acid were increased in intercultivar grafts compared with intracultivar grafts, and showed positive relationships with Pseudomonas and Talaromyces. Conclusion: Scion cultivars modulated the assembly of rhizomicrobiome and the root exudation. Intercultivar grafting narrowed the differences between the rhizomicrobiomes of different cultivars, with a profound increase of Pseudomonas and Talaromyces, and root exudates, m-coumaric acid, methyl jasmonate, and sebacic acid.