Effects of Grafting on the Structure and Function of Coffee Rhizosphere Microbiome

Heterologous double-root grafting represents an effective strategy to mitigate challenges associated with continuous coffee cropping and reduce soil-borne diseases. However, its specific regulatory mechanism remains unclear. Therefore, a field experiment was conducted including six different grafting combinations for C. canephora cv. Robusta (Robusta) and Coffea Liberica (Liberica): Robusta scion with a homologous double root (R/RR), Liberica scion with a homologous double root (L/LL), Robusta scion with a heterologous double root (R/RL and L/RL), and Liberica scion with a heterologous double root (L/LR and R/LR); these combinations were conducted to clarify the effects of heterologous double-root grafting combinations on the root exudates and soil microbial diversity, structure, and function of Robusta and Liberica. The results demonstrated notable differences in root exudates, rhizosphere microbial structure, and function between Robusta and Liberica. Despite Liberica having lower diversity in its rhizosphere microbial communities and relatively higher levels of potential pathogenic bacteria, it showed stronger resistance to diseases. Roots of Robusta in heterologous double-root coffee seedlings significantly enhanced the secretion of resistance compounds, increased the relative abundance of potentially beneficial bacteria, and reduced the relative abundance of potential pathogenic fungi. This enhances the rhizosphere immunity of Robusta against soil-borne diseases. The results indicated that grafting onto Liberica roots can strengthen resistance mechanisms and enhance the rhizosphere immunity of Robusta, thereby mitigating challenges associated with continuous cropping.