Sheath blight caused by Rhizoctonia solani poses a serious threat to the production of tartary buckwheat （Fagopyrum tataricum）. Previous work by our group suggested that FtADPG2， a gene from the polygalacturonase （PG） family， might be associated with sheath blight resistance in tartary buckwheat. To gain deeper insights into the functional role of this gene in disease resistance， we cloned FtADPG2 from the cultivar Zhongku 3. The gene encodes a stable protein with a molecular weight of 41.65 kDa. Expression analysis revealed that FtADPG2 transcription was significantly induced upon R. solani infection， and this induction showed a coordinated upregulation with the expression of the pathogenesis-related protein PR1 and the accumulation of jasmonic acid. Heterologous overexpression of FtADPG2 significantly enhanced disease susceptibility in both tobacco and Arabidopsis. Haplotype analysis identified a natural variation （Ala22Val） within the first exon， defining a haplotype designated Hap2. Notably， Hap2 was associated with higher enzymatic activity and conferred a greater susceptibility phenotype. Based on transcriptomic data and AlphaFold structure prediction， we identified a candidate fungal virulence protein， RsEgD. Protein-protein interaction between FtADPG2 and RsEgD was subsequently confirmed by yeast two-hybrid and luciferase complementation imaging assays. Our results demonstrate that FtADPG2 is a key susceptibility gene in tartary buckwheat， promoting infection through a physical interaction with the pathogen effector RsEgD. This study provides crucial targets and a theoretical foundation for elucidating the molecular mechanisms of F.tataricum-R.solani interaction and for breeding buckwheat varieties with enhanced disease resistance.