Objective To clarify the differences in epiphytic bacterial communities on the fruit surfaces of walnut varieties with different resistances to anthracnose, and to provide a basis for the prevention and control of this disease using beneficial microorganisms.

Method The pathogen was isolated and identified through tissue isolation, morphology, multi-gene phylogenetic analysis, and pathogenicity determination to verify the validity of the collected samples. The 16s amplicon sequencing technology was used to analyze and compare the composition and differences of epiphytic bacterial communities on the fruit surfaces of walnut varieties with different resistances to anthracnose, including "Xiangling" (susceptible variety), "Lukang No.1" (resistant variety), "Qiuxiang" (resistant variety), as well as on diseased and healthy fruits.

Result Colletotrichum gloeosporioides was identified as the pathogen infecting diseased fruits of all three varieties, while no pathogen was isolated from healthy fruits. Pathogen invasion significantly affected the Chao1 index of epiphytic bacterial communities on the fruit surfaces of both susceptible and resistant varieties. Compared with susceptible varieties, the invasion of the pathogen had no significant impact on the Shannon and Pielou’s evenness indices of bacterial communities on the fruit surfaces of resistant varieties. The dominant genera on healthy fruits of susceptible and resistant varieties were Methyloversatilis spp. and Ralstonia spp. respectively. On diseased fruits of susceptible varieties, Methyloversatilis spp. and Ralstonia spp., remained dominant, whereas diseased fruits of resistant varieties were predominantly colonized by Pantoea spp. The unique genus enriched on the surface of diseased fruits of the resistant variety "Lukang No. 1" was Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium, and the unique genus enriched on the surface of diseased fruits of "Qiuxiang" was Ochrobactrum spp. The results of MetagenomeSeq analysis showed that after the pathogen infected different walnut varieties with anthracnose, the number of high-abundance ASVs enriched on the fruit surfaces varied, in the order of "Lukang No. 1", "Qiuxiang", and "Xiangling". The enriched ASVs mainly belonged to Erwiniaceae and Rhizobiaceae.

Conclusion The epiphytic bacterial communities on fruit surfaces differ between walnut varieties susceptible and resistant to anthracnose. Moreover, resistant varieties recruit distinct microbial taxa on diseased fruits, which may contribute to their resistance mechanism.