Abstract: In this work，a pan-genome from 34 genomes of Candidatus Liberibacter asiaticus（CLas）was constructed and the extensive analyses of evolution and copy number variations were completed. The CLas pan-genome was composed of 36 593 genes and 1 188 gene clusters，including 872 core gene clusters，271 accessory gene clusters，and 45 strain-specific gene clusters. An examination for selection pressures of all gene clusters showed that 159 of them underwent adaptive evolution. Two genes associated with pathogenicity or treatment resistance in CLas were mined in combination with GO annotation data. An in-depth analysis of copy number variations in eight genes revealed that five genes were connected to pathogenicity or resistance of CLas. This result revealed that CLas develops resistance to antiseptics by increasing the copy number of relevant genes.

Key words: citrus, Huanglongbing, pan-genome, adaptive evolution, copy number variation