Citrus Pan-Genome to Breeding Database (CPBD): A comprehensive genome database for citrus breeding

Dear Editor, The genus Citrus comprises more than 30 species worldwide(Swingle,1943).However,citrus genetics and traditional breeding are hindered due to asexual reproduction,long generation time,and empirical utilization of the germplasm.The whole-genome information of different citrus species accelerates the genetic studies and improves the breeding efficiency by high-density markers.We had published the draft genome of the Citrus sinensis(Xu et al.,2013)and Citrus sinensis Annotation Project database(Wang et al.,2014)to provide a preliminary platform for such a purpose.However,there are only a few databases specially designed for citrus.The Citrus Genome Database()contains 25 citrus genomes as well as plentiful markers,phenotypes of citrus species,and quantitative trait loci of agronomic traits.CitGVD()mainly centers on SNPs and insertions or deletions(indels)of citrus species,while citSATdb()mostly focuses on molecular markers mined from 6 citrus spe-cies.Data of gene expression,genomic variations,and DNA methylome of citrus as well as tools for CRISPR,KEGG/GO Enrichment,and genome-wide association studies(GWASs)are necessary for a comprehensive database.Recently,we updated genome information of Citrus sinensis(two new versions)(Wang et al.,2021),sequenced 12 new genomes,and integrated published citrus genomes including clementine mandarin,pummelo,Mangshan wild mandarin,citron,lchang papeda,kumquat,Trifoliate orange,and Chinese box orange.Based on the above genomes,we constructed a comprehensive database,named the Citrus Pan-genome to Breeding Database(CPBD),which includes many large-scale datasets of fruit transcriptomes,genome variations,and DNA methylome as well as practical tools for citrus breeding.