A highly contiguous genome sequence of Alternaria porri isolate Apn-Nashik causing purple blotch disease in onion

Purple blotch, caused by the necrotrophic pathogen Alternaria porri, is one of the most economically significant diseases of onion and allied crops. While the virulent nature of many Alternaria spp. has been identified, the pathogenic repertoire of A. porri is still unknown. The objective of this work was to sequence the genome of A. porri using the PacBio SMRT sequencing strategy and analyse the repertoire of CAZymes, secondary metabolites, secretome and effectors in A. porri. Our research group is working to identify onion germplasm with purple blotch resistance and to understand the genetics of the pathogen. The reported de-novo assembly will contribute to the analysis of potential variants and the gene repertoire contributing to the virulence and pathogenicity of the purple blotch pathogen.

Long-read sequencing on a PacBio Sequel II system resulted in a 32.98 Mb (20 contigs) assembly with an N50 of 2, 657, 264 bp, the longest contig length of 5.05 Mb, and a GC content of 51.06%. The Benchmarking Universal Single-Copy Orthologs (BUSCO) analysis resulted in 99.7% genome completeness at the Dothideomycetes lineage, representing a high-quality genome assembly. AUGUSTUS ab initio analysis resulted in 9875 protein-coding genes. Of the 6776 pathogenicity-related genes, 537 genes with effector functions were identified. Likewise, the glycoside hydrolases (434) were the most dominant group of the total 837 predicted CAZymes. The assembled genome of A. porri showed distinctive similarities to the genomes of A. alternata and A. brassicicola, the causal agents of leaf blight of onion and leaf spot of Brassica crops, respectively.