Evaluation of NGS DNA barcoding for biosecurity diagnostic applications: Case study from banana freckle incursion in Australia

Molecular diagnostics in combination with morphological identification is the method of choice for several cryptic microbial plant pathogens. For some diagnostic applications, traditional sequencing techniques can be time consuming, making them ill-suited for biosecurity incursion responses, where accurate results are needed in real time. More rapid next generation sequencing tools must be tested and compared with traditional methods to assess their utility in biosecurity applications. Here utilizing 95 samples infected with fungal pathogen Phyllosticta cavendishii, from a recent incursion in Australia, we compare species identification success using Internal Transcribed Spacer (ITS) gene barcode on conventional Sanger and Oxford Nanopore MinION sequencing platforms. For Sanger sequencing, the average pairwise identity percentage score between generated consensus sequences and P. cavendishii sequence from holotype material on NCBI database was 99.9% ± SE 0.0 whereas for MinION sequencing the average pairwise identity percentage was 99.1% ± SE 0.1. Relatively larger consensus sequences (mean 486 bp ± SE 2.4) were generated by Sanger sequencing compared to MinION sequencing (mean 435 bp ± SE 4.6). Our results confirm that both sequencing methods can reliably identify P. cavendishii. MinION sequencing, provided quicker results compared to Sanger sequencing and demonstrated diagnostic competence, with the added advantage of being portable, for front-line “point of incursion” biosecurity applications.