Complete genome sequence of citrus tristeza virus isolate PB61, a commercially deployed mild strain for cross-protection in grapefruit

Abstract Citrus tristeza virus (CTV; species Closterovirus tristezae ) is ubiquitous in Australia, occurring in all production areas. Stem-pitting disease in white grapefruit varieties caused by CTV is managed by mild strain cross-protection. However, the protective isolate of CTV used for cross-protection, labelled PB61, is not fully characterised at the molecular level, even though most grapefruit budwood is inoculated with this virus isolate before release. In this study, we employed high throughput sequencing to assemble the 19,254 nucleotide-long genome of virus isolate PB61. Phylogenetic analysis revealed that PB61 belongs to the resistance-breaking (RB) genotype group first identified in New Zealand. PB61 is the first CTV isolate of any genotype from Australia to be sequenced in entirety, and the generation of this data provides a foundation for better understanding the mechanism of cross-protection in grapefruit.