Pectobacterium carotovorum subsp. actinidiae associated with canker on pear trees in Brazil

Abstract

In summer of 2016, cankers were observed on 8-year-old pear trees (Pyrus communis L.) cv. Yali grafted on the Caleriana rootstock, in a commercial orchard in Monte Castelo, SC. Eight hundred out of 1200 trees died and the rest of the orchard was eradicated. Affected plants showed cankers on trunks and twigs with exudation; the branches turned brown and slowly died. Bacterial colonies were isolated on King’s B medium from infected tissues. Pathogenicity, biochemical tests were conducted and some isolates selected for whole genome sequencing using Ion Personal Genome Machine™ (PGM™) System (ThermoFisher Scientific). PCR with Y1/Y2 and PcaF/PcaR primers, specific for Pectobacterium carotovorum and Pectobacterium carotovorum subsp. actinidiae, respectively, were also carried out. The section of inoculated apple and pear branches showed longitudinal darkening, with wilt and leaf blight. Shoots of kiwifruit Actinidia deliciosa cv. Hayward inoculated with the bacterium showed no symptoms. The bacterium was re-isolated from all symptomatic tissues, satisfying Koch’s postulates. Selected isolates were gram-negative, facultative anaerobic, rod-shaped and exhibited a strong pectolytic activity in potato and carrot disks, and showed similar biochemical profile using a BIOLOG GEN III MicroPlate. The pathogen of the symptoms observed on pear trees in Brazil show highest genome (87.1%; DDH analysis) and proteome identity (99.8%; Patric analysis) with P. carotovorum subsp. actinidiae. A product of the expected size was obtained in both specific PCR (Y1/Y2 (434 bp) and PcaF/PcaR (343 bp) primer pairs). Results from the present study clearly show that P. carotovorum subsp. actinidiae was associated with canker on pear trees in Santa Catarina, Brazil.