Pantoea dispersa causing bulb decay of onion in Taiwan

Abstract

Onion (Allium cepa L.) bulbs showing symptoms similar to those caused by slippery skin disease were sampled during a market survey in Chiayi city, Taiwan during 2017–2018. Interestingly, a bacterium which phenotypically differed from Burkholderia was isolated along with the slippery skin pathogen from the rotted scales. The purified isolates were initially identified as Pantoea dispersa by the phenotypic and biochemical characterization. Further molecular identification based on the 16S rDNA sequence analysis and multilocus sequence analysis with the atpD, gyrB, and infB sequences confirmed that the isolates are P. dispersa. For pathogenicity assay, surface-sterilized onion bulbs were injected with the isolates, and P. dispersa type strain LMG 2603T was included as a reference strain. Upon artificial inoculation of onion bulbs, all P. dispersa isolates and the strain LMG 2603T induced decays of the internal fleshy scales and yellow to tan discoloration similar to those caused by onion pathogenic Pantoea spp. The same bacterium was consistently re-isolated from the artificially inoculated onion bulbs, fulfilling Koch’s postulates. Moreover, a single injection of a P. dispersa suspension at a concentration of 1 × 104 CFU/mL was sufficient to cause disease. Accordingly, this study indicates, for the first time, that P. dispersa is an onion pathogen causing bulb decay in Taiwan.