Characterisation of the Pseudomonas savastanoi pv. phaseolicola population found in Eastern Australia associated with halo blight disease in Vigna radiata

Abstract

This study analysed the phenotypic and genotypic variation among 511 Pseudomonas savastanoi pv. phaseolicola (Psp) isolates, causing halo blight in mungbeans. Collected from symptomatic mungbean (Vigna radiata) crops throughout Australia between 2005 and 2018, a total of 352 Psp isolates were phenotypically screened. Our in planta screening against a set of four mungbean cultivars with known susceptible and resistant reactions revealed five distinctive pathotypes. Isolates belonging to pathotype 2 were the most prevalent at 84% and were found to be highly pathogenic towards all tested mungbean genotypes. Genomic variation was investigated for 205 isolates using DNA fingerprints, splitting the halo blight pathogen population into two broad genetic lineages. Further genetic testing for two known avirulence genes, avrPphE and avrPphF, identified the avrPphE gene in all the tested isolates and avrPphF present in all but two. To identify candidate avirulence genes unique to Psp isolates infecting mungbean in Australia, a comparative genomics study was undertaken on the whole-genome sequences of two epidemiologically important Psp isolates, T11544 and K4287. The information presented in this study has the potential to dramatically improve mungbean disease resistance now and into the future.