Abstract
We propose Pseudomonas coronafaciens sp. nov. as a new species in genus Pseudomonas, which is diverse from P. syringae. We also classified strains from onions which are responsible for yellow bud (YB) disease as P. coronafaciens. Sequencing of 16S rRNA gene and multi-locus sequence analysis (MLSA) of housekeeping genes (gyrB, rpoD, gltA and gap1 genes) for the P. syringae pv. coronafaciens strains along with other strains of P. syringae pathovars resulted in a distinct cluster separate from other P. syringae pathovars. Based on DNA-DNA relatedness, pathotype strain of P. syringae pv. coronafaciens (CFBP 2216PT) exhibited ≤35.5% similarity with the pathotype strains of P. syringae pv. syringae (CFBP 1392PT, 4702T) but exhibited ≥90.6% with the YB strains (YB 12–1, YB 12–4, YB 09–1). Also, the YB strains (YB 12–1, YB 12–4, YB 09–1) were able to infect only onion but not oat, rye and Italian ryegrass (common hosts for P. syrinage pv. coronafaciens). Contrastingly, P. syringae pv. coronafaciens strains (NCPPB 600PT, ATCC 19608, Pcf 83–300) produced typical halo blight symptoms on oat, rye and Italian rye grass but did not produce any symptoms on onion. These results provide evidence that P. syringae pv. coronafaciens should be elevated to a species level and the new YB strains may potentially be a novel pathovar of hereto proposed P. coronafaciens species.
Highlights
The taxonomy of Pseudomonas syringae sensu lato and its pathovars has evolved and been a matter of debate for last 34 years [1]
We propose the elevation of P. syringae pv. coronafaciens to a species level as P. coronafaciens, which was confirmed by various molecular and biochemical methods including sequencing of the 16S rRNA gene, and multi-locus sequence analysis (MLSA) based on sequences of housekeeping genes gyrB, rpoD, gltA, and gap1, substrate utilization tests (BIOLOG), polymerase chain reaction (PCR) analysis using plasmid, coronafactate ligase and HrpZ effectors genes-specific primers, and DNA-DNA-hybridization
Based on 16S rRNA gene sequences, strains of P. syringae pv. coronafaciens [NCPPB 600 PT, ATCC 19608, 93–2, 83–300] and yellow bud (YB) from onion (09–1, 12–1, 12–4, and 12–5), and the pathotype strains of P. syringae pv. porri (NCPPB 3364 PT), P.syringae pv. oryzae (NCPPB 3683PT), and P.syringae pv. garcea (NCPPB 588PT) formed a clade that was distinct from other P. syringae pathovars (Fig 1)
Summary
The taxonomy of Pseudomonas syringae sensu lato and its pathovars has evolved and been a matter of debate for last 34 years [1]. A revised taxonomic classification placing 41 nomenspecies of P. syringae as pathovars, was proposed in the 1st edition of Bergey’s Manual of Systematic Bacteriology [4]. Overlap in host-range among different P. syringae pathovars often occur. Genomospecies 4 ( called phylogroup 4) included pathovars of graminaceous species [P. syringae pv. Gardan et al (1999) [8] refrained from making a formal proposal to elevate P. coronafaciens to species level and it remained as a pathovar of P. syringae Striafaciens; they later concluded that these bacterial species/pathovars are synonymous These strains did not differ in their physiological, immunological and substrate utilization tests. We characterized strains from onion which are responsible for yellow bud (YB) disease [10] and concluded that they may potentially be a novel pathovar of hereto proposed P. coronafaciens species
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