Understanding How a Harmful Bacterium Affects Sweet Cherry Trees

Greg Howard
5th September, 2024

Understanding How a Harmful Bacterium Affects Sweet Cherry Trees

Image Source: Natural Science News, 2024

Key Findings

  • The study from the University of California, Davis, analyzed 86 fluorescent pseudomonads from sweet cherry tissues in California
  • Researchers identified five genomospecies of Pseudomonas syringae, including a newly discovered genomospecies A
  • Pathogenicity tests showed that P. syringae pv. syringae caused multiple symptoms, while genomospecies A was less virulent
  • The study found high copper resistance in P. syringae pv. syringae but no resistance to kasugamycin, suggesting it as an effective treatment
Understanding the diversity of pathogens affecting crops is crucial for developing effective management strategies. A recent study from the University of California, Davis, delved into the diversity of Pseudomonas syringae sensu lato affecting sweet cherry in California[1]. This study sequenced and analyzed the genomic architecture of 86 fluorescent pseudomonads from symptomatic and asymptomatic cherry tissues, providing new insights into the pathogens responsible for diseases in sweet cherry. The researchers classified 58 isolates within the P. syringae species complex into five genomospecies: P. syringae pv. syringae, P. syringae, Pseudomonas cerasi, Pseudomonas viridiflava, and a newly identified genomospecies A. By annotating components of the type III secretion system and phytotoxin-encoding genes, they correlated these genomic features with pathogenicity phenotypes. This analysis revealed that intact probable regulatory protein HrpR was present in all isolates of P. syringae pv. syringae, P. syringae, P. cerasi, and genomospecies A, while P. viridiflava had an atypical version of this protein. The study found that syringomycin and syringopeptin-encoding genes were present in all genomospecies except for A and P. viridiflava. Pathogenicity tests in the field showed that isolates of P. syringae pv. syringae caused cankers, leaf spots, and fruit lesions, while P. syringae and P. cerasi caused only cankers. Some isolates of P. viridiflava also caused cankers, but isolates of genomospecies A did not cause any symptoms, suggesting that phytotoxins are essential for pathogenicity. Detached immature cherry fruit pathogenicity assays showed that isolates of all five genomospecies produced symptoms, but those of genomospecies A were significantly less severe. This suggests that while genomospecies A can infect cherry fruits, it is less virulent than the other genomospecies. The study also investigated antibiotic resistance. They found a relatively high level of resistance to copper among the population of P. syringae pv. syringae (47.5%), indicating that copper cannot be effectively used to control bacterial blast and bacterial canker of sweet cherries. However, no isolates were resistant to kasugamycin, suggesting that this antibiotic could be effectively used for disease control. This research builds on previous studies that have explored the diversity and pathogenicity of Pseudomonas syringae in various hosts. For example, earlier studies identified P. syringae pv. syringae as a significant pathogen in stone fruits, with a distinct genetic fingerprint separating it from strains isolated from other hosts[2]. Another study on almond canker pathogens identified P. syringae pv. syringae, P. cerasi, and P. viridiflava as key pathogens, with P. syringae pv. syringae being the most frequently isolated[3]. The current study extends this knowledge to sweet cherries, confirming the presence of P. cerasi and P. viridiflava in California sweet cherries for the first time. The findings of this study have important implications for managing bacterial diseases in sweet cherries. By identifying the specific pathogens involved and their resistance to copper, the study provides valuable information for developing targeted management strategies. The effectiveness of kasugamycin as a control measure offers a promising alternative to copper-based treatments, potentially improving disease control in sweet cherry orchards. In conclusion, this study from the University of California, Davis, enhances our understanding of the diversity and pathogenicity of Pseudomonas syringae sensu lato in sweet cherries. By integrating genomic and pathogenicity data, the researchers have provided critical insights into the management of bacterial diseases in sweet cherry, paving the way for more effective and sustainable disease control strategies.

GeneticsBiochemPlant Science

References

Main Study

1) Pathogenicity, phylogenomic, and comparative genomic study of Pseudomonas syringae sensu lato affecting sweet cherry in California.

Published 3rd September, 2024

https://doi.org/10.1128/spectrum.01324-24

Related Studies

2) Genetic characterization of pseudomonas syringae pv. syringae strains from stone fruits in california.

Journal: Applied and environmental microbiology, Issue: Vol 64, Issue 10, Oct 1998

3) Phylogenomic analyses and comparative genomics of Pseudomonas syringae associated with almond (Prunus dulcis) in California.

https://doi.org/10.1371/journal.pone.0297867


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