Novel small molecule growth inhibitors of xanthomonas spp. causing bacterial spot of tomato

Vishal Srivastava, Loic Deblais, Dipak Kathayat, Francesca Rotondo, Yosra A. Helmy, Sally A. Miller, Gireesh Rajashekara

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


Bacterial spot (BS) of tomato, caused by Xanthomonas gardneri, X. perforans, X. vesicatoria, and X. euvesicatoria, is difficult to control because of the high prevalence of copper- and streptomycin-resistant strains and the lack of resistance cultivars and effective bactericides. The objective of this study was to identify novel growth inhibitors of BS-causing Xanthomonas (BS-X) species by using small molecules (SM; n = 4,182). Several SMs (X1, X2, X5, X9, X12, and X16) completely inhibited the growth of BS-X isolates (n=68 X. gardneri, 55 X. perforans, 4 X. vesicatoria, and 32 X. euvesicatoria) at 12.5 mM by disrupting Xanthomonas cell integrity through weakening of the cell membrane and formation of pores. These SMs were also effective against biofilm-embedded, copper- and streptomycin-resistant Xanthomonas strains while having minimal impact on other plant pathogenic (n = 20) and beneficial bacteria (n = 12). Furthermore, these SMs displayed equivalent antimicrobial activity against BS-X in seeds and X. gardneri in seedlings compared with conventional control methods (copper sulfate and streptomycin) at similar concentrations while having no detectable toxicity to tomato tissues. SMs X2, X5, and X12 reduced X. gardneri, X. perforans, X. vesicatoria, and X. euvesicatoria populations in artificially infested seeds £3.4-log CFU/seed 1 day postinfection (dpi) compared with the infested untreated control (P£ 0.05). SMs X1, X2, X5, and X12 reduced disease severity £72% and engineered bioluminescent X. gardneri populations £3.0-log CFU/plant in infected seedlings at 7 dpi compared with the infected untreated control (P£ 0.05). Additional studies are needed to increase the applicability of these SMs for BS management in tomato production.

Original languageEnglish
Pages (from-to)940-953
Number of pages14
Issue number6
StatePublished - Jun 2021

Bibliographical note

Funding Information:
Funding: This work is supported by the U.S. Department of Agriculture, National Institute for Food and Agriculture, Specialty Crop Research Initiative grant 2015-51181-24312.

Publisher Copyright:
© 2021 American Phytopathological Society. All rights reserved.


  • Bacterial pathogens
  • Bacterial spot
  • Bioluminescence
  • Disease control and pest management
  • Growth inhibitors
  • High-throughput screening
  • Small molecules
  • Xanthomonas

ASJC Scopus subject areas

  • Agronomy and Crop Science
  • Plant Science


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