Potential Biocontrol Activities of Populus Endophytes against Several Plant Pathogens Using Different Inhibitory Mechanisms

Sharon L Doty; Pierre M Joubert; Andrea Firrincieli; Andrew W Sher; Robert Tournay; Carina Kill; Shruti S Parikh; Patricia Okubara

doi:10.3390/pathogens12010013

Potential Biocontrol Activities of Populus Endophytes against Several Plant Pathogens Using Different Inhibitory Mechanisms

Pathogens. 2022 Dec 22;12(1):13. doi: 10.3390/pathogens12010013.

Authors

Sharon L Doty¹, Pierre M Joubert^{1

2}, Andrea Firrincieli^{1

3}, Andrew W Sher¹, Robert Tournay¹, Carina Kill^{1

4}, Shruti S Parikh^{1

5}, Patricia Okubara⁶

Affiliations

¹ School of Environmental and Forest Sciences, College of the Environment, University of Washington, Seattle, WA 98195, USA.
² Department of Plant & Microbial Biology, University of California, Berkeley, CA 94720, USA.
³ Department for Innovation in Biological, Agro-Food and Forest Systems, University of Tuscia, 01100 Viterbo, Italy.
⁴ Native Roots School, Taos, NM 87571, USA.
⁵ Department of Food Science and Technology, University of California, Davis, CA 95616, USA.
⁶ Department of Plant Pathology, Washington State University, Pullman, WA 99164, USA.

Abstract

The plant microbiome can be used to bolster plant defense against abiotic and biotic stresses. Some strains of endophytes, the microorganisms within plants, can directly inhibit the growth of plant fungal pathogens. A previously isolated endophyte from wild Populus (poplar), WPB of the species Burkholderia vietnamiensis, had robust in vitro antifungal activity against pathogen strains that are highly virulent and of concern to Pacific Northwest agriculture: Rhizoctonia solani AG-8, Fusarium culmorum 70110023, and Gaemannomyces graminis var. tritici (Ggt) ARS-A1, as well as activity against the oomycete, Pythium ultimum 217. A direct screening method was developed for isolation of additional anti-fungal endophytes from wild poplar extracts. By challenging pathogens directly with dilute extracts, eleven isolates were found to be inhibitory to at least two plant pathogen strains and were therefore chosen for further characterization. Genomic analysis was conducted to determine if these endophyte strains harbored genes known to be involved in antimicrobial activities. The newly isolated Bacillus strains had gene clusters for production of bacillomycin, fengicyn, and bacillibactin, while the gene cluster for the synthesis of sessilin, viscosin and tolaasin were found in the Pseudomonas strains. The biosynthesis gene cluster for occidiofungin (ocf) was present in the Burkholderia vietnamiensis WPB genome, and an ocf deletion mutant lost inhibitory activity against 3 of the 4 pathogens. The new isolates lacked the gene cluster for occidiofungin implying they employ different modes of action. Other symbiotic traits including nitrogen fixation, phosphate solubilization, and the production of auxins and siderophores were investigated. Although it will be necessary to conduct in vivo tests of the candidates with pathogen-infected agricultural crops, the wild poplar tree microbiome may be a rich source of beneficial endophyte strains with potential for biocontrol applications against a variety of pathogens and utilizing varying modes of action.

Keywords: Burkholderia; Fusarium; Gaemannomyces; Pythium; Rahnella; Rhizoctonia; antimicrobial; biocontrol; endophytes; plant pathogens.

Grants and funding

none/University of Washington CoMotion Innovation Fund; Byron and Alice Lockwood Foundation