DNA Polymorphisms and Biocontrol of Bacillus Antagonistic to Citrus Bacterial Canker with Indication of the Interference of Phyllosphere Biofilms

Abstract

Citrus bacterial canker caused by Xanthomonas axonopodis pv. citri is a devastating disease resulting in significant crop losses in various citrus cultivars worldwide. A biocontrol agent has not been recommended for this disease. To explore the potential of bacilli native to Taiwan to control this disease, Bacillus species with a broad spectrum of antagonistic activity against various phytopathogens were isolated from plant potting mixes, organic compost and the rhizosphere soil. Seven strains TKS1-1, OF3-16, SP4-17, HSP1, WG6-14, TLB7-7, and WP8-12 showing superior antagonistic activity were chosen for biopesticide development. The genetic identity based on 16S rDNA sequences indicated that all seven native strains were close relatives of the B. subtilis group and appeared to be discrete from the B. cereus group. DNA polymorphisms in strains WG6-14, SP4-17, TKS1-1, and WP8-12, as revealed by repetitive sequence-based PCR with the BOXA1R primers were similar to each other, but different from those of the respective Bacillus type strains. However, molecular typing of the strains using either tDNA-intergenic spacer regions or 16S–23S intergenic transcribed spacer regions was unable to differentiate the strains at the species level. Strains TKS1-1 and WG6-14 attenuated symptom development of citrus bacterial canker, which was found to be correlated with a reduction in colonization and biofilm formation by X. axonopodis pv. citri on leaf surfaces. The application of a Bacillus strain TKS1-1 endospore formulation to the leaf surfaces of citrus reduced the incidence of citrus bacterial canker and could prevent development of the disease.

Biocontrol of Citrus Canker Disease Caused by Xanthomonas citri subsp. citri Using an Endophytic Bacillus thuringiensis

“…6). Reductions in citrus canker severity and incidence were also reported for citrus species treated with the Bacillus strains WG6-14 and TKS1-1 and with B. subtilis (S-12) (Das et al, 2014; Huang et al, 2012). B. subtilis , B. amyloliquefaciens , B. pumilus , B. mycoides , B. pasteurii , and B. cereus induce plant disease resistance and are commercially available as biocontrol agents (Kloepper et al, 2004; Nam et al, 2016).…”

A Novel Two-Component Response Regulator Links rpf with Biofilm Formation and Virulence of Xanthomonas axonopodis pv. citri

“…Our previous study indicated that Bacillus subtilis TKS1-1 and Bacillus amyloliquefaciens WG6-14 can interfere with phyllosphere biofilm formation by X. axonopodis pv. citri , which may contribute to the attenuation of citrus bacterial canker symptom development [6]. These results and findings from other plant-associated bacteria suggest that biofilm formation plays important roles in pathogenesis [5], [6], [7], [8].…”

“…citri , which may contribute to the attenuation of citrus bacterial canker symptom development [6]. These results and findings from other plant-associated bacteria suggest that biofilm formation plays important roles in pathogenesis [5], [6], [7], [8]. Thus, experiments were conducted to uncover genes and gene clusters that are involved in biofilm formation and virulence as well as to reveal potential interactions between these two processes in X. axonopodis pv.…”

Distinct Phyllosphere Bacterial Communities on Arabidopsis Wax Mutant Leaves

“…antimicrobial compounds) manner [54], [77], [78]. For example, it has been shown that pre-inoculation of Citrus and tomato plants with plant growth promoting and biocontrol bacteria like Azospirillum brasiliense or Bacillus strains, which themselves have no negative effects on the plants, prevents the development of large populations of pathogenic bacteria [79], [80]. For Arabidopsis , antagonistic effects of specifically plant-associated Sphingomonas strains to a plant-pathogenic Pseudomonas syringae strain were described [81].…”