Bacillus-Secreted Oxalic Acid Induces Tomato Resistance Against Gray Mold Disease Caused by Botrytis cinerea by Activating the JA/ET Pathway.

Bacillus spp. are known for their ability to control plant diseases; however, the mechanism of disease control by Bacillus spp. is still unclear. Previously, bacterial organic acids have been implicated in the process of disease suppression. We extracted the total organic acid from Bacillus cereus AR156 culture filtrate and identified oxalic acid (OA) as the programmed cell death-inducing factor. OA strongly suppressed the lesion caused by Botrytis cinerea without significant antagonism against the fungus. Low concentration of OA produced by Bacillus spp. inhibited cell death caused by high concentrations of OA in a concentration- and time-dependent manner. Pretreatment with a low concentration of OA led to higher accumulation of active oxygen-scavenging enzymes in tomato leaves and provoked the expression of defense-related genes. The activation of gene expression relied on the jasmonic acid (JA) signaling pathway but not the salicylic acid (SA) pathway. The disease suppression capacity of OA was confirmed on wild-type tomato and its SA accumulation-deficient line, while the control effect was diminished in JA synthesis-deficient mutant, suggesting that the OA-triggered resistance relied on JA and ethylene (ET) signaling transduction. OA secretion ability was widely distributed among the tested Bacillus strains and the final environmental OA concentration was under strict regulation by a pH-sensitive degradation mechanism. This study provides the first systematic analysis on the role of low-concentration OA secreted and maintained by Bacillus spp. in suppression of gray mold disease and determines the dependence of OA-mediated resistance on the JA/ET signaling pathway. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 "No Rights Reserved" license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2022.

Selecting Bacterial Antagonists for Cucurbit Downy Mildew and Developing an Effective Application Method.

To identify new bacterial antagonists for cucurbit downy mildew (CDM) caused by Pseudoperonospora cubensis, 163 bacterial isolates were recovered from different microenvironments of field-grown cucumber plants. In the greenhouse, 19 representative isolates were applied to cucumber plants as a foliar spray (FS); 7 isolates achieved the efficacy over 60% against CDM, with 5 (DS22, HS10, DP14, HP4, and DS57) identified as Bacillus pumilus, B. licheniformis, Enterobacter sp., Bacillus sp., and Stenotrophomonas maltophilia, respectively. Strains DP14, DS22, and HS10 were assessed for their biocontrol effect on naturally occurring CDM in 2-year field trials (2010 and 2011), in which their overall efficacy relative to that of propamocarb was 106.25 to 117.17% with foliar spray plus root drench (FS+RD) but only 70.98 to 84.03% with FS. Coincidently, DP14 and HS10 applied as root drench (RD) alone also significantly reduced CDM. Under field conditions, DP14, DS22, and HS10 all successfully colonized cucumber leaves and the rhizosphere, and also significantly increased fruit yield by 37.60 to 51.03%, as well as nutrient levels. Taken together, Enterobacter sp. DP14, B. licheniformis HS10, and B. pumilus DS22 are plant-growth-promoting rhizobacteria effective in controlling CDM in the field, whose efficacy increased with FS+RD compared with FS alone.

[SNP marker and allele-specific diagnostic PCR for authenticating herbs of Perilla].

AIM: To authenticate all the varieties of Perilla (single-species genus), to analyze sequences of rDNA ITS regions and single nucleotide polymorphism (SNP) within them and based on these, to design allele-specific diagnostic PCR primers. METHODS: The rDNA ITS regions of the perilla varieties were sequenced and analyzed by Clustal X 1.8, MEGA 3.0. Allele-specific diagnostic PCR primers that can authenticate all the perilla varieties were designed based on SNPs loci. RESULTS: The length of rDNA ITS sequences of perilla varieties ranged from 612 to 615 bp in size, including ITS1 (230 -232 bp), 5.8S (179 bp) and ITS2 (203 -204 bp). The GC content is about 61.5% - 61.9%. There is not only SNPs in non-coding region ITS1 and ITS2 (ncSNP), but also three coding SNPs (cSNP) loci in the conservative region of 5.8S. All the SNPs have only two allele loci polymorphism. The cSNP in 5.8S is related to the morphology variation among the varieties. Allele-specific diagnostic PCR primers have been designed according to SNPs loci to authenticate accurately all the seeds and leaves of Perilla varieties. CONCLUSION: SNPs in rDNA ITS region can be used as an effective molecular markers to authenticate all the varieties of Perilla.