Action mechanism of the potential biocontrol agent Brevibacillus laterosporus SN19-1 against Xanthomonas oryzae pv. oryzae causing rice bacterial leaf blight.

The causal agent of rice bacterial leaf blight (BLB) is Xanthomonas oryzae pv. oryzae (Xoo), which causes serious damage to rice, leading to yield reduction or even crop failure. Brevibacillus laterosporus SN19-1 is a biocontrol strain obtained by long-term screening in our laboratory, which has a good antagonistic effect on a variety of plant pathogenic bacteria. In this study, we investigated the efficacy and bacterial inhibition of B. laterosporus SN19-1 against BLB to lay the theoretical foundation and research technology for the development of SN19-1 as a biopesticide of BLB. It was found that SN19-1 has the ability to fix nitrogen, detoxify organic phosphorus, and produce cellulase, protease, and siderophores, as well as IAA. In a greenhouse pot experiment, the control efficiency of SN19-1 against BLB was as high as 90.92%. Further investigation of the inhibitory mechanism of SN19-1 on Xoo found that the biofilm formation ability of Xoo was inhibited and the pathogenicity was weakened after the action of SN19-1 sterile supernatant on Xoo. The activities of enzymes related to respiration and the energy metabolism of Xoo were significantly inhibited, while the level of intracellular reactive oxygen species was greatly increased. Scanning electron microscopy observations showed folds on the surface of Xoo. A significant increase in cell membrane permeability and outer membrane permeability and a decrease in cell membrane fluidity resulted in the extravasation of intracellular substances and cell death. The results of this study highlight the role of B. laterosporus SN19-1 against the pathogen of BLB and help elucidate the underlying molecular mechanisms.

Simultaneous Detection of Multiple Plant Growth Regulator Residues in Cabbage and Grape Using an Optimal QuEChERS Sample Preparation and UHPLC-MS/MS Method.

BACKGROUND: At present, plant growth regulators (PGRs) are widely used in agricultural and forestry production. PGRs, like traditional pesticides, have certain toxicities. Naively excessively applying them will cause the acute and chronic poisoning of humans and animals and potentially harm human health. OBJECTIVE: In order to assess, prevent, and control the residues of PGRs in fruits and vegetables, a set of quick, easy, cheap, effective, rugged, and safe (QuEChERS) analytical methods that simultaneously detect multiple PGR residues are urgently needed for quality and safety inspection of agricultural product. METHODS: In this study, grapes (representative of fruits) and cabbages (representative of vegetables) were used as the detected objects. The 30 commercial product residues of PGRs were detected in both with an ultra-high performance liquid chromatography (UHPLC)-tandem mass spectrometry (MS/MS) method, based on optimized chromatographic, MS, and preparation conditions (extraction solvent and cleanup conditions). Grape and cabbage samples were extracted with acetonitrile containing 5% (v/v) acetic acid, dehydrated using a salt package, purified using the QuEChERS method, ionized using electrospray ionization under positive and negative ion switching mode, detected using multi-reaction monitoring, and quantification using an external standard method of matrix matching standard curve. RESULTS: Methanol was selected as the strong elution phase. A methanol-0.1% formic acid-5 mmol/L ammonium acetate solution was selected as the best mobile phase. The optimal extraction solvent was acetonitrile containing 5% acetic acid. Primary secondary amine cleanup could met the determination requirements of PGR residues. The developed method for determination of 30 commercial products of PGR, such as betaine, showed excellent linearity in 1-500, 10-1000, ∼500, ∼2000, and 100-10 000 µg/kg (R ≥ 0.98). At the 0.001 (0.01), 0.05, 0.20, and 1.00 mg/kg additive concentrations, the average addition standard recovery of 30 commercial products of PGR were 61-132% with the relative standard deviations of 1-14% and the LOQs were confirmed to be 1.0-100 µg/kg through the actual addition values of samples. CONCLUSION: The set of optimized QuEChERS UHPLC-MS/MS methods simultaneously detect residues of PGRs in fruits and vegetables with one-time sample preparation for high-throughput, rapid quantitative screening, and confirmation. The methods cover a wide range of PGRs with simple and convenient preparation and small amounts of solvent, and can provide technical support for the supervision of PGR residues in fruits and vegetables. HIGHLIGHTS: The optimizations of extraction solvent screening, different ratios of various purification packages in the QuEChERS method, and UPLC-MS conditions were conducted and the precision, sensitivity, and recovery rates of the methods were investigated in order to establish a QuEChERS UPLC-MS/MS method for simultaneously detecting 30 kinds of PGR residues in fruits and vegetables. The methods allow high-throughput determination of multiple PGR residues in fruits and vegetables and can also provide technical references for related compound residue detection of other matrixes.