Yan Wang

To develop an effective approach to inhibit Botrytis cinerea , a new biocontrol strain, Pseudomonas chlororaphis ZL3, was screened and exhibited excellent biocontrol potential. Nevertheless, the antifungal mechanism of P. chlororaphis volatile organic compounds (VOCs) against B. cinerea is still unclear. In this study, VOCs emitted from P. chlororaphis ZL3 were found to have potent inhibitory effects on mycelium growth, conidia germination, and sclerotium formation. Subsequently, the antifungal mechanism was revealed via the biophysical, transcriptomic, and metabolomic analysis. Compared to the control groups, the relative conductivities increased dramatically, while the ergosterol content decreased sharply, determining that VOCs could enhance cell membrane permeability and destroy cell membrane integrity. Additionally, VOCs could also inhibit ATPase activity and reduce reactive oxygen species (ROS) accumulation, thereby adversely interfering with energy metabolism. The superoxide dismutase (SOD) and catalase (CAT) activities were significantly reduced in B. cinerea mycelia, presenting the impairment of the antioxidant defense mechanism. Furthermore, most of the differential expression genes (DEGs) were involved in lipid metabolism, membrane transport, energy production, and conversion, indicating that the VOCs might affect the structure and function of cell membranes and energy metabolism. The differential metabolites were mainly involved in the alteration of amino acid metabolism and lipid metabolism. Together, these findings provide valuable insights into the molecular responses of B. cinerea to P. chlororaphis ZL3 VOCs and support the potential development of novel biological fumigants. IMPORTANCE: Biological control is a sustainable alternative way for the control of gray mold. The volatile organic compounds emitted from Pseudomonas chlororaphis ZL3 had high inhibitory activity against Botrytis cinerea , but the antifungal mechanism is largely unknown. This study attempted to interpret the comprehensive antifungal mechanism, providing a theoretical foundation for the application of volatile organic compound (VOC)-mediated biological fumigants in the future.

Root rot, mainly caused by Fusarium oxysporum, is one of the most destructive diseases and leads to significant economic loss of Astragalus membranaceus. To develop an effective strategy for the management of this serious disease, a bacterial strain 2-12 was screened from A. membranaceus rhizosphere soil and identified as Bacillus paralicheniformis based on the phylogenetic analyses of gyrase subunit B gene (gyrB) and RNA polymerase gene (rpoB) sequences. Interestingly, the volatile organic compounds (VOCs) produced by B. paralicheniformis 2-12 exhibited potent antifungal activities against F. oxysporum, as well as fifteen other plant pathogens. Under scanning electron microscopy observation, hyphae treated with the VOCs exhibited abnormal variation such as distortion, twist, and vesiculation, leading to distinctive protoplasm shrinkage. After treatment with B. paralicheniformis 2-12 VOCs, the lesion diameter and disease incidence both reduced significantly compared to control (p < 0.05), thus demonstrating prominent biological efficiency. Moreover, B. paralicheniformis 2-12 VOCs were composed of 17 VOCs, including 9 alkanes, 3 alcohols, 3 acids and esters, 1 aromatic compound, and 1 alkyne compound. A total of 1945 DEGs, including 1001 up-regulated and 944 down-regulated genes, were screened via transcriptome analysis. These DEGs were mainly associated with membranes and membrane parts, amino acid metabolism, and lipid metabolism. The findings in this work strongly suggested that B. paralicheniformis 2-12 VOCs could be applied as a new candidate for the control of A. membranaceus root rot.

Fusarium root rot is usually classified as an extremely destructive soilborne disease. From 2020 to 2021, Fusarium root rot was observed in production areas and seriously affected the yield and quality of Scutellaria baicalensis in Shanxi Province, China. Based on morphological characteristics and combined analysis of the internal transcribed spacer region of ribosomal DNA and translation elongation factor 1-alpha sequences, 68 Fusarium isolates obtained in this work were identified as F. oxysporum (52.94%), F. acuminatum (20.59%), F. solani (16.17%), F. proliferatum (5.88%), F. incarnatum (2.94%), and F. brachygibbosum (1.47%). In the pathogenicity tests, all Fusarium isolates could infect S. baicalensis roots, presenting different pathogenic ability. Among these isolates, F. oxysporum was found to have the highest virulence on S. baicalensis roots, followed by F. acuminatum, F. solani, F. proliferatum, F. brachygibbosum, and F. incarnatum. According to fungicide sensitivity tests, Fusarium isolates were more sensitive to fludioxonil and difenoconazole, followed by carbendazim, thiophanate-methyl, and hymexazol. In brief, this is the first report of Fusarium species ( F. oxysporum, F. acuminatum, F. solani, F. proliferatum, F. incarnatum, and F. brachygibbosum) as causal agents of root rot of S. baicalensis in Shanxi Province, China. The fungicide sensitivity results will be helpful for formulating management strategies of S. baicalensis root rot.

Triadimefon, a type of triazole systemic fungicide, has been extensively used to control various fungal diseases. However, triadimefon could lead to severe environmental pollution, and even threatens human health. To eliminate triadimefon residues, a triadimefon-degrading bacterial strain TY18 was isolated from a long-term polluted site and was identified as Enterobacter hormaechei. Strain TY18 could grow well in a carbon salt medium with triadimefon as the sole nitrogen source, and could efficiently degrade triadimefon. Under triadimefon stress, a total of 430 differentially expressed genes (DEGs), including 197 up-regulated and 233 down-regulated DEGs, were identified in strain TY18 using transcriptome sequencing (RNA-Seq). Functional classification and enrichment analysis revealed that these DEGs were mainly related to amino acid transport and metabolism, carbohydrate transport and metabolism, small molecule and pyrimidine metabolism. Interestingly, the DEGs encoding monooxygenase and hydrolase activity acting on carbon–nitrogen were highly up-regulated, might be mainly responsible for the metabolism in triadimefon. Our findings in this work suggest that strain E. hormaechei TY18 could efficiently degrade triadimefon for the first time. They provide a great potential to manage triadimefon biodegradation in the environment successfully.

To develop an effective and environmentally safe strategy to control postharvest gray mold caused by Botrytis cinerea, Bacillus siamensis strain YJ15 isolated from blueberry was used to test the biocontrol potential. It is interesting to find that the volatile organic compounds (VOCs) emitted from strain YJ15 exhibited significant antifungal activity against Botrytis cinerea as well as 11 other plant-pathogenic fungi, with a percentage of mycelial growth inhibition from 74.96 to 92.81%. Additionally, VOCs from strain YJ15 could reduce significantly the disease incidence and lesion diameter with the increasing of fermentation time, indicating great biocontrol potential for controlling blueberry postharvest gray mold. Furthermore, the VOCs were collected by using headspace solid-phase microextraction fiber, and the composition of VOCs was further revealed by using gas chromatography coupled with quadruple mass spectrometry. In total, 24 kinds of VOCs, including 5 alkanes, 2 aldehydes, 3 ketones, 5 alcohols, 1 alkene, 5 acids and esters, 2 aromatic compounds, and 1 sulfur compound, were emitted at 1, 3, 5, and 7 days after inoculation. Among these VOCs, eight antifungal VOCs could inhibit mycelial growth of B. cinerea. It is important to highlight that, although 1-butanol and 3-methyl-1-butanol were the most abundant compounds, 2-ethylhexanol, 1-heptanol, and 1,3-xylene have proved to be more toxic to B. cinerea than 3-methyl-1-butanol, propanethioic acid, 2,2-dimethyl-, ethyl 2-methylbutyrate, 2-heptanone, and 1-butanol, which provide new, promising biofumigants for the control of postharvest gray mold caused by B. cinerea.

Highbush blueberry (Vaccinium corymbosum L.), a flowering plant with dark-purple berries, mainly used for fresh consumption, juice, jellies, jams and pies (Kwon et al. 2011), is cultivated in southwest and northeast China on approximately 20,000 ha. In August 2015 in Changchun City, Jilin Province, China, fungal fruit rot was observed on stored highbush blueberry at about 5% incidence. Symptoms consisted of soft, slightly sunken, water-soaked lesions covered with abundant white and pink mycelia. Diseased fruits were surface-disinfested with 75% ethanol for 30 sec, 0.1% HgCl2 for 1 min, washed three times in sterile water, dried, plated on potato dextrose agar (PDA), and incubated at 25 °C for 7 days. Four isolates with similar morphology were isolated from single spores. Colonies grew slowly with growth diameters of 48 mm after 7 days, producing white mycelia and gradually becoming floccose with bright orange to rose pigmentation on PDA. On carnation leaf agar (CLA), abundant macroconidia were formed in s...