Pepper anthracnose, one of the main diseases in pepper production, seriously affects yield and fruit quality of pepper plants. To clarify the sensitivity of Colletotrichum scovillei to some commonly used fungicides in controlling pepper anthracnose in Shanxi Province, and also the resistance risk of C. scovillei to tebuconazole, the sensitivity of 93 C. scovillei strains from different pepper-producing areas in Shanxi Province to the 4 fungicides was determined by using the mycelial growth rate method. Ten tebuconazole-resistant C. scovillei isolates were generated by fungicide adaptation, and the fitness of these resistant isolates was investigated. The results showed that the average EC₅₀ values of tebuconazole, difenoconazole and prochloraz against C. scovillei were 0.364 1 ± 0.019 2, 3.126 7 ± 1.221 2 and 0.817 1 ± 0.328 3 μg·mL^-1, respectively; the sensitivity frequency of the C. scovillei isolates to these 3 fungicides was all distributed as a continuous unimodal curve (an approximately normal distribution), and no population with reduced sensitivity was observed. The average EC₅₀ value of pyraclostrobin to C. scovillei was 0.123 6 ± 0.190 8 μg·mL^-1, with a 2 930.98-fold difference between the maximum and minimum values; the sensitivity frequency of the C. scovillei isolates to pyraclostrobin was distributed as a left-skewed curve, and population with reduced sensitivity appeared. Among the 10 tebuconazole-resistant C. scovillei isolates, including 6 lowly resistant and 4 moderately resistant isolates, the resistance of 6 isolates could be stably inherited. Compared with the tebuconazole-susceptible parent C. scovillei strains, the mycelial growth rate, sporulation and pathogenicity of the tebuconazole-resistant strains were decreased. Further investigation showed that cross-resistance existed between tebuconazole and difenoconazole in C. scovillei, while no cross-resistance existed between tebuconazole and prochloraz or pyraclostrobin. The results provide a basis for the prevention and control of pepper anthracnose in Shanxi Province.

To clarify the population composition of pathogens causing citrus brown spot in China and their sensitivity to succinate dehydrogenase inhibitors (SDHIs), 135 diseased samples from 7 major citrus-producing regions were collected and pathogen isolation and identification was conducted in this study. Meanwhile, fungicide sensitivity test of the dominant pathogen species was carried out. Among 155 Alternaria strains isolated, the number of A. gaisen has surpassed that of A. alternata, becoming the new dominant pathogenic population. The sensitivity of 100 A. gaisen strains to boscalid and fluopyram was determined using the mycelial growth rate method. The results showed that the EC₅₀ values for boscalid ranged from 0.4129 to 4.7137 mg·L^-1, with an average value of 1.9257 mg·L^-1; for fluopyram, the EC₅₀ values ranged from 0.1272 to 3.3648 mg·L^-1, with an average value of 1.1149 mg·L^-1. The sensitivity curves of the A. gaisen population to these two fungicides were continuous and unimodal, conforming to a normal distribution according to the Kolmogorov-Smirnov test (K-S test), and no strains showed resistance. Therefore, 1.9257 mg·L^-1 and 1.1149 mg·L^-1 were established as the sensitivity baselines for A. gaisen to boscalid and fluopyram, respectively. Moreover, there were no significant differences (P＞0.05) in sensitivity of A. gaisen from different regions to these two fungicides, with all strains showing generally higher sensitivity to fluopyram than to boscalid. This study provides important data support and technical basis for the utilization of boscalid and fluopyram in the control of citrus brown spot disease.

Wheat Fusarium crown rot (FCR) is a soil-borne disease caused by F. pseudograminearum. The pathogen can produce various mycotoxins and cause wheat plants with white head, which poses a serious threat to wheat yield and food security. In order to clarify the inhibitory effects of tebuconazole on different growth stages of F. pseudograminearum and the efficacy of tebuconazole in controlling FCR, the effects of tebuconazole on mycelial growth, conidial germination, germ tube elongation and sporulation of F. pseudograminearum were studied, and the field control efficacy test was carried out. The results showed that the EC₅₀ value of tebuconazole on mycelial growth of F. pseudograminearum was (0.056 0±0.032 1) μg·mL^-1, and the EC₅₀ value on conidial germination was > 50 μg·mL^-1. By comparing the activity of tebuconazole on three F. pseudograminearum strains at mycelial growth, sporulation, conidial germination and germ tube elongation stagey, it was found that the EC₅₀ value of conidial germination was the highest (> 8 μg·mL^-1) while EC₅₀ values of germ tube elongation and sporulation were the lowest (< 0.01 μg·mL^-1). The teratogenic effect was increased as the concentration of tebuconazole higher. The results of field control efficacy of 430 g·L^-1 tebuconazole FS on FCR at different growth stages of wheat showed that the relative control effects at jointing stage of wheat were 67.38 % and 71.85 % for Yichuan experimental field and Xin 'an experimental field, respectively. At the late filling stage, the relative control effect for Yichuan experimental field was 37.19 %, and for Xin 'an experimental field it was 36.89 %. At the milky stage, the white head ratio of wheat in Yichuan experimental field was 6.30 %, and that was 7.21 % in Xin'an experimental field. There was no significant difference in the control efficacy between 430 g·L^-1 tebuconazole FS and the control fungicide 25 g·L^-1 fludioxonil FS. There was also no significant change in 1000-grain weight after treatment with the two fungicides compared with the control, indicating that wheat seeds dressed with tebuconazole FS did not affect the quality of wheat grains in the coming year. The results showed that tebuconazole had a strong inhibitory efficacy on mycelial growth, sporulation and germ tube elongation of F. pseudograminearum, and field experiments showed that tebuconazole seed dressing could effectively control FCR.

To determine the biocontrol effect of volatile organic compounds (VOCs) produced by Bacillus velezensis C11 strain against Botrytis cinerea, the pathogen causing tomato gray mold, a double petri dish assay was performed to evaluate the effect of B. velezensis C11 VOCs on mycelial growth, micromorphology, sporulation and cell membrane permeability of B. cinerea, on the occurrence and severity of gray tomato through detached leaf inoculation test, and on the activity of defense-related enzymes including POD and CAT in tomato leaves. The results showed that VOCs produced by B. velezensis C11 significantly inhibited mycelial growth of B. cinerea, with an inhibition rate of 78.35%; led to significant decrease in sporulation, cell membrane damage, and change in mycelial micromorphology; had a control effect of 76.9% on tomato gray mold. SPME-GC-MS assay was further employed to analyze the active components of B. velezensis C11 VOCs, and 27 substances were identified, 8 of which accounted for a relatively high proportion (5.43%). All these 8 compounds showed significantly inhibitory effect against B. cinerea at a concentration of 0.5 nmol·mL^-1. In conclusion, B. velezensis C11 strain can inhibit B. cinerea by producing VOCs. This study provides a theoretical basis for further investigation of the antagonistic mechanism of B. velezensis C11 strain.

Hulless barley (Hordeum vulgare L. var. nudum), known as Qingke, is the only cereal staple food crop widely planted on the Tibet Plateau (TP). Ear rot is an important new disease of Qingke occurring throughout the TP in recent years. The causal agent Dactylobotrys graminicola is a critical source of food for grass mite (Siteroptes spp.), and grass mite in turn serves as a vector for spreading the fungus. As a result, mutualistic symbiosis relationship is established between them. However, no effective method is available for controlling the disease. It is important to investigate the diversity of symbiotic bacteria of grass mite and find out the predominant bacteria, which is helpful for exploring regulation mechanisms in maintaining the stability of grass mite-D. graminicola system. This study sheds light on the development of new green control method of Qingke ear rot. In this study, adult grass mites were collected from diseased Qingke ears and the surface soil of Qingke-planting fields where ear rot occurred. The symbiotic bacteria (both on the surface and inside of mite body) or those (only inside of mite body) were isolated from living mites or their ground tissues, respectively. Bacterial isolates were sequenced with specific primers of 16S rDNA and the resulting data were statistically analyzed. For the grass mites collected from surface soil, symbiotic bacteria of 23 genera were detected from both surface and inside of mite body, and 16 genera were found only inside of mite body, of which 9 were confirmed to distribute both on surface and inside of mite body; Microbacterium, Rhodococcus and Streptomyces of the phylum Actinomycetota were the predominant bacteria among the symbiotic bacteria (both on the surface and inside of mite body), followed by Pseudomonas and Stenotrophomonas; The percentages of Microbacterium (52.1%) and Pseudomonas (22.1%) inside of mite body were significantly higher than those from both surface and inside of mite body (33.7% and 6.8%), and Streptomyces was merely detected on mite body surface. For the grass mites collected from diseased Qingke eras, symbiotic bacteria from both surface and inside of mite body were identified as 16 genera , and those inside of mite body were classified into 18 genera, of which 14 were detected from both surface and inside of mite body; Three genera Stenotrophomonas, Pseudomonas and Alcaligenes of the phylum Pseudomonadota were the predominant symbiotic bacteria of grass mites on diseased ears, with a higher percentage than that of mites in surface soil, followed by Microbacterium and Rhodococcu of phylum Actinomycetota, with remarkably lower percentages than that of soil mites. The number of Actinomycetota isolates from grass mites in epidemic field soil was 2.1 to 2.8 times of the one of Pseudomonadota isolates, whereas the number of Pseudomonadota isolates from grass mites on diseased ears was 1.9 to 2.4 times of the one of Actinomycetota isolates. So, significant differences existed in symbiotic bacterial community detected on grass mites from surface soil and from diseased Qingke ears. Among all the detected bacteria, Microbacterium, Rhodococcus, Streptomyce, Pseudomonas and Stenotrophomonas were the most dominant bacteria, which may play critical roles in facilitation of infection of younger Qingke ears by D. graminicola and fungal reproduction, providing indispensable nutrient source for grass mites.

In order to study the control effect of photosynthetic bacteria isolated from kiwi rhizosphere soil samples of Yuxi City, Yunnan province on tobacco mosaic virus (TMV) , we measured the yield of the secondary metabolite 5-aminolevulinic acid (5-ALA) from the isolated photosynthetic bacteria, and screened out a strain YN-1 with the highest yield of 5-ALA. Subsequently, the control effect of YN-1 and its secondary metabolite 5-ALA on TMV was tested, and the mechanism was investigated. The strain was identified as Rhodopseudomonas palustris by morphological identification, gram staining, physiological and biochemical tests of carbon and nitrogen sources and 16S rDNA sequence analysis. The 5-ALA yield of this strain is as high as 4.37 mol·L^-1. The incidence of TMV was decreased by spraying YN-1 fermentation liquid and secondary metabolite 5-ALA respectively. The results showed that the incidence of TMV on plants treated with YN-1fermentation liquid was 69.88% and 24.24% lower than those with water and 5% amino oligosaccharide 300 times treatments, respectively. The incidence of TMV on plants treated with 40 mg/L 5-ALA decreased by 74.70% and 36.37% compared with those with water and 5% amino oligosaccharide treatments, respectively. Through the analysis of plant resistance genes, it was found that the resistance genes in SA pathway were significantly upregulated compared with the control. The results showed that YN-1 fermentation liquid and 40 mg·L^-1 5-ALA could effectively reduce the infection degree of TMV.

Cucumber seedling damping-off caused by Pythium aphidermatum is one of the main soil-borne diseases seriously affecting the survival of cucumber seedlings. With the expansion of eggplant cultivation area in greenhouse, the occurrence and damages of the disease are increasing year by year. In this study, a bacterial strain ZF514, capable of producing volatile substance with antagonistic effect against P. aphidermatum, was isolated from rhizosphere soil of healthy cucumber plants in Hangzhou, China. According to morphological cha-racteristics, physiological and biochemical properties, and multi-gene (16S rDNA-gyrA-rpoB) phylogenetic analysis, strain ZF514 was identified as Bacillus velezensis. Strain ZF514 also exhibited significant antagonistic effects on the 5 common phytopathogenic fungi by dual culture on two-section of a Petri dish. The results of pot experiments showed that simulated fumigation treatment of soil with strain ZF514 significantly reduced disease incidence of cucumber seedling damping-off, and the control effect reached 63.69%. In summary, the volatile substance-producing B. velezensis strain ZF514 has potential to be explored as an environment-friendly microbial fumigant against soil-borne diseases.

Clubroot caused by Plasmodiophora brassicae has been a major threat to the production of crucife-rous vegetables, screening and identifying antagonistic bacteria with potential application is therefore most important for the bio-control of the disease. In this study, endophytic bacteria were isolated from root tissues of healthy Chinese cabbage in the field where clubroot disease occurred seriously. Using Phytophthora capsici as an indicator, a bacterial strain JP2 with biocontrol effect on Chinese cabbage clubroot was obtained by both dual-culture test and pot experiment in greenhouse. Combined with morphological characteristics, physiological and biochemical properties, and 16S rDNA-based phylogenetic analysis, the strain JP2 was identified as Pseudomonas brassicacearum. The fermentation broth of JP2 (culturing for 48 h) displayed a chitinase activity of 0.034 U·mL^-1, cellulose decomposition capacity (H value) of 1.89, and siderophore activity of 57.24%. Fluorescein siderophore (PVD)- and 2, 4-diacetylphloroglucinol (DAPG)-synthesizing genes were identified in the genome of strain JP2. In addition, JP2 exhibited good antagonistic effects on the six common phytopathogenic fungi, indicating its broad inhibitory spectrum against plant fungal diseases. The crude extract of JP2 showed good lethal effect on resting spores of P. brassicae, with a mortality rate of 44.44%. At 30 d post-inoculation, the colonization density of JP2 in the rhizosphere soil of Chinese cabbage remained at 3.03×10² CFU·g^-1, significantly reducing the number of resting spores of P. brassicae in the soil. The control effect of JP2 on P. brassicae in pot experiment was 58.83 %. These results indicate that JP2 strain has good biocontrol potential against Chinese cabbage clubroot.

Pogostone (Po) was synthesized in one step and its structure was characterized by ¹H NMR, ¹³C NMR, HRMS and X-ray single crystal diffraction analysis. Its antifungal and antioomycete activities were evaluated against ten phytopathogens. The in vitro bioassays revealed that Po displayed significant inhibition on the mycelial growth of Sclerotinia sclerotiorum, Rhizoctonia solani and Pythium recalcitrans with EC₅₀ values of 5.32, 5.53 and 7.83 μg·mL^-1, respectively, being potent than the control, carvacrol. At a concentration of 200 μg·mL^-1, Po exhibited a protective efficacy of 97.9% against sclerotinia rot (S. sclerotiorum) on detached rape leaves, which was comparable to the boscalid (15 μg·mL^-1, 99.0%) and carvacrol (1 000 μg·mL^-1, 99.7%). Pot experiments showed that the protective efficacies of Po were 94.6% and 91.8% at 500 μg·mL^-1 against the soybean seedling blight (R. solani) and tobacco damping-off (P. recalcitrans), respectively, which were comparable to those of carvacrol at 1 000 μg·mL^-1(93.1% and 91.2%, respectively). The protective efficacy of Po at 100 μg·mL^-1 against wheat powdery mildew was 94.1%, which was similar to that of carbendazim at 50 μg·mL^-1 (93.5%) or carvacrol at 500 μg·mL^-1 (93.0%). The results of this study could serve as a basis for the development and application of Po as botanical fungicide.

Fludioxonil is the main fungicide used for the prevention and control of vegetable gray mold caused by Botrytis cinerea. To determine the resistance status of B. cinerea to fludioxonil in Shanxi Province, 312 B. cinerea isolates were obtained from Shanxi Province and their resistance level to fludioxonil was investigated by using the hyphal growth rate method. The mutation sites in the Bos1 gene and biological phenotypes of fludioxonil-resistant B. cinerea isolates, and the cross-resistance between fludioxonil and the other 4 fungicides (pyraclostrobin, difenoconazole, pyrimethanil and prochloraz) in these resistant isolates were studied. The results showed that the resistance frequency of the tested B. cinerea isolates to fludioxonil was 7.37%, with the resistance level mainly in a low and medium level, and only 2 isolates showing high resistance to fludioxonil were found. All the resistant isolates had mutation in Bos1 gene, mainly in the TAR, HAMP and REC domains, with resistance types of F127S, V287G, I365N, I365S, Q369P+N373S, V1136I and A1259T. Additionally, it was found that the hyphal growth rate, sclerotium production, sporulation capacity and pathogenicity of the resistant isolates were lower than those of the susceptible isolates, indicating compromised fitness. There was no cross-resistance between fludioxonil and the 4 tested fungicides, and fludioxonil can therefore be used to control grey mold in rotation or in combination with these fungicides. This study provides a theoretical basis for rational utilization of fungicides in chemical control of grey mold disease.

To identify the pathogen causing anthracnose disease on quinoa plants and investigate its biological characteristics, we collected diseased quinoa plants with typical anthracnose symptoms and conducted pathogen isolation and purification experiments. A representative strain LMTJ was obtained and determined as the pathogen of quinoa anthracnose by completing Koch′s postulates. Combined with morphological characteristics and the result of multi-gene phylogenetic analyses (ACT, CHS-1, GAPDH, ITS and TUB2), the pathogen was identified as Colletotrichum spinaciae. The suitable culture condition for mycelial growth of C. spinaciae LMTJ strain is that with starch as carbon source, peptone as nitrogen source, temperature at 20~25 ℃ and pH value of 6.0~7.0, while for sporulation is with sucrose as carbon source, sodium nitrate as nitrogen source, temperature at 20~25 ℃ and pH value of 6.0. To screen effective fungicides for the prevention and control of quinoa anthracnose, the toxicity of 5 fungicides to C. spinaciae LMTJ strain was tested. The results showed that all the tested fungicides could inhibit mycelial growth of LMTJ, of which 92.8% iprodione exhibited the strongest inhibitory effect, with EC₅₀ of 2.7654 mg·L^-1. The results provide scientific basis for the diagnosis and control of quinoa anthracnose.

To investigate the occurrence of gummy stem blight (GSB) on Trichosanthes kirilowii and the causing pathogen of the disease, and to screen effective plant-derived antimicrobial agents, we collected the plants with symptoms of GSB at T. kirilowii-planting regions in Qianshan City, Anhui Province, and conducted pathogen isolation and purification experiments. Based on morphological characteristics and the result of molecular identification, the isolates were identified as Stagonosporopsis caricae. Meanwhile, the inhibitory effects of 20 Chinese herbal medicine extracts against S. caricae were determined, and over 90% inhibition rate was obtained when ethanol extract from Cnidii Fructus (CF) or Macleaya Fructus (MF) was used at a concentration of 15 mg·mL^-1, while over 80% inhibition rate for Sophorae Flavescentis Radix (SFR) or Polygoni Cuspidati Rhizoma et Radix (PCRR) extract. Further tests showed that both CF and SFR extracts showed significant inhibitory effect on mycelial growth of S. caricae, with EC₅₀ values of 0.1648-0.5289 and 0.7347-0.8332 mg·mL^-1, respectively. This study provides a theoretical basis for the environment-friendly control of GSB on T. kirilowii.

Bacteria from the genus of Pectobacterium are the important plant pathogens causing significant economic losses worldwide, and the emergence of antibiotic-resistant strains further exacerbates the challenges in Pectobacterium-caused disease prevention and control.This study used Pectobacteriums isolated from different host plants as materials and used plate analysis to obtain streptomycin-resistant strains formed in the wild. Clarify its taxonomic status through genome sequencing and comparative genome research, and streptomycin resistance genes were predicted. The results shown that among the eight strains isolated from different hosts, NJAU2 obtained from Yunnan yellow-flowered calla lily disease strains is highly resistant to streptomycin. NJAU2 genome was 5 062 459 bp in length, with G+C content of 51.83% and N50 length of 306 378 bp, containing 4 568 protein-coding genes. NJAU2 clusters on the same branch as the type strain P. aroidearum SCRI 109^T and the reported strain P. aroidearum PC1 based on the Multi-Locus Sequence Analysis results of 8 housekeeping genes (fliA, fusA, glyA, gyrB, purA, rpoA, rpoS, secY). This result is consistent with the phylogenetic relationship constructed based on the 16S rRNA gene sequence. Furthermore, the Average Nucleotide Identity (ANI) and DNA-DNA Hybridization (isDDH) analysis with various Pectobacterium strains also support this classification. Therefore, the naturally occurring streptomycin-resistant strain NJAU2 is classified as a new species within the Pectobacterium genus: Pectobacterium aroidearum, and named Pectobacterium aroidearum NJAU2. P. aroidearum NJAU2 carrying sets of genes encoding proteins for streptomycin-resistanc in its genome. Comparison with the Comprehensive Antibiotic Resistance Database (CARD) identified 328 genes belonging seven types of drug resistance mechanisms. Moreover, in NJAU2 genome, 15 genes were annotated encoding aminoglycoside antibiotic resistance, including rpsL and gidB that are related to streptomycin resistance. The discovery of P. aroidearum NJAU2 provides new material for research in the direction of streptomycin resistance in Pectobacterium spp..

In order to explore the influence of Polygonatum sibiricum rotation on the soil microbial community of Panax notoginseng, evaluate the restoration ability of crop rotation and natural restoration. The influence of Polygonatum sibiricum rotation on the microbial structure and microflora change of soil continuous cropping with Panax notoginseng was studied. The results showed that seedling rate was 88.33%, significantly higher than the incidence rate of fallow treatment, which was less than 20%, but the difference was not significant. The diversity of soil fungi and bacteria was significantly reduced (P<0.01). The results showed that crop rotation could signi-ficantly affect the β diversity of soil fungi and bacteria in Panax notoginseng (P<0.001), and could significantly increase the relative abundance of Ascomycota and reduce the relative abundance of Basidiomycota and Triguta. Firmicutes, Budlesomonas, Chloritans, Acinetobacter, Bacteroidetes, etc. LEfSe results showed that after the rotation of the pathogens, Fusarium, Ilyonectria, and other fungi. Rhizosphere soil microbial fungi mainly saprophytic, pathological and mixed nutrition mode, after the rotation treatment, plant pathogen fungi abundance, pathogenic bacteria of decline, associated with the disease, at the same time after rotation bacterial L-valine biosynthesis pathway, L-isoleucine biosynthesis I (from threonine) pathway, L-isoleucine biosynthesis II, Aerobic respiration I (cytochrome C) pathway is significantly lower. The rotation of Polygonatum sibiricum can improve soil microorganisms and it’s potential to alleviate the obstacles of Panax notoginseng.

Cucumber leaf spot caused by Corynespora cassiicola is an important disease in cucumber production, and diseased residues in soil have been proved to be the main source of its initial infection. To clarify the effect of droplet splash on the dispersal of the pathogen, a real-time fluorescence quantitative PCR (qPCR)-based system for rapid detection of C. cassiicola in soil was established. Through this system, C. cassiicola was detected in soil samples collected from greenhouses where Corynespora leaf spot was naturally occurred, with concentrations ranging from 27.00×10⁰ to 7.95×10⁵ pg DNA·g^-1. The results of artificial simulation of droplet splashing experiment showed that the impact of droplets carrying C. cassiicola led to splash dispersal of the pathogen and increased disease severity, with disease index of 65.56 and 41.56 for C. cassiicola-infected soil and substrate, respectively. Mulching soil and substrate surface in the above experiment significantly reduced disease severity, with disease index of 13.79 and 13.83 for C. cassiicola-infected soil and substrate, respectively. The results of this study indicate that droplet splash is an important route for the transmission of soil-borne C. cassiicola, providing not only technical assistance for monitoring and early warning of Corynespora leaf spot but also theoretical basis for the prevention and control of the disease.

Rice bacterial leaf streak, the main bacterial disease caused by Xanthomonas oryzae pv. oryzicola (Xoc), seriously affects rice production. Exploring safe and efficient biological resources is very important for the control of the disease. In this study, an endophytic bacterial strain XP-1 was obtained from rice leaves by confronting incubation method, with an inhibition zone diameter of (56.1±0.1) mm against Xoc. XP-1 also exhibited good antagonistic activity against 5 common bacterial phytopathogens (Ralstonia solanacearum, Xanthomonas oryzae pv. oryzae, Ralstonia solanacearum, Pectobacterium carotovorum subsp. carotovorum, Xanthomonas fragariae and Xanthomonas campestris pv. campestris). Physiological and biochemical test showed that XP-1 strain can produce IAA and siderophore, and solubilize phosphate but cannot solubilize potassium and fix nitrogen. Through indoor seed soaking test and greenhouse pot experiment, it was showed that the diluted fermentation broth of XP-1 could promote seed germination and seedling growth of rice plants, and inhibit leaf lesion on 3 rice varieties, with an inhibition rate of 63.72%-94.47%. The beneficial endophytic XP-1 strain, which has a wide antimicrobial spectrum, was identified as Pantoea ananatis based on morphological characteristics, physiological and biochemical properties and molecular identification results. This study provides the foundation for further exploration of biological resources for rice bacterial leaf streak control.

Root-knot disease, caused by Meloidogyne incognita, seriously threatens the production of many crop plants. To further explore biocontrol resources for this disease, two bacterial strains showing nematicidal activity were isolated from vegetable rhizopsheric soil in Yangzhou City, China. These two strains, named HJ03 and HJ04, were identified as Bacillus amyloliquefaciens and B. safensis, respectively, based on their morphologi-cal characteristics, biochemical properties, and phylogenetic analysis results. The corrected mortalities of HJ03 and HJ04 cell suspensions against second-stage juveniles (J2s) of M. incognita after 24 h of treatment were 77.3% and 79.3%, respectively, while those for culture filtrates of the two strains were 75.9% and 80.1%. No significant difference in corrected mortalities was observed between treatments with cell suspension and culture filtrate. Cell suspensions of HJ03 and HJ04 cultured for 24 h showed good nematicidal activity, and extended culture time did not significantly increase nematicidal activity. Cell suspensions (OD₆₀₀=1.2) of HJ03 and HJ04 diluted to 1:2 resulted in mortalities of 77.7% and 78.6%, respectively, similar to those caused by their mother solutions, but showed significantly decreased mortalities when diluted to 1:5. The biocontrol mechanisms of HJ03 and HJ04 against M. incognita were revealed as follows: HJ03 and HJ04 can inhibit egg hatching of M. incognita, with inhibition rates of 71.1% and 64.0%, respectively, compared to LB medium-treated control; significantly inhibit the chemotaxis of J2s. The number of J2s in tomato rhizosphere (1 cm) treated with HJ03 and HJ04 was reduced by 90.9% and 87.6%, respectively, compared with that of control; dramatically inhibit nematode infection, with inhibition rates of 85.4% and 85.2%, respectively, after treated with HJ03 and HJ04 for one week; inhibit gall formation, with gall indexes of 1.1 and 1.6 for HJ03 and HJ04, respectively, at 40 d after treatment, whereas 3.3 for control; inhibit the formation of egg masses, with inhibition rates of 75.7% and 73.1% for HJ03 and HJ04, respectively, at 60 d after treatment; reduce the size of M. incognita-induced giant cells. In addition, HJ03 and HJ04 can promote seed germination and seedling growth of tomato. This study enriches the biocontrol resources against root-knot disease and lays a basis for further development of biocontrol agents.

Fusarium wilt of cucumber, caused by Fusarium oxysporum f. sp. cucumerinum (Foc), is an important soil-borne disease that is difficult to control. The disease usually causes plant wilt, leading to significant yield loss. In this study, a Trichoderma strain 3199, which produces antimicrobial peptaibol, was obtained from the Agricultural Research Service Culture Collection (NRRL). The strain was identified as Trichoderma arundinaceum based on morphological characteristics and the result of molecular identification. Confronting incubation results showed that T. arundinaceum strain 3199 had obviously inhibitory effect on Foc. In pot experiment, root irrigation of cucumber seedlings with spore suspension (1×10⁸ spores·mL^-1) of strain 3199 showed 51.3% biocontrol effects against Fusarium wilt caused by Foc. Furthermore, the ethyl acetate extract (12 mg·mL^-1) from fermentation broth of strain 3199 could effectively inhibit the growth of Foc. The results indicate that T. arundinaceum strain 3199 has great potential for the biocontrol of Fusarium wilt of cucumber by producing bioactive secondary metabolites.