To investigate the diversity of microbial communities and to obtain culturable strains from healthy and rusty root-rot rhizosphere soil samples of Panax quinquefolius L., it is necessary to provide a reference for the occurrence mechanism and prevention and control strategies for rusty root-rot. Traditional isolation and high-throughput sequencing were used for analyzing the healthy and rusty root-rot soil samples of Panax quinquefolius L. to explore their structural composition and diversity. In total, 24 strains of bacteria and 25 strains of fungi were isolated using the traditional isolation techniques, and the dominant genera were Pseudomonas, Bacillus, and Penicillium. The results of Illumina Miseq high-throughput sequencing revealed that Cyanobacteria and Proteobacteria dominated the bacterial communities in the healthy and rusty root-rot soil samples. Notably, the phylum proportions of Cyanobacteria, Proteobacteria, and Tenericutes in the rusty root-rot soil samples significantly decreased, whereas those of Bacteroidetes, Actinobacteria, Firmicutes, and Acidobacteria significantly increased. Furthermore, the bacterial diversity of the infected rusty root-rot rhizosphere soil decreased significantly. In conclusion, the composition and quantity of soil microbial communities were significantly different between the healthy and rusty root-rot soil samples, and this provides a theoretical basis for the study of the occurrence mechanism and prevention and control strategies for rusty root-rot Panax quinquefolium L.

Because of low temperatures in northern China during winter, straw with low decomposition efficiency is directly returned to the field, making pathogen accumulation easy. To promote in-situ decomposition of straw and reduce the accumulation of pathogenic bacteria, a strain of Trichoderma, C47-3, which degrades straw at a low temperature, was obtained through low temperature culture combined with cellulase, hemicellulase, and laccase activity screening. The strain was inoculated in straw liquid medium, and the straw degradation rate was 22.28% after 15 days of cultivation at 15 ℃. Morphological observation and molecular biology analysis revealed that the strain was Trichoderma paratroviride. The Trichoderma strain C47-3 and its volatile substances inhibited the growth of eight pathogens, including Botryosphaeria dothidea, Rhizoctonia cerealis, and Botrytis cinerea, and the inhibition rate of Fusarium pseudograminearum was greater than 60%. The screened Trichoderma strain C47-3 can improve straw decomposition efficiency at low temperatures and has biocontrol potential, providing strain resources for the efficient utilization of corn straw after returning to the field in winter and the biological control of soil-borne diseases in northern China.

This study aims to label the biocontrol agent Burkholderia vietnamiensis B418 with the red fluorescent protein DsRed and investigate the functional stability of the labeled strain. The recombinant plasmid pGEX-4T-1-DsRed containing the DsRed gene was transformed into B418 by the aminoclay-mediated transformation system. Germicul ture, subculture, and dual-culture techniques were used to determine the functional stability of the labeled strain B418-Ds Red.The growth curve and morphological characteristics of the strain B418-DsRed after aminoclay transformation were essentially the same as the wild strain B418. After ten generations of subculturing, bright red fluorescence could still be observed under a confocal microscope and the DsRed gene could be detected by polymerase chain reaction, after plasmid extraction from the strain B418-DsRed, which showed its good genetic stability. Dual-culture confrontation assay revealed that the inhibition rates of the strain B418-DsRed against Fusarium oxysporum and Verticillium dahliae were 55.25% and 67.55%, respectively, with no significant difference when compared to the wild strain B418. It was indicated that the introduction of a foreign plasmid showed no impact on their antifungal activity. Results demonstrated that the red fluorescent protein labeling of the strain B418 was successfully achieved by an aminoclay-mediated transformation system and the labeled strain B418-DsRed with stable function could be used in the future for the colonization of the strain B418 and interaction with pathogens in the plant rhizosphere.

The diversity of fungal communities is an important evaluation indicator for the environmental quality and health of cultivated soil. In this study, four vegetable (onion,ginger,strawberry,cucumber) soils were investigated to analyze the physical and chemical properties as well as the composition and diversity of fungal communities via Quantitative Polymerase Chain Reaction and high-throughput sequencing.The results showed that the fungal abundance inonion soil was the lowest and significantly different from that in the other three crops (strawberry,cucumber,ginger;P< 0.05).The Shannon index and OTUs of the onion and ginger soil were high, indicating higher fungal diversity,whereas the Shannon index and OTUs of cucumber and strawberry were low, indicating lower diversity. The relative abundances of Ascomycota,Basidiomycota, and Mortierellomycota were higher, with the relative abundance of Ascomycota being especially high in diseased soil. Soil fungal communities were affected by environmental factors, with pH and available phosphorus having the greatest influence.These results provided a theoretical basis for clarifying the relationship between the diversity of fungal communities and the quality of vegetable soil,which helped in improving the ecological quality of vegetable soil.

The effects of different pH, medium, carbon source, nitrogen source, and C/N ratios on the colony growth and spore yield of two salt-tolerant Trichoderma strains, Trichoderma atroviride TW320 and Trichoderma. koningiopsis TW1876, were studied in order to optimize the growth and spore production conditions of the two strains. The results showed that the salt-tolerant T. atroviride TW320 could grow and produce spores on potato dextrose agar (PDA) medium with a pH of 4 to 11, and the optimum pH for mycelial growth and spore production was 5. On soybean corn flour medium, TW320 grew the fastest and produced the most spores. The best carbon source for TW320 mycelial growth and sporulation was xyaccharide, respectively, and the best nitrogen source for TW320 was yeast extract. When the C/N ratio is 12:1, TW320 produces the most spores. The optimum pH for mycelial growth and sporulation of T. koningiopsis TW1876 was 11, and the optimal medium was PDA. TW1876 has the highest sporulation capacity, with lactose being the best carbon source, glycine being the best nitrogen source, and the C/N ratio being 9:1.

To explore the measures for safely producing leafy vegetables and remediation effects of Brassica chinensis in continuous cropping obstacles soil, the greenhouse plot experiment was conducted in this study using soil with conditioner combined with Trichoderma LTR-2, taking soil pH, soil conductivity, disease control efficiency, and yield increase rate as evaluation indexes. According to the results of soil nutrient content, the experiment of fertilizer reduction. The results showed that the soil pH increased from 4.50 to 6.95 and soil conductivity decreased from 675.10 to 519.70 μS/cm after treatment with a 7 500 kg/hm² conditioner. Compared with before fertilization, soil pH decreased and soil conductivity increased in B (conditioner + organic fertilizerⅠ+ compound fertilizer) and C (conditioner + organic fertilizerⅠ+ LTR-2 + compound fertilizer) treatment groups after fertilization. After one stubble of planting, pH value decreased from 6.43 and 6.57 to 6.06 and 6.26, respectively, and soil conductivity decreased from 1 011.43 and 959.47 μS/cmto 955.70 and 863.43 μS/cm, respectively. Compared with the conventional treatment group A (organic fertilizerⅡ+ compound fertilizer), there were significant differences in soil pH and soil conductivity in B and C treatment groups before and after Brassica chinensis vegetated. The control effects of root rot were 65.39% and 80.77%, and the yield increase rates were 27.48% and 33.59% in treatment groups B and C, respectively. The available nutrients of A, B, and C had different excess accumulations in the soil. Compared with conventional treatment A' (organic fertilizer III + compound fertilizer), under 66.67% compound fertilizer reduction, the yield increase rate of treatment group D' (organic fertilizerⅠ+ LTR-2 + 1/3 compound fertilizer) was 9.31%.

To explore the effect of Trichoderma harzianum LTR-2 on wheat grain quality and provide a practical method for improving wheat quality, parameters such as thousand seed weight as well as amino acid, protein, and wet gluten contents of winter wheat grains (cultivar Jimai 44) were analyzed after spraying different concentrations of T. harzianum LTR-2 suspension at the booting stage. The results demonstrate that the analyzed parameters had improved compared with the controls at the booting stage. The aforementioned results indicated that spraying of T. harzianum LTR-2 at the booting stage could improve the yield of wheat as well as nutritional and processing quality of wheat grain.