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Soil fungi communities play a vital role in the plant-soil ecosystem and affect plant growth and health, but the underlying mechanism controlling soil fungi communities in understory wild ginseng soil is still unknown. To study that mechanism, a pot culture experiment adding different leaf litters based on a completely randomized design was carried out. The results indicated that 1990 operational taxonomic units were obtained from eighteen samples. Ascomycota and Basidiomycota, the two dominant phyla, accounted for 84.57% of the total valid reads at the phylum level. The observed species and Chao 1 index in treatment E were significantly lower than those in the other treatments, although no significant differences were found among the Shannon index of all treatments (p > 0.05). Different types of leaf litter significantly changed the fungal community composition; specifically, Ascomycota was higher in broad leaf litter treatments (A, C, D and E) than in the coniferous leaf litter treatment (B), but Basidiomycota showed the opposite trend, indicating that Ascomycota and Basidiomycota could be used to identify the species of coniferous and broad leaves. The active biomarker fungal (Bmf), 36 different phylotypes, were identified by a linear discriminant analysis effect size algorithm in all treatments, and some Bmf may participate in the decomposition of different tree litters. Additionally, the changes in fungal community diversity and composition were closely related to the changes in soil microbial biomass carbon, total nitrogen and available phosphorus in all treatment soils. Overall, our study indicated that leaf litter changed the soil fungal community structure, and some Bmf were directly involved in leaf litter decomposition. Bmf is more indicative and helpful for distinguishing leaf species.

Potassium fulvic acid (BSFA) and potassium humate (KHM), as organic fertilizers, can improve soil structure, increase soil nutrient levels and prevent plant diseases. However, knowledge is limited regarding how BSFA and KHM influence soil microbial communities and the interrelationships between community members associated with Panax ginseng. Soil pH and nutrient content increased significantly as a result of the addition of BSFA and KHM. The pH, NH4+-N, NO3--N, AP and AK increased by 1.72 %-5.55 %, 70.09 %-108.39 %, 35.38 %-216.20 %, 1.21 %-14.19 % and 3.40 %-5.94 %, respectively, in the BSFA and KHM treatments. The soil nutrient increase may be related to Micrococcaceae and arbuscular mycorrhizal fungi (AMF). The structure of the microbial community also changed radically from that of the control group, and Chloroflexi (2.69 %-3.15 %), Actinobacteria (4.33 %-7.53 %) and Acidobacteria (9.44 %-11.62 %) were the dominant microorganisms at the phylum level in bacteria. In contrast, the dominant fungi at the phylum level were Ascomycota (77.39 %-78.08 %), Glomeromycota (0.36 %-2.68), Olpidiomycota (0.02 %-3.78 %) and Basidiomycota (0.80 %-1.17 %). Fusarium oxysporum and Ascomycota were biomarkers for BSFA and KHM, which may be related to pathogenic bacteria. Network analysis revealed that the association among members of the soil microbial community was more positive than negative following application of KHM, and more positive (62.5 %) than negative (37.5 %) correlations were observed between bacteria, whereas the fungal community exhibited more positive (97.3 %) than negative (2.7 %) correlations. PICRUST predicted the microbial function of adding KHM and BSFA to the soil, and these pathways mainly belong to the degradation and metabolism of organic matter, saprophytic organisms and plant pathogens. In summary, our study demonstrated that the addition of BSFA and KHM increased the nutrients in the ginseng soil and reshaped the microbial function in soils, providing a theoretical foundation for soil improvement and biological control of ginseng diseases. However, due to the limitations of greenhouse cultivation, additional long-term experiments on farmland with different climate changes are recommended.

Rusty root is a widespread problem in ginseng production, which can reduce ginseng quality and root price. The formation of rusty root is a complex process caused by multiple factors, primarily soil physicochemical factors and microorganisms. However, the precise roles played by these factors in the development of this disease remain unclear, especially the role of microorganisms. Deciphering the structure of the rhizosphere microbial communities will provide a more comprehensive and deeper understanding of rusty root disease. Rhizosphere microbial communities from five ginseng fields with different rusty root grades and indices were characterized by MiSeq sequencing. The pattern of beta diversity indicated that rusty root disease might be positively correlated with bacterial community structure, but not with fungal community structure. Rusty root may be caused by excessive Fe (II) oxidation and Fe (III) deposition accompanied by aluminum (Al) and manganese (Mn), in which nitrate-dependent Fe (II)-oxidizing bacteria, including Acidobacteria, Chloroflexi, and Nitrospirae, play a driving role. Moreover, the accumulation of iron (Fe), Al, and Mn could enhance growth and weak invasion of some fungi, thus exacerbating the rust symptoms. However, no correlation was found between the relative abundance of the genus Ilyonectria and rusty root grade or index (P > 0.05); suggesting that Ilyonectria species may not be essential for rusty root disease. Thus, the oxidation and deposition of rhizosphere Fe, Al, and Mn facilitated by nitrate-dependent Fe (II)-oxidizing bacteria might be key factors contributing to rusty root disease. Further studies on the inhibition of Fe, Al, and Mn transformation and accumulation, and application of iron/nitrogen-cycling related bacteria in ginseng soil might elucidate effective methods for preventing rusty root.

Asian ginseng (Panax ginseng) is a valuable medicinal plant that is commercially cultivated in China. A long postharvest storage period is required before ginseng is processed. From October 2019 to May 2020, snow rot was observed on the roots of 4- and 5-year-old fresh ginseng stored in three cold storage facilities located in Tonghua and Changbai cities in northeastern China, which are the most important regions for Asian ginseng production. We sampled 1,000 ginseng roots from the three cold storage facilities, and the average disease incidence was 21%. Initially, sparse hyphae and microsclerotia appeared on the root epidermis. Lesions gradually softened and the epidermis detached easily. Multiple infected sites slowly converged, resulting in the formation of a dense complex of multiple sclerotia and thick hyphae on the surface of the ginseng root as well as internal decay. The infection eventually spread to the adjacent ginseng roots (Fig. 1). Sixteen diseased ginseng roots were collected and then sclerotia were removed from the root surface, immersed in 1% NaClO for 2 min, rinsed three times with sterile water, and placed on potato dextrose agar (PDA) containing streptomycin (40 μg/mL) in Petri dishes. After a 3-day incubation at 20 °C in darkness, 22 suspected Sclerotinia isolates were obtained. Isolates SN1 and SN2 were randomly selected for identification. On PDA, fast-growing colonies produced white, sparse, powdery, and cotton-like aerial mycelia, and the reverse side showed the same color (Fig. 2). Small and white sclerotial primordia formed 3 days later and a ring of sclerotia was detected at the plate periphery. At 7 to 10 days after incubation, the mature sclerotia were black, spherical-to-subspherical, and elongated or fused to form irregular shapes. Each Petri dish produced 55-65 sclerotia, measuring 1.1 × 1.2 to 3.2 × 3.9 mm (n = 100). The sclerotia were firmly attached to the agar surface. The isolates were initially identified as Sclerotinia sp. (Saito 1997). After sequencing the nuclear ribosomal internal transcribed spacer region (MW927134 and MW927135) and the β-tubulin gene (MW929179 and MW929180) (White et al. 1990; Glass and Donaldson 1995), BLAST searches revealed 100% homology with JX262268 and JX296007 of the published S. nivalis strain KGC-S0601, respectively. The pathogenicity of the two isolates was tested using detached ginseng roots. Briefly, healthy roots were washed, surface-disinfested with 75% alcohol, and rinsed with sterile water. Mycelial plugs (5 mm diameter) removed from the margin of actively growing colonies on PDA were placed on the ginseng roots. For each isolate, four roots were inoculated, with two plugs per root. Additionally, PDA plugs without mycelia were used as the negative control. The roots were placed in a fresh-keeping box at 20 °C in darkness and evaluated after 7 days. The pathogenicity test was repeated twice. The symptoms on the inoculated roots were the same as those observed on the roots during cold storage, whereas the control roots remained symptomless. The same fungus was reisolated consistently from all infected roots and its identity was confirmed by resequencing, thereby fulfilling Koch's postulates. To the best of our knowledge, this is the first report of S. nivalis causing postharvest snow rot on Asian ginseng in China. The occurrence of this disease threatens the postharvest storage of Asian ginseng. Hence, effective management strategies must be developed.

Background This study analyzed the effect of silicon (Si) application on the occurrence of ginseng black spot caused by Alternaria panax. We explored the differences in soil physical and chemical factors and microbial community structure following Si application as well as the key factors that affected the occurrence of ginseng black spot in soil. Potted Panax ginseng plants were used to assess the effect of Si treatment on ginseng black spot. Soil physical and chemical properties were comprehensively analyzed. Bacterial communities were analyzed using Illumina HiSeq sequencing targeting the 16S rRNA gene. Results After inoculation with A. panax, the morbidity (and morbidity index) of ginseng with and without Si was 52% (46) and 83% (77), respectively. Soil physical and chemical analysis showed that under the ginseng black spot inoculation, bacterial communities were mainly affected by pH and available potassium, followed by ammonium nitrogen and available Si. NMDS and PLS-DA analyses and the heat maps of relative abundance revealed that Si application elevated the resistance of ginseng black spot as regulated by the abundance and diversity of bacterial flora in rhizosphere soils. Heatmap analysis at the genus level revealed that A. panax + Si inoculations significantly increased the soil community abundance of Sandaracinus, Polycyclovorans, Hirschia, Haliangium, Nitrospira, Saccharothrix, Aeromicrobium, Luteimonas, and Rubellimicrobium and led to a bacterial community structure with relative abundances that were significantly similar to that of untreated soil. Conclusions Short-term Si application also significantly regulated the structural impact on soil microorganisms caused by ginseng black spot. Our findings indicated that Si applications may possibly be used in the prevention and treatment of ginseng black spot.

Continuous cropping of American ginseng (Panax quinquefolius L.) is often associated with the scarcity or unavailability of soil nutrients and an imbalance of rhizosphere microbiota, resulting in low yield and poor plant quality. Inoculation with arbuscular mycorrhizal fungi (AMF) improves plant growth and production by facilitating nutrient acquisition and by modifying the abundance and diversity of rhizosphere microorganisms. In the present study, we investigated the mechanisms by which continuous cropping of American ginseng caused growth inhibition and how AMF biofertilizer application relieved these cropping obstacles. The results showed that: 1) continuous cropping of American ginseng significantly decreased the emergence rate, shoot and root dry weight, rhizosphere soil pH, the contents of ammonium, available phosphorus (P), and available potassium (K) in the rhizosphere, while increasing the root rot disease index and the soil content of nitrate; 2) continuous cropping of American ginseng decreased the diversity of bacteria, while increasing the diversity of fungi, and increased the relative abundances of Acidobacteria and Ascomycota, while decreasing the relative abundances of Actinobacteria, Firmicutes and Zygomycota; 3) in contrast, the application of AMF biofertilizer relieved the negative effects of continuous cropping American ginseng; 4) significant positive correlations were found between Pseudarthrobacter, Streptomyces and the content of ammonium, between Bacillus and the content of available K, and between Mortierella elongata and the content of available P, suggesting that the increase of rhizosphere plant-beneficial bacteria and fungi promoted the contents of available nutrients in the rhizosphere; 5) application of AMF biofertilizer significantly decreased the abundances of soil-borne pathogenic fungi Fusarium oxysporum, F. solani and the deleterious bacteria Candidatus Solibacter. In summary, our results suggest that AMF biofertilizer application improved the continuous cropping of American ginseng growth by increasing the AMF inoculation rate, by recruiting rhizosphere beneficial bacteria and fungi that promote plant-uptake of nitrogen (N) and P, and by suppressing soil-borne pathogens. Therefore, AMF biofertilizer is a probiotic agent that prevents microbial imbalances and nutrient deficiencies during continuous cropping of American ginseng.

Ginseng (Panax ginseng) is a perennial herbaceous plant and a precious traditional Chinese medicine. P. ginseng is widely cultivated in Asia, particularly the Changbai Mountain area in China (Wang et al. 2019). Alternaria species can grow under a wide range of temperatures that occur worldwide (Konstantinova et al. 2002). Alternaria panax was reported as the main cause of Alternaria leaf spot of ginseng (Deng et al. 2013); however, a small-spored Alternaria species was isolated from leaf spot symptoms during recent surveys. In our study, leaf spot disease of P. ginseng was observed during 2017 in the Fusong district, Jilin, China. The disease was widespread, with 20 to 30% of the fields affected. Leaves of the affected plants showed brown to black necrotic spots. The fungus was isolated from symptomatic leaves on potato dextrose agar and characterized morphologically under the microscope. Colonies of pure cultures were initially dark brown and then turned black after 7 days. Strains (TCS 15013001 and TCS 15013002) were grown on water agar embedded with surface-sterilized ginseng spot tissues under a 12/12-h light/dark cycle at room temperature. Conidia observed on the lesions were dark brown or olive-brown, ovoid or ellipsoid, short beaked, with three to seven transverse and zero to five longitudinal septa, and 14.9 to 36.5 μm (average 25.8 μm) × 5.8 to 17.9 μm (average 12.5 μm). Based on its morphological characteristics, the pathogen was identified as Alternaria sp. (Simmons 2007). Single-spore cultures were obtained, and their genomic DNA was extracted. The rDNA internal transcribed spacer (ITS, GenBank accession nos. MN394879 and MN394880), endopolygalacturonase (endoPG, MN410909 and MN410910), Alternaria major allergen (Alta1, MN410911 and MN410912), and the portion of the histone 3 (H3, MN410913 and MN410914), elongation factor 1-alpha (EF1-α, MN410915 and MN410916), the RNA polymerase II 2nd largest subunit (RPB2, MN410917 and MN410918), and glyceraldehyde 3-phosphate dehydrogenase (gpd, MN410919 and MN410920) gene were amplified from the two isolates, respectively (Woudenberg et al. 2015). Sequence analysis of the two isolates showed 99 to 100% identity to that of A. alternata (MG182428 for ITS, MG598798 for endoPG, MG598796 for Alt a1, MG182429 for H3, KU738723 for EF1-α, KU738707 for RPB2, and KP851761 for gpd). Pathogenicity tests were conducted in a greenhouse. Sixty healthy 2-year-old P. ginseng seedlings grown in potting medium were tested in a greenhouse at 20/26°C and about 90% relative humidity with natural light. Of the plants, 30 were sprayed with spore suspension (1 × 10⁵ spores/ml) until most of the leaves were wet. Control treatments (30 plants) were treated with distilled water. The two isolates were tested, and all test plants were covered with clear plastic bags for 3 days to increase humidity. Each treatment had three replicate plants. Six days after inoculation, leaf spots similar to the original ones developed at inoculation sites for all isolates, and A. alternata was consistently reisolated from the induced symptoms. The pathogenicity test was performed three times. A. alternata causing leaf spot of American ginseng was reported in China (Hill and Hausbeck 2008). Also, leaf spot of Panax notoginseng caused by A. alternata was reported in China (Yang et al. 2018). To our knowledge, this is the first report of A. alternata on P. ginseng in China.