Search Results (8)

A previous report showed that methanol extracts from soil collected one year after harvesting American ginseng (Panax quinquefolius) contained activity that increased root rot caused by Ilyonectria mors-panacis. This effect was associated with suppression of the defense responses of P. quinquefolius. The activity was undetectable in soil not previously planted with ginseng, and it was hypothesized that it may be a factor in the development of ginseng replant disease (GRD). GRD can persist for 30 or more years and is associated with root rot from I. mors-panacis. A survey of activity that increases root rot was made of the soil at different times before and after commercial ginseng root harvesting. No activity that increased root rot from I. mors-panacis was detected in the soil of a first American ginseng crop over the three years from planting until prior to harvesting. After harvesting the first crop, no activity was detected during the fall or early spring, but I. mors-panacis’s ability to increase root rot was detected in the soil during late spring, when ginseng crop debris from the first crop had almost completely decayed and the soil had warmed. Activity increasing root rot from I. mors-panacis was also detected in the soil from 1 to 30 years after ginseng harvesting. These results indicate that activity in soil that increases root rot from I. mors-panacis is not detectable until after the crop has been first harvested and then can persist for many years, which is consistent with the long persistence of GRD. Full article

A prior report showed that soil previously planted with American ginseng (Panax quinquefolius) contained compound(s) which could reduce ginseng resistance to root infection by Ilyonectria mors-panacis, and this was not found in extracts from ginseng roots or soils not previously planted with ginseng. However, the origin of this ginseng-related factor in ginseng soils is unknown. An isolate of Pseudomonas plecoglossicida obtained from soil where P. quinquefolius had been harvested grew more in culture media when ginseng root extract was included, indicating the use of compounds in the extract as nutrients. Treatment with cell-free extracts from media containing ginseng root extracts where P. plecoglossicida had been cultured resulted in root lesions caused by I. mors-panacis being significantly larger than roots treated with fresh media containing root extract or with cell-free media inoculated with the same bacterial isolate without root extract. Levels of ginsenosides in the media decreased over time with incubation. Genome sequencing revealed that the bacterium had genes homologous to those reported for ginsenoside metabolism, which can release sugars for microbial growth. Thus, a ginseng soil bacterium, P. plecoglossicida, can create compound(s) suppressive to root rot resistance, similar to that found in soils previously planted with ginseng, indicating that the activity suppressing root rot resistance in soil previously planted with ginseng may be of microbial origin, utilizing compounds from ginseng roots. Full article

Negative plant–soil feedback (PSF) arises when localized accumulations of pathogens reduce the growth of conspecifics, whereas positive PSF can occur due to the emergence of mutualists. Biochar, a carbon-rich material produced by the pyrolysis of organic matter, has been shown to modulate soil microbial communities by altering their abundance, diversity, and activity. For this reason, to assess the long-term impact of biochar on soil microbiome dynamics and subsequent plant performance, we conducted a PSF greenhouse experiment using field soil conditioned over 10 years with Vitis vinifera (L.), without (e.g., C) or with biochar at two rates (e.g., B and BB). Subsequently, the conditioned soil was employed in a response phase involving either the same plant species or different species, i.e., Medicago sativa (L.), Lolium perenne (L.), and Solanum lycopersicum (L.). We utilized next-generation sequencing to assess the abundance and diversity of fungal pathogens and arbuscular mycorrhizal fungi (AMF) within each conditioned soil. Our findings demonstrate that biochar application exerted a stimulatory effect on the growth of both conspecifics and heterospecifics. In addition, our results show that untreated soils had a higher abundance of grape-specialized fungal pathogens, mainly Ilyonectria liriodendra, with a relative abundance of 20.6% compared to 2.1% and 5.1% in B and BB, respectively. Cryptovalsa ampelina also demonstrated higher prevalence in untreated soils, accounting for 4.3% compared to 0.4% in B and 0.1% in BB. Additionally, Phaeoacremonium iranianum was exclusively present in untreated soils, comprising 12.2% of the pathogens’ population. Conversely, the application of biochar reduced generalist fungal pathogens. For instance, Plenodomus biglobosus decreased from 10.5% in C to 7.1% in B and 2.3% in BB, while Ilyonectria mors-panacis declined from 5.8% in C to 0.5% in B and 0.2% in BB. Furthermore, biochar application was found to enrich the AMF community. Notably, certain species like Funneliformis geosporum exhibited increased relative abundance in biochar-treated soils, reaching 46.8% in B and 70.3% in BB, compared to 40.5% in untreated soils. Concurrently, other AMF species, namely Rhizophagus irregularis, Rhizophagus diaphanus, and Claroideoglomus drummondii, were exclusively observed in soils where biochar was applied. We propose that the alleviation of negative PSF can be attributed to the positive influence of AMF in the absence of strong inhibition by pathogens. In conclusion, our study underscores the potential of biochar application as a strategic agricultural practice for promoting sustainable soil management over the long term. Full article

Commercial harvesting of American ginseng (Panax quinquefolius) results in root debris in the soil, but the rate of decay is unknown. In this study, post-harvest root debris decayed mostly over the fall and winter, with almost no ginseng debris remaining in the soil by late spring of the following year. However, a small number of intact pencil-shaped roots were able to survive after harvest and sprout the following spring without any evidence of root decay. Root rot lesions were observed, which included many associated with the root rot pathogen Ilyonectria mors-panacis, with disappearing root rot symptoms observed in the following spring. Ginsenosides in soil were highest just prior to harvest, declining until an increase the following spring. Soil bacterial and fungal populations changed over time after harvest with several peaks in bacterial populations mostly in the fall, but this was less clear for fungal populations, which were dominated by only a few taxa. Harvesting ginseng can leave considerable debris in the soil, impacting its chemistry and microbiota. Ginseng replant disease, where the second crop shows high levels of root rot due to I. mors-panacis infection compared to low levels in the first crop, could be related to the decay of post-harvest crop debris, but additional research is needed to demonstrate this. Full article

Panax quinquefolius shows much higher mortality to Ilyonectria mors-panacis root rot when grown in soil previously planted with ginseng than in soil not previously planted with ginseng, which is known as ginseng replant disease. Treatment of ginseng roots with methanol extracts of previous ginseng soils significantly increased root lesion sizes due to I. mors-panacis compared to roots treated with water or methanol extracts of ginseng roots or non-ginseng soils. Inoculation of water-treated roots with I. mors-panacis increased expression of a basic chitinase 1 gene (PqChi-1), neutral pathogenesis-related protein 5 gene (PqPR5) and pathogenesis-related protein 10-2 gene (PqPR10-2), which are related to jasmonic acid (JA), ethylene (ET) or necrotrophic infection, and also increased expression of an acidic β-1-3-glucanase gene (PqGlu), which is related to salicylic acid (SA). Infection did not affect expression of a cysteine protease inhibitor gene (PqCPI). Following infection, roots treated with ginseng root extract mostly showed similar expression patterns as roots treated with water, but roots treated with previous ginseng soil extract showed reduced expression of PqChi-1, PqPR5, PqPR10-2 and PqCPI, but increased expression of PqGlu. Methanol-soluble compound(s) in soil previously planted with ginseng are able to increase root lesion size, suppress JA/ET-related gene expression and trigger SA-related gene expression in ginseng roots during I. mors-panacis infection, and may be a factor contributing to ginseng replant disease. Full article

A comparison of the virulence, saprophytic growth, and genomes of 12 isolates of Ilyonectria mors-panacis and 4 isolates of I. robusta from Canada pathogenic to Panax quinquefolius was made. There were no significant differences in the average lesion size on detached roots between isolates of the two Ilyonectria species or isolates that originated from infected roots in first- or second-crop ginseng soils. This did not support the hypotheses that I. mors-panacis is always more virulent than I. robusta or that there is selection for higher virulence during the first crop. However, the average growth rate on potato dextrose agar for I. robusta was significantly greater than that of I. mors-panacis, and the average total genome size of I. robusta isolates was significantly smaller with a significantly higher GC content. On dendrograms based on nucleotide sequences of all predicted exons of the genomes, I. robusta isolates were distinguishable from I. mors-panacis isolates, which were similar but could be separated into types 1 and 2. The difference between type 1 and type 2 I. mors-panacis was not related to geographical origin, virulence, growth rate, or mating type. However, the division was also observed for the total predicted secretome, most notably small secreted cysteine-rich proteins and secreted proteases, indicating that type 1 and 2 isolates of I. mors-panacis may interact differently with their environment. Full article

The Ilyonectria radicicola species complex (A.A. Hildebr.) A. Cabral and Crous 2011 contains species of soilborne necrotrophic plant pathogens. The most aggressive to ginseng roots is I. mors-panacis, whereas I. robusta, I. crassa, I. panacis and I. radicicola are less aggressive. Infected ginseng roots show orange-red to black-brown lesions that can expand into a severe root rot, known as disappearing root rot, where only epidermal root tissue remains. Leaves become red-brown with wilting, and stems can have vascular discoloration with black-brown lesions at the base. Less aggressive Ilyonectria species trigger jasmonic acid (JA)-related defenses inducing host ginsenosides, pathogenesis-related (PR) proteins, wound periderm, and cell wall thickening. In contrast, I. mors-panacis triggers reactive oxygen species (ROS) and salicylic acid (SA) production but suppresses JA-related defenses and ginsenoside accumulation. It is also able to suppress SA-related PR protein production. Virulence factors include potential effectors that may suppress PAMP (Pathogen Associated Molecular Patterns) triggered immunity (PTI), polyphenoloxidases, Hsp90 inhibitors, siderophores and cell-wall-degrading enzymes, such as pectinases. Overall, I. mors-panacis appears to be more aggressive because it can suppress JA and SA-related PTI allowing for more extensive colonization of ginseng roots. While many possible mechanisms of host resistance and pathogen virulence mechanisms have been examined, there is a need for using genetic approaches, such as RNAi silencing of genes of Panax or Ilyonectria, to determine their importance in the interaction. Full article

Ginseng root is an economically valuable crop in Canada at high risk of yield loss caused by the pathogenic fungus Ilyonectria mors-panacis, formerly known as Cylindrocarpon destructans. While this pathogen has been well-characterized from morphological and genetic perspectives, little is known about the secondary metabolites it produces and their role in pathogenicity. We used an untargeted tandem liquid chromatography-mass spectrometry (LC-MS)-based approach paired with global natural products social molecular networking (GNPS) to compare the metabolite profiles of virulent and avirulent Ilyonectria strains. The ethyl acetate extracts of 22 I. mors-panacis strains and closely related species were analyzed by LC-MS/MS. Principal component analysis of LC-MS features resulted in two distinct groups, which corresponded to virulent and avirulent Ilyonectria strains. Virulent strains produced more types of compounds than the avirulent strains. The previously reported I. mors-panacis antifungal compound radicicol was present. Additionally, a number of related resorcyclic acid lactones (RALs) were putatively identified, namely pochonins and several additional derivatives of radicicol. Pochonins have not been previously reported in Ilyonectria spp. and have documented antimicrobial activity. This research contributes to our understanding of I. mors-panacis natural products and its pathogenic relationship with ginseng. Full article