Root Rot Infection Research Articles

Genomic insights and biocontrol potential of ten bacterial strains from the tomato core microbiome.

Despite their adverse environmental effects, modern agriculture relies heavily on agrochemicals to manage diseases and pests and enhance plant growth and productivity. Some of these functions could instead be fulfilled by endophytes from the plant microbiota, which have diverse activities beneficial for plant growth and health. We therefore used a microbiome-guided top-down approach to select ten bacterial strains from different taxa in the core microbiome of tomato plants in the production chain for evaluation as potential bioinoculants. High-quality genomes for each strain were obtained using Oxford Nanopore long-read and Illumina short-read sequencing, enabling the dissection of their genetic makeup to identify phyto-beneficial traits. Bacterial strains included both taxa commonly used as biofertilizers and biocontrol agents (i.e. Pseudomonas and Bacillus) as well as the less studied genera Leclercia, Chryseobacterium, Glutamicibacter, and Paenarthorbacter. When inoculated in the tomato rhizosphere, these strains promoted plant growth and reduced the severity of Fusarium Crown and Root Rot and Bacterial Spot infections. Genome analysis yielded a comprehensive inventory of genes from each strain related to processes including colonization, biofertilization, phytohormones, and plant signaling. Traits directly relevant to fertilization including phosphate solubilization and acquisition of nitrogen and iron were also identified. Moreover, the strains carried several functional genes putatively involved in abiotic stress alleviation and biotic stress management, traits that indirectly foster plant health and growth. This study employs a top-down approach to identify new plant growth-promoting rhizobacteria (PGPRs), offering an alternative to the conventional bottom-up strategy. This method goes beyond the traditional screening of the strains and thus can expand the range of potential bioinoculants available for market application, paving the way to the use of new still underexplored genera.

CRISPR-Cas9-mediated editing of GmARM improves resistance to multiple stresses in soybean

The growth and development of soybean plants can be affected by both abiotic and biotic stressors, such as saline-alkali stress and Phytophthora root rot. In this study, we identified a stress-related gene—GmARM—whose promoter contained several hormone-response and stress-regulatory elements, including ABRE, TCA element, STRE, and MBS. qRT-PCR analysis showed that the expression of GmARM was the highest in seeds at 55 days after flowering. Furthermore, this gene was upregulated after exposure to saline-alkali stress and Phytophthora root rot infection at the seedling stage. Thus, we generated GmARM mutants using the CRISPR-Cas9 system to understand the role of this gene in stress response. T3 plants showed significantly improved salt tolerance, alkali resistance, and disease resistance, with a significantly higher survival rate than the wildtype plants. Moreover, mutations in GmARM affected the expression of related stress-resistance genes, indicating that GmARM mutants achieved multiple stress tolerance. Therefore, this study provides a foundation for further exploration of the genes involved in resistance to multiple stresses in soybean that can be used for breeding multiple stress-resistance soybean varieties.

Bacillus velezensis B63 and chitosan control root rot, improve growth and alter the rhizosphere microbiome of geranium

The root rot complex of geranium plants caused by Rhizoctonia solani and Macrophomina phaseolina is a major threat, and control of these pathogens predominantly relies on chemicals. This study explored multifaceted applications of Bacillus velezensis (strain B63) and chitosan, assessing their biocontrol efficacy against root rot, and their subsequent effects on rhizosphere communities. Strain B63 was antagonistic to R. solani and M. phaseolina. Under field conditions, greatest efficacy was obtained with strain B63 (36% and 33% disease reductions in, respectively, two growing seasons), chitosan soaking + foliar spray 0.2% (CSF 0.2%) (33 and 27% reductions), and 0.1% chitosan soaking + foliar spray (CSF 0.1%) (33 and 26% reductions). These treatments also changed rhizosphere microbiota, as shown by numbers of colony-forming units (CFU) and 16S rRNA gene microbiome analyses. Concomitant with rhizosphere shifts, essential oil yields and composition were positively affected, as shown by gas chromatography analyses. Chitosan soaking + foliar spray 0.2% increased concentrations of citronellol (1.36-fold), geraniol (1.37-fold), citronellyl formate (1.54-fold), and geranyl formate (1.94-fold) in geranium essential oil, compared with the experimental controls. Strain B63 also increased these essential oils by 1.04- to 1.27-fold. B63 also enhanced eugenol levels by 1.35-fold. Treatments with B63 were more effective than chitosan in improving the geranium plant morphological parameters (plant height, numbers of branches, biomass). These results show that B. velezensis strain B63 treatments have potential for enhancing yields and product quality from geranium plant under root rot infection.

Immunological structure and yield of winter rye varieties bred by the Federal Agricultural Research Center of the North-East named N. V. Rudnitsky

The study was carried out in the conditions of Kirov region in 2019–2023. Against provocative and infectious backgrounds of snow mold, root rot, ergot, powdery mildew, leaf and stem rust, the immunological state and yield of 15 varieties of winter rye created over a 73-year period were studied. Taking into account the breeding methods, the source material used and the year of creation, they were conditionally distributed over five successive periods of breeding and variety change: I – Vyatka 2, Kirovskaya 89; II – Falenskaya 4, Snezhana, Rushnik; III – Flora, Grafinya, Batist; IV – Lika, Talitsa; V – Symphoniya, Garmoniya, Graphit, Graphit FP, Perepel. When recording diseases, well-known methods were used. Research has shown that as a result of breeding, on artificial infectious backgrounds newly created varieties showed a decrease in the development of root rot (Flora, Perepel, Garmoniya – degree of damage 14.6, 15.5 and 15.0 %) and ergot (Flora, Grafinya, Batist, Lika, Symphoniya, Graphit FP, Garmoniya – damage 11.4...15.9 %), grain contamination with sclerotia – 0.38...1.84 %. In varieties of the I period of breeding the degree of root rot infection was 18.8 %, ergot infection – 31.7 %. There is no progress in breeding for resistance to powdery mildew and rust types. The most productive varieties are Lika and Batist (769.3 and 738.7 g/m2), which significantly exceed the Falenskaya 4 standard (578.8 g/m2). A close and significant dependence (p ≥ 095) was revealed between the yield of winter rye varieties and regrowth of plants after snow mold infection (r = 0.693...0.830) as well as grain contamination with sclerotia (r = -0.531...-0.712). The relationship between the yield of winter rye and the development of other studied diseases is insignificant and weak. Considering the high harmfulness of snow mold and ergot in the research region, it is necessary to continue to carry out breeding improvement of varieties for these characteristics, as well as to increase resistance to powdery mildew and types of rust.

Root rot induces a core assemblage of bacterial microbiome to prevent disease infection in Sanqi ginseng

Plants rely on rhizosphere microbes as the first line of defense against pathogen invasion and for maintaining the health of itself. Increasing evidence suggests that plants recruit beneficial microbes to the roots, strengthening their resistance to pathogens. However, the response of the rhizosphere core bacterial microbiome to root rot infection remains largely unclear. In this study, we investigated the rhizosphere and bulk soil core bacterial microbiome of healthy and root rot-diseased Sanqi ginseng in genuine production areas in China. We utilized 16S amplicon sequencing, co-occurrence network analysis, and strain culture approaches to explore whether root rot-induced plant rhizosphere alterations in the bacterial core microbiome could improve disease suppression. Root rot infection had a significant impact on the rhizosphere core bacterial microbiome of Sanqi ginseng. Root rot led to a reduction in the diversity and evenness of the core bacterial microbiome in the rhizosphere, while the variability of the core bacterial community in the rhizosphere increased. In response to fungal root rot pathogen infestation, Sanqi ginseng recruited potentially beneficial bacteria with disease-suppressive functions to the rhizosphere, such as Sphingobium, Pseudoxanthomonas, Pseudomonas, Stenotrophomonas, and Flavobacterium. Function prediction analysis demonstrated a remarkable enrichment of several functional genes involved in antibiotic biosynthesis in the rhizosphere that was infected with root rot. Strain isolation and pot addition experiments further confirmed the effectiveness of root rot rhizosphere-specific enrichment of Operational Taxonomic Units (OTUs) for controlling root rot. Furthermore, co-occurrence network analysis indicated that root rot activated the disease-suppressive functions of the rhizosphere core bacterial microbiome by enhancing complexity and connectivity at the expense of network stability. These findings expand our knowledge of plant-microbe interactions and provides new evidence supporting the “cry for help” strategy for rhizosphere responses to root rot.

Root rot destabilizes the Sanqi rhizosphere core fungal microbiome by reducing the negative connectivity of beneficial microbes.

The stability of microbial communities, especially among core taxa, is essential for supporting plant health. However, the impacts of disease infection on the stability of rhizosphere fungal core microbiome remain largely unexplored. In this study, we delved into the effects of root rot infestation on the community structure, function, network complexity, and stability of Sanqi fungal core microbiomes, employing amplicon sequencing combined with co-occurrence network and cohesion analyses. Our investigation revealed that root rot disease led to a decrease in the α-diversity but an increase in the β-diversity of the Sanqi fungal core microbiomes in the rhizosphere. Notably, Ilyonectria, Plectosphaerella, and Fusarium emerged as indicator species in the rhizosphere core microbiome of root rot-infected Sanqi plants, while Mortierella predominated as the dominant biomarker taxa in healthy soils. Additionally, root rot diminished the complexity and modularity of the rhizosphere networks by reducing the metrics associated with nodes, edges, degrees, and modularity. Furthermore, root rot resulted in a reduction in the proportion of negative connections in the network and the negative/positive cohesion of the entire core fungal microbiome. Particularly noteworthy was the observation that root rot infection destabilized the rhizosphere core fungal microbiome by weakening the negative connectivity associated with beneficial agents. Collectively, these results highlight the significance of the negative connectivity of beneficial agents in ensuring the stability of core microbial community.IMPORTANCERoot rot disease has been reported as the most devastating disease in the production process of artificial cultivated Sanqi ginseng, which seriously threatens the Sanqi industry. This study provides valuable insights into how root rot influences microbial relationships within the community. These findings open up opportunities for disease prevention and the promotion of plant health by regulating microbial interactions. In summary, the research sheds light on the ecological consequences of root rot on rhizosphere fungal microbiomes and offers potential strategies for managing soil-borne diseases and enhancing plant health.

Utilizing biowaste-derived chemicals in designing, preparing, and evaluating the biopesticidal activity of a new formulation for controlling root rot and root knot infection in green beans

Utilizing biowaste-derived chemicals in designing, preparing, and evaluating the biopesticidal activity of a new formulation for controlling root rot and root knot infection in green beans

Shift in the rhizosphere soil fungal community associated with root rot infection of Plukenetia volubilis Linneo caused by Fusarium and Rhizopus species.

Plukenetia volubilis Linneo is an oleaginous plant belonging to the family Euphorbiaceae. Due to its seeds containing a high content of edible oil and rich in vitamins, P. volubilis is cultivated as an economical plantworldwide. However, the cultivation and growth of P. volubilis is challenged by phytopathogen invasion leading to production loss. In the current study, we tested the pathogenicity of fungal pathogens isolated from root rot infected P. volubilis plant tissues by inoculating them into healthy P. volubilis seedlings. Metagenomic sequencing was used to assess the shift in the fungal community of P. volubilis rhizosphere soil after root rot infection. Four Fusarium isolates and two Rhizopus isolates were found to be root rot causative agents of P. volubilis as they induced typical root rot symptoms in healthy seedlings. The metagenomic sequencing data showed that root rot infection altered the rhizosphere fungal community. In root rot infected soil, the richness and diversity indices increased or decreased depending on pathogens. The four most abundant phyla across all samples were Ascomycota, Glomeromycota, Basidiomycota, and Mortierellomycota. In infected soil, the relative abundance of each phylum increased or decreased depending on the pathogen and functional taxonomic classification. Based on our results, we concluded that Fusarium and Rhizopus species cause root rot infection of P. volubilis. In root rot infected P. volubilis, the shift in the rhizosphere fungal community was pathogen-dependent. These findings may serve as a key point for a future study on the biocontrol of root rot of P. volubilis.

Evaluation of reference genes for accurate normalization of qPCR data under biotic stresses in mulberry (Morus indica L.)

Biotic stresses adversely affect the leaf quality as well as the yield of mulberry (Morus spp.) which is used to feed mulberry silkworm (Bombyx mori L.). The different biotic stresses which are of economic importance in mulberry are tukra caused by mealybug insect, root knot disease by nematode, powdery mildew, and root rot by fungi. Reverse transcription-quantitative PCR (RT-qPCR) is a preferred technique to assess the transcript abundance of target genes associated with the diseases using a suitable reference gene as a normalizer. However, no study has been conducted to identify suitable reference genes during different biotic stresses in mulberry. In the present work, six candidate reference genes were quantified through qPCR during different biotic stresses in mulberry and their stability was compared using geNorm, NormFinder and RefFinder algorithms. The analysis of data revealed that actin was the preferred gene during root rot and root knot nematode infection for normalizing gene expression. Ubiquitin gene was the best-scoring gene for mealybug infestation resulting in tukra disease. PP2A (Protein phosphatase 2A) and RPL3 (60S ribosomal protein L3) were highly stable expressing genes during powdery mildew fungi infection. In the combined analysis of all tested biotic stresses, actin gene was the most preferred one followed by ubiquitin and PP2A as reference genes. This study identified the best scoring reference genes in various biotic stresses which will contribute for the precise quantification of target genes by RT-qPCR in mulberry as a tool to unravel the disease resistance mechanism.

Enhancing Vicia faba’s immunity against Rhizoctonia solani root rot diseases by arbuscular mycorrhizal fungi and nano chitosan

BackgroundThe spreading of root rot disease of faba bean plant (Vichia faba L, VF) in Egypt is still of great challenge faced researchers since VF is an important legume in Egypt, because their seeds are used for human feeding. Fungicides are used for treatment of either seeds or soil; unfortunately they cause environmental pollution. Therefore, there is a need to continue research to find out safe natural solutions. In this regard, Arbuscular mycorrhizal fungi (AMF) and chitosan (micro or nanoform) were used as an inhibitory product against Rhizoctonia solani OM918223 (R.solani) either singly or in combinations.ResultsThe results employed herein have exhibited that R.solani caused root rot disease of VF plants in more than 80% of the plants under investigation. Chitosan nanoparticles (Chitosan NPs) were prepared by ionic gelatin method and characterized by using dynamic light scattering (DLS), transmission electron microscopy (TEM) imaging and Fourier transform infra-red (FTIR). Chitosan NPs are spherical with a diameter of 78.5 nm and exhibited the presence of different functional groups. The inhibitory natural products against R.solani were arranged according to their ability to inhibit the pathogen used in the following descending manner; combination of AMF with Chitosan NPs, AMF with micro chitosan and single AMF, respectively. Where, Chitosan NPs showed a potent influence on R.solani pathogen and reduced the pre-and post-emergence of R. solani. In addition, Chitosan NPs reduced Disease Incidence (DI %) and Disease Severity (DS %) of root rot disease and are widely functional through mixing with AMF by about 88% and 89%. Further, Chitosan NPs and micro chitosan were proved to increase the growth parameters of VF plants such as nutritional status (mineral, soluble sugar, and pigment content), and defense mechanisms including total phenol, peroxidase, and polyphenol oxidase in mycorrhizal plants more than non-mycorrhizal one either in infected or healthy plants. Moreover, activity of AMF as an inhibitory against R.solani and improvement natural agent for VF growth parameters was enhanced through its fusing with Chitosan NPs.ConclusionsThe use of AMF and Chitosan NPs increased faba bean plant resistance against the infection of root rot R. solani, with both prevention and cure together. Therefore, this research opens the door to choose natural and environmental friendly treatments with different mechanisms of plant resistance to disease.

Incorporation of zinc sulfide nanoparticles, Acinetobacter pittii and Bacillus velezensis to improve tomato plant growth, biochemical attributes and resistance against Rhizoctoniasolani

Green nanobiotechnology and beneficial bacterial strains as biofertilizers are crucial in agriculture to achieve food security. Both these strategies have been individually studied in improving plant resistance against phytopathogens along with enhancing plant productivity. Therefore, objective of this study was to explore the eco-friendly and cost-effective approach of utilizing plant growth promoting and disease suppressing bacterial strains and nanoparticles, individually as well as in combination, as bio-stimulants to improve plant growth, antioxidant defense system, nutrition and yield of tomato. A pot experiment was conducted to investigate the zinc sulfide nanoparticles (ZnS NPs) synthesized by using Jacaranda mimosifolia flower extracts (JFE), Acinetobacter pittii and Bacillus velezensis either individually or in combinations to check their potential against Rhizoctonia solani in tomato to suppress root rot infection and improve growth and yield. Among all the combinations the JFE-ZnS NPs + B. velezensis compared to untreated infected plants showed minimum disease incidence and maximum significant protection (66%) against R. solani instigated root rot that was followed by JFE-ZnS NPs + A. pittii and individual application of JFE-ZnS NPs by 58%. The same treatment showed maximum significant increase in plant fresh and dry biomass. B. velezensis significantly increased the photosynthetic pigments when applied individually. However, JFE-ZnS NPs alone and in mixed treatments with B. velezensis efficiently improved total soluble protein, sugar and phenolic contents. The same interactive application of JFE-ZnS NPs + B. velezensis improved the tomato plant nutrition (silicon (Si), magnesium (Mg), calcium (Ca) and potassium (K)) and redox quenching status by improving the activity of antioxidant defense enzymes. Overall, the interactive use of JFE-ZnS NPs with A. pittii and B. velezensis very appropriately prepared the host plant to fight against the negative effects of root rot pathogen in tomato. Advancements in interactively investigating the nanoparticles with beneficial plant growth promoting bacterial strains importantly can contribute in resolving the challenges of food security. According to our information, this is a pioneer report for implying JFE-ZnS NPs in synergism with A. pittii and B. velezensis to hinder the root rot in tomatoes.

Shift in fungal communities associated with Pinus sylvestris stands affected by root rot

Introduction
 Scots pine (Pinus sylvestris) covers large areas in European regions with significant economic importance to Ukrainian forest industry. Root rot caused by the wood-decay fungus Heterobasidion annosum damages both below- and above-ground parts of Scots pines. The disease progress is likely to be affected by reshaping in the forest such as soil properties, vegetation composition, and tree age. These changes are apparently followed up by paralleled shifts in fungal community composition on forest soil with potential feedback on ecosystem functioning.
 The objective of the study was to screen fungal groups associated with the root system of P. sylvestris in stands affected by H.annosum s.s. to better understand the pathogenesis and development of root rot infection, as well as to recognize whether root size and disease severity affect diversity of fungi of the root system in the forest-steppe conditions of Ukraine. The additional object was to study other resident microflora of P. sylvestris root infested by H.annosum s.s. to find out whether the H. annosum s.s. impacts the overall diversity of other fungi.
 Materials and Methods
 The field study was carried out in 2018–2020. Field study sites were pure pine forest stands located in Kharkiv region (compartment 126, subcompartment 7, tract Bugri, Kharkiv Forest Research Station). Wood core and root samples from P. sylvestris were collected from the five infected (50–100 m apart from each other) and five non-infected trees (up to 500 m apart from the infested area and 50–100 m apart from each other). Wood and root samples were used for fungal culturing and direct sequencing using ITS1F and ITS4 primers.
 Results
 In the present study, we tried to evaluate fungal communities across diseased Pinus sylvestris stands and investigated correlations between taxonomic composition and forest health. Not surprisingly, root rot infestation had a significant effect on root-associated fungal abundance and diversity. During disease development, the root-associated fungal community shifted in composition from dominance by saprotrophic fungi to ectomycorrhizal and pathogenic fungal species. Our results suggested that maintenance of functional diversity in the root-associated fungal community may sustain long-term forest health or even root rot resistance to some extent by retaining a capacity for symbiosis-driven recycling of organic nutrients; however, this hypothesis is necessary to carefully examine and prove further.
 Conclusions
 Fungal culturing from 10 surface-sterilized wood cores resulted in 21 fungal cultures, 2.1 per wood segment. Direct sequencing from 40 surface-sterilized segments of lateral roots resulted in 247 fungal sequences or 6.2 per root segment on average. The most dominant fungi from the infested trees of Pinus sylvestris were Dactylonectria macrodidyma (4.98%), Acremonium sp (4.52%), Cladosporium cladosporioides (4.07%) from Ascomycota and Heterobasidion annosum s.s. (4.07%) from Basidiomycota, while for non-infested group Unidentified Ascomycota175244 (13.19%), Penicillium spinulosum (9.89%), Acremonium sp. (8.79%), Bionectriaceae sp. (8.79%) were the most common.
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Coptischinensis Franch root rot infection disrupts microecological balance of rhizosphere soil and endophytic microbiomes.

The ecological balance of the plant microbiome, as a barrier against pathogens, is very important for host health. Coptis chinensis is one of the important medicinal plants in China. In recent years, Illumina Miseq high-throughput sequencing technology was frequently used to analyze root rot pathogens and the effects of root rot on rhizosphere microorganisms of C. chinensis. But the effects of root rot infection on rhizosphere microecological balance of C. chinensis have received little attention. In this study, Illumina Miseq high-throughput sequencing technology was applied to analyze the impact on microbial composition and diversity of C. chinensis by root rot. The results showed that root rot infection had significant impact on bacterial α-diversity in rhizome samples, but had no significant effect on that in leaf samples and rhizosphere soil samples, while root rot infection exhibited significant impact on the fungal α-diversity in leaf samples and rhizosphere soil samples, and no significant impact on that in rhizome samples. PCoA analysis showed that the root rot infection had a greater impact on the fungal community structure in the rhizosphere soil, rhizome, and leaf samples of C. chinensis than on the bacterial community structure. Root rot infection destroyed the microecological balance of the original microbiomes in the rhizosphere soil, rhizome, and leaf samples of C. chinensis, which may also be one of the reasons for the serious root rot of C. chinensis. In conclusion, our findings suggested that root rot infection with C. chinensis disrupts microecological balance of rhizosphere soil and endophytic microbiomes. The results of this study can provide theoretical basis for the prevention and control of C. chinensis root rot by microecological regulation.

UAV-Based Hyperspectral Imagery for Detection of Root, Butt, and Stem Rot in Norway Spruce

Numerous species of pathogenic wood decay fungi, including members of the genera Heterobasidion and Armillaria, exist in forests in the northern hemisphere. Detection of these fungi through field surveys is often difficult due to a lack of visual symptoms and is cost-prohibitive for most applications. Remotely sensed data can offer a lower-cost alternative for collecting information about vegetation health. This study used hyperspectral imagery collected from unmanned aerial vehicles (UAVs) to detect the presence of wood decay in Norway spruce (Picea abies L. Karst) at two sites in Norway. UAV-based sensors were tested as they offer flexibility and potential cost advantages for small landowners. Ground reference data regarding pathogenic wood decay were collected by harvest machine operators and field crews after harvest. Support vector machines were used to classify the presence of root, butt, and stem rot infection. Classification accuracies as high as 76% with a kappa value of 0.24 were obtained with 490-band hyperspectral imagery, while 29-band imagery provided a lower classification accuracy (~60%, kappa = 0.13).

Evaluation of Fungicide Soil Drench Treatments to Manage Black Root Rot Disease of Avocado.

Four common fungicidal products were evaluated for their effect on symptoms caused by two nectriaceous black root rot fungi, Calonectria ilicicola and Dactylonectria macrodidyma, when applied as pot drenches to avocado (Persea americana) seedlings in the greenhouse. Applications of fludioxonil, thiophanate-methyl + etridiazole, prochloraz, and prochloraz MnCl at 2 and 4 weeks after inoculation with C. ilicicola significantly reduced root necrosis and improved root and aboveground plant biomass compared with water-treated controls. Fludioxonil reduced necrosis by 60% and had a significantly lower frequency of reisolation of C. ilicicola than the other three fungicide treatments. D. macrodidyma inoculation caused less severe symptoms in seedlings than C. ilicicola despite the longer duration of the trial. Pot drenches with fludioxonil, thiophanate-methyl + etridiazole, and prochloraz MnCl, but not prochloraz alone, significantly reduced root necrosis caused by D. macrodidyma. Prochloraz MnCl was the only fungicide treatment to increase root and plant biomass compared with water-treated controls. Both fludioxonil and prochloraz MnCl reduced the frequency of reisolation of D. macrodidyma from necrotic roots by about 50% compared with the other fungicides or water controls. The results indicated that drenches with these fungicides may suppress existing low to moderate black root rot infection, allowing new root growth and improved establishment in the orchard. Fungicide drenching must not replace best-practice disease management strategies in nurseries but may be a useful tool in crisis situations.

Opportunities and limitations of thinning to increase resistance and resilience of trees and forests to global change

AbstractWe reviewed recent literature to identify the positive and negative effects of thinning on both stand- and tree-level resistance and resilience to four stressors that are expected to increase in frequency and/or severity due to global change: (1) drought, (2) fire, (3) insects and pathogens, and (4) wind. There is strong evidence that thinning, particularly heavy thinning, reduces the impact of drought and also the risk and severity of fire when harvest slash is burned or removed. Thinning also increases the growth and vigor of residual trees, making them less susceptible to eruptive insects and pathogens, while targeted removal of host species, susceptible individuals and infected trees can slow the spread of outbreaks. However, the evidence that thinning has consistent positive effects is limited to a few insects and pathogens, and negative effects on root rot infection severity were also reported. At this point, our review reveals insufficient evidence from rigorous experiments to draw general conclusions. Although thinning initially increases the risk of windthrow, there is good evidence that thinning young stands reduces the long-term risk by promoting the development of structural roots and favouring the acclimation of trees to high wind loads. While our review suggests that thinning should not be promoted as a tool that will universally increase the resistance and resilience of forests, current evidence suggests that thinning could still be an effective tool to reduce forest vulnerability to several stressors, creating a window of opportunity to implement longer term adaptive management strategies such as assisted migration. We highlight knowledge gaps that should be targeted by future research to assess the potential contribution of thinning to adaptive forest management. One of these gaps is that studies from boreal and tropical regions are drastically underrepresented, with almost no studies conducted in Asia and the southern hemisphere. Empirical evidence from these regions is urgently needed to allow broader-scale conclusions.

Beyond blight: Phytophthora root rot under climate change limits populations of reintroduced American chestnut

AbstractAmerican chestnut (Castanea dentata) was functionally extirpated from eastern US forests by chestnut blight, caused by a fungus from Asia. As efforts to produce blight‐resistant American chestnut germplasm advance, approaches to reintroduce chestnut throughout its former range are being developed. However, chestnut is also quite susceptible to a root disease in the southern half of its former range, and the pathogen that causes the disease (Phytophthora cinnamomi) is expected to move northward as climate warms. Genetic resistance to root rot appears to vary among individual chestnut trees, and the prevalence of resistance is highly uncertain. Because restoration of a self‐sustaining chestnut population is ultimately a landscape‐scale problem, we used a process‐based forest landscape model (LANDIS‐II) to conduct experiments to quantify the effects of root rot on the effectiveness of chestnut population restoration efforts in the center of the former range of chestnut under various climate scenarios. We developed a new LANDIS‐II extension to simulate root rot‐induced tree mortality as a function of temperature and soil moisture. We conducted a factorial simulation experiment with climate and resistance to root rot as factors and found that root rot greatly reduced chestnut biomass on the landscape, even when resistance to root rot infection was at the highest levels currently observed in published studies. Warming climate enhanced the virulence of the pathogen and resulted in a greater reduction in chestnut biomass. Results indicate that root rot has the potential to seriously hamper chestnut restoration efforts if resistance of chestnut is not enhanced through breeding and biotechnology, suggesting restoration efforts will be more successful if targeted to latitudes, elevations, and site conditions where root rot is not expected to be present well into the future, including areas north of the historical chestnut range (Canada). These results demonstrate the vital importance of incorporating root rot resistance into the larger blight resistance breeding program.

Coptis Chinensis Franch Root Rot Infection Disrupts Microecological Balance of Rhizosphere Soil and Endophytic Microbiomes

Coptis Chinensis Franch Root Rot Infection Disrupts Microecological Balance of Rhizosphere Soil and Endophytic Microbiomes

Infection and Spread of Root Rot Caused by Heterobasidion parviporum in Picea abies Stands after Thinning: Case Studies on Former Pasture and Meadow Lands

Afforestation of former agricultural lands is a common practice in several countries. This is beneficial for avoiding diseases carry-over from previous forest generations and to expand forest areas. However, several biotic and abiotic risks have been reported in such stands, including a higher risk of Heterobasidion root rot after thinning. Therefore, this study investigates the spread of Heterobasidion root rot in three Picea abies (L.) Karst. plantations in Latvia established on former pasture and meadow lands and subjected to forest management practices. Initially, to determine average infection rate, we sampled all standing trees (157 in total) along transects within sampling areas. On the transects, the proportion of trees suffering from Heterobasidion root rot varied from 16 to 33% among stands. Based on those data and observed dieback over all the stands, we established circular sample plots in disease centres where all trees and stumps were analysed. The average infection rate in the circular plots varied from 34 to 41%. Obtained Heterobasidion isolates were analysed with species-specific primers and were all determined to be Heterobasidion parviporum Niemelä & Korhonen. Isolates were paired to detect the number and size of genotypes. Of 141 genets examined, 99 were isolated from only one tree or stump, while 42 formed genets including two or more trees or stumps indicating spread of infection through root contacts. The total number of Heterobasidion genets per hectare in studied stands varied from 72 to 484. The following conclusions were reached: (i) stands on former non-forest lands (pastures and meadows) can be highly susceptible to Heterobasidion infection after thinning, (ii) the pathogen may form expanding territorial clones in both former pasture and meadows and (iii) stump treatment with biological or chemical control agents is recommended to prevent Heterobasidion infections.

Phytosanitary problems in the development of No-Till technology in the Stavropol Territory

Relevance. The technology of cultivation of field crops without soil tillage — No-Till has been actively started to be introduced in agriculture of Stavropol Territory and other regions of the country. While mastering this technology, changes occurred in the species composition of harmful objects affecting the formation of crops. Methods. The purpose of the research is to study the phytosanitary condition of crops in field crop rotations without soil tillage, compared to the traditional technology. The research was conducted on the experimental fields of “North Caucasian FNAC” and industrial crops of agricultural enterprises in the Stavropol Territory. Pest numbers were determined and accounted for using methods and reference books generally accepted in plant protection. Results . As a result of research, the negative impact of post-harvest plant residues of winter wheat on subsequent crops in crop rotation, such as winter wheat, rape and others, was determined. In addition, winter wheat straw, which is not put into the soil, is a source of root rot infection. For the first time, a cotton shovel significantly damaged winter wheat in the arid regions of Stavropol Krai. For the first time, cereal leaflets started to damage corn and sunflower, damaging up to 70% of sprouts, while neighboring fields with traditional technology were not inhabited. Damaged by caterpillars, the young leaves of sunflower at the point of growth deformed, which later led to the formation of new underdeveloped stems. Mouse-like rodents on corn and sunflower, where the population reaches 200 colonies per 1 ha, were found to be harmful, while they were not found on traditional technology. The new pest of sunflower and corn field slug can completely destroy sprouts of these crops cultivated with No-Till technology. Studies have shown that it is necessary to adjust the system of plant protection for field crops cultivated using the technology without soil tillage.