Root Rot Pathogen Research Articles

Untargeted Metabolomic Analysis Reveals a Potential Role of Saponins in the Partial Resistance of Pea (Pisum sativum) Against a Root Rot Pathogen, Aphanomyces euteiches.

In soilborne diseases, the plant-pathogen interaction begins as soon as the seed germinates and develops into a seedling. Aphanomyces euteiches, an oomycete, stays dormant in soil and is activated by sensing the host through chemical signals present in the root exudates. The composition of plant exudates may, thus, play an important role during the early phase of infection. To better understand the role of root exudates in plant resistance, we investigated the interaction between partially resistant lines (PI660736 and PI557500) and susceptible pea cultivars (CDC Meadow and AAC Chrome) against A. euteiches during the pre-invasion phase. The root exudates of the two sets of cultivars clearly differed from each other in inducing oospore germination. PI557500 root exudate not only had diminished induction but also inhibited the oospore germination. The contrast between the root exudates of resistant and susceptible cultivars was reflected in their metabolic profiles. Data from fractionation and oospore germination inhibitory experiments identified a group of saponins that accumulated differentially in susceptible and resistant cultivars. We detected 56 saponins and quantified 44 of them in pea root and 30 from root exudate; the majority of them, especially soyasaponin I and dehydrosoyasaponin I with potent in vitro inhibitory activities, were present in significantly higher amounts in both roots and root exudates of PI660736 and PI557500 compared with Meadow and Chrome. Our results provide evidence for saponins as deterrents against A. euteiches, which might have contributed to the resistance against root rot in the studied pea cultivars. [Formula: see text] Copyright © 2024 His Majesty the King in Right of Canada, as represented by the Minister of Agriculture and Agri-Food Canada and the National Research Council of Canada. This is an open access article distributed under the CC BY 4.0 International license.

Antagonistic effect of symbiotic bacteria from entomopathogenic nematodes and Bacillus spp. against Panax ginseng root rot pathogens

Ginseng root rot is a destructive disease of Panax ginseng that seriously affects the yield and quality of P. ginseng. Based on the broad-spectrum suppression properties of entomopathogenic nematode (EPN) symbiotic bacteria, four symbiotic bacteria were selected: Xenorhabdus bovienii (Xbf), Xenorhabdus nematophila (Xna), Xenorhabdus nematophila Cxrd (Xnc) and Xenorhabdus budapestensis (Xbc). Meanwhile, six beneficial Bacillus strains (Bacillus velezensis S1A; Bacillus amyloliquefaciens H4C; Bacillus subtilis N5D; and Bacillus albus HYS, K8, and N2A) were tested. Their individual and combined effects (both in vitro and in P. ginseng slices) on fungi pathogenic to P. ginseng, Fusarium solani, Fusarium proliferatum and Fusarium oxysporum were evaluated. Xenorhabdus budapestensis had the highest suppression effects (up to 82%) on F. solani and F. oxysporum, and a 60% inhibition rate on F. proliferatum, significantly higher than Xnc, Xbf and Xna. Bacillus velezensis and B. subtilis had the strongest suppression rates on F. solani (40%). The combined effects of Xbc and B. subtilis K8 on F. solani and F. oxysporum were stronger than their individual effects. The P. ginseng slice experiment further confirmed the enhanced inhibition of Fusarium by mixing Xbc with B. subtilis K8. In conclusion, we used EPN symbiotic bacteria to suppress P. ginseng root rot and screened two EPN symbiotic bacteria that were highly effective against Fusarium spp. The combination of Bacillus strains with EPN symbiotic bacteria enhanced the suppression effect. Our results provide new biological materials and directions for biological control of P. ginseng root rot.

Differential Responses of Root Rot Pathogen Rhizoctonia solani in Tolerant and Susceptible Varieties of Tomato at Various Physiological Levels

Introduction: This study investigates the defense responses of tolerant versus susceptible varieties of tomato against the hemi biotroph pathogen Rhizoctonia solani. Method: The early infection of Rhizoctonia solani was characterized by a tolerant Pusa Ruby and a susceptible tomato variety, Oriental (VT- 946). Result: The microscopy experiments showed more hyphal growth in a susceptible plant than in a tolerant one. The hyphae formed extensive branching, contacting the host surface to form a greater number of various infection structures for penetration in the susceptible host compared to the tolerant variety. Biochemical assays showed differences in the production of phenolics, proline, hydrogen peroxide, and catalase in the tomato varieties. Conclusion: The differential expression profiles of the early response allene oxide synthase AOS gene were obtained over time in the two hosts.

Reduction of oxidative damage caused by Fusarium falciforme and Fusarium foetens in schefflera plants using chitosan nanoparticles loaded with l-proline or indole butyric acid

BackgroundRoot rot, wilt diseases, and rooting processes have been the major factors that constrain schefflera production. This study focuses on the impact of innovative applications of eco-friendly materials like chitosan nanoparticles loaded with l-proline or indole butyric acid to replace traditional chemical fungicides in controlling root rot and wilt diseases, as well as the vegetative propagation success of leafy stem schefflera cuttings.ResultsFusarium foeten (strain 1) and Fusarium falciforme (strains 2 and 4) were first identified as root rot and wilt pathogens of schefflera in Egypt based on morphological features and confirmed with molecular analyses. Fusarium foetens (strain 1) and F. falciforme (strain 2) have the most aggressive action, as the infection percentages significantly increased in the pathogenicity test. The disease incidence reached 38.88 and 44.44%, respectively, whereas the disease severity was 18.51 and 26.84%, respectively. Chitosan nanoparticles at a concentration of 25 mg/L were the most effective dose, leading to a significant reduction in disease incidence to 25.00%, disease severity to 4.17%, and playing a vital role in activating plant defense, which correlates well with improved growth characteristics. The novel strategy of L-proline loaded on chitosan nanoparticles (LP-CSNPs) application occupied the first rank at protective influence against root rot and wilt disease-induced oxidative stress, signaling a defensive function that was freelance verified. L-proline loaded on chitosan nanoparticles (LP-CSNPs) at 0.125–0.25 g/L had a significant impact on reducing the incidence and severity of root rot and wilt diseases, as well as improving photosynthetic pigments and free radical scavenging activities, which included strengthening plant defense and further validating the findings from the biochemical trait analysis. The TT biplot graph was an influential statistical tool to study the impacts of treatments on schefflera production and its attributes and to discover the interrelationships among them.ConclusionsApplying LP-CSNPs is one of the best techniques to manage schefflera root rot and wilt diseases, since it can be utilized as a growth stimulator and defense activator with sustainable increased efficiency.Graphical

First report of Fusarium falciforme causing root and stem rot in cowpea (syn. black-eyed pea; Vigna unguiculata) in California.

In both April 2018 and September 2019, cowpeas / black-eyed peas (Vigna unguiculata) in one field in Tulare County, California were observed with tap root rot, both underground (foot) and aboveground stem rot, and in some cases canopy decline, compromising bean formation. In both fields, < 5% of plants appeared affected. Foot and stem segments (~1 cm) of 5-10 plants / field were disinfested sequentially with 0.1% Tween 20 (dip), 70% ethanol for 30 s, and 1% sodium hypochlorite for 2 min and placed on 1:10 potato dextrose agar with 0.03% tetracycline and Fusarium selective medium (Leslie and Summerell 2006). Fusarium-like isolates (dominant in isolation plates) were transferred to 0.6% KCl agar, where fusiform, curved macroconidia and varied microconidia in false heads on elongated monophialides were observed, characteristic of the Fusarium solani species complex (FSSC) (Leslie and Summerell 2006). Isolates CS221, CS222, and CS520 (representing different plants and locations) were saved as single hyphal tip cultures. An Illumina-derived genome sequence was assembled (Burkhardt et al. 2019) and partial tef1ɑ and rpb2 sequences (O'Donnell et al. 2022) were extracted from genome sequences in silico. Sequences were 99.9-100% identical to one another and to deposited F. falciforme isolates based on Fusarium ID and Fusarium MLST for tef1ɑ and rpb2, respectively (tef1a accessions: NRRL 28562 and NRRL 32331; rpb2 accession: NRRL 22857), and were deposited in GenBank (accessions in supplementary table). Pathogenicity was evaluated in three-week-old cowpea plants (cv. CB46rk2) in the greenhouse (13.5-33.6℃; 12:12 h L:D). The tap root / stem was wounded (1 mm wide, 2 mm deep) ~ 2 cm below the soil line and drenched with 50 ml of 106 spores / ml 0.1% water agar or with 0.1% water agar (negative control). The trial was arranged in a Randomized Complete Block Design with three blocks and 2-3 plants / isolate / block, and conducted twice. 52 d post-inoculation, below ground tap root / stem rot developed in 83% of F. falciforme-inoculated plants, with lesion lengths ranging from 25.2 ± 4.2 to 29.2 ± 8.0 mm (P = 0.893 for isolate, ANOVA). Canopy decline developed in 33-50% of plants across treatments in trial 1 (P = 0.859 for isolate) but not in trial 2, likely due to cooler conditions in trial 2 (January-March) vs. trial 1 (May-July), which were less stressful. F. falciforme isolates did not affect bean biomass (dry weight) vs. negative controls (12.5-14.8g / plant; P = 0.949 for pathogen treatment). FSSC isolates were recovered from 100% of symptomatic plants in the inoculated treatments but not in negative controls (both trials) and representative isolates from all treatments were confirmed as F. falciforme (tef1a analysis; trial 2 only). This study establishes F. falciforme as a root and stem rot pathogen of cowpea in California-a disease previously attributed to the morphologically and phylogenetically distinct F. phaseoli (syn. F. solani f. sp. phaseoli), but which lacked modern etiological studies (Frate et al. 2018; Geiser et al. 2021). This work is consistent with previous reports of F. falciforme as a root / stem rot pathogen in cowpea (Ajamu et al. 2023) and other beans (Sousa et al. 2017; Duarte et al. 2019). Clarification of disease etiology will improve accurate diagnosis and effective crop rotation-based management, since F. falciforme is also a pathogen of other California crops including melon, tomato and pistachio.

Influence of electron radiation of spring barley seeds on phytopathogenic microflora

Under the conditions of a model pot experiment, the effect of electron irradiation on the phytopathogenic microflora of plant roots and leaves was studied. The studies were carried out on spring barley seeds of the Vladimir variety (reproduction 1), affected by helminthosporiosis (pathogen Bipolaris sorokiniana Shoem.), (natural infectious background). This pathogen causes root rot and leaf spot. The grain was irradiated using a wide-aperture electron accelerator “Duet” with a mesh plasma cathode and the output of the generated beam of a large cross-section into the atmosphere in doses of 1, 2, 3, 4 and 5 kGy. The total administered dose was increased by changing the number of pulses. The radiation dose rate was 100 Gy/pulse, the electron energy was 130 keV (mode 1) and 160 keV (mode 2). The depth of dose absorption did not exceed 300 μm. Based on the conducted studies on the effect of electron irradiation on root rot (pathogen Bipolaris sorokiniana) of spring barley, it was noted that in the tillering and heading phases, when irradiating seed material with a dose of 2 kGy in mode 1 (130 keV), the disease incidence and prevalence decreased by more than 1.5 times compared to the non-irradiated control. In the phase of full grain maturity, the highest value of root infestation (45–50%) and prevalence (95–100%) of Bipolaris sorokiniana were recorded, but statistically significant differences between the irradiated variants and the control were absent. The records of the damage of vegetative plants showed that in the tillering phase, for all irradiation variants in mode 1, the degree of damage to leaves 1–3 increased by 23% compared to the control, and in the heading phase, the degree of damage to the upper leaves (1–3) exceeded the control when irradiated at doses of 2–5 kGy (mode 1) and 1–5 kGy (mode 2) – 2.1–2.8 times for 1 leaf, 1.9–2.0 times for 2 leaves and 1.2 times for 3 leaves.

First report of Botryosphaeria dothidea causing root rot of sugar beet in Serbia.

Botryosphaeria dothidea (Moug.:Fr.) Ces. & De Not. is predominantly recognized as a pathogen of various woody plants, inducing symptoms of stem canker, dieback, and fruit rot worldwide. However, sporadic reports suggest its impact on field crops, including B. dothidea associated with stem canker in soybean and tobacco (Bian et al. 2015; Chen et al. 2021), as well as B. quercuum on sugar beet (Alfieri et al. 1984). In September 2023, during a survey of root rot pathogens of sugar beet (Beta vulgaris L.) in Rimski Šančevi, Serbia (N 45°19´57″; E 19°49'58″), 3% of collected samples exhibited root rot symptoms. Externally, the lesions exhibited a dark brown coloration. On cross-section, the tissue displayed a gradient of discoloration ranging from light to dark brown throughout the roots. The roots were completely rotted. From these samples, two fungal isolates (SR28/II and SR4/III) were obtained from rotted internal root fragments, after washing, surface disinfection (70% ethanol), and plating on potato dextrose agar (PDA). Colonies on PDA were fluffy with abundant aerial mycelium, surface light to dark grey-brown, reverse black in the centre and grey-brown towards the irregular margin, after 7 days at 25°C in the dark. To induce sporulation, isolates were cultivated on 2% water agar with pine needles and incubated under continuous near ultraviolet (NUV) light at room temperature for 30 days. Conidia were hyaline, aseptate, fusiform, subtruncate at the base, subobtuse at the apex, and measured (19.56-) 24.12 - 26.31 (-28.99) x (5.13-) 5.94 - 6.54 (-7.44) µm (mean 25.06 x 6.26 µm, n=100), consistent with description of B. dothidea (Phillips et al. 2013). For molecular identification, DNA was extracted from mycelium of 7-day-old cultures, and internal transcribed spacer region (ITS), partial translation elongation factor 1-alpha gene (TEF) and partial β-tubulin gene (TUB) were amplified using the primer pairs ITS1/ITS4 (White et al. 1990), EF1-728F/EF1-986R (Carbone and Kohn 1999), and Bt2a/Bt2b (Glass and Donaldson 1995), respectively. Multiple sequence alignment and BLAST analyses showed that our isolates had 100% sequence similarity with reference isolates of B. dothidea, including ex-type isolate CBS 115476 (= CMW 8000) in ITS (AY236949), TEF (AY236898), and TUB (AY236927). Maximum likelihood phylogeny of concatenated sequences confirmed the identity of the isolates as B. dothidea. Sequences of ITS, TEF and TUB of isolate SR4/III were submitted to GenBank under accession numbers PP908658, PP911334, PP911333, respectively. The pathogenicity of obtained isolates was assessed on 3-month-old sugar beet plants grown in sterile substrate in the greenhouse. For inoculation, the upper parts of the roots were wounded (10x3 mm) 1 cm above the substrate, using a sterilized nail, and 2x2 mm mycelial plugs of 7-day-old culture grown on PDA were inserted and sealed with parafilm. Control plants were inoculated with sterile PDA plugs. Six plants were used per isolate and for control. After 3 weeks of incubation, the inoculated plants were removed from the substrate and brown rot symptoms were observed upon cross-sectional examination, whereas control roots remained asymptomatic. The pathogen was successfully reisolated and morphologically identified as B. dothidea, fulfilling Koch's postulates. The production of sugar beet, an important industrial crop in Serbia valued for its sugar content, is imperiled by various pathogens. To our knowledge, this is the first report of B. dothidea causing root rot of sugar beet in Serbia and the world. Given its widespread distribution on other hosts and potential aggressiveness, the presence of B. dothidea in sugar beet should not be neglected.

Herbal materials used as soil amendments alleviate root rot of Panax ginseng

Root rot is a serious soil-borne fungal disease that seriously affects the yield and quality of Panxa ginseng. To develop a sustainable strategy for alleviating ginseng root rot, an herb-based soil amendment is suggested in this study. Mixed powers of medicinal herbs (MP) and corn stalks (CS) were used as soil amendments, respectively, along with a control group (CK) without treatment. The application of MP and CS led to significant relief from ginseng root rot. The disease index (%) represents both the incidence rate and symptom severity of the disease. The disease index of the MP and CS group was 18.52% and 25.93%, respectively, lower than that of CK (40.74%). Correspondingly, three soil enzyme activities improved; the antifungal components in the soil increased; and the relative abundances of root rot pathogens decreased in response to MP Soil enzyme activities were negatively correlated with disease grades. MP group also led to possible interactive changes in the communities of soil fungi and chemical components. In conclusion, our results suggest that the use of herb-based soil amendments has significant potential as an ecological and effective approach to controlling root rot disease of ginseng by the changing rhizosphere fungal community and soil compositions.

Genome sequence of Heterobasidion occidentale, a fungus that causes annosus root and butt rot among conifer trees in North America.

We report an annotated draft genome of Heterobasidion occidentale, a fungus (Basidiomycota, Agaricomycetes) that has pathogenic and saprophytic lifestyles. This fungus belongs to the H. annosum (Fr.) Bref. sensu lato species complex that comprises several root rot pathogens. Heterobasidion occidentale causes annosus root and butt rot primarily in true fir (Abies spp.) and spruce (Picea spp.) species throughout western North America.

Корневая гниль яровой пшеницы в условиях Зауралья, варианты оперативной защиты

Abstract. Root rot is a harmful and widespread disease of cereal crops. In the conditions of the Urals, Siberia, and Northern Kazakhstan, its causative agents are various species of fungi of the genus Fusarium and the fungus Bipolaris sorokiniana. The purpose of this study was to comparatively determine the effectiveness of microbiological, chemical and combined protection of spring wheat seeds. Field experiments were carried out on the experimental field of the Kurgan Scientific Research Institute of Agriculture – branch of the Ural Federal Agrarian Scientific Research Centre of the Ural Branch of the Russian Academy of Sciences (Kurgan SRIA – branch of FSBSI UrFASRC, UrB of RAS) in 2019, 2021, 2022. Scientific novelty lies in the determining the competitiveness of various methods of protecting spring wheat seeds in the conditions of the Trans-Urals within the framework of modern cultivation technology. The methods used are generally accepted in the Russian Federation. Results. In conditions of almost annual occurrence of negative natural phenomena for the growth and development of plants (droughts, frosts, sudden changes in temperature, dry winds, etc.), the use of seed treaters can be an additional stress for plants; the presence of the effect of shortening the underground internode can negatively affect field germination culture. To reduce these risks, as well as the pesticide load, we recommend using a combined method of seed protection. It involves the use of a mixture of a bacterial fungicide based on Bacillus subtilis with a chemical disinfectant at half the consumption rate. At the same time, the level of control of phytopathogens is maintained, there is no retardant effect, and economic efficiency is not inferior to the level of using a two-component chemical seed protectant (113–114 %). Chemical protection of seeds reduced the development of root rot pathogens by 63–72 %. The use of combined protection provided good control of phytopathogens, including the dominant fungi Fusarium. The predominant species from the genus Fusarium were the highly dangerous F. oxysporum, F. graminearum, F. sporotrichioides.

Diversity and pathogenicity of Fusarium spp. isolated from cultivated sorghum stems and roots in eastern Australia

AbstractStalk and root rots of cultivated sorghum (Sorghum bicolor) are caused by several Fusarium species worldwide. This study evaluated Fusarium diversity, pathogenicity and population structure amongst 212 isolates obtained from 169 sorghum plants from commercial field crops in eastern Australia. Sequences of translation elongation factor‐1α (tef‐1α), RNA polymerase II largest subunit (rpb1), RNA polymerase II second largest subunit (rpb2) and calmodulin (cmdA) were used to construct multilocus phylogenies that enabled the identification of 16 Fusarium species in Fusarium chlamydosporum species complex (FCSC), Fusarium fujikuroi species complex (FFSC), Fusarium incarnatum‐equiseti species complex and Fusarium oxysporum species complex (FOSC). The majority of isolates (n = 171) belonged to FFSC. The pathogenicity of 17 selected isolates was determined by artificial inoculation of sorghum seedlings and completing Koch's postulates. Isolates of species in FFSC were significantly (p &lt; 0.05) more aggressive as root pathogens in sorghum seedlings than isolates of other species tested and widely distributed across all sampling sites. Amongst the 35 isolates of FOSC, 26 belonged to Fusarium cili, which is only known as an endophyte from healthy roots of Rosa roxburghii in China. Fusarium sporodochiale (in FCSC) and Fusarium contaminatum (in FOSC) are reported as sorghum seedling root rot pathogens for the first time.

First Report of Root Rot on Rhizome of Polygonatum kingianum Caused by Aspergillus awamori

Polygonatum kingianum Coll. et Hemsl (Huangjing), which belongs to the family Asparagaceae, is a perennial traditional Chinese herb with homologous medicinal and edible value (Liu et al., 2021). Huangjing is known to promote blood circulation; it has anti-inflammatory properties, increases immunity, and provides hypoglycemic treatments (Ma et al., 2019). Root rot-infected P. kingianum exhibited withering yellow leaves and stems, rhizome rot, slowed growth, and plant death. In recent years, with an average incidence of up to 45%, the spread of HJ root rot (rhizome and stem bases) has resulted in a significant reduction in the quality and up to 63% reduction in the yields of Sichuan Junlian (104.5°E, 28.2°N) and Guizhou Zhunyi (107.0°E, 27.7°N). After collecting the diseased samples, we used the tissue isolation method to isolate the pathogenic fungi (Wu et al., 2020). Four fungal isolates associated with root rot were obtained: HJ-G2 (two strains), HJ-G3 (one strain), HJ-G4 (one strain), and HJ-G6 (two strains), of which HJ-G2 and HJ-G6 were the dominant species. To determine pathogenicity of each strain, tests were conducted by wounding rhizomes wth an inoculation needle and the pathogen strain was inoculated onto the wound and symptoms observed. The results reveal that HJ-G6 exhibited the strongest pathogenicity against P. kingianum (Figure 1). The HJ-G6 colonies were black, grew rapidly, and produced a large number of spores (Figure 1). A spherical apical sac (conidial head) is formed at the top with two palisades of cells, metulae and phialides, which are shaped radially and produce a large number of spores with 2-5 um in diameter (Figure 2). Morphological observations revealed that the isolate was consistent with Aspergillus awamori (Naher et al., 2021). To further confirm the fungal species, the ribosomal internal transcribed spacer (ITS), β-tubulin (TUB), and elongation factor 1-alpha (EF-1a) gene regions were amplified with ITS1/ITS4, Bt2a/ Bt2b, and EF1/EF2. Primer and PCR amplification were performed as previously described (Paul et al., 2017). The sequences were compared with those obtained from GenBank. The ITS sequences (GenBank accession number OR682143) of the isolates (HJ-G6) were 100% identical to those of the strain PANCOM10 (GenBank accession number MT007535.1) of Aspergillus awamori. The EF-1a sequences (GenBank accession OR752352) of the isolates (HJ-G6) were 98% identical with strain ITEM 4777 (GenBank accession FN665402.1) of Aspergillus awamori. The TUB sequences (GenBank accession number OR752351) of the isolate (HJ-G6) were 100% identical with strain AF158 (GenBank accession MH781275.1) of Aspergillus awamori. Three maximum likelihood trees were constructed using MEGA v5.0 (Kumar et al., 2018) based on the sequences (ITS, TUB, and EF-1a) of the HJ-G6 strain and that of Aspergillus spp. previously deposited in GenBank (Paul et al., 2017). Phylogenetic analysis showed that HJ-G6 belonged to the Aspergillus awamori clade (Figure 3). Combined with morphological analysis and DNA sequencing, HJ-G6 was identified as Aspergillus awamori. To verify pathogenicity, P. kingianum roots were inoculated with the colonized agar discs of the isolates. P. kingianum plants inoculated with uncolonized agar discs were used as controls. After inoculation, P. kingianum roots were moved to the inoculation chamber under high humidity at 28 °C for 1 d and then transferred to a greenhouse. Previous studies have reported that Fusarium sp. are root rot pathogens in the rhizomes of medicinal plants (Pang et al., 2022; Song et al., 2023). In this study, HJ-G2, HJ-G3, and HJ-G4 were used as the positive controls. Typical symptoms of root rot appeared 3 days after inoculation and were similar to those observed in the field, whereas the control plants remained symptomless. According to the results of the inoculation experiment, the pathogenicity of Aspergillus awamori to P. kingianum root rot was significantly stronger than that of Fusarium (Figure 1). The pathogen was isolated from the rotting root of P. kingianum and the ITS region was sequenced again. Alignment analysis of the ITS sequences revealed that the causal agents were consistent with those of the original isolates. These studies fulfill Koch’s postulates. As far as we know, this is the first report of Aspergillus awamori causing root rot in P. kingianum.

Loop-mediated isothermal amplification (LAMP) assay proved the mechanism of biological control against root rot pathogens

BackgroundThe soil-borne fungi, Rhizoctonia solani and Sclerotium rolfsii, are major pathogens of Brassicae crops. This study was performed to clarify the relationship between the accumulation pattern of the genus Trichoderma and disease suppression in frequently inoculated soils with binucleate Rhizoctonia (BNR), Rhizoctonia solani and Sclerotium rolfsii.ResultsAs compared to the control group, five Trichoderma virens strains isolated from soil inoculated with R. solani or BNR significantly reduced the severity of S. rolfsii (85.6–100% covering percentage) and R. solani (95.7–100% covering percentage). Similarly, five T. hamatum strains obtained from soil inoculated with R. solani were shown to be highly suppressive against S. rolfsii (83.9–97.1% covering percentages) and R. solani (60.2–96.2% covering percentages). Four out of five T. hamatum strains obtained from soil infected with S. rolfsii exhibited considerable suppression against S. rolfsii (63.7–91.2% covering percentages), while the SM5 strain did not. The phylogenetic analysis of the TEF and ITS regions of Trichoderma hamatum revealed that most isolates were classified into the same cluster with homology of 99–100%. Five strains of each T. virens and T. hamatum were isolated from the suppressive soil with high antagonistic potentials against R. solani and S. rolfsii. Suppression and antagonistic activity of T. hamatum isolated from soil frequently inoculated with sterile barley grains were negligible, whereas T. hamatum isolated from frequently inoculated soil with BNR and R. solani demonstrated considerable suppression of the pathogens and antagonistic activity. Accumulation and quantification of T. virens and T. hamatum were confirmed using loop-mediated isothermal amplification (LAMP).ConclusionIn conclusion, disease suppression in frequently inoculated soil with BNR, R. solani and S. rolfsii was due to Trichoderma spp. accumulated selectively in each replicate of soil inoculation.

Bioprospecting of microbial agents and their metabolites as potential inhibitors of Phytophthora cinnamomi, the causal agent of avocado root rot

Phytophthora Root Rot (PRR) is one of the economically important diseases infecting avocado causing substantial yield losses worldwide. In this study, the root rot pathogen infecting avocado has been characterized and potential bioagents targeting PRR have been identified through molecular approaches. Field surveys revealed varying degrees of disease severity (54 %–17.5 %) and incidence (50 %–10 %) in Western Ghats of Tamil Nadu, India. The pathogen was isolated and identified as Phytophthora spp. based on morphology which depicted typical coralloid-type growth patterns. Besides, phylogenetic analysis with the ITS, ras-related protein and COX genes showed closed similarity with P. cinnamomi. The isolates showed significant variation in pathogenicity, with PC(TKI)-10 exhibiting the highest severity (70 %) developing typical symptoms. In vitro efficacy assays through dual-plate and volatiles revealed potential inhibitory effects of Trichoderma harzianum T (MP)-7 (81.11 %) and Bacillus amyloliquefaciens B (TI)-3 (76.67 %) against P. cinnamomi, and Scanning Electron Microscopy (SEM) provided insights into the antagonistic mechanisms, revealing physical interactions and enzymatic lysis of the pathogen by T (MP)-7 and B (TI)-3. Furthermore, Gas Chromatography-Mass Spectrometry (GC-MS) analysis identified bioactive compounds in the crude extracts of these bioagents, elucidating their metabolic pathways and potential modes of action against P. cinnamomi. Our findings highlights the importance of P. cinnamomi in avocado and the mechanism of fungal and bacterial bioagents in the sustainable management of the disease.

Ecological and morphological perspectives of root rot pathogens of peanut (Arachis hypogea L.) in Pothwar region of Punjab, Pakistan

Ecological and morphological perspectives of root rot pathogens of peanut (Arachis hypogea L.) in Pothwar region of Punjab, Pakistan

Forest and soil fungal community dynamics are fuelled by root rot pathogen‐induced gaps

Abstract Forest dynamics are driven by micro‐disturbances leading to gap formation. Root rot pathogens can cause mortality to adult trees, which die forming gaps. However, little is known about the biotic and abiotic factors that govern gap creation and expansion such as tree infection or drought resilience, and what are the consequences for nutrient cycling and soil microbiota. We studied the dynamics of gaps created by Heterobasidion abietinum in mountain silver fir (Abies alba) forests from the Spanish Central Pyrenees. Tree‐ring width information was used to evaluate growth patterns of trees located within and at the edge of gaps and under closed canopy conditions. We analysed soil nutrient content and microbial structure at different positions with respect to the gap. Soil fungal community was also characterized by sequencing the ITS2 region. Gaps created by H. abietinum ranged 582–1072 m2 and gathered large amounts of standing and laying dead wood biomass amounting to up to 500 m3 ha−1 of coarse woody debris. This indicates that tree mortality had been occurring over decades, and it was preceded by a long‐term growth decline and impaired drought resilience. Root rot affected trees beyond the current limit of the gaps leading to growth decline, preventing canopy closure and allowing the release of suppressed trees within the gap. Gap formation did neither affect soil fertility nor fungal and bacterial biomass and diversity, but long‐distance ectomycorrhizal fungi were more abundant within gaps. Synthesis. Root rot pathogens play key ecological roles in forest dynamics at fine spatial scale. Heterobasidion abietinum infection, and its interaction with drought, creates and expands gaps by killing large trees and preventing surrounding trees from closing the gap. The survival of mycorrhizal networks to gap formation suggests little disruption of soil fungal communities.

In vitro Evaluation of Bio Control Agents and Botanicals against Mulberry Root Rot Pathogen Lasiodiplodia theobromae

Mulberry root rot is fast spreading disease caused by L. theobromae. The pathogen can be managed by synthetic fungicides. However, enormous use of synthetic fungicides leads to residual toxicity which affects the growth and development of silkworm. In this context, an attempt was made to use potential bio control agents for the management of this pathogen. Seven fungal and five bacterial bio agents evaluated out of them T. viride (Tv – B2), T. harzianum (Th - 44), B. subtilis (Bs - M) and (Bs - O) proved as best for inhibition of mycelial growth of the pathogen. Out of eleven botanical extracts used, garlic proved best at 15 per cent and 20 per cent and agave at 20 per cent concentration against root rot causing pathogen L. theobromae.

First report of root rot of strawberry caused by Fusarium cugenangense, a member of the F. oxysporum species complex, in Tennessee, USA.

Strawberry (Fragaria × ananassa Duch) in Tennessee is cultivated on plastic mulched beds annually, and production is limited primarily by multiple oomycete and fungal root rot pathogens that result in reduced vigor and black root rot disease symptoms. In early June 2018, plants (cv. Chandler) with reduced shoot vigor and size, and black, necrotic stunted roots were collected from Rhea County, TN. Roots and crowns of 10 plants were cut into 1-3 cm pieces and surface sterilized with 0.6% NaOCl, followed by 70% ethanol for 1 min each, and plated on water agar. White mycelia produced after 3 days were transferred to potato dextrose agar amended with 10 mg/liter rifampicin. After 10 days, fungal colonies were light purple on the surface and dark purple on the colony underside, later developing blue-black pigmentation on the underside. Microconidia on carnation leaf agar were ovoid to ellipsoid, aseptate or septate and 8.0 to 24.2 (13.7) × 3.0 to 4.5 (3.8) μm in size, macroconidia were 3 to 5 septate and falcate to almost straight and 33.7 to 52.8 (44.4) × 4.0 to 5.5 (4.9) μm in size (n=80); both conidia were produced on monophialides. Chlamydospores were globose and subglobose, formed terminally and intercalary on aerial, submerged, and surface mycelium, singly or in pairs and were abundantly produced in sucrose broth and on synthetic nutrient-poor agar (SNA) (diam. 7.6 μm). Morphology was consistent with Fusarium oxysporum (Leslie and Summerell, 2006) and F. cugenangense, a member of the F. oxysporum species complex, as described by Maryani et al. (2019). Fungal mycelia were used for PCR (Phire Plant Direct PCR Master Mix, Thermo Scientific, CA) and the translational elongation factor 1-α (EF1α) region was amplified with primers EF-1/EF-2 (O'Donnell et al., 1998), internal transcribed spacer (ITS) regions amplified with primers ITS1/ITS2 (White et al. 1990), and the RNA polymerase second largest subunit region (RPB2) with primer pairs 5f2/7cr and 7cf/11ar (O'Donnell et al., 2022). PCR products of isolate SC5 were sequenced, and sequences compared to all sequences in the FUSARIOID-ID database using polyphasic identification (Crous et al., 2021) with EF1α (GenBank Accession No. ON703236) and RPB2 (OR472390) sequences. The highest similarity (100%) was with isolates of F. cugenangense, including ex-type isolate InaCC F984 (99.94% similarity) (Maryani et al., 2019). F. cugenangense is closely related to F. callistephi and F. elaeidis, but both species lack chlamydospores, and F. elaeidis has polyphialides (Lombard et al, 2019). To satisfy Koch's postulates, healthy rooted strawberry plants produced in soilless media were transplanted into 4 plastic pots (1.2-liter) containing 5% (w/v) fungal inoculum (grown on barley grain) and mixed into the top 5-cm of peat-based soilless medium. Pots were incubated at 25°C and 50% RH in a growth chamber. Four pots without inoculum served as controls. The trial was repeated. Within 8 weeks, all inoculated plants had low vigor, with necrotic and stunted roots. Root sections of control and inoculated plants were plated, and the pathogen was re-isolated from diseased roots of all inoculated plants only and confirmed as F. cugenangense based on morphology and sequence analysis. To our knowledge, this is the first report of F. cugenangense, or any member of the F. oxysporum species complex, causing root rot of strawberry in Tennessee and could be an important component of the production-limiting black root rot disease complex of strawberry.

Diversity and Pathogenicity of Fusarium Root Rot Fungi from Canola (Brassica napus) in Alberta, Canada.

Root rot disease poses a significant threat to canola (Brassica napus), underscoring the need for a comprehensive understanding of its causal agents for more effective disease mitigation. The composition and diversity of fungal pathogens associated with root rot of canola in Alberta, Canada, were evaluated from plant tissue samples collected in 2021 and 2022. The study revealed Fusarium spp. as the predominant pathogens found in almost all surveyed fields. Fusarium avenaceum, F. redolens, and F. solani were among the most frequently recovered species. Greenhouse trials confirmed their pathogenicity, with F. avenaceum and F. sporotrichioides found to be particularly aggressive. Additionally, F. sporotrichioides and F. commune were identified for the first time as canola root rot pathogens. Inoculation with isolates of most species resulted in significant reductions in seedling emergence, plant height, and shoot and root dry weights. Analysis of translation elongation factor 1-α (TEF-1α) and internal transcribed spacer (ITS) sequences confirmed the identity of the Fusarium spp., while concatenating the ITS and TEF-1α sequences enabled improved species differentiation. Geographic and year effects did not influence fungal diversity or aggressiveness, as determined by principal component analysis. This study emphasized the high diversity and impact of Fusarium spp. in causing canola root rot.

Investigating the impact of temperature on growth rate of the root rot fungus, Gymnopus fusipes.

Gymnopus fusipes is an understudied root rot pathogen associated with multiple tree species and is linked to episodes of oak decline across the United Kingdom and Europe. Although the reported distribution of G. fusipes is broad, many observations rely solely on visual identification of fruiting bodies, which can be unreliable, and lack confirmation by molecular and/or isolation data to verify this broad ecological range. Given the paucity of information regarding the true ecological distribution of G. fusipes, it is difficult to predict and model the potential distribution of the species under both current and future climate scenarios. In this study, to determine the growth capabilities of G. fusipes across a range of ecologically relevant temperatures, five geographically diverse isolates of G. fusipes were grown at five different temperatures ranging from 4-37°C, to determine the optimal temperature for G. fusipes growth, and to establish whether geographically diverse isolates exhibit local adaptation to temperature tolerance. Incubation temperature had a significant effect on G. fusipes growth rate, with 25°C representing the optimum (P<0.001). Isolates had differing growth rates at each of the temperatures, with an isolate from the UK having the highest overall growth rate across all five temperatures tested (P<0.001), and at the optimum, increased by a mean value of over 4915 mm2. Local adaptation to temperature tolerance was not found in the isolates tested. These data demonstrate the optimal incubation temperature for future laboratory studies on G. fusipes and provide the first data on the growth rate of this pathogen across ecologically relevant climate ranges that may inform land managers, modellers, and policy makers in predicting the current and potentially future geographical limits of this widespread root rot pathogen.