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Ridomil Gold SL (45.3% a.i. mefenoxam) is a widely used chemical fungicide for the control of oomycetes. However, its impact on fungal communities remains unexplored. Therefore, the goal of this study was to examine the effects of mefenoxam on the temporal dynamics of fungal taxonomic and functional diversities during carrot cultivation under four treatment groups: mefenoxam application with and without Pythium inoculation, and untreated control groups with and without Pythium inoculation. Our in vitro sensitivity assay showed that the maximum recommended concentration of mefenoxam, 0.24 ppm, did not suppress the mycelial growth of P. irregulare. At 100 ppm, mycelial growth was only reduced by 11.4%, indicating that the isolate was resistant to mefenoxam. MiSeq sequencing data revealed transient taxonomic variations among treatments 2 weeks post-treatment. Mortierella dominated the fungal community in the mefenoxam-Pythium combination treatment, as confirmed through PCR using our newly designed Mortierella-specific primers. Conversely, mefenoxam-Pythium combination had adverse effects on Penicillium, Trichoderma, and Fusarium, and decrease the overall alpha diversity. However, these compositional changes gradually reverted to those observed in the control by the 12th week. The predicted ecological functions of fungal communities in all Pythium and mefenoxam treatments shifted, leading to a decrease in symbiotrophs and plant pathogen functional groups. Moreover, the community-level physiological profiling approach, utilizing 96-well Biolog FF microplates, showed discernible variations in the utilization of 95 diverse carbon sources among the treatments. Notably, arbutin, L-arabinose, Tween 80, and succinamic acid demonstrated a strong positive association with Mortierella. Our findings demonstrate that a single application of mefenoxam at its recommended rate triggers substantial taxonomic and functional shifts in the soil fungal community. Considering this impact, the conventional agricultural practice of repeated mefenoxam application is likely to exert considerable shifts on the soil ecosystem that may affect agricultural sustainability.

Picarbutrazox is the active ingredient of Vayantis®, a novel seed treatment fungicide developed by Syngenta and discovered by Nippon Soda. Vayantis® received registration from the US EPA in 2021. Picarbutrazox is a systemic fungicide and belongs to the tetrazolyloximes chemical group of fungicides, and its mode of action is still unknown (FRAC group U17). Picarbutrazox targets oomycete plant pathogens and controls diseases caused by Pythium, Phytophthora, and downy mildews. Picarbutrazox is in a new mode-of-action group with no known cross-resistance to other oomycete compounds. The sensitivity to Picarbutrazox of 528 isolates belonging to 40 different Pythium species was determined in vitro. Pythium isolates were collected from infected plants including corn, soybean, cotton, and other crops from 17 different states. Pythium isolates were also obtained from collections kept at universities. Isolates were identified at the species level using morphological and molecular tools. Mycelial growth inhibition was quantified using the following Picarbutrazox concentrations: 0, 0.00001, 0.0001, 0.001, 0.01, and 0.1 mg/L. All the species of Pythium tested were sensitive to Picarbutrazox. The sensitivity distribution (EC50 values) across all the Pythium species tested had a mean sensitivity of 0.000376 mg ai/L. The Picarbutrazox sensitivity of 40 species of Pythium species has been documented, and results demonstrate the high in vitro intrinsic activity of this fungicide to control Pythium species. The high potency of Picarbutrazox to control Pythium diseases in corn, soybeans, cotton, and other crops has also been demonstrated under field conditions when used as a seed treatment. Picarbutrazox, with its novel mode of action, will contribute to the management of potential fungicide resistance issues developed by other fungicide products controlling Pythium, including mefenoxam and ethaboxam. [ABSTRACT FROM AUTHOR]

Carrot is a major root vegetable crop grown in many parts of the world. In Europe, cavity spot disease continues to have a major impact on marketable yield. The disease is caused by several Pythium spp., with P. violae the main pathogen in the UK and results in small black lesions on mature carrot roots. The lack of reliable inoculation methods for these Pythium pathogens has, for many years, hampered the identification of new effective crop protection products or carrot varieties that are resistant to the disease. In this research, inoculation methods were developed for P. violae using mycelium or oospores, each of which successfully induced typical cavity spot symptoms in both pot‐ and field‐grown carrots as well as consistent root stunting in the former. These methods were also used to successfully identify carrot cultivars with resistance to cavity spot and confirmed the efficacy of the fungicide metalaxyl‐M against the disease. Results therefore demonstrated that the inoculation methods should be reliable for identifying the efficacy of crop protection products, assessing cavity spot resistance and for further studies investigating the biology and epidemiology of the pathogen. [ABSTRACT FROM AUTHOR]

To describe the first case of Pythium insidiosum keratitis masquerading as dematiaceous fungal keratitis in a seropositive male. A 44-year-old seropositive male previously treated for acute retinal necrosis presented with pain and defective vision in the right eye following a mud injury 5 days back. Presenting visual acuity was hand movements close to the face. Ocular examination revealed a 7 × 7 mm dense, greyish-white mid stromal infiltrate with pigmentation and few tentacles. The clinical diagnosis suggested fungal keratitis. Corneal scraping on 10% KOH and Gram stain revealed slender, aseptate hyaline hyphae. Before culture results, the patient was treated with topical 5% natamycin and 1% voriconazole, but the infiltrate progressed. Culture on 5% sheep blood agar revealed white fluffy, submerged, shiny, and appressed colonies, and Pythium insidiosum was confirmed by zoospore formation. The patient was further managed with topical linezolid 0.2% hourly, azithromycin 1% hourly, and adjuvant drugs. This is an uncommon presentation of Pythium keratitis masquerading as dematiaceous fungal keratitis in an immunocompromised male. [ABSTRACT FROM AUTHOR]

Pythium sensu stricto (s.s.) and Globisporangium species are important components of the soil microbial community and exhibit diverse lifestyles, including mycoparasitism. However, a comprehensive understanding of the species diversity of these mycoparasites in the West Azarbaijan province of Iran is lacking. In this study, a total of 114 mycoparasitic Pythium s.s. and Globisporangium isolates were obtained from agricultural soils collected from six regions in the province. Through DNA barcoding, all Globisporangium isolates were identified as G. nunn, while the barcode markers were insufficient to accurately resolve species boundaries in Pythium s.s. By combining morphological and multilocus sequence data, five species within the genus Pythium s.s. were identified: P. salmasense sp. nov., a potentially new species, and three known species, P. acanthicum, P. ornamentatum, and P. periplocum. Pythium ornamentatum was the most common species and found in all regions studied, followed by G. nunn and P. acanthicum, which were both isolated from four regions. While the isolates of G. nunn showed no mycoparasitic activity against Sclerotinia sclerotiorum, all Pythium s.s. species were capable of infecting the hyphae of this pathogen. The existence of mycoparasitic species is promising for biological control of soil‐borne fungal pathogens in the province. The widespread occurrence of P. ornamentatum, G. nunn, and P. acanthicum may suggest their adaptation to local soil and environmental conditions, indicating their potentially superior effectiveness in controlling plant diseases across different regions if used as biocontrol agents. [ABSTRACT FROM AUTHOR]

Bacterial endophytes from plants harbor diverse metabolites that play major roles in biocontrol and improve plant growth. In this study, a total of 12 endophytic bacteria were isolated from the ginger rhizome. The strain K3 was highly effective in preventing mycelia growth of Pythium myriotylum (78.5 ± 1.5% inhibition) in dual culture. The cell‐free extract (2.5%) of endophyte K3 inhibited 76.3 ± 4.8% mycelia growth, and 92.4 ± 4.2% inhibition was observed at a 5% sample concentration. The secondary metabolites produced by Bacillus licheniformis K3 showed maximum activity against Pseudomonas syringae (24 ± 1 mm zone of inhibition) and Xanthomonas campestris (28 ± 3 mm zone of inhibition). The strain K3 produced 28.3 ± 1.7 IU mL−1 protease, 28.3 ± 1.7 IU mL−1 cellulase, and 2.04 ± 0.13 IU mL−1 chitinase, respectively. The ginger rhizome treated with K3 in the greenhouse registered 53.8 ± 1.4% soft rot incidence, and the streptomycin‐treated pot registered 78.3 ± 1.7% disease incidence. The selected endophyte K3 improved ascorbate peroxidase (1.37 ± 0.009 µmole ASC min−1 mg−1 protein), catalase (8.7 ± 0.28 µmole min−1 mg−1 protein), and phenylalanine ammonia‐lyase (26.2 ± 0.99 Umg−1) in the greenhouse. In addition, K3 treatment in the field trial improved rhizome yield (730 ± 18.4 g) after 180 days (p < 0.01). The shoot length was 46 ± 8.3 cm in K3‐treated plants, and it was about 31% higher than the control treatment (p < 0.01). The lytic enzyme‐producing and growth‐promoting endophyte is useful in sustainable crop production through the management of biotic stress. [ABSTRACT FROM AUTHOR]

Introduction: The composition and structure of natural soil are very complex, leading to the difficult contact between hydrophobic organic compounds and degrading-bacteria in contaminated soil, making pollutants hard to be removed from the soil. Several researches have reported the bacterial migration in unsaturated soil mediated by fungal hyphae, but bacterial movement in soil of different particle sizes or in heterogeneous soil was unclear. The remediation of contaminated soil enhanced by hyphae still needs further research. Methods: In this case, the migration and biodegradation of Diaphorobacter sp. LW2 in soil was investigated in presence of Pythium ultimum. Results: Hyphae could promote the growth and migration of LW2 in culture medium. It was also confirmed that LW2 was able to migrate in the growth direction and against the growth direction along hyphae. Mediated by hyphae, motile strain LW2 translocated over 3 cm in soil with different particle size (CS1, 1.0-2.0 mm; CS2, 0.5-1.0mm; MS, 0.25-0.5 mm and FS, <0.25 mm), and it need shorter time in bigger particle soils. In inhomogeneous soil, hyphae participated in the distribution of introduced bacteria, and the total number of bacteria increased. Pythium ultimum enhanced the migration and survival of LW2 in soil, improving the bioremediation of polluted soil. Discussion: The results of this study indicate that the mobilization of degrading bacteria mediated by Pythium ultimum in soil has great potential for application in bioremediation of contaminated soil. [ABSTRACT FROM AUTHOR]

An investigation into oomycete diversity in rice paddies of Fars Province in Iran led to the identification of two new Pythium sensu lato (s.l.) species as Globisporangium izadpanahii sp. nov. and Pythium banihashemianum sp. nov. The identification was based on morphological and physiological features as well as on the phylogenetic analysis of nuclear (ITS and βtub) and mitochondrial (cox1 and cox2) loci using Bayesian inference and Maximum Likelihood. The present paper formally describes these two new species and defines their phylogenetic relationships with other congeneric species. According to multiple gene genealogy analysis, G. izadpanahii sp. nov. was grouped with other species of Globisporangium (formerly, clade G of Pythium s.l.) and was closely related to both G. nagaii and the recently described G. coniferarum. The second species, designated P. banihashemianum sp. nov., was grouped with other species of Pythium sensu stricto (formerly, clade B of Pythium s.l.) and, according to the phylogenetic analysis, shared an ancestor with P. plurisporium. The production of globose hyphal swellings was a major characteristic of G. izadpanahii sp. nov., which did not produce vesicles and zoospores. In pathogenicity tests on rice seedlings, P. banihashemianum sp. nov. isolates were highly pathogenic and caused severe root and crown rot, while G. izadpanahii sp. nov. isolates were not pathogenic. [ABSTRACT FROM AUTHOR]

Plant resistance inducers (PRIs) are of increasing interest for disease control in sustainable viticulture, but their efficacy in vineyards is still under investigation. We studied the effects of four commercial PRIs, of natural and microbial origin, on the development of powdery mildew (PM) on grapevine leaves over a 3‐year period. Disease and sporulation severity were evaluated following the artificial inoculation of PRI‐treated leaves with Erysiphe necator conidia at 1, 3, 7 and 12 days after treatment (DAT). Laminarin (LAM) and cos‐oga (COS) were the most effective in reducing both disease (57.1% and 49.5%, respectively) and sporulation (85.3% and 90.2%, respectively) severity; the reduction in PM severity provided by cerevisane (CER) was lower (27%), and that of Pythium oligandrum (PYT) was intermediate (44.9%). LAM was effective from 1 DAT, while COS and PYT were more effective when E. necator was inoculated at 7 to 12 DAT. These results open new perspectives on how PRIs are used as single, preventative interventions performed 1 to 3 days before E. necator infection, depending on the product used. The effect of PRIs on the sporulation of E. necator colonies also suggests a broader and longer effect on PM epidemics. [ABSTRACT FROM AUTHOR]

Avocado tree wilt is a disease caused by Phytophthora cinnamomi Rands. Recently, this disease has been associated to Pythium amazonianum, another causal agent. Avocado tree wilt is being currently controlled with synthetic fungicides that kill beneficial microorganisms, polluting the environment and leading to resistance problems in plant pathogens. The current research work aims to provide alternative management using extracts from Proboscidea parviflora W. and Phaseolus lunatus L. to control the development of mycelia in P. amazonianum in vitro. Raw extracts were prepared at UAAAN Toxicology Laboratory, determining the inhibition percentages, inhibition concentrations and inhibition lethal times. Several concentrations of the plant extracts were evaluated using the poisoned medium methodology, showing that both extracts control and inhibit mycelial development, in particular P. lutatus, which inhibits mycelial growth at concentrations lower than 80 mg/L, being lower than P. parviflora extracts. These extracts are promising candidates for excellent control of Pythium amazonianum. [ABSTRACT FROM AUTHOR]

Pythium insidiosum is an important oomycete pathogen of mammals that causes pythiosis, an endemic disease in warm climates that stands out for its unfavorable prognosis, lethality in the affected species, and difficulties in treatment. This study evaluated in vitro anti-P. insidiosum potential of aqueous, hydroethanolic, and ethanolic extracts of indigenous wild mushrooms from southern Brazil. The extracts were prepared from Amanita gemmata, Amanita muscaria, Auricularia auricula, Gymnopilus junonius, Lactarius deliciosus, Laccaria laccata, Psilocybe cubensis, and Russula xerampelina. In vitro susceptibility assays employed the microdilution technique according to the M38-A2 protocol CLSI. The hydroethanolic and ethanolic extracts of R. xerampelina showed anti-P. insidiosum activity at minimum inhibitory concentrations ranging from 1.87--7.50 mg/mL. The other mushroom species extracts showed no inhibitory effects on growth of P. insidiosum. This is the first study to evaluate the antimicrobial activity of mushrooms on oomycetes, evidencing the antimicrobial potential of R. xerampelina on the pathogen P. insidiosum. So, the present study expands new perspectives, since the secondary metabolites produced by mushrooms can be potential targets for the development of new categories of medicines. However, considering the wide biodiversity of Brazilian mushrooms, we suggested that the search for other basidiomycetes species with anti-P. insidiosum action needs to be expanded. [ABSTRACT FROM AUTHOR]

Abstract. Pythium-induced damping-off is a disease that causes the decay of germinating seeds and young seedlings of tomato, and it is one of the most significant yield constraints for farmers in both nurseries and fields. Conventional fungicides are widely used to manage this disease, leading to two major consequences. Excessive fungicide use not only endangers human health and raises environmental concerns but also promotes the emergence of pesticide-resistant microorganisms in the environment. Consequently, there is growing interest in developing long-term damping-off management strategies that minimize reliance on conventional pesticides. To facilitate decision-making, a better understanding of pathogen biology and disease epidemiology is required. The major findings of this review works are as follows: i) Pythium-induced damping-off is an emerging disease that affects tomatoes in nurseries and fields and causes economic loss; ii) Epidemiological factors identified as most favorable for disease development include high soil moisture (70% or higher), low light, and moderate soil temperatures around 25°C.; and iii) Considerable research efforts in recent years have focused on developing bio-control solutions for damping-off, showing promising future prospects. To ensure higher tomato production, researchers and growers should manage Pythium-induced damping off in their fields. This review serves as a useful guide for the management of this disease.

Pythium amaminum sp. nov. was isolated from river and reservoir water on Amami island, Kagoshima Prefecture, Japan. The species can grow at temperatures between 10 °C and 35 °C. At the optimum temperature of 25 °C, the radial growth rate is 22.5 mm per day. Pythium amaminum produces filamentous sporangia consisting of branched, lobulate or digitate elements forming large complexes. Zoospores form inside the vesicle, which is discharged through a long tube at least 320 μm. Globose oogonia are ornamented with conical blunt spines. Oospores are aplerotic and globose. Antheridia twine around the oogonia or stick to them. These features having a both of the long discharge tube from sporangium and oogonia with spines are not observed in any other species of the genus Pythium, and thus we conclude that P. amaminum is a new Pythium species. [ABSTRACT FROM AUTHOR]

Pythium tracheiphilum is a narrow host range oomycete first described infecting lettuce in Italy. Subsequently, the pathogen was reported in many other countries. From 2015 to 2019, Pythium isolates were recovered from lettuce plants with symptoms of leaf rot, wilting and vascular necrosis, collected from commercial fields in different rural localities of Brasilia‐DF, Brazil. The isolates were identified as P. tracheiphilum based on morphological and molecular genetic analysis. Pathogenicity tests conducted with four P. tracheiphilum isolates confirmed that the isolates were pathogenic to detached leaves of a loose‐hearted lettuce cultivar. This is the first report of P. tracheiphilum infecting lettuces in Brazil. [ABSTRACT FROM AUTHOR]

In February 2021, damping off and collar and root rot on coriander (Coriandrum sativum L.) became widespread in the municipality of Vitória da Conquista, Bahia, Brazil. An oomycete was isolated from root and collar segments of affected seedlings and caused the same symptoms in inoculated seedlings. Based on morphological features and DNA sequences from the ITS and cox2 region, the pathogen was identified as Pythium aphanidermatum. To the best of our knowledge, this is the first report of the occurrence of P. aphanidermatum on coriander plants in Brazil. [ABSTRACT FROM AUTHOR]

Root rot of hydroponically grown Welsh onion has caused considerable economic losses every year since commercial cultivation began in 1988 in Hiroshima Prefecture, Japan. The primary pathogens, which have not been reported to form sexual structures, are Pythium spp. including Pythium clusters B2a sp., which is most prevalent, and B1d sp. and Pythium clade A sp. These pathogens infect Welsh onion roots by producing sporangia and zoospores. The objective of this study was to elucidate the inhibitory effects of low-pH solutions on root-rot pathogens of hydroponically grown Welsh onion. Naturally occurring disease was significantly lower after treatment with nutrient solutions with a pH maintained at 4.3–4.9 than with conventional unmanaged solutions (pH 5.4–6.4). In a greenhouse after inoculation of infected Welsh onion with Pythium cluster B2a sp., low-pH solutions (pH 4.0 and 4.5) significantly suppressed zoospore production and reduced the percentage of root infections compared to the conventional solution (pH 5.5). In other greenhouse inoculation tests with Pythium clusters B2a sp. and B1d sp. and Pythium clade A sp., the low-pH solution (pH 4.0) substantially decreased zoospore density and root infection compared to the conventional solution (pH 5.5). The low-pH solutions did not negatively impact crop yield in the greenhouse tests and thus can be used to suppress root rot in hydroponically grown Welsh onions. [ABSTRACT FROM AUTHOR]

Fungal phytopathogens cause significant reductions in agricultural yields annually, and overusing chemical fungicides for their control leads to environmental pollution and the emergence of resistant pathogens. Exploring natural isolates with strong antagonistic effects against pathogens can improve our understanding of their ecology and develop new treatments for the future. We isolated and characterized a novel bacterial strain associated with the species Burkholderia cenocepacia, termed APO9, which strongly inhibits Zymoseptoria tritici, a commercially important pathogenic fungus causing Septoria tritici blotch in wheat. Additionally, this strain exhibits inhibitory activity against four other phytopathogens. We found that physical contact plays a crucial role for APO9's antagonistic capacity. Genome sequencing of APO9 and biosynthetic gene cluster (BGC) analysis identified nine classes of BGCs and three types of secretion systems (types II, III, and IV), which may be involved in the inhibition of Z. tritici and other pathogens. To identify genes driving APO9's inhibitory activity, we screened a library containing 1,602 transposon mutants and identified five genes whose inactivation reduced inhibition efficiency. One such gene encodes for a diaminopimelate decarboxylase located in a terpenoid biosynthesis gene cluster. Phylogenetic analysis revealed that while some of these genes are also found across the Burkholderia genus, as well as in other Betaproteobacteria, the combination of these genes is unique to the Burkholderia cepacia complex. These findings suggest that the inhibitory capacity of APO9 is complex and not limited to a single mechanism, and may play a role in the interaction between various Burkholderia species and various phytopathogens within diverse plant ecosystems. [ABSTRACT FROM AUTHOR]

Pythium-induced damping-off of cucumber is a major constraint to cucumber production in different parts of the world. Although chemical fungicides are used for managing this disease, they have many drawbacks to the environment. The ability of the antagonistic fungi isolated from the rhizosphere and endosphere of Dactyloctenium robecchii and Moraea sisyrinchium in the control of soilborne pathogen Pythium aphanidermatum was inspected. Native Trichoderma isolates, Trichoderma ghanense and Trichoderma citrinoviride, were isolated from plant stem and soil samples collected from Al-Seeb, Oman. Using a dual culture technique, the antagonistic activity of the fungal isolates against P. aphanidermatum was examined in vitro. Among Trichoderma isolates, T. ghanense was more efficient in restraining the mycelial growth of P. aphanidermatum, causing an inhibition percentage of 44.6%. Further, T. citrinoviride induced significantly lower cessation of P. aphanidermatum mycelial growth (31.3%). Microscopic and electrolyte leakage inspection of the pathogen mycelia depicted extreme morphological malformations in their mycelium, which can be attributed to the antifungal metabolites of antagonists. Greenhouse studies demonstrated the effectivity of T. ghanense in controlling Pythium damping-off of cucumber plants, where the number of surviving plants was over 90% when the biocontrol agents were used compared to 0 in the control plants. Furthermore, treatment of the plants with the antagonists promoted growth characteristics of plants compared to uninoculated plants. This included improvements in shoot and root lengths, leaf length and width, and dry weight. These findings suggest that T. ghanense and T. citrinoviride can be developed as alternatives to synthetic chemical fungicides to manage soilborne pathogens of cucumber. This research is also the first to clarify the biocontrol ability of T. citrinoviride and T. ghanense against cucumber damping-off caused by P. aphanidermatum. [ABSTRACT FROM AUTHOR]

The biocontrol agent Pythium oligandrum, which is a member of the phylum Oomycota, can control diseases caused by a taxonomically wide range of plant pathogens, including fungi, bacteria, and oomycetes. However, whether P. oligandrum could control diseases caused by plant root-knot nematodes (RKNs) was unknown. We investigated a recently isolated P. oligandrum strain GAQ1, and the P. oligandrum strain CBS530.74, for the control of an RKN Meloidogyne incognita infection of tomato (Solanum lycopersicum L.). Initially, P. oligandrum culture filtrates were found to be lethal to M. incognita second-stage juveniles (J2s) with up to 84% mortality 24 h after treatment compared to 14% in the control group. Consistent with the lethality to M. incognita J2s, tomato roots treated with P. oligandrum culture filtrates reduced their attraction of nematodes, and the number of nematodes penetrating the roots was reduced by up to 78%. In a greenhouse pot trial, the P. oligandrum GAQ1 inoculation of tomato plants significantly reduced the gall number by 58% in plants infected with M. incognita. Notably, the P. oligandrum GAQ1 mycelial treatment significantly increased tomato plant height (by 36%), weight (by 27%), and root weight (by 48%). A transcriptome analysis of tomato seedling roots inoculated with the P. oligandrum GAQ1 strain identified ~2500 differentially expressed genes. The enriched GO terms and annotations in the up-regulated genes suggested a modulation of the plant hormone-signaling and defense-related pathways in response to P. oligandrum. In conclusion, our results support that P. oligandrum GAQ1 can serve as a potential biocontrol agent for M. incognita control in tomato. Multiple mechanisms appear to contribute to the biocontrol effect, including the direct inhibition of M. incognita, the potential priming of tomato plant defenses, and plant growth promotion. [ABSTRACT FROM AUTHOR]

Aims Determine the wheat rhizosphere competence of Trichoderma gamsii strain A5MH and in planta suppression of the Pythium root and Fusarium crown rot pathogens Globisporangium irregulare and Fusarium pseudograminearum. Methods and results Wheat was continuously cropped (eight years) at a minimum tillage, low growing season rainfall (GSR ≤ 170 mm) site shown as highly conducive to Pythium root and Fusarium crown rots. Root isolation frequency (RIF) and qPCR were used to determine the rhizosphere dynamics of strain A5MH and the target pathogens at tillering, grain harvest, and in postharvest stubble over the final 2 years. Strain A5MH actively colonized the wheat rhizosphere throughout both growing seasons, had high root abundance at harvest [log 4.5 genome copies (GC) g−1] and persisted in standing stubble for at least 293-d postinoculation. Globisporangium irregulare was most abundant in roots at tillering, whereas F. pseudograminearum was only abundant at harvest and up to 9-fold greater in the drier, second year (GSR 105 mm). Strain A5MH decreased RIF of both pathogens by up to 40%, root abundance of G. irregulare by 100-fold, and F. pseudogaminearum by 700-fold, but was ineffective against crown rot in the second year when pathogen abundance was >log 6.0 GC g−1 root. Strain A5MH increased crop emergence and tillering biomass by up to 40%. Conclusions Further trials are required to determine if the A5MH-induced pathogen suppression translates to yield improvements in higher rainfall regions where non-cereal rotations reduce crown rot inoculum. [ABSTRACT FROM AUTHOR]

The Oomycetes fungi, known as water molds are a group of numerous hundred microorganisms that comprise certain of the most disturbing phytopathogens. They can cause damping-off, seedling blights, foliar blights, downy mildew and root rots. Tomato (Lycopersicon esculentum) is an economically and nutritionally important species grown worldwide. Late blight and damping off are two major diseases, which are caused by oomycetes. The present study collected infected samples of tomatoes from four geographic locations in Karnataka, India and identified the pathogens through morphological and molecular methods. Ten different fungal species were identified through microscopic study, with dominance of Pythium and Phytophthora species at all locations. Molecular characterization through ITS sequences and phylogenetic analysis confirmed the presence of two oomycetes Pythium aphanidermatum and Phytophthora infestans. ITS sequences of these two fungi were deposited at NCBI with accession numbers OR677915 and OR677916, respectively. Experimental inoculation of Pythium aphanidermatum (20ml Inoculum/litre) in soil having 20-day-old tomato plants resulted in the 100% yellowing, wilting, collapse, and death of plants within 7 days of inoculation. Inoculation of Phytophthora infestans (20ml Inoculum/litre) was sprayed on fruiting tomato plants resulting in black/brown lesions followed by up to 80% wilting of leaves and fruits within 7 days of spray. This research contributes to our understanding of fungal diseases affecting tomato crops in Karnataka, India and provides a foundation for future studies aimed at developing sustainable disease management practices. [ABSTRACT FROM AUTHOR]

Phenanthrene, one of the polycyclic aromatic hydrocarbons, is stubborn and persistent and exists widely in petroleum-contaminated soil. Filamentous fungi are good assistants to bacterial transport, by hyphae passing through soil pores and reaching further positions. An isolated bacterial strain, from the contaminated soil of the coking plant, was identified as Diaphorobacter and named LW2, which could use phenanthrene as the only carbon source and energy for its growth. LW2 could degrade phenanthrene in a wide range of pH, temperature and initial concentration. When pH was 6 and 10, the removal rate of phenanthrene was 38.59% and 76.44%, respectively, and the removal rate of phenanthrene was 68.25% at 15 ℃. And LW2 could degrade 86.64% phenanthrene when the initial concentration was 100 mg L−1. The detection of DI-N-octyl phthalate, phthalic acid and p-hydroxybenzoic acid revealed that the strain LW2 metabolised phenanthrene through the phthalic acid pathway. Meanwhile, swimming and swarming test results suggested that LW2 was motile. The auxiliary effect of Pythium ultimum on LW2 migration was assessed. In the presence of Pythium ultimum, LW2 could migrate within the range of centimters by its mycelium, which was also observed by fluorescence microscopy. Meanwhile, the degradation ability of LW2 after the migration was also explored. The results proved that the migration process had no significant effect on its degradation ability, and LW2 still showed good phenanthrene metabolism ability. This study provides more possibilities for the bioremediation of phenanthrene-contaminated soil by screening the degradation bacteria and testing the effect of fungi on its migration. [ABSTRACT FROM AUTHOR]

Only a handful of microbial mosquito larval pathogens have been described to date. Sampling several natural enzootic infections of mosquito larvae in southwestern Florida indicated the presence of microbial pathogens capable of extensive larval mortality. A microscopic analysis of one sample site revealed extensive apparent growth of a Pythium-like microbe on mosquito larvae, with the highest degree of infection observed in the siphon and head regions. Structures consistent with sporangia were seen on infected insects after lactophenol blue staining, and higher-resolution scanning electron microscopy (SEM) micrographs showed sporangia and encysted zoospores targeting the head and siphon regions. The isolate was single-colony purified, and molecular identification targeting the ITS and COX1 loci coupled to phylogenetic reconstruction indicated that the isolate belonged to the Pythium genus but was distinct from its closest characterized species, P. inflatum. Morphological features were characterized, with the isolate showing rapid growth on all mycological media tested and relatively high thermotolerance, capable of robust growth at 37 °C; hence, it was designated P. thermoculicivorax. Sampling from a second series of natural infections of mosquito larvae resulted in the molecular identification of three Trichoderma isolates, one with high similarity to T. strigosum and the other two clustering closely with T. asperellum. These data highlight the occurrence of natural enzootic infections of mosquito larvae, potentially as a resource for the identification of new mosquito pathogens. [ABSTRACT FROM AUTHOR]

In this study, antagonistic effects of Pythium acanthophoron, P. lycopersicum, P. oligandrum and P. paroecandrum against Fusarium oxysporum f. sp. lycopersici and Botrytis cinerea were investigated by in vitro and in vivo trials. In vitro mycoparasitic activities of Pythium species were determined by dual culture, inverted plate culture and agar diffusion tests. As a result of dual culture tests, suppressive effects of all mycoparasites were over 70% against mycelial growth of the pathogens. Inverted plate tests showed that antagonistic effects of mycoparasites regarding their volatile compounds were rather low. In the agar diffusion test, all mycoparasites showed antibiosis effect, however P. lycopersicum had the highest suppressive effect on both pathogens. In pot trials, mycoparasites were effective to protect tomato seedlings when pathogens were seperately inoculated, and suppressed the symptoms. When two pathogens were inoculated together, P. paroecandrum was ineffective against B. cinerea, but decreased the severity of wilt symptoms, while other mycoparasites totally inhibited both diseases. Chromatographic analyses made by using leaf samples taken 12, 24, 48 and 72 hours after pathogen inoculation showed meaningful increase on chlorogenic acid, caffeic acid and epicatechine, in the samples taken 48 hours after inoculation. Analyses after the inoculations of tomatoes with the mycoparasites and/or pathogens showed that mycoparasites also caused increase in the amounts of phenolics. This indicated that the mycoparasites could be effective to induce defense mechanisms of tomato plants against pathogens. Among them, P. oligandrum can be mentioned as the most effective mycoparasite regarding the induction of phenolics. Keywords: Solanum lycopersicum, Fusarium wilt, Gray mold, Biocontrol, Pythium spp. [ABSTRACT FROM AUTHOR]

Pythium-induced damping-off is a disease that causes the decay of germinating seeds and young seedlings of tomato, and it is one of the most significant yield constraints for farmers in both nurseries and fields. Conventional fungicides are widely used to manage this disease, leading to two major consequences. Excessive fungicide use not only endangers human health and raises environmental concerns but also promotes the emergence of pesticide-resistant microorganisms in the environment. Consequently, there is growing interest in developing long-term damping-off management strategies that minimize reliance on conventional pesticides. To facilitate decision-making, a better understanding of pathogen biology and disease epidemiology is required. The major findings of this review works are as follows: i) Pythium-induced damping-off is an emerging disease that affects tomatoes in nurseries and fields and causes economic loss; ii) Epidemiological factors identified as most favorable for disease development include high soil moisture (70% or higher), low light, and moderate soil temperatures around 25°C.; and iii) Considerable research efforts in recent years have focused on developing bio-control solutions for damping-off, showing promising future prospects. To ensure higher tomato production, researchers and growers should manage Pythium-induced damping off in their fields. This review serves as a useful guide for the management of this disease. [ABSTRACT FROM AUTHOR]

Pythium insidiosum, an Oomycete, causes severe keratitis that endangers vision. Its clinical, morphological, and microbiological characteristics are often indistinguishable from those of fungal keratitis, earning it the moniker "parafungus". Distinctive clinical hallmarks that set it apart from other forms of keratitis include radial keratoneuritis, tentacles, marginal infiltration, and a propensity for rapid limbal spread. The therapeutic approach to Pythium keratitis (PK) has long been a subject of debate, and topical and systemic antifungals and antibacterials have been tried with limited success. Approximately 80% of these eyes undergo therapeutic keratoplasty to salvage the eye. Hence, there is a need to innovate for alternative and better medical therapy to safeguard these eyes. The resistance of Pythium to standard antifungal treatments can be attributed to the absence of ergosterol in its cell wall. Cell walls of plants and algae have cellulose as an essential constituent. Cellulose imparts strength and structure and acts as the "skeleton" of the plant. Fungal and animal cell walls typically lack cellulose. The cellular architecture of Pythium shares a similarity with plant and algal cells through the incorporation of cellulose within its cell wall structure. Inhibitors targeting cellulose biosynthesis (CBI), such as Indaziflam, Isoxaben, and Quinoxyphen, serve as critical tools for elucidating the pathways of cellulose synthesis. Furthermore, the enzymatic action of cellulase is instrumental for the extraction of proteins and DNA. To circumvent this issue, we hypothesize that CBI's and cellulase enzymes can act on the Pythium cell wall and may effectively treat PK. The available literature supporting the hypothesis and proof of concept has also been discussed. We have also discussed these drugs' molecular mechanism of action on the Pythium cell wall. We also aim to propose how these drugs can be procured and used as a potential medical management option for this devastating entity. [ABSTRACT FROM AUTHOR]

IntroductionSoil-borne pathogens cause considerable crop losses and food insecurity in smallholder systems of sub-Saharan Africa. Soil and crop testing is critical for estimating pathogen inoculum levels and potential for disease development, understanding pathogen interactions with soil nutrient and water limitations, as well as for developing informed soil health and disease management decisions. However, formal laboratory analyses and diagnostic services for pathogens are often out of reach for smallholder farmers due to the high cost of testing and a lack of local laboratories.MethodsTo address this challenge, we assessed the performance of a suite of simplified soil bioassays to screen for plant parasitic nematodes (e.g., Meloidogyne, Pratylenchus) and other key soil-borne pathogens (Pythium and Fusarium). We sampled soils from on-farm trials in western Kenya examining the impact of distinct nutrient inputs (organic vs. synthetic) on bean production. Key soil health parameters and common soil-borne pathogens were evaluated using both simple bioassays and formal laboratory methods across eleven farms, each with three nutrient input treatments (66 samples in total).Results and DiscussionThe soil bioassays, which involved counting galls on lettuce roots and lesions on soybean were well correlated with the abundance of gall forming (Meloidogyne) and root lesion nematodes (e.g., Pratylenchus) recovered in standard laboratory-based extractions. Effectiveness of a Fusarium bioassay, involving the counting of lesions on buried bean stems, was verified via sequencing and a pathogenicity test of cultured Fusarium strains. Finally, a Pythium soil bioassay using selective media clearly distinguished pathogen infestation of soils and infected seeds. When examining management impact on nematode communities, soils amended with manure had fewer plant parasites and considerably more bacterivore and fungivore nematodes compared to soils amended with synthetic N and P. Similarly, Pythium presence was 35% lower in soils amended with manure, while the Fusarium assays indicated 23% higher Fusarium infection in plots with amended manure. Our findings suggest that relatively simple bioassays can be used to help farmers assess soil-borne pathogens in a timely manner, with minimal costs, thus enabling them to make informed decisions on soil health and pathogen management.

Alfalfa (Medicago sativa) seeds planted in cold, wet soil are prone to seed rot, pre- and postemergence damping-off, and seedling root rot. These diseases reduce initial stand density and affect forage yields and winter survival when root systems are stunted by infection. Successful management depends on identifying the causal agents but isolation in pure culture is time consuming and may fail to recover slow-growing organisms or those requiring special growth conditions. Here, the oomycetes in rhizosphere soil and roots from eight locations with a history of poor alfalfa establishment were identified by amplicon sequence analysis. Seedling bioassays were done with bulk soil and quantitative PCR (qPCR) assays were done using DNA from bulk soil, rhizosphere soil, and the root tissue for Aphanomyces euteiches, Phytophthora medicaginis, Pythium irregulare, P. sylvaticum, and P. ultimum var. ultimum. In the root tissue and rhizosphere, A. euteiches was the dominant taxon, followed by Phytophthora medicaginis and P. sansomeana, a broad-host-range pathogen not previously known to infect alfalfa. Pythium inflatum and Globisporangium perplexum were also significantly overrepresented in roots at five of the eight locations, indicating that these taxa are commonly enriched in alfalfa roots but had not previously been identified as alfalfa pathogens. The qPCR assays of bulk soil showed that A. euteiches and Phytophthora medicaginis were unevenly distributed in the plots and low concentrations of the pathogens led to high levels of root rot disease. These results support development of cultivars with high levels of resistance to the most common oomycete pathogens.

The use of fungicides to manage disease has led to multiple environmental externalities, including resistance development, pollution, and non-target mortality. Growers have limited options as legacy chemistry is withdrawn from the market. Moreover, fungicides are generally labeled for traditional soil-based production, and not for liquid culture systems. Biocontrol agents for disease management are a more sustainable and environmentally friendly alternative to conventional agroprotectants. Pythium ultimum is a soil borne oomycete plant pathogen with a broad taxonomic host range exceeding 300 plants. Cucumber seedlings exposed to P. ultimum 1 day after a protective inoculation with bacterial endophyte accession IALR1619 (Pseudomonas sp.) recorded 59% survival; with the control assessed at 18%. When the pathogen was added 5 days post endophyte inoculation, 74% of the seedlings treated survived, compared to 36% of the control, indicating a longer-term effect of IALR1619. Under hydroponic conditions, IALR1619 treated leaf type lettuce cv. 'Cristabel' and Romaine cv. 'Red Rosie' showed 29% and 42% higher shoot fresh weight compared to their controls, respectively. Similar results with less growth decline were observed for a repeat experiment with IALR1619. Additionally, an experiment on hydroponic lettuce in pots with perlite was carried out with a mixture of P. ultimum and P. dissotocum after IALR1619 inoculation. The endophyte treated 'Cristabel' showed fresh weight gain, but the second cultivar 'Pensacola' yielded no increase. In summary, the endophyte IALR1619 provided short term as well as medium-term protection against Pythium blight in cucumber seedlings and may be used as an alternative to conventional fungicides in a greenhouse setting. This study also demonstrated the potential of ALR1619 as a biocontrol agent against Pythium blight in hydroponic lettuce. [ABSTRACT FROM AUTHOR]

Oomycetes are devastating soil-borne plant pathogens, and cause numerous losses on diverse crops worldwide. In this study, our aim was to identify actinomycetes with antimicrobial activity towards oomycetes from the rhizosphere of soybean. Strong growth inhibition of P. myriotylum was found in dual culture with a strain called 11 × 1, and also from using the 11 × 1 cell-free culture filtrate and EtOAc extract. The P. myriotylum growth-inhibiting activity of the 11 × 1 culture filtrates was stable at high temperatures, and acidic and alkaline conditions. The 11 × 1 strain was identified as a Streptomyces strain with the highest 16S rDNA sequence identity to S. scabiei, and phylogenomic analysis also showed clustering with S. scabiei strains. Applying the 11 × 1 culture filtrates to ginger and soybean leaves inhibited the necrosis caused by P. myriotylum and P. sojae, respectively. Pot assay experiments showed a strong control effect of the 11 × 1 culture filtrate against P. myriotylum-caused soft-rot disease of ginger, and against P. sojae caused root-rot of soybean. Analysis of the biosynthetic gene clusters from the genome of 11 × 1 predicted the production of staurosporine, and staurosporine was subsequently identified from LC-MS analysis of the 11 × 1 extract. The concentrations of staurosporine quantified in the 11 × 1 extracts were in the range of the staurosporine minimum inhibitory concentrations for P. myriotylum, supporting the contribution of staurosporine to the biocontrol effect of 11 × 1. The use of 11 × 1 culture filtrate to control both ginger and soybean diseases could be beneficial in an intercropping system of ginger and the leguminous nitrogen-fixing soybean. [ABSTRACT FROM AUTHOR]

In fall 2021, reddish and wilting of leaves and crown rot were observed on cauliflower plants with an incidence of up to 60% in a field in Eboli, South Italy. The causal agent was identified as Globisporangium perplexum based on morphological features of the colonies and by microscopy analyses. The identification was further confirmed by sequencing the internal transcribed spacer (ITS) region of rDNA. The pathogenicity tests reproduced symptoms under laboratory conditions that matched those observed in the field. To our knowledge, this is the first report of Globisporangium perplexum causing crown rot and wilting on cauliflower in Italy and worldwide. [ABSTRACT FROM AUTHOR]

Unlike most pathogenic oomycetes, Pythium insidiosum infects humans and animals instead of plants. P. insidiosum has three clinically relevant genotypes/clades that cause a severe disease called pythiosis. To develop strategies for infection control, it is necessary to understand the biology and pathogenesis of this pathogen. Investigating the evolutionary mechanisms behind the host-specific adaptation is vital, and comparative genomic analysis can help with this. To facilitate genomic analysis, an online bioinformatics tool called P. insidiosum (Pins) Gene Table v2.0 was developed. This tool includes genomic data from 37 genetically diverse P. insidiosum strains and four related species. The database contains 732,686 genes, grouped into 80,061 unique clusters and further divided into core and variable categories at genus, species, and genotype levels. A high-resolution phylogenomic relationship among P. insidiosum strains and other oomycetes was projected through hierarchical clustering and core gene analyses. 3156 P. insidiosum-specific genes were shared among all genotypes and may be responsible for causing disease in humans and animals. After comparing these species-specific genes to the MvirDB database, 112 had significant matches with 66 known virulence proteins, some of which might be involved in vascular occlusion, which is a pathological feature of pythiosis. The correlation of genotypes, geographic origins, and affected hosts of P. insidiosum suggests that clade-I strains are more specific to animals, while clade-II/III strains are more specific to humans. The clade-specific genes might link to host preference. In summary, Pins Gene Table v2.0 is a comprehensive genome database accessible to users with minimal bioinformatics experience for the analysis of P. insidiosum genomes. [ABSTRACT FROM AUTHOR]

Damping‐off oomycete and fungal plant pathogens reduce the germination, emergence, and survival of seedlings. In agricultural systems, this poses a significant problem as it may reduce productivity; in contrast, the impact is more subtle in natural ecosystems and may be essential for maintaining the structure and diversity of plant communities. The oomycete genus Phytophthora is frequently detected in natural plant communities causing disease in mature plants, but it is rarely assessed as a damping‐off pathogen. A pathogenicity experiment was established with five oomycete treatments, three putatively native Phytophthora species, the invasive P. cinnamomi, and Pythium irregulare, to determine the damping‐off host range in selected plant species from a hyper‐diverse Mediterranean‐type ecosystem. Additionally, plant and seed traits were analysed to determine if they were correlated with susceptibility to pre‐emergent damping‐off. Phytophthora arenaria was the only putatively native generalist damping‐off pathogen, causing 12 of 19 plant species to experience significantly reduced seedling emergence or survival relative to the control treatment. Pythium irregulare and the introduced P. cinnamomi caused significant damping‐off for 12 and 13 plant species, respectively. Plant species that were slowest to germinate and emerge were the most susceptible to pre‐emergence damping‐off caused by P. arenaria. These results suggest native and invasive Phytophthora may substantially influence the structure and diversity of natural plant communities through damping‐off. While mature plant species are the most common focus in Phytophthora research, our study indicates damping‐off should be considered to determine the full impact of these soil‐borne plant pathogens. [ABSTRACT FROM AUTHOR]

In February 2023 in Japan, seedlings of wax gourd [Benincasa hispida (Thunb.) Cogn.] in seedling boxes developed water-soaked rot on hypocotyls typical of damping off and eventually died. A Pythium sp. was isolated from the hypocotyls and was identified as Pythium aphanidermatum based on morphological characteristics and DNA sequence data. The same symptoms developed after seedlings were inoculated with the isolated fungus, and the same fungus was reisolated from the seedlings. This is the first report of damping off in wax gourd seedlings caused by P. aphanidermatum in seedling boxes in Japan. [ABSTRACT FROM AUTHOR]

The Zingiberaceae family is widely recognized for its therapeutic and medicinal properties. Most of the members of this family being valuable spice crop, significantly boost the local economy in the areas where they are grown. Ornamental value of some members reserves a unique position. Tropical and subtropical nations rely heavily on the commercial cultivation of ginger and turmeric. India is home to some of the most varied and abundant populations of Zingiberaceae. Rhizome rot is the most devastating disease caused by Pythium species evidenced with almost 90% crop loss. Current approaches of disease control cannot be fully relied upon. So, there is an urgent need for effective alternatives. Endophytes are being extensively investigated as a potent biotic agent to manage a variety of diseases in many crop plants. The purpose of this review is to enumerate the studies conducted on the feasibility of using endophytes against Pythium infection in Zingiberaceae. [ABSTRACT FROM AUTHOR]

Pythium root rot has been reported in several countries, but in Greece this disease was first detected in 2021, causing severe yield losses in a hydroponic lettuce crop. Isolations, morphological and molecular characterization, as well as pathogenicity assays identified a Pythium Cluster B2a species causing the disease in hydroponically grown lettuce. This is the first report of Pythium Cluster B2a sp. causing lettuce root rot in Greece. [ABSTRACT FROM AUTHOR]

The blueberry industry is one of the successful and expanding agricultural cropping systems in South Africa. As a result of this growth, research into identifying plant disease agents has become increasingly important, yet there are relatively few scientific reports published on the subject in the country. The aim of this study was to identify the causal agents of stunting and leaf scorch on blueberry plants and evaluate their pathogenicity. Root samples were collected from a commercial southern highbush blueberry planting in North West, South Africa. The resulting isolates were identified based on sequence data from the rDNA‐ITS. Three Pythiaceae were identified including Globisporangium ultimum var. sporangiiferum, Globisporangium splendens and Pythium aphanidermatum. Results of pathogenicity trials showed that the isolated species were able to cause disease on 40% of the plants. This is the first official report for G. ultimum var. sporangiiferum in South Africa and the first report of G. ultimum var. sporangiiferum and P. aphanidermatum from blueberry plants. [ABSTRACT FROM AUTHOR]

An investigation into oomycete diversity in rice paddies of Fars Province in Iran led to the identification of two new Pythium sensu lato (s.l.) species as Globisporangium izadpanahii sp. nov. and Pythium banihashemianum sp. nov. The identification was based on morphological and physiological features as well as on the phylogenetic analysis of nuclear (ITS and βtub) and mitochondrial (cox1 and cox2) loci using Bayesian inference and Maximum Likelihood. The present paper formally describes these two new species and defines their phylogenetic relationships with other congeneric species. According to multiple gene genealogy analysis, G. izadpanahii sp. nov. was grouped with other species of Globisporangium (formerly, clade G of Pythium s.l.) and was closely related to both G. nagaii and the recently described G. coniferarum. The second species, designated P. banihashemianum sp. nov., was grouped with other species of Pythium sensu stricto (formerly, clade B of Pythium s.l.) and, according to the phylogenetic analysis, shared an ancestor with P. plurisporium. The production of globose hyphal swellings was a major characteristic of G. izadpanahii sp. nov., which did not produce vesicles and zoospores. In pathogenicity tests on rice seedlings, P. banihashemianum sp. nov. isolates were highly pathogenic and caused severe root and crown rot, while G. izadpanahii sp. nov. isolates were not pathogenic.

Objectives: Pythium insidiosum causes a difficult-to-treat infectious condition called pythiosis, with high morbidity and mortality. So far, genome data of at least 10 strains of P. insidiosum, primarily classified in the phylogenetic clades I and II, have been sequenced using various next-generation sequencing platforms. The MGI short-read platform was employed to obtain genome data of 2 clade-III strains of P. insidiosum (recently reclassified as Pythium periculosum) from patients in Thailand and the United States. This work is a part of our attempt to generate a comprehensive genome database from diverse pathogen strains. Data description: A 150-bp paired-end library was prepared from a gDNA sample of P. insidiosum (P. periculosum) strains Pi057C3 and Pi050C3 (also known as ATCC90586) to generate draft genome sequences using an MGISEQ-2000RS sequencer. As a result, for the strain Pi057C3, we obtained a 42.5-Mb assembled genome (164x coverage) comprising 14,134 contigs, L50 of 241, N50 of 45,748, 57.6% CG content, and 12,147 ORFs. For the strain Pi050C3, we received a 43.3-Mb draft genome (230x coverage) containing 14,511 contigs, L50 of 245, N50 of 45,208, 57.7% CG content, and 12,249 ORFs. The genome sequences have been deposited in the NCBI/DDBJ databases under the accession numbers JAKCXM000000000.1 (strain Pi057C3) and JAKCXL000000000.1 (strain Pi050C3). [ABSTRACT FROM AUTHOR]

Pythium oligandrum is a soil-borne oomycete associated with rhizosphere and root tissues. Its ability to enhance plant growth, stimulate plant immunity and parasitize fungal and oomycete preys has led to the development of agricultural biocontrol products. Meanwhile, the effect of P. oligandrum on mutualistic interactions and more generally on root microbial communities has not been investigated. Here, we developed a biological system comprising P. oligandrum interacting with two legume plants, Medicago truncatula and Pisum sativum. P. oligandrum activity was investigated at the transcriptomics level through an RNAseq approach, metabolomics and finally metagenomics to investigate the impact of P. oligandrum on root microbiota. We found that P. oligandrum promotes plant growth in these two species and protects them against infection by the oomycete Aphanomyces euteiches, a devastating legume root pathogen. In addition, P. oligandrum up-regulated more than 1000 genes in M. truncatula roots including genes involved in plant defense and notably in the biosynthesis of antimicrobial compounds and validated the enhanced production of M. truncatula phytoalexins, medicarpin and formononetin. Despite this activation of plant immunity, we found that root colonization by P. oligandrum did not impaired symbiotic interactions, promoting the formation of large andmultilobed symbiotic nodules with Ensifer meliloti and did not negatively affect the formation of arbuscular mycorrhizal symbiosis. Finally, metagenomic analyses showed the oomycete modifies the composition of fungal and bacterial communities. Together, our results provide novel insights regarding the involvement of P. oligandrum in the functioning of plant root microbiota. [ABSTRACT FROM AUTHOR]

The Globisporangium ultimum (formerly Pythium ultimum) species complex was previously composed of two morphological varieties: var. ultimum and var. sporangiiferum. Prior attempts to resolve this morphology-based species complex using molecular techniques have been inconclusive or conflicting. The increased availability of sequenced genomes and isolates identified as G. ultimum var. ultimum and var. sporangiiferum has allowed us to examine these relationships at a higher resolution and with a broader scope than previously possible. Using comparative genomics, we identified highly variable gene regions and designed primers for four new protein-coding genes for phylogenetics. These were then used alongside three known markers to generate a nuclear multigene genealogy of the species complex. From a collection of 163 isolates belonging to the target taxa, a subset of 29 was chosen to be included in this study (verified with nuclear rDNA internal transcribed spacer 1 [ITS1] and mitochondrial cytochrome c oxidase subunit 1 [cox1] sequences). Seventeen isolates of var. ultimum were selected to be representative of variations in genotype, morphology, and geographic collection location. The 12 isolates of var. sporangiiferum included all available specimens identified either morphologically (in previous studies) or through sequence similarity with ITS1 and cox1. Based on the fulfillment of reciprocal monophyly and observed genealogical concordance under the genealogical concordance phylogenetic species recognition, we determined that the Globisporangium ultimum species complex is composed of four genetically distinct species: Globisporangium ultimum, Globisporangium sporangiiferum, Globisporangium solveigiae, and Globisporangium bothae. [ABSTRACT FROM AUTHOR]

Common bean (Phaseolus vulgaris L.) is an important food legume crop and major protein source in Kenya and many parts of the world. However, the yields are low due to the diseases like anthracnose caused by Colletotrichum lindemunthianum and Pythium root rots. The study, therefore, sought to screen Kenyan common bean genotypes for anthracnose and Pythium resistance and to improve the resistance of local landraces to the two diseases. Local landraces and commercial cultivars were screened for resistance under greenhouse conditions for Pythium and in vitro for anthracnose. The results showed that majority of the landraces were moderately resistant to anthracnose and Pythium root rot. The study further utilized molecular markers linked to anthracnose and Pythium resistance, respectively, to determine their potential to detect specific resistance genes among the test genotypes. None of the markers amplified the test genotypes except the control genotypes pointing toward different resistance genes. Further, cultivars G2333 and KK8 were used as donor parents for anthracnose and Pythium resistance, respectively, in a marker-assisted backcross breeding program involving three high-yielding farmer-preferred landraces. A number of lines were developed that carry both resistance genes. These lines can be advanced for release as new cultivars to enhance common bean production in Kenya. [ABSTRACT FROM AUTHOR]

The oomycete Pythium flevoense was diagnosed as the cause of dermatitis in a young adult female harbour porpoise (Phocoena phocoena) that had been trapped in a pound net in a temperate saltwater environment. Disease from Pythium sp. infection—pythiosis—is infrequently diagnosed in humans, horses, dogs, cattle, and few other mammalian species. Pythiosis is typically associated with exposure to tropical or subtropical freshwater conditions, and typically caused by Pythium insidiosum. However, until now, pythiosis has been reported in neither marine mammals nor temperate saltwater conditions, and P. flevoense is not known as a cause of pythiosis in mammals. This porpoise developed generalised dermatitis despite treatment and euthanasia was necessary. Histopathological evaluation revealed a chronic active erosive dermatitis, with intralesional hyphae morphologically consistent with a Pythium sp. PCR analysis and sequencing of affected skin matched Pythium flevoense with a 100% similarity to the reference strain. Additional diagnostics excluded other pathogens. Based on this case report, P. flevoense needs to be considered as a mammalian pathogen. Furthermore, harbour porpoises and possibly other marine mammals may be at risk of infection with P. flevoense, and pythiosis should be included in the differential diagnosis of dermatitis in marine mammals. [ABSTRACT FROM AUTHOR]

Plant growth-promoting rhizobacteria are helpful soil microorganisms that are used extensively in the agricultural industry. In the current investigation, a total of 120 extremophilic bacterial isolates were successfully obtained from a variety of drastic soils. These bacterial isolates were tested to determine their effectiveness as plant growth promoters and biocontrol agents against the two most frequent soil-borne plant pathogenic fungi, Pythium ultimum, and Rhizocotnia solani. Results indicated that numerous isolates demonstrated antifungal activity against P. ultimum and R. solani, through the production of diffusible antifungal metabolites, cell-wall degrading enzymes (chitinase, cellulase), and siderophores. In addition, many of these extremophilic bacteria fixed atmospheric nitrogen, solubilized insoluble phosphate and zinc, and produced indole-3-acetic acid (IAA) and salicylic acid. The 16 S rRNA analysis revealed that the most potent isolates with multiple modes of action were identified as Bacillus halotolerans, Massilia alkalitolerans, and Bacillus aryabhattai. Under greenhouse conditions, these three isolates, either individually or in combination were used as microbial inoculants, and their effects on the development of tomato and maize were evaluated both with and without the presence of the two pathogens. Application of the three isolates as individual or combined treatments significantly (P < 0.05) reduced the growth of P. ultimum and R. solani in vivo, and significantly (P < 0.05) increased the percentage of survived seedlings as evidenced by the significant (P < 0.05) increase in plant resistance as measured by the in planta contents of total phenols, polyphenol oxidase, and peroxidase. Additionally, the treatment of any one of the three isolates, either individually or in combination, significantly (P < 0.05) improved the development of tomato and maize, as evidenced by a considerable increase in the amount of total nitrogen and dry weight yield. The utilization of these bacterial isolates presents a potentially fruitful alternative to the excessive use of potentially harmful agrochemicals. [ABSTRACT FROM AUTHOR]

Objectives: Pythium insidiosum is the causative agent of pythiosis, a difficult-to-treat condition, in humans and animals worldwide. Biological information about this filamentous microorganism is sparse. Genomes of several P. insidiosum strains were sequenced using the Illumina short-read NGS platform, producing incomplete genome sequence data. PacBio long-read platform was employed to obtain a better-quality genome of Pythium insidiosum. The obtained genome data could promote basic research on the pathogen's biology and pathogenicity. Data description: gDNA sample was extracted from the P. insidiosum strain Pi-S for whole-genome sequencing by PacBio long-read NGS platform. Raw reads were assembled using CANU (v2.1), polished using ARROW (SMRT link version 5.0.1), aligned with the original raw PacBio reads using pbmm2 (v1.2.1), consensus sequence checked using ARROW, and gene predicted using Funannotate pipeline (v1.7.4). The genome completion was assessed using BUSCO (v4.0.2). As a result, 840 contigs (maximum length: 1.3 Mb; N50: 229.9 Kb; L50: 70) were obtained. Sequence assembly showed a genome size of 66.7 Mb (178x coverage; 57.2% G-C content) that contained 20,375 ORFs. A BUSCO-based assessment revealed 85.5% genome completion. All assembled contig sequences have been deposited in the NCBI database under the accession numbers BBXB02000001 - BBXB02000840. [ABSTRACT FROM AUTHOR]

A highly controlled environment inside the greenhouse could provide suitable temperatures, nutrients, and light intensity for the crops. However, Pythium root rot continually threatens the productivity of numerous kinds of crops in hydroponic systems, including tomato, poinsettia, spinach, lettuce, and rose. It is caused by Pythium aphanidermatum, which grows well in the warmer temperatures inside the green house and is able to survive in low temperatures as well. In this research, we studied 165 isolates of P. aphanidermatum collected from three prefectures in Japan. We developed 10 reliable microsatellite markers to evaluate the genetic diversity of P. aphanidermatum. In total, 34 multilocus genotypes (MLGs) were observed. The index of association suggested that the population was highly clonal. This result was supported by the low result of Fst (0.075) and the short genetic distance per locus visualized in the minimum spanning network. The clonal population suggested that asexual reproduction was dominant. [ABSTRACT FROM AUTHOR]

The soil microbiome is known to be crucial for the control of soil-borne plant diseases. However, there is still little knowledge on how to modify the soil microbiome to induce or increase disease suppressiveness. In the present study, we applied eleven soil health treatments combined with conventional and organic agricultural management in a long-term field experiment. Suppressiveness against Pythium ultimum and Rhizoctonia solani was assessed in bioassays for 2 years. In addition, the microbiome community composition and microbial abundance were determined. We found that while several treatments changed the microbial community composition compared to the control, only a combination treatment of anaerobic soil disinfestation, hair meal, and compost addition resulted in suppressiveness against P. ultimum. Pythium suppressiveness is likely to have been caused by an increased microbial abundance and activity. Moreover, the increased abundance of several bacterial taxa, such as Pseudomonas sp., Chryseobacterium sp., members of the family Chitinophagaceae, and the fungal genus Mortierella sp. and family Trichosporonaceae, was measured. There was no overall difference in suppressiveness between conventional and organic land management. Also, no suppressiveness against R. solani could be detected. Our results indicate that a treatment combining the reduction of microorganisms followed by a recovery phase with high amounts of organic amendments may be more effective in inducing suppressiveness than treatments consisting of only one of these measures. [ABSTRACT FROM AUTHOR]

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