Search

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.

Peat-based growing media products are being phased out in the UK. Alternative constituents may be at risk of harbouring oomycete plant pathogens. Thirty-five peat-free growing media samples were tested for oomycete pathogens by baiting and DNA metabarcoding. No Phytophthora species was detected by baiting, but seven species of Pythium, Phytopythium and Elongisporangium, including four species not previously reported in the UK, were baited. DNA matching eleven Phytophthora species was detected by metabarcoding across a range of samples. A coir sample was also found to contain DNA of Peronosclerospora, a genus of tropical downy mildew pathogens. DNA matching six Phytophthora pathogens, including P. bishii, a pathogen of strawberry not previously reported in the UK, was detected in recycled coir that had been used for strawberry production in The Netherlands. We discuss the implications of the species detected in terms of risks to plant health and the need for further evidence-gathering. [ABSTRACT FROM AUTHOR]

Pythium insidiosum-antigen (PIA) immunotherapy has been used to treat human pythiosis. This study compared PIA-stimulated and unstimulated neutrophils on zoospore viability of P. insidiosum strains. We cultured and collected zoospores of 6 P. insidiosum strains, CBS 777.84, ATCC 58643, ATCC 90586, PEC1, PC10, and CBS 101039. PIA concentrations of 0.01, 0.1, 1, and 10 µg/ml were prepared and were used to stimulate neutrophils isolated from healthy volunteers. The MTT (3-(4, 5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide) assay was used to calculate the zoospore viability of P. insidiosum strains. Neutrophils stimulated with 0.01 or 0.1 µg/ml PIA, or both, showed a significant reduction in the viability of zoospores of CBS 777.84, ATCC 58643, CBS 101039, PC10, and PEC1 strains. Furthermore, 1 µg/ml PIA-induced neutrophils elicited a significant decrease in the viability of zoospores of ATCC 58643, CBS 101039, and PC10 strains. However, a higher dose of PIA (10 µg/ml) did not demonstrate superiority in reducing the zoospore viability of all six strains. Our findings suggest that PIA immunotherapy improves the zoospore-killing activity of neutrophils, and neutrophils might be involved in the forefront mechanism responsible for the beneficial effects of PIA immunotherapy. [ABSTRACT FROM AUTHOR]

AbstractAn improved sporulation method for Pythium aphanidermatum on 10% V8-juice agar was developed to generate substantial quantities of zoospores. We conducted experiments using a 4 × 4 factorial design to evaluate the effects of temperature (20, 25, 30, and 35 °C) and incubation time (2, 3, 4, and 5 days) on zoospore production from isolates HSv05 and KACC 48066. The results indicated that a temperature of 30 °C consistently yielded the highest numbers of zoospores across all incubation periods. Applying the same temperature (30 °C) and all incubation periods to other isolates (CCp03, CCp04, CCp05, HSv10, and KACC 40156) also resulted in higher numbers of zoospores regardless of incubation times compared with that under the control condition (25 °C and 2 days). Further virulence tests of isolate HSv05 revealed that high concentrations of zoospores (5 × 102 − 105 zoospores/ml) induced severe rot symptoms; however, a low concentration of 102 zoospores/ml produced only considerably weak symptoms on inoculated potato tubers. No symptoms appeared in tubers inoculated with 0 (uninoculated control) or 101 zoospores/ml. These findings suggest that our sporulation method can help obtain adequate zoospores for various basic and applied studies, including pathogen identification, virulence assessment, resistance resource screening, and control strategy development. [ABSTRACT FROM AUTHOR]

Copyright of Mycosystema is the property of Mycosystema Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Strawberry growers across the United States are looking for sustainable alternatives to conventional pesticides for management of soil-borne or crown-rot causing pathogens, such as plant-extracts like thyme oil. The objectives of this study were to determine the impact of soil-applied thyme oil fungicides on strawberry plant health, yield, sweetness, and foliar disease, and on the assemblage of soil microbial communities in strawberry plasticulture systems. In 2021 and 2022 the interaction of three soil-applied fungicides and three foliar fungicide programs were explored. Thyme oil was not found to improve strawberry plant growth or yield when compared to strawberries in the control. However, plants treated with mefenoxam exhibited an average winter crown weight of 2.11 g, significantly lower than control and thyme oil treatments at 3.14 g and 3.16 g, respectively. This translated into a significant yield loss where mefenoxam treated plants exhibited lowered yields at 416.04 g of fruit per plant compared to 523.57 g and 521.53 g per plant in the control and thyme oil treatments, respectively. A high incidence of foliar and fruit diseases was present; however, no interaction of soil and foliar fungicide treatments were observed for yield or fruit sweetness. Minimal root protection from pathogens was observed for all treatments and Fusarium, Pythium and Phytophthora fungi were regularly observed. Mefenoxam was observed to increase the recovery of oomycetes, which may cause Pythium and Phytophthora. No benefit from thyme oil was observed at our site and its addition as a soil fungicide would likely not benefit most growers.

During a survey on the biodiversity of oomycetes in aquatic environments in northwest Iran (East Azarbaijan and West Azarbaijan provinces), three Pythium and four Globisporangium isolates were recovered from agricultural water pools and irrigation canals, respectively. Through a polyphasic approach combining morphology and phylogenetic analysis using the nuclear rDNA ITS1-5.8 S-ITS2 (ITS) and partial sequences of the cytochrome c oxidase subunit I and II (COX1 and COX2), three novel species were identified namely Globisporangium tabrizense sp. nov., G. mahabadense sp. nov., and Pythium bostanabadense sp. nov. Furthermore, experiments confirmed the pathogenicity of all identified species on cucumber seedlings, suggesting a pathogenic lifestyle also in aquatic systems. Our research contributes to a better understanding of the diversity, host range and distribution of oomycetes genera Globisporangium and Pythium in northwestern Iran. Detailed morphological descriptions and illustrations are provided for all species. [ABSTRACT FROM AUTHOR]

Pythium spp. are soil-borne pathogens that cause damping-off and root rot diseases in many plant species such as cucumber. In the current study, the effect of dried roots–stems and leaves of Ageratina adenophora (Sprengel) R. King and H. Robinson (=Eupatorium adenophorum Sprengel) alone and in combination with pyrogenic biomass biochar to control Pythium aphanidermatum (Edson) Fitz was assessed. In four treatments of leaves, roots–stems, leaves + biochar, and roots–stems + biochar, it was observed that the treatment with leaves at an Emax (maximal effective concentration on control fungi) of 79 g/kg of soil had the most antifungal effect on P. aphanidermatum. Also, the Cmax (the highest level of control) increased with time and reached 82.4% and 71% on days 30 and 60, respectively. The highest cucumber fresh fruit weight and the highest height of the stems in the greenhouse were observed in leaf treatment of A. adenophora. Biochar did not have any remarkable controlling effect on P. aphanidermatum, and its population increased. The main compounds extracted from the dried leaves and roots–stems of A. adenophora, including α-pinene, nonanone, hexahydronaphthalene, 3-undecanone, muurolene, and heneicosane, had antifungal properties. We concluded that the leaves of A. adenophora have the potential to be used as a bio-fumigant for P. aphanidermatum management. [ABSTRACT FROM AUTHOR]

Premise: The soils in lowland tropics are teeming with microbial life, which can impact plant community structure and diversity through plant–soil feedbacks. While bacteria and fungi have been the focus of most studies in the tropics, oomycetes may have an outsized effect on seed and seedling health and survival, given their affinity for moister, warmer environments. Methods: We assessed the diversity and pathogenicity of oomycete species present in a lowland tropical forest in Panama. We used a culture‐dependent leaf‐baiting assay and culture‐independent soil DNA metabarcoding methods to quantify zoospore abundance and species diversity. A subset of the isolates from the baiting assay were used to evaluate pathogenicity and symptom severity on seedlings of three tree species. Results: Oomycetes were ubiquitous and common members of the soil microbial community in lowland tropical forests, and zoospore abundance was far greater compared to similar studies from temperate and mediterranean forests. The various oomycete species also varied in the ability to infect host plants. Species of Pythium were more virulent, while species of Phytopythium caused less severe symptoms but were more diverse and commonly isolated from the soil. Finally, we found that individual hosts accumulated a distinct oomycete community and was the only factor that had an effect on community structure. Conclusions: Collectively, these findings demonstrate that oomycetes are ubiquitous, host‐generalist pathogens and saprophytes, that can impact seed and seedling survival in lowland tropical forests. [ABSTRACT FROM AUTHOR]

Human pythiosis is a rarely encountered yet potentially harmful infectious disease. It is mostly caused by Pythium insidiosum, an aquatic fungal‐like organism, and primarily manifests in tropical locales such as India and Thailand. Cutaneous/subcutaneous pythiosis accounts for a small proportion of all clinical forms. The relationship between cutaneous pythiosis and hemoglobinopathy remains uncertain, unlike the vascular form. The histopathology of the disease demonstrates eosinophilic granulomatous inflammation and dense eosinophilic material enveloping the organism, known as the Splendore–Hoeppli phenomenon. These histopathologic characteristics resemble those observed in entomophthoromycosis. Until now, the histopathology of human cutaneous pythiosis has been scarcely delineated in the literature. Herein, we report a case of cutaneous pythiosis in an adult thalassemic agricultural worker who presented with a 2‐month history of a progressive, painful, erythematous infiltrative plaque on the left leg. The definitive diagnosis was ascertained through histopathologic examination and the identification of anti‐P. insidiosum antibodies in the serum utilizing enzyme‐linked immunosorbent assay. This report demonstrates the exquisite histopathologic findings of a rare case of human cutaneous pythiosis. [ABSTRACT FROM AUTHOR]

Ten Argentinean Waitea circinata-like isolates (Corticiales, Basidiomycota) obtained from soil samples were identified to species level based on morphological features and molecular tools, and tested in order to explore their biological control abilities. Eight of them were identified as Waitea arvalis and two as W. circinata. Waitea arvalis isolates were tested as antagonists, and W. circinata isolates were used as pathogens. Most isolates performed well in in vitro antagonistic assays, inhibiting by 54–59% the growth of seven plant pathogens: Bipolaris sorokiniana, Fusarium graminearum, Fusarium oxysporum, Pythium irregulare, two different isolates of W. circinata and Sclerotium rolfsii. The most inhibited pathogen was P. irregulare (72.6%), followed by S. rolfsii (66.7%) and W. circinata (~ 65%). There was no evidence of mycoparasitism. Their capacity for chitinase, cellulase, protease and ligninase (laccase, Mn-peroxidase and lignin-peroxidase) secretion was evaluated. Most of the isolates tested positive for chitinase activity. All the evaluated W. arvalis isolates produced cellulase, protease and laccase activities, and some of them also rendered positive results for Mn-peroxidase and decolorized the dye Azure B. Isolates INTA-L003 and INTA-L005 displayed top results for cellulase activity (both in carboxymethylcellulose plate assay and in filter paper tube assay). These activities might be responsible for their better antagonistic behavior on Pythium sp. Thus, these isolates are promising as biocontrol agents and as sources of new enzymes for industrial applications. Moreover, to the best of our knowledge, this is the first citation of W. arvalis in Argentina. [ABSTRACT FROM AUTHOR]

BACKGROUND: Picarbutrazox is a new tetrazolyloxime fungicide discovered in 2014 by Nippon Soda. It is mostly used to protect against Phytophthora spp. and Pythium spp. However, little is known of its inhibition spectrum, protective and curative activity, and systemic translocation in plants. RESULTS: While picarbutrazox did not show obvious antifungal activity, it exhibited significant activity against oomycetes, including Phytophthora spp., Pythium spp. and Phytopythium spp.. The effective concentration for 50% growth inhibition (EC50) values of picarbutrazox against 16 oomycetes ranged from 3.1 × 10−4 and 7.27 × 10−3 μg mL−1. Furthermore, picarbutrazox could markedly inhibited the mycelial development, sporangia production, zoospore release, and cyst germination of Phytophthora capsici, with EC50 values of 1.34 × 10−3, 1.11 × 10−3, 4.85 × 10−3, and 5.88 × 10−2 μg mL−1, respectively. Additionally, under greenhouse conditions, the protective and curative activities of picarbutrazox at 200 mg L−1 (100%, 41.03%) against the P. capsici infection in peppers were higher than those of the reference fungicide dimethomorph at 200 mg L−1 (77.52%, 36.15%). High‐performance liquid chromatography analysis confirmed that picarbutrazox showed excellent systemic translocation in pepper plants. CONCLUSION: The results showed that picarbutrazox markedly inhibited the important plant oomycete pathogens including Phytophthora spp., Pythium spp. and Phytopythium spp.. It also displayed excellent protective, curative and systemic translocation activity. Picarbutrazox thus has significant potential for preventing and controlling diseases caused by oomycetes. © 2024 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Pythiosis is a severe disease in humans and animals globally, caused by the pathogenic oomycete Pythium insidiosum. Early and accurate detection is crucial for effective treatment, but traditional diagnostic methods have limitations. This study presents an alternative approach using Matrix-Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS) for lipid profiling to efficiently identify P. insidiosum. The study involved extracting microbial lipid components using optimized chloroform: methanol biphasic method and creating a lipid profile database with samples from 30 P. insidiosum isolates and 50 various fungi. The methodology was validated on 25 blinded samples for assay detection performance. Unique lipid profiles allowed species-specific identification with high efficiency: scores ≥ 2.682 indicated P. insidiosum, scores ≤ 2.512 suggested fungi, and scores in between pointed to other oomycetes. The assay demonstrated sensitivity, specificity, and accuracy of 100%, 80%, and 88%, respectively, for detecting P. insidiosum. The limited detection specificity was due to false positive samples from closely related Pythium species, which are not a significant clinical concern. The findings show that MALDI-TOF MS lipid profiling can efficiently identify P. insidiosum, offering significant advantages in sample preparation, stability, and reproducibility over protein profile-based methods. This study marks the first instance of lipid profiles being reported for P. insidiosum, paving the way for clinical use in improving accurate detection and facilitating timely treatment interventions. [ABSTRACT FROM AUTHOR]

Volatile organic compounds (VOCs) mediate biological interactions and are produced by Pythium and Phytophthora species. These VOCs are biotechnologically relevant because the genera include important plant pathogens, whereby VOCs can aid in disease detection, and biological control agents, whereby VOCs contribute to disease control. Studies on VOC production, identification, and characterization of individual VOCs produced by Pythium and Phytophthora species are reviewed. VOCs detected in plants infected with Phytophthora species are also reviewed as potentially oomycete-derived VOCs. The Pythium- and Phytophthora-produced VOCs are compared with other microorganisms, and the main effects of these VOCs on microbial inhibition and plant-mediated effects are reviewed. These effects are summarized from direct demonstration studies and inferences based on the known functions of the identified Pythium- and Phytophthora-produced VOCs. There are two main applications of VOCs to plant disease control: the use of VOCs to detect pathogenic Pythium and Phytophthora species, e.g., e-nose detecting systems, and the use of VOC-producing biological control agents, e.g., Pythium oligandrum. Future research could understand how the VOCs are produced to engineer VOC levels in strains, analyze more oomycete species and strains, accurately quantify the VOCs produced, and exploit recent developments in analytical chemistry technology. Key points: • Compiled inventory of volatiles produced by Phytophthora and Pythium species • Volatilomes contain microbe-inhibiting and plant growth-promoting compounds • Volatile potential in disease detection and control supports analyzing more species [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]

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]

Damping-off is the most serious disease of tobacco in nursery conditions caused by Pythium aphanidermatum. Total fifteen isolates of P. aphanidermatum were recovered from infested soil samples of bidi tobacco growing areas of middle Gujarat which are designated as Pa 1 to Pa 15. The isolates showed incredible variability in cultural and morphological characters on oat meal agar media. The isolates show white to light white types of colony appearance whereas, he aerial, moderately aerial, flat, fluffy, fluffy and dense and fluffy aerial types of topography and margin were observed in the fifteen different isolates. Evident differences in size of mycelium, oospore and number of oospores were observed among the isolates even when same medium was used for the growth. The pathogenic variability among the different isolates revealed that maximum mortality due to damped-off was recorded in Pa 4 (98%), followed by Pa 14, Pa 8, Pa 3, Pa 7, Pa 11, Pa 12, Pa 2, Pa 13, Pa 9, Pa 15, Pa 10, Pa 1, Pa 6 and Pa 5 isolates. All the seedlings were healthy in uninoculated, which proved that all the fifteen isolates were pathogenic and isolates Pa 4 and Pa 14 were found highly virulent. [ABSTRACT FROM AUTHOR]

Pythium sensu lato (s.l.) is a genus of parasitic oomycetes that poses a serious threat to agricultural production worldwide, but their severity is often neglected because little knowledge about them is available. Using an internal transcribed spacer (ITS) amplicon-based-metagenomics approach, we investigate the occurrence, abundance, and diversity of Pythium spp. s.l. in 127 corn fields of 11 European countries from the years 2019 to 2021. We also identify 73 species, with up to 20 species in a single soil sample, and the prevalent species, which show high species diversity, varying disease potential, and are widespread in most countries. Further, we show species-species co-occurrence patterns considering all detected species and link species abundance to soil parameter using the LUCAS topsoil dataset. Infection experiments with recovered isolates show that Pythium s.l. differ in disease potential, and that effective interference with plant hormone networks suppressing JA (jasmonate)-mediated defenses is an essential component of the virulence mechanism of Pythium s.l. species. This study provides a valuable dataset that enables deep insights into the structure and species diversity of Pythium s.l. communities in European corn fields and knowledge for better understanding plant-Pythium interactions, facilitating the development of an effective strategy to cope with this pathogen. Pythium sensu lato (s.l.) is an oomycete that poses a serious threat to agricultural production worldwide. This study, using metabarcoding, provides insights into the diverse soil communities of Pythium s.l. across 127 locations and their disease potential in European corn fields. [ABSTRACT FROM AUTHOR]

Long-term use of chemical fungicides to control plant diseases caused by fungi and oomycetes has led to pathogen resistance and negative impacts on public health and environment. There is a global search for eco-friendly methods and antagonistic bacteria are emerging as alternatives. We isolated a potent antagonistic bacterial strain (S1Bt23) from woodland soil in Québec, Canada. Taxonomic characterization by 16S rRNA, multi-locus sequence analysis, pairwise whole-genome comparisons, phylogenomics and phenotypic data identified strain S1Bt23 as a novel subspecies within Pseudomonas chlororaphis. In dual culture studies, strain S1Bt23 exhibited potent mycelial growth inhibition (60.2–66.7%) against Pythium ultimum. Furthermore, strain S1Bt23 was able to significantly bioprotect potato tuber slices from the development of necrosis inducible by P. ultimum. Annotations of the whole genome sequence of S1Bt23 revealed the presence of an arsenal of secondary metabolites including the complete phenazine biosynthetic cluster (phzABCDEFG). Thin-layer (TLC) and high-performance liquid (HPLC) chromatographic analyses of S1Bt23 extracts confirmed the production of phenazines, potent antifungal compounds. CRISPR/Cas9-mediated deletion of phzB (S1Bt23ΔphzB) or phzF (S1Bt23ΔphzF) gene abrogated phenazine production based on TLC and HPLC analyses. Also, S1Bt23ΔphzB and S1Bt23ΔphzF mutants lost antagonistic activity and bioprotection ability of potato tubers against P. ultimum. This demonstrated that phenazines are involved in the antagonistic activity of S1Bt23 against P. ultimum. Finally, based on genotypic and phenotypic data, we taxonomically conclude that S1Bt23 represents a novel subspecies for which the name Pseudomonas chlororaphis subsp. phenazini is proposed. [ABSTRACT FROM AUTHOR]

Parasitism is an important lifestyle in the Trichoderma genus but has not been studied in a genus-wide way toward Pythium and Globisporangium hosts. Our approach screened a genus-wide set of 30 Trichoderma species in dual culture assays with two soil-borne Pythium and three Globisporangium plant-parasitic species and used exo-proteomic analyses, with the aim to correlate Trichoderma antagonism with potential strategies for attacking Pythium and Globisporangium. The Trichoderma spp. showed a wide range of antagonism from strong to weak, but the same Trichoderma strain showed similar levels toward all the Pythium and Globisporangium species. The Trichoderma enzymes from strong (Trichoderma asperellum, Trichoderma atroviride, and Trichoderma virens), moderate (Trichoderma cf. guizhouense and Trichoderma reesei), and weak (Trichoderma parepimyces) antagonists were induced by the autoclaved mycelia of one of the screened Pythium species, Pythium myriotylum. The variable proportions of putative cellulases, proteases, and redox enzymes suggested diverse as well as shared strategies amongst the antagonists. There was a partial positive correlation between antagonism from microscopy and the cellulase activity induced by autoclaved P. myriotylum mycelia in different Trichoderma species. The deletion of the cellulase transcriptional activator XYR1 in T. reesei led to lower antagonism toward Pythium and Globisporangium. The antagonism of Pythium and Globisporangium appears to be a generic property of Trichoderma as most of the Trichoderma species were at least moderately antagonistic. While a role for cellulases in the antagonism was uncovered, cellulases did not appear to make a major contribution to T. reesei antagonism, and other factors are also likely contributing. [ABSTRACT FROM AUTHOR]

Oomycetes are water molds that are frequently isolated during a survey of waterways. Biodiversity of oomycetes in the estuary region of the Veleka River in Bulgaria was investigated in 2021. A total number of 32 isolates were derived using the baiting method. Species identification based on sequencing of the ITS region divided them into four different genera: Phytophthora (P.), Phytopythium (Pp.), Pythium (Py.) and Elongisporangium (E.). The most abundant species in the studied region was P. lacustris (sixteen isolates), followed by P. honggalleglyana (nine isolates). P. bilorbang and P. inundata were represented by only one isolate each and were recognized for the first time in Bulgaria. The genus Phytopythium was presented by two isolates that belong to different species, Pp. litorale and Pp. citrinum. In the obtained collection, the genera Pythium and Elongisporangium were represented by only one species each, Py. angustatum (one isolate) and E. anandrum (two isolates), respectively. Colony morphology of the eight collected oomycete species was characterized by cultivation of selected isolates on three different media. Potential host species of the isolated estuarine oomycetes were estimated by pathogenicity tests conducted with sixteen plants from ten diverse families. P. lacustris and P. honggalleglyana demonstrated a higher aggressiveness among Phytophthora isolates, whereas P. bilorbang and P. inundata showed less ability to infect the tested plant species. Similar pathogenicity and a potential host range for both Phytopythium species were observed. Less aggressive against analyzed plants in this study were Py. angustatum and E. anandrum. [ABSTRACT FROM AUTHOR]

Red rot disease is one of the notorious algal diseases that threaten the cultivation of Pyropia in China, and two Pythium pathogens, i.e., Pythium porphyrae and P chondricola, have been reported as causative agents. To monitor the pathogens, a fluorescent quantitative polymerase chain reaction (PCR) method was developed to quantitatively detect their abundance. Using overlapping PCR and pathogen-specific primer pairs, two pathogen-specific fragments were concatenated to construct an internal standard plasmid, which was used for quantification. For zoospores of known numbers, the results showed that this method can detect as less as 100 and 10 zoospores mL-1 in a 200 mL solution for P porphyrae and P chondricola, respectively. Using monthly collected seawater at 10 sites in Haizhou Bay, a typical aquaculture farm in China, a significantly higher temperature and a significantly lower salinity were determined in December 2021. P. porphyrae was determined to be more abundant than P. chondricola, though with similar temporal distribution patterns from December 2021 to February 2022. When a red rot disease occurred in December 2021, the two pathogens were significantly more abundant at two infected sub-sites than the uninfected sub-site within both seawater and sediment, though they were all significantly more enriched in sediment than in seawater. The present method provides the capability to quantify and compare the abundance of two pathogens and also has the potential to forecast the occurrence of red rot disease, which is of much significance in managing and controlling the disease. [ABSTRACT FROM AUTHOR]

Introduction: Soil-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. Methods: To 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 Discussion: The 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 Fusariumstrains. 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. [ABSTRACT FROM AUTHOR]

The conclusions of EFSA following the peer review of the initial risk assessments carried out by the competent authority of the rapporteur Member State Belgium for the pesticide active substance Pythium oligandrum strain B301 and the considerations as regards the inclusion of the substance in Annex IV of Regulation (EC) No 396/2005 are reported. The context of the peer review was that required by Regulation (EC) No 1107/2009 of the European Parliament and of the Council. The conclusions were reached on the basis of the evaluation of the representative uses of Pythium oligandrum strain B301 as a resistance inducer/elicitor to control trunk diseases on grapevines. The reliable endpoints, appropriate for use in regulatory risk assessment, are presented. Missing information identified as being required by the regulatory framework is listed. Concerns are reported where identified. [ABSTRACT FROM AUTHOR]

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]

Protected cropping utilizing hydroponic systems are particularly vulnerable to the impacts of waterborne diseases which result in substantial crop damage and yield loss. This study assessed the potential of a citronella, red thyme, and clove bud essential oil blend (EOB) for plant safety, and pesticidal and antimicrobial activities. Results within model systems identified efficacy of EOB against aphids (p < 0.001), spider mites (p < 0.001), and fungus gnats (p < 0.001), and 250-fold diluted EOB against Pythium (p < 0.001), Phytophthora (p = 0.001), and Fusarium (p < 0.001). The plant safety trial indicated no impacts of 250-fold diluted EOB to capsicum health and glasshouse experiments demonstrated both curative and preventative efficacies against Pythium, based on reductions in the incidence and severity of infection. These results highlight the potential for the utilization of biopesticides for the effective and environmentally friendly management of common pests and diseases within hydroponic crop systems. [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]

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]

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]

Genotypic studies using molecular markers, such as genomic prediction (GP), have been implemented in maize (Zea mays L.) breeding, leading to a better understanding of significant traits. Pythium root and stalk rot (RSR) resistance is an important trait in maize bred in Japan. The study aims to (1) develop a GP model for Pythium RSR resistance in maize bred within the Japanese public sector and (2) utilize GP to analyze untested maize germplasms for Pythium RSR resistance via a combined training set derived from different heterotic groups (dent and flint). Through 1,000 repetitions of sampling and five-fold cross-validation, a high average prediction accuracy (r = 0.695, 95% confidence interval: 0.682-0.708) was achieved across populations. Prediction accuracy improved as the number of markers increased, but it eventually reached a plateau that exceeded 1,000 markers. The population component and linkage disequilibrium between markers confirmed previous reports. These findings show the feasibility of GP, even with a small population (N = 41) and marker size (approximately 1,000). Several old inbred lines were identified with lower predicted RSR scores, indicating their potential as breeding materials. This is the first report on the prediction of maize Pythium RSR resistance using GP and emphasizes new possibilities for addressing Pythium RSR resistance in maize breeding. [ABSTRACT FROM AUTHOR]

This study aimed to examine the effect of co-cultured consortium of four Trichoderma spp., including T. asperellum, T. koningii, T. polysporum and T. gamsii on Pythium root rot of greenhouse cucumbers grown in rockwool hydroponic culture. Experiments were carried out: (1) in experimental hydroponic system constructed with reused rockwool slabs “naturally” infested with Pythium spp. and additionally inoculated with P. aphanidermatum, P. ultimum, Pythium groups G and F; and (2) in commercial greenhouse wherein cucumber plants (c. Boncanale) were grown in reused Pythium infested rockwool system. The bioagents were co-produced on autoclaved barley grain. The abundant spore mass was suspended in ready-to-use fertigation solution, filtered twice and adjusted to 5.0-7.5 x 107 spores ml-1. 150 ml of this solution were applied to the roots of treated plants zero, once, twice or three times. Treatments were performed manually in the experimentally constructed system starting at day 7th after sowing and followed at intervals of 14 days, or through the dripping irrigation system in the commercial greenhouse where the first treatment was performed immediately after planting while next two followed at 30 days intervals. Significant reduction in disease incidence was achieved through two or three subsequent treatments: total numbers of wilted and dead plants were reduced by 50% and 73%, respectively, in the experimental system, and by 60% and 40% in the commercially conducted experiments. This study suggests innovative biocontrol approach using preparation of multicomponent bioagent spore suspension directly in the fertigation solution, and application to the plants through dripping irrigation system. [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]

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]

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]

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 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]

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]

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]

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]

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]

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]

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]

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]

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.

Allelopathic chemicals produced by a cereal rye (CR; Secale cereale L.) cover crop have been implicated in the negative effect of CR on corn planted into decomposing CR residue. Production of allelochemicals varies among CR cultivars. In the current study, the allelopathic effect of crude extracts from five CR cultivars (Elbon, Hazlet, Serafino, Tayo, and Yankee) was evaluated on corn seedling growth, mycelial growth of Pythium lutarium, and root rot of corn caused by P. lutarium using a plate assay. In general, crude extracts from all CR cultivars slowed pathogen growth and reduced corn coleoptile and radicle lengths. When corn was grown on media amended with crude extracts from the CR cultivars and colonized with P. lutarium, corn growth was reduced and root rot severity increased compared with the check (no extract with pathogen). Subsequently, a cup assay was used to further investigate the allelopathic effect of Elbon, Hazlet, and Serafino on corn seedling growth and root rot. Corn grown in cups into which each cultivar had been planted had shorter radicles and coleoptiles compared with the check (no CR), regardless of the CR cultivar. Results from this study suggest that allelochemicals released from decomposing CR vary among cultivars, and their interaction with Pythium spp. could affect seedling disease on corn. Consequently, choice of CR cultivar may be an important management decision to reduce the negative effects of CR on corn. [Figure: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

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]

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]