Pythium Species Research Articles

Optical density assay to determine the sensitivity of Globisporangium and Pythium isolates to mefenoxam

Several species of Globisporangium and Pythium cause cavity spot of carrot. Disease management in conventional production relies primarily on applications of the fungicide mefenoxam. Growers’ reports in Ontario, Canada of severe cavity spot, even when using mefenoxam applications, suggests mefenoxam resistance may be prevalent in pathogen populations in this region. The objectives of the study were to develop a rapid and accurate optical density (OD) assay to assess mefenoxam sensitivity of 188 isolates of Globisporangium and Pythium species collected from 13 carrot fields in Ontario from 2020 to 2023. The isolates belonged to seven species: G. intermedium, G. irregulare, G. rostratifingens, G. sylvaticum, G. ultimum, G. violae, and P. sulcatum. The OD was measured at 600 nm in broth amended at different concentrations of mefenoxam, with OD readings at nine positions per well in a 96-well plate. The OD assay was validated by comparing EC50 values with a standard fungicide-amended agar medium assay using 20 representative isolates. There was a significant linear relationship (R2 = 0.97, P = <0.0001) between the two assays. Of the 188 isolates tested, 24% exhibited <60% inhibition of mycelial growth at 5 μg mefenoxam mL-1, 50% were inhibited by >60% at 5 μg mL-1, 19% were inhibited by >60% at 1 μg mL-1, and 7% were inhibited >60% even at 0.1 μg mL-1. The OD assay proved to be efficient, rapid, and accurate for monitoring mefenoxam sensitivity of these oomycetes.

Oomycete communities in lowland tropical forest soils vary in species abundance and comprise saprophytes and pathogens of seeds and seedlings of multiple plant species.

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. 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. 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. Collectively, these findings demonstrate that oomycetes are ubiquitous, host-generalist pathogens and saprophytes, that can impact seed and seedling survival in lowland tropical forests.

Characterization of the species of Pythium associated with corn seedlings in Delaware.

Corn (Zea mays L.) is the top grain crop by hectares grown in Delaware (DE). Increased pre- and post-emergence damping-off in corn caused by Pythium species have been observed in recent seasons. To date, no characterization studies have been performed to understand Pythium species diversity in DE. Symptomatic corn seedlings were collected from 33 fields across DE in 2019 and 2020. Isolates were obtained from infected root tissues and identified by molecular sequencing. In total, 14 species were recovered: P. aristosporum, P. arrhenomanes, P. attrantheridium, P. catenulatum, P. dissotocum, P. graminicola, P. inflatum, P. irregulare, P. oligandrum, P. periplocum, P.spinosum, P. sylvaticum, P. tardicrescens, and P. torulosum. The dominant species recovered was P. graminicola, accounting for 66% of the isolates. Five species were screened for fungicide sensitivity to calculate the EC50 of mefenoxam, ethaboxam, and picarbutrazox which are the most commonly used active ingredients to manage species of Pythium in corn seed treatment packages. All species tested were sensitive to mefenoxam and picarbutrazox. For ethaboxam, P. torulosum was the only species with an EC50 value > 10 µg ml 1. Ten species were screened for fungicide sensitivity to mefenoxam, ethaboxam, or picarbutrazox at 18, 21, and 25ºC. As temperatures increased, percent inhibition was reduced in 40, 70, and 80% of the species screened for sensitivity to ethaboxam, picarbutrazox, and mefenoxam, respectively. Nine of these species were screened for isolate aggressiveness in greenhouse panels to examine impact on emergence, shoot height, shoot weight, and root weight. While all species were recovered from inoculated roots, P. arrhenomanes, P. attrantheridium, P. spinosum, and P. sylvaticum had the greatest root weight reduction.

Enhanced detection of Pythium insidiosum via lipid profiling with matrix-assisted laser desorption ionization time of flight mass spectrometry

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.

Diagnostic Guide for Pythium Root Rot in Hydroponic Leafy Green and Herb Production

Pythium root rot is a ubiquitous disease of leafy greens and herbs in hydroponic systems. This disease is caused by multiple species of Pythium with P. aphanidermatum, P. dissotocum, P. myriotylum, and P. oopapillum most reported. This diagnostic guide is intended to inform growers and plant health professionals of the causal agent, host range, distribution, diagnostic approaches, and signs and symptoms of Pythium root rot in hydroponic systems.

Detection of oomycete pathogens in UK peat-free growing media and implications for plant health

ABSTRACT 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.

A comprehensive review of integrated management strategies for damping-off disease in chili.

Damping-off disease in chili (Capsicum annum L.) cultivation is a significant global issue, severely affecting seeds, seedlings, and young plants, regardless of the location of cultivation, whether in greenhouses or open fields. Despite chili being a widely popular vegetable used in various cuisines globally, farmers face challenges in meeting the growing demand due to the extensive damage caused by this disease, ranging from 20 to 85%. The shelf life and quality of mature pods are also severely affected. Damping-off disease is mainly caused by soil-borne fungus from the Pythium species, with additional contributions from Phytophthora, Fusarium, and Rhizoctonia species. These pathogens' adaptability to diverse environmental conditions and resistance to synthetic fungicides make controlling damping-off on a commercial scale challenging. However, integrated disease management has shown promising results as a remedial approach. In this review, we discuss the current state of chili diseases, the nature of the pathogens causing damping-off, the epidemiology of the disease, and various control mechanisms. In this review, we broadly discuss the current state of chili diseases, the nature of the pathogens causing damping-off, the epidemiology of the disease, and various control mechanisms. Furthermore, we highlight the importance and efficacy of integrated disease management techniques, along with future prospects in unexplored areas, such as host-pathogen interaction and sustainable disease control measures. The information in this review aims to assist chili growers in understanding the epidemiology and management of damping-off in chili cultivation.

Lasiodiplodia theobromae keratitis – A rare case mimicking Pythium keratitis

A 61-year-old male presented with a corneal ulcer in the right eye and gave a history of trauma with cow-tail 5 days back. The best corrected visual acuity was finger counting at 1 meter, less than n -36 in the right eye. Potassium hydroxide mount revealed broad aseptate filaments. On suspicion of Pythium keratitis, hourly linezolid eyedrop was started but no improvement was seen. The culture grew Lasiodiplodia theobromae, and the ulcer started healing within 2 weeks of starting natamycin 5% eyedrop. This case report highlights the similarities of filaments of Lasiodiplodia and Pythium species on microscopic examination of corneal scraping.

Exploring the Effects of Trichoderma virens Biofungicide on Carrot Cavity Spot and Soil Fungal Community Dynamics

Carrot cavity spot (CCS) has conventionally been managed with fungicides. However, fungicide resistance, their potential risks to human health and the environment, and the increasing demand for organic produce necessitate the exploration of biofungicides as alternatives. In this study, we evaluated varying concentrations of SoilGard (Certis USA, Columbia, MD), a Trichoderma virens-based biofungicide, for efficacy against different CCS-causing Pythium species in vitro. Additionally, its effects on taxonomic and functional diversities of soil fungal communities were studied in vivo in the greenhouse. To our knowledge, this is the first study reporting SoilGard's effectiveness against CCS, with emphasis on its potential as an alternative for fungicide-resistant Pythium isolates. Our in vitro study revealed that SoilGard efficacy was significantly dose-dependent and isolate-specific, thus highlighting the importance of selecting its application rate and the target isolate. Analysis of soil fungal communities using Illumina MiSeq sequencing revealed that SoilGard exerted a significant, albeit temporary, effect on the fungal community structure. It negatively impacted co-occurrence network complexity and alpha diversity in carrot-cultivated soil, whereas bare soil communities remained largely unaffected, thus explaining why preplant applications may yield better results. Our study showed that carrot cultivation without SoilGard enhanced fungal diversity, which was more pronounced late in the season, possibly due to carrot root-associated exudates. Our study sheds light on how complex interactions within soil fungal communities can be impacted by the application of beneficial/pathogenic microbes.

Application and antagonistic mechanisms of atoxigenic Aspergillus strains for the management of fungal plant diseases.

This review covers, for the first time, all methods based on the use of Aspergillus strains as biocontrol agents for the management of plant diseases caused by fungi and oomycetes. Atoxigenic Aspergillus strains have been screened in a variety of hosts, such as peanuts, maize kernels, and legumes, during the preharvest and postharvest stages. These strains have been screened against a wide range of pathogens, such as Fusarium, Phytophthora, and Pythium species, suggesting a broad applicability spectrum. The highest efficacies were generally observed when using non-toxigenic Aspergillus strains for the management of mycotoxin-producing Aspergillus strains. The modes of action included the synthesis of antifungal metabolites, such as kojic acid and volatile organic compounds (VOCs), secretion of hydrolytic enzymes, competition for space and nutrients, and induction of disease resistance. Aspergillus strains degraded Sclerotinia sclerotiorum sclerotia, showing high control efficacy against this pathogen. Collectively, although two Aspergillus strains have been commercialized for aflatoxin degradation, a new application of Aspergillus strains is emerging and needs to be optimized.

РОДОВОЙ СОСТАВ И АГРЕССИВНОСТЬ ГРИБНЫХ БОЛЕЗНЕЙ У ОДНОЛЕТНИХ ЦВЕТОЧНЫХ КУЛЬТУР

In the context of the development of the agro-industrial complex and the replacement of imported plant material in the Russian Federation, the development of methods and technologies for the prevention and control of diseases and pests is a priority area of agrarian science. Fungal diseases cause great damage to both vegetable and ornamental crops. Some of the most harmful phytopathogens are fungi of the genus Fusarium (Fusarium Link). The objective of the study is to identify and determine the aggressiveness of the pathogenic mycobiota complex present on annual flowering plants of the Lamiaceae Bromhead family. During immunological studies on plants, fungal pathogens from the genera Alternaria Nees, Fusarium Link, some species of Pythium spp. and representatives of lower mold fungi Penicillium Link, Mucor Fresen were identified. Based on this, a collection of the most common pathogens from the genera Alternaria (5 samples) and Fusarium (10 samples) was created. When testing the selected samples using the method of L.M. Sokolova, the strains of alternariosis did not show high pathogenicity, the damage score of the tested material was from 0.5 to 1.0. When testing the strains of fusarium, the damage score varied from 1.0 to 4.0. Based on this, only one aggressive strain FAK-7 was selected, which had a damage score of 4.0 for the tested material. This pathogenic strain was isolated from the root system of the snapdragon selection line A-5-1. This strain will be involved in the selection process to work on the resistance of snapdragon lines and varieties to root rot.

Pythium and Globisporangium species associated with cucumber rhizosphere causing damping-off and their effects on cucumber seed decay in Oman.

Pythium sensu lato (s.l.) is a pathogenic oomycete. The present study was conducted to isolate and identify Pythium s.l. species associated with the rhizosphere and roots of greenhouse-growing cucumbers showing damping-off symptoms in 10 Omani governorates (provinces). A total of 166 isolates were recovered from 276 rhizosphere soil and root samples and were identified based on the ribosomal DNA (rDNA) internal transcribed spacer (ITS) region and the cytochrome c oxidase subunit I (COX I) gene region. Pythium aphanidermatum, P. myriotylum, Globisporangium spinosum, Globisporangium sp.1 (isolates Kb003/PySyCu-1 and Kb004/PySyCu-2), and Globisporangium sp.2 (isolate Ib002R) were identified. Among these species, P. aphanidermatum was the most abundant species, represented by 143 isolates (86.1%), followed by G. spinosum with 18 isolates (10.8%), Globisporangium sp.1 and P. myriotylum each with 2 isolates (2.4%), and Globisporangium sp.2 with 1 isolate (0.6%). Pathogenicity tests were also conducted for 38 isolates, including P. aphanidermatum (25), P. myriotylum (2), Globisporangium sp.2 (1), G. spinosum (8), and Globisporangium sp.1 (2). Among the tested isolates, only Globisporangium sp.2 isolate was avirulent, and none of the seeds were rotted at the end of the treatment. However, the other species induced the symptoms of seed decay with the incidence ranged from 86.7 to 100%. Phylogenetic analyses were conducted based on 222 ITS and 53 COX I sequences, and confirmed morphological identification. In addition, the genetic diversity of 93 P. aphanidermatum isolates was assessed via the amplified fragment length polymorphism (AFLP) method. The analysis produced 93 genotypes and 449 polymorphic loci. Pythium aphanidermatum populations were found to have moderate levels of genetic diversity (H = 0.2) and a moderate Shannon information index (I = 0.3793). Analysis of molecular variance (FST = 0.1, P = 0.0) revealed a moderate level of genetic differentiation among P. aphanidermatum isolates between Oman governorates. The sensitivity of 15 P. aphanidermatum isolates was evaluated against hymexazol at different concentrations (10, 100, and 1000ppm). The results revealed that P. aphanidermatum could grow well at concentrations of up to 100ppm hymexazol. However, hymexazol at 1000ppm retarded the growth of P. aphanidermatum. This study showed that P. aphanidermatum is the most prevalent species in greenhouses in Oman and exhibited a moderate level of genetic diversity. Most of the isolates exhibited differences in tolerance to hymexazol but showed no resistance.

Genus-wide analysis of Trichoderma antagonism toward Pythium and Globisporangium plant pathogens and the contribution of cellulases to the antagonism.

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.IMPORTANCETrichoderma is an important genus widely distributed in nature with broad ecological impacts and applications in the biocontrol of plant diseases. The Pythium and Globisporangium genera of fungus-like water molds include many important soil-borne plant pathogens that cause various diseases. Most of the Trichoderma species showed at least a moderate ability to compete with or antagonize the Pythium and Globisporangium hosts, and microscopy showed examples of parasitism (a slow type of killing) and predation (a fast type of killing). Hydrolytic enzymes such as cellulases and proteases produced by Trichoderma likely contribute to the antagonism. A mutant deficient in cellulase activity had reduced antagonism. Interestingly, Pythium and Globisporangium species contain cellulose in their cell walls (unlike true fungi such as Trichoderma), and the cellulolytic ability of Trichoderma appears beneficial for antagonism of water molds.

A Large-Scale Hydroponic Evaluation of Rice Mutants for Pythium Resistance.

Rice is a major staple crop worldwide. However, the occurrence of rice diseases during cultivation poses a significant challenge to achieving optimal yields. Among the major pathogens, Pythium species, which cause seedling blight, are of particular concern. Pythium infects rice roots through zoospores, mycelia, or oospores, leading to root rot, stunting, yellowing, and ultimately seedling damping-off. While many disease resistance-related genes have been reported in rice, only very limited research has been associated with resistance to Pythium infection. In this study, we aimed to establish a rapid screening system to identify rice lines that are resistant or susceptible to the Pythium pathogen in rice nurseries. We conducted evaluations on important factors, including virulence, inoculation method, seed-soaking period, and the measurement of disease severity. As a result, we successfully developed a screening system that allows for high-throughput and rapid screening of the Taiwan Rice Insertional Mutant (TRIM) library for mutant lines exhibiting resistance to P. arrhenomanes. Furthermore, we identified a slightly resistant TRIM line and explored potential genes encoding endoglucanase-1 precursor and malonyl-CoA decarboxylase that may be involved in conferring resistance to P. arrhenomanes.

Identification of Growing Media Favorable for the Growth of Pythium aphanidermatum, a Telluric Pathogen of Papaya (Carica papaya L.) in Côte d’Ivoire

Pawpaw (Carica papaya L.) is an economically important plant in Côte d'Ivoire. However, its cultivation is subject to numerous biotic constraints, including root and crown rot, caused by several species of Pythium, Phytophthora, and Rhizoctonia. Of all these fungi, Pythium aphanidermatum is the most dreaded in Ivorian plantations, causing root, crown, trunk, and fruit rot. This causes enormous production losses, reducing farmers’ incomes. The present study was initiated with a view to finding a suitable culture medium for the development of P. aphanidermatum, which is responsible for root and crown rot of papaya trees, through the study of its morphology and biology. To this end, the mycelial growth of P. aphanidermatum was evaluated on different culture media (PDA, V8, CMA and Papaya). The results showed that all these culture media were favorable for the mycelial growth of P. aphanidermatum. However, in terms of propagule production, PDA and V8 culture media were the most favorable. The CMA medium produced fewer propagules than the PDA and V8 media. Papaya culture medium inhibited oospore production. Sporocysts and chlamydospores were observed in all media. The culture medium did not influence the mycelial growth of P. aphanidermatum but rather oospore production.

Non-Pathogenic Pythium Induced the Resistance in Hydroponic Lettuce Against Root Rot Disease

Hy droponics is a common soilless type of culture. It is clean and gives high-yield crop production. Lettuce is the most widely grown leafy vegetable in hydroponics. The Pythium species causes root rot, a serious disease in lettuce. In this study, we investigated an effective elicitor to promote resistance in lettuce after pathogen infection. To evaluate the plant defense gene response profile, the expression stability of five candidate genes was studied using RT-qPCR. The LsPR1 and LsLTC2 gene expression were higher in lettuce leaves treated with non-pathogenic Pythium PyASR23 than in roots compared to untreated plants. To assess the disease, the rate of relative gene expression of LsLTC2, LsPR-1b like, LsERF, LsAOS, and LsDEF was associated with Pythium root rot pathogenesis. As a result, it was revealed that alterations in these gene expressions were a defense response to Pythium infection, which increased after pre-treatment with various elicitors for 24 hours. When the chemically stimulated lettuce was infected with pathogenic PySR31, the expression of these genes increased dramatically. These results suggested that non-pathogenic PyASR23 might be employed as an elicitor in lettuce roots and contribute to disease control by activating plant defense gene expression against the Pythium pathogen.

First report of Pythium aphanidermatum and Pythium myriotylum causing root rot on chili pepper (Capsicum annuum L.) in Guizhou, China

Chili peppers (Capsicum annuum L.) are popular globally as a vegetable and condiment and are particularly popular in Guizhou, China. Root rot, the most prevalent soil-borne disease affecting chili peppers, is widespread in Guizhou. In 2023, it was observed in 10–20% of six fields, leading to significant economic losses. Eight strains were isolated from rotten roots of ‘Huaxi’ chili samples to support the need for appropriate pathogen control. Four strains were identified as Pythium aphanidermatum (strains: HSLJ-2, HSLJ-4) and Pythium myriotylum (strains: LDLJY-1, LDLJJ-3) through morphological analysis of sporangia, oospores, antheridia, and oogonia; multi-locus phylogenetic analysis of the internal transcribed spacer and mitochondrial cytochrome c oxidase subunit 1 gene regions; followed by pathogenicity testing using inoculated autoclaved wheat seeds. The two Pythium species were thus identified as novel causal agents of chili pepper root rot in Guizhou, China.

Specific Detection of Phytophthora parasitica by Recombinase Polymerase Amplification Assays Based on a Unique Multicopy Genomic Sequence.

Phytophthora parasitica is a highly destructive oomycete plant pathogen that is capable of infecting a wide range of hosts including many agricultural cash crops, fruit trees, and ornamental garden plants. One of the most important diseases caused by P. parasitica worldwide is black shank of tobacco. Rapid, sensitive, and specific pathogen detection is crucial for early rapid diagnosis, which can facilitate effective disease management. In this study, we used a genomics approach to identify repeated sequences in the genome of P. parasitica by genome sequence alignment and identified a 203-bp P. parasitica-specific sequence, PpM34, that is present in 31 to 60 copies in the genome. The P. parasitica genome specificity of PpM34 was supported by PCR amplification of 24 genetically diverse strains of P. parasitica, 32 strains representing 12 other Phytophthora species, one Pythium species, six fungal species, and three bacterial species, all of which are plant pathogens. Our PCR and real-time PCR assays showed that the PpM34 sequence was highly sensitive in specifically detecting P. parasitica. Finally, we developed a PpM34-based high-efficiency recombinase polymerase amplification assay, which allowed us to specifically detect as little as 1 pg of P. parasitica total DNA from both pure cultures and infected Nicotiana benthamiana at 39°C using a fluorometric thermal cycler. The sensitivity, specificity, convenience, and rapidity of this assay represent a major improvement for early diagnosis of P. parasitica infection.

Antagonistic activities of mycoparasitic Pythium species against Fusarium oxysporum f. sp. lycopersici and Botrytis cinerea on tomatoes

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.

Sensitivity of 40 Pythium species to the new fungicide Picarbutrazox

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.