Aphanomyces Cochlioides Research Articles

Use of pre-sowing soil microbiological analysis to predict the spread of sugar beet root rot

Aphanomyces cochlioides and Rhizoctonia solani are two of the main soil phytopathogens of sugar beet, which lead to substantial losses in yield and quality. Since disease control capabilities are complex and pathogen monitoring is important for predicting risks, it is of great importance in rural production to create available methods for preliminary field assessment. The purpose of the study was to introduce a predictive methodology for assessing the potential of soils for their suitability for growing sugar beet in the system of short-rotation crop rotations. As an indicator plant, sugar beet seeds were used, which are not characterised by genetic resistance against these diseases. The possibility of using the pre-growing disease index (PPDI), which has a gradation from 0 to 100 and covariance with the actual yield, sugar content and gross sugar yield per hectare, is tested. The pre-sowing PPDI value is compared with the actual yield from each specific field to really assess the possibility of using the PPDI index to characterise yield losses on production crops. It is determined that with an increase in the PPDI value, the gross yield of sugar beet, sugar content, and gross sugar yield decreased. The results of studies show that one unit of PPDI causes a loss of gross yield at the level of 0.24 t/ha and a decrease in the sugar harvest by 0.018 t/ha. That is why, to manage the risks of growing sugar beet, it is necessary to assess the phytopathogenic load of the soil. It is established that the most harmful and permanently identified phytopathogens are Rhizoctonia solani and Fusarium ssp, which indicates the need to select hybrids that are characterised by resistance or high tolerance to these pathogens. The information obtained can be used for timely identification of infection risks, development of effective management strategies, and improvement of agricultural techniques for growing sugar beet to reduce crop losses and increase the efficiency of agricultural products

Rapid detection and quantification of Aphanomyces cochlioides in sugar beet

Sugar beet (Beta vulgaris L.) is an economically important crop in temperate climates providing nearly 30% of sugar production worldwide. The oomycete Aphanomyces cochlioides is the causative agent of seedling damping-off and root rot disease in sugar beet. The pathogen is responsible for plant degeneration and drastic yield losses in all major sugar beet producing areas. The identification of resistant germplasm is essential to reduce the use of chemical treatments as well as the costs of protective measures and to effectively limit the damage caused by the pathogen. In this study we aimed to establish a qPCR-based method to quantify the pathogen DNA in infected plants and to predict the resistance levels of different sugar beet genotypes in response to A. cochlioides. The difference in the response to A. cochlioides isolates with different geographical origins was investigated. In addition, confocal microscopy was performed in order to observe the spatial and temporal colonization pattern in infected seedlings of susceptible and partially resistant breeding lines. The research presented in this article provides a tool to understand the progress of the infection in infected tissues and to identify the genetic background of resistance to A. cochlioides that can be used to support breeding programs.

First Report of Rhizopus causing Hypocotyl and Root Rot in Sugar Beet (Beta vulgaris. L) Seedlings in Montana, USA.

Sugar beet is commercially grown in Minnesota, Idaho, North Dakota, Michigan, Nebraska, Montana, California, Wyoming, Colorado, Oregon, and Washington [3].The cultivars are relatively high-yielding and are moderately resistant to most of the common soil-borne and foliar pathogens. Most cultivars have a minimum level of resistance to root pathogens such as Rhizoctoniasolani, Aphanomyces cochlioides, Clonostachysrosea, Globisporangiumultimum, Rhizopus stolonifera, and Fusarium equiseti [1, 2, 3, 4].

First Record of Geotrichum candidum Causing Root Rot to Sugar beet (Beta vulgaris. L) in Wyoming and Michigan, USA

Sugar beet (Beta vulgaris L.) root rotten is caused by a number of soil-borne pathogens included Rhizoctonia solani, Aphanomyces cochlioides, Clonostachys rosea, Globisporangium ultimum, Rhizopus stolonifera, and Fusarium equiseti [1-4]. In September 2019, watersoaked soft rot with brown irregular lesions with a fermented smell, and thick foamy white mycelial growth symptoms were observed on sugar beet roots collected from Wyoming and Michigan (Figure 1 and 2). The symptoms covered approximately 40% of the sugar beet root surface. Diseased beet root tissues were excised from the junction of diseased and healthy tissue. Small pieces (10mm2) were surface sterilized with 10% sodium hypochlorite for 1min, rinsed thrice with sterile distilled water, air-dried on laminar airflow cabinet for 5 minutes, and transferred to corn meal agar (CMA), and clarified V8 (CV8)- incubated at 25°C with a 12-h photoperiod for 7 days. White, thin, flatted, and feathery colonies appeared on both media (Figure 3 and 4). Conidia were arthrosporous, mostly like chains, segmented, hyaline, subglobose, and single-celled (Figure 5). The dimension of conidia varied from 5-12 x 2-5 μm [5]. Based on microscopic and macroscopic characters, the fungus was speculated to be Geotrichum species. Ten isolates were developed by the single spore isolation technique. To confirm the species of the fungus, Genomic DNA was extracted from two representatives of the isolates and the internal transcribed spacer (ITS) region was amplified using the ITS1/ITS4 primers [6]. The amplified PCR products were cleaned and sent for Sanger sequencing by GenScript (GenScript, Piscataway, NJ). A Blastn search of the ITS sequences from the isolates showed 100% identity to those of Geotrichum candidum isolates KF713519.1 and MF782775.1.

Sensitivity of Aphanomyces cochlioides from Sugar Beet to selected Fungicides

Sensitivity of Aphanomyces cochlioides from Sugar Beet to selected Fungicides

Sugar beet root rot caused by oomycetous pathogens in Turkey and their control by seed treatmen

The aim of this study was to determine the oomycetous pathogens causing root rot on sugar beet and test their control by seed treatment in Konya Province, Turkey. Oomycetous fungus-like pathogens of sugar beet were investigated using 866 plant samples collected at 2 growth stages, early seedling and late root, from fields in the Konya region of Turkey and 1 sample from the Thrace region. Herein, 10 oomycetous species belonging to 3 genera: Aphanomyces cochlioides, Phytophthora cryptogea, Ph. pseudocryptogea, Ph. megasperma, Ph. inundata, Pythium aphanidermatum, Py. helicoides, Py. heterothallicum, Py. sylvaticum, and Py. ultimum var. ultimum (Globisporangium ultimum var. ultimum) were discovered at various times with in the 2 growth periods, all of which were the first records for Turkey. A. cochlioides was the most serious pathogen, both in terms of its wide distribution and aggressiveness. The pathogen produced more than 90% disease severity when tested by soil infestation at the seedling stage, although it also occurred at the late root growth stage. Pythium species were also ascommon, such as A. cochlioides, the majority of which were very aggressive, producing more than 84% disease severity at the seedling stage, except for Py. aphanidermatum. Half-strength potato dextrose agar medium was found to be very useful for the isolation of all of the pathogens from the plant samples at both stages. Morphological features of all of the pathogens were abundantly produced when the pathogens were grown on amended grated carrot agar medium and culture disks of fungal growth of this medium were submerged in sterile and nonsterile soil extracts. Out of the 15 fungicide mixes tested, 2 mixes, thiram+metalaxyl+hymexazole and thiram+metalaxyl+hymexazole+ pyraclostrobin reduced seedling root rot caused by both A. cochlioides and Pythium ultimum var. ultimum, while the standard seed treatment fungicide mix of thiram+hymexazole was not effective against either of the pathogens.

Occurrence and importance of root rots caused by fungal pathogens on sugar beet grown in Konya province of Turkey

Sugar beet is extensively grown in Konya province of Turkey and about one third of production of Turkey is obtained from this region. Recently root rots have been observed at all the growth stages of sugar beet especially at later stages near the harvest. During 2015–2017 growing years, 866 fields were visited and diseased samples having root rot symptoms were collected. Various root rot pathogens were isolated from 691 fields; Rhizoctonia solani being the most common (15% of the fields) followed by Fusarium oxysporum, F. solani, Phoma betae, Aphanomyces cochlioides and Pythium spp. Apart from these pathogens, Fusarium culmorum, F. equiseti, F. sambucinum, F. verticillatum, unidentified Fusarium spp., Macrophomina phaseolina and Phytophthora spp. were also determined. All the fungal pathogens were isolated from both of the sugar beet growing stages of 0–12 BBCH and 31–49 BBCH, some of them being high ratios at the late stages. Some isolates of A. cochlioides, P. betae, Pythium spp., Phytophthora spp., and R. solani were highly aggressive when tested by a soil inoculum layer technique. Effects of twelve fungicides, in sixteen different combination and rate, on the most virulant and common four pathogens, A. cochlioides P. betae, Py. ultimum var. ultimum, Rhizoctonia solani, were investigated by the same technique. None of the fungicide mixes inhibited all four pathogens. Thiram + metalaxyl + hymexazol + pyraclastrobin mix sufficiently prevented disease development of the first three pathogens but not R. solani.

Influence of soil characteristics on yield response to lime in sugar beet

Sugar beet is an economically important crop grown on around 30,000 ha in the province of Skåne in the south of Sweden. This project examined the effects of lime on soil factors and yield response in sugar beet in 52 soils in Skåne. Previous research in sugar beet in this area has postulated the importance of appropriate calcium concentrations in the soil to avoid yield losses caused by the root pathogen Aphanomyces cochlioides. Field trials on liming in Sweden have, however shown contrasting results on yield and subsequent economic benefits. The practice of liming has therefore been neglected and resulted in suboptimal pH for plant growth and development in many soils. The aim of the present investigation was to identify and evaluate soil factors of importance for a positive yield response in sugar beet after application of two different lime products: factory lime and limestone meal in rates with similar neutralizing effect (4 tons CaO/ha). Data on soil texture, cation exchange capacity (CEC) and clay mineralogy were available for each site. After liming, nutritional status and Aphanomyces root rot potential in the soil were analysed in each treatment and finally the yield was measured. In total, 52 soils were treated with the two lime products. In addition, 12 of these were also treated with increasing doses of limestone meal.In average for all 52 soils, the yield increased significantly after treatment with either of the lime products. Similarly, the root rot potential of A. cochlioides decreased significantly with no difference between the products. In 12 field trials with 4, 8, 16 and 32 ton/ha limestone meal, 8 ton/ha gave the highest yield. In classifying the soils according to pH and prevailing recommendations, soils with an initial pH >7.0 and with no liming requirement responded positively with significant increases in sugar yield. Soils with initial pH 6.5–7.0 and with a liming requirement, showed less response, with no significant increase in sugar yield. However, the concentration of calcium increased above the suggested threshold of 250 mg/100 g soil and the root rot potential of A. cochlioides decreased significantly in this group. For soils with an initial pH <6.5, the calcium content remained unchanged after liming. Also, Aphanomyces root rot, which was most prevalent in these soils, was not affected by liming. These soils have a low buffering capacity due to the combined effects of clay mineralogy with a low proportion swelling clay minerals and a low clay content. Sugar beets have been shown to acidify the rhizosphere and a high buffering capacity and a high base saturation maintain an optimal pH for nutrient uptake. The results suggest that for crop rotations including sugar beet, liming should be done on a regular basis, also for soils with a pH >7.0. It is of special importance in soils with low pH and CEC to maintain or increase calcium concentrations to a level >250 mg/100 g, which reduce the propagation of A. cochlioides.

Registration of FC1740 and FC1741 Multigerm, Rhizomania‐Resistant Sugar Beet Germplasm with Resistance to Multiple Diseases

FC1740 (Reg No. GP‐293, PI 681717) and FC1741 (Reg No. GP‐294, PI 681718) sugar beet germplasm (Beta vulgaris L.) were developed by the USDA‐ARS at Fort Collins, CO, Salinas, CA, and Kimberly, ID, in cooperation with the Beet Sugar Development Foundation, Denver, CO. These germplasm are diploid, multigerm sugar beet populations in normal cytoplasm, segregating for self‐sterility (Sf:SsSs), genetic male sterility (A:aa), and hypocotyl color (R:rr). FC1740 and FC1741 have excellent resistance to rhizomania (Beet necrotic yellow vein virus). FC1740 was selected as homozygous resistant to markers linked to both Rz1 and Rz2 genes for rhizomania resistance. FC1741 was selected as homozygous to the marker linked to the Rz2 gene for resistance. Both germplasm also have resistance to beet curly top (Beet curly top virus) and Fusarium yellows (Fusarium oxysporum Schlechtend.:Fr. f. sp. betae (D. Stewart) W. C. Snyder &amp; H. N. Hans. and other Fusarium spp.), as well as moderate resistance to Aphanomyces root rot (Aphanomyces cochlioides Drechs.). Neither line exhibited resistance to Cercospora leaf spot (Cercospora beticola Sacc.), Rhizoctonia crown and root rot (Rhizoctonia solani Kuhn.) or sugar beet root aphid (Pemphigus spp.). These germplasm provide sources from which to select disease‐resistant, multigerm pollinator parents with either or both of the Rz1 and Rz2 sources of rhizomania resistance. Because they are from the same population, they also are useful as controls of known genetic background in comparing entries screened for rhizomania resistance conditioned by Rz1 or Rz2.

Inhibitory Effects of Macrotetrolides from Streptomyces spp. On Zoosporogenesis and Motility of Peronosporomycete Zoospores Are Likely Linked with Enhanced ATPase Activity in Mitochondria.

The release of zoospores from sporangia and motility of the released zoospores are critical in the disease cycle of the Peronosporomycetes that cause devastating diseases in plants, fishes, animals and humans. Disruption of any of these asexual life stages eliminates the possibility of pathogenesis. In the course of screening novel bioactive secondary metabolites, we found that extracts of some strains of marine Streptomyces spp. rapidly impaired motility and caused subsequent lysis of zoospores of the grapevine downy mildew pathogen Plasmopara viticola at 10 μg/ml. We tested a number of secondary metabolites previously isolated from these strains and found that macrotetrolide antibiotics such as nonactin, monactin, dinactin and trinactin, and nactic acids such as (+)-nonactic acid, (+)-homonactic acid, nonactic acid methyl ester, homonactic acid methyl ester, bonactin and feigrisolide C impaired motility and caused subsequent lysis of P. viticola zoospores in a dose- and time-dependent manners with dinactin being the most active compound (MIC 0.3 μg/ml). A cation channel-forming compound, gramicidin, and a carrier of monovalent cations, nigericin also showed similar biological activities. Among all 12 compounds tested, gramicidin most potently arrested the motility of zoospores at concentrations starting from 0.1 μg/ml. All macrotetrolide antibiotics also displayed similar motility impairing activities against P. viticola, Phytophthora capsici, and Aphanomyces cochlioides zoospores indicating non-specific biological effects of these compounds toward peronosporomyctes. Furthermore, macrotetrolide antibiotics and gramicidin also markedly suppressed the release of zoospores from sporangia of P. viticola in a dose-dependent manner. As macrotetrolide antibiotics and gramicidin are known as enhancers of mitochondrial ATPase activity, inhibition of zoosporogenesis and motility of zoospores by these compounds are likely linked with hydrolysis of ATP through enhanced ATPase activity in mitochondria. This is the first report on motility inhibitory and lytic activities of macrotetrolide antibiotics and nactic acids against the zoospores of peronosporomycete phytopathogens.

Differentiation of the disease caused by Aphanomyces cochlioides and girth scab on sugar beet roots - a review

Severe symptoms of root rot on sugar beet have been observed in Poland and Germany since 2001. The symptom classification suggested girth scab as it was mistakenly classified on the basis of current classification, e.g. in LIZ. However, the cause of the disease was Aphanomyces cochlioides infection, not Streptomyces spp. According to these findings we cannot call the symptoms caused by A. cochlioides as ‘girth scab’. The typical scab (girth scab) symptoms can be promoted by A. cochlioides infections. In many cases, A. cochlioides developed at the beginning of the season, during the seedling stage. Its further development was due to rainfall and was not routinely recognised in disease-changed tissues if in the middle of the summer the rainfall level was reduced. According to the described findings, renewed description and differentiation of the girth scab symptoms caused by Streptomyces spp. and root rot caused by A. cochlioides on sugar beet roots are suggested. Typical symptoms of the disease caused by A. cochlioides occur mainly on the upper part of the root but can also occur on its lower part, if weather conditions are favourable for the pathogen. The coexistence of A. cochlioides and Pythium spp. in the same niches is also possible. Currently the illustrations showing these symptoms are included in the ‘girth scab’ descriptions.

Penthiopyrad applied in close proximity to Rhizoctonia solani provided effective disease control in sugar beet

Rhizoctonia solani Kühn is an important pathogen of sugar beet (Beta vulgaris L.) that can cause damping-off and crown and root rot. Commercial cultivars which are highly resistant to the pathogen are not as high yielding as susceptible cultivars under low or absent disease pressure. These resistant cultivars often do not have resistance to other common pathogens such as Aphanomyces cochlioides, Cercospora beticola, and Fusarium oxysporum. Fungicides, such as azoxystrobin which belongs to the quinone outside inhibitors (QoI) class, are necessary for controlling Rhizoctonia solani, but there are concerns about the buildup of fungicide-resistant strains in the targeted pathogen population. There is a need to find effective fungicides from different chemical groups so they can be rotated with the current widely-used azoxystrobin to manage R. solani. The objective of this greenhouse study was to evaluate the efficacy of penthiopyrad, a succinate dehydrogenase inhibitor (SDHI), in managing R. solani on sugar beet using three different application methodologies. Penthiopyrad effectively controlled R. solani on sugar beet when applied at 210, 280, 420, or 550 g a.i./ha in-furrow at planting and as a soil drench at the 4-leaf stage. However, foliar application of penthiopyrad failed to provide disease control. These trials indicated that penthiopyrad needs to be in close proximity or direct contact with R. solani in the soil to provide effective control. Penthiopyrad has the potential to be used as an effective alternate partner with azoxystrobin for controlling R. solani and to help in mitigating the development of fungicide resistant isolates of R. solani.

Disease risk assessment of sugar beet root rot using quantitative real-time PCR analysis of Aphanomyces cochlioides in naturally infested soil samples

Sugar beet root rot, caused by the oomycete Aphanomyces cochlioides, is a serious and economically important disease of sugar beets world-wide. Today, disease risk assessment consists of a time-consuming greenhouse bioassay using bait plants. In the present study, a real-time quantitative PCR (qPCR) assay for determination of A. cochlioides DNA in field-infested soil samples was developed and validated using the standard bioassay. The qPCR assay proved to be species-specific and was optimized to give high amplification efficiency suitable for target copy quantification. A high correlation (R2 > 0.98, p < 0.001) with pathogen inoculum density was shown, demonstrating the suitability for monitoring soil samples. The limit of detection (LOD) was evaluated in several different soil types and varied between 1 and 50 oospores/g soil, depending on clay content. Soils with a high LOD were characterised as having a low clay content and high content of sand. Varying levels of the A. cochlioides target sequence were detected in 20 of the 61 naturally infested soil samples. Discrepancies between the bioassay and the qPCR assay were found in soils from low- and medium-risk fields. However, the qPCR diagnostic assay provides a potentially valuable new tool in disease risk assessment, enabling sugar beet growers to identify high-risk fields.

Development of a DNA Microarray-Based Assay for the Detection of Sugar Beet Root Rot Pathogens.

Sugar beet root rot diseases that occur during the cropping season or in storage are accompanied by high yield losses and a severe reduction of processing quality. The vast diversity of microorganism species involved in rot development requires molecular tools allowing simultaneous identification of many different targets. Therefore, a new microarray technology (ArrayTube) was applied in this study to improve diagnosis of sugar beet root rot diseases. Based on three marker genes (internal transcribed spacer, translation elongation factor 1 alpha, and 16S ribosomal DNA), 42 well-performing probes enabled the identification of prevalent field pathogens (e.g., Aphanomyces cochlioides), storage pathogens (e.g., Botrytis cinerea), and ubiquitous spoilage fungi (e.g., Penicillium expansum). All probes were proven for specificity with pure cultures from 73 microorganism species as well as for in planta detection of their target species using inoculated sugar beet tissue. Microarray-based identification of root rot pathogens in diseased field beets was successfully confirmed by classical detection methods. The high discriminatory potential was proven by Fusarium species differentiation based on a single nucleotide polymorphism. The results demonstrate that the ArrayTube constitute an innovative tool allowing a rapid and reliable detection of plant pathogens particularly when multiple microorganism species are present.

Registration of FC305 Multigerm Sugarbeet Germplasm Selected from a Cross to a Crop Wild Relative

FC305 (Reg. No. GP-286, PI 671963) sugarbeet (Beta vulgaris L.) germplasm was developed and released by the USDA–ARS, at Fort Collins, CO, Salinas, CA, and East Lansing, MI, in cooperation with the Beet Sugar Development Foundation, Denver, CO. This germplasm is a diploid, sugarbeet population in normal cytoplasm, segregating for self-sterility (Sf:SsSs), multigermity (M:mm), and hypocotyl color (R:rr). FC305 has moderate resistance to cercospora leaf spot (CLS) (caused by Cercospora beticola Sacc.), aphanomyces root rot (caused by Aphanomyces cochlioides Drechsl.), and beet curly top (Beet curly top virus), as well as resistance to Fusarium yellows [caused by Fusarium oxysporum Schlecht. f. sp. betae (Stewart) Snyd. & Hans.]. This germplasm is segregating for resistance to rhizomania (Beet necrotic yellow vein virus) and contains both Rz1 and Rz2 genes for resistance. There was no resistance to root-rotting strains (AG-2–2) of Rhizoctonia solani Kühn. FC305 could provide an alternate source of resistance to CLS and Fusarium yellows in a diverse genetic background to enrich the cultivated sugarbeet germplasm base. FC305 provides a source from which to select disease-resistant, multigerm pollinator parents. Because monogerm and O-type is within its parentage, it should be possible to select monogerm, O-type, CMS-maintainer lines from FC305 as well.

Utilizing a Preplant Soil Test for Predicting and Estimating Root Rot Severity in Sugar Beet in the Central High Plains of the United States.

Aphanomyces cochlioides and Rhizoctonia solani are important soilborne pathogens causing root diseases that are primary constraints to sugar beet production in Nebraska, Colorado, and Wyoming. These types of diseases are difficult to control because they are often not noticed until substantial damage has already occurred. Efforts to manage them would be more effective if techniques were available that were more predictive than reactive. Therefore, a preplant soil test was developed to estimate the relative pathogen populations in the soil and to predict potential root disease problems later in the growing season. Preplant soil samples collected from fields to be sown with sugar beet were planted with a susceptible cultivar and tests were conducted for 1 month in the greenhouse. A preplant disease index was developed based on the time period during the test that seedlings became infected and was calculated on a 0-to-100 scale. Disease index values were compared with yields obtained from the same fields after harvest. Analysis of data collected for 5 years (2003 to 2007) with analysis of covariance revealed a strong relationship between the preplant disease index values and recoverable sucrose and root yields but not sucrose concentration. Results indicated that, for each unit increase in the preplant disease index, root yield decreased by 0.27 metric tons (270 kg) per hectare (P < 0.05, R2 = 0.44) and recoverable sucrose decreased by 49 kg/ha (P < 0.05, R2 = 0.45). We concluded that this preplant soil test can accurately predict root disease potential due to R. solani and A. cochlioides, and has the potential to help producers make effective management decisions in production fields using the index procedure. This soil assay has additionally provided new information on the biology, incidence, and distribution of root pathogens in production fields throughout the Central High Plains.

Production of antioomycete compounds active against the phytopathogens Phytophthora sojae and Aphanomyces cochlioides by clavicipitoid entomopathogenic fungi

A total of 412 strains belonging to 14 genera of clavicipitoid entomopathogenic fungi (EPF) were screened for activities against two economically important plant pathogenic oomycetes, Phytophthora sojae and Aphanomyces cochlioides. To identify the antioomycete compounds produced by EPF, the extracts of 13 highly active EPF strains were characterized in detail by high performance liquid chromatography with diode array detection and high-resolution mass spectrometric detection and antioomycete assay. The antioomycete activity of several Metarhizium extracts was associated with previously isolated aurovertins, fungerin, N-(methyl-3-oxodec-6-enoyl)-2-pyrroline, and N-(methyl-3-oxodecanoyl)-2-pyrroline. The depsipeptide beauvericin was confirmed to be one of the active principles of three strains of Isaria tenuipes, which strongly inhibited mycelial growth of both P. sojae and A. cochlioides. Two known bioactive metabolites, paecilosetin and aranorosinol A, together with a novel and potent antioomycete compound, farinomalein, were isolated from the extracts of Isaria farinosa and all compounds were confirmed to have antioomycete activity. Identification of 8 antioomycete compounds from 13 clavicipitioid EPF demonstrated a new potential use of EPF as a source of compounds for the control of soil-borne plant pathogenic oomycetes.

Steroids and Ceramide from the Stem Bark of Odyendyea gabonensis

Two new steroids, 22E, 24R-stigmast-22-ene-3,6,11-trione (1) and 22E, 24R-3-acetylstigmasta- 5,22-diene-7,11-dione (2), and one new ceramide, (2S,3S,4R,5R) N-(1,3,4,5-tetrahydroxyundecan- 2-yl)tetradecanamide (7), together with eleven known compounds were isolated from the CH2Cl2 extract of the stem bark of Odyendyea gabonensis. The structures of all compounds were determined by comprehensive analyses of their 1D and 2D NMR, mass spectral (EI and ESI) data, chemical reactions, and comparison with previously known analogs. Pure compounds were tested for their activity against the bacteria Bacillus subtilis, Staphylococcus aureus and Escherichia coli, the fungi Mucor miehei and Candida albicans, and the plant pathogen oomycetes Aphanomyces cochlioides, Pythium ultimum and Rhizoctonia solani using the paper disk agar diffusion assay. For active compounds, MICs were determined by the broth microdilution assay. Cytotoxic activity against the human lung adenocarcinoma cell line A 549 was evaluated by the MTT assay. All compounds delivered low to missing antimicrobial activities in the agar diffusion assay and MICs &gt; 1 μg mL-1. The alkaloids 10 and 11 displayed cytotoxic activity against the human lung adenocarcinoma cell line A549 with IC50 2.5 and 4:5 μm respectively.

Epicoccolides: Antimicrobial and Antifungal Polyketides from an Endophytic Fungus Epicoccum sp. Associated with Theobroma cacao

AbstractIn the search for new compounds to protect plants from fungi, an endophytic fungus, Epicoccum sp. CAFTBO, obtained from Theobroma cacao was found to produce three polyoxygenated polyketides, namely epicolactone (1) and epicoccolides A (2) and B (3), together with seven known metabolites. The structures of these compounds were elucidated by a combination of detailed spectroscopic and spectrometric analyses as well as DFT calculations of the electronic circular dichroism spectra and the single‐crystal X‐ray diffraction analysis of 1. Compounds 1–3 showed potent antimicrobial activities and significant inhibitory effects on the mycelial growth of two peronosporomycete phytopathogens, Pythium ultimum and Aphanomyces cochlioides, and the basidiomycetous fungus Rhizoctonia solani.

Biocontrol of Sugar Beet Seedling and Taproot Diseases Caused by Aphanomyces cochlioides by Pythium oligandrum Treatments before Transplanting

Biocontrol activities in the oospore suspensions of 17 isolates of Pythium oligandrum (PO) were examined for their effect against post-emergence seedling diseases. The seeds of sugar beet that had been commercially chemical-pelleted to prevent pre-emergence damping-off were sown in Aphanomyces cochlioides-infested soil on trays. PO isolate MMR2 proved most effective in controlling post-emergence damping-off, at a level equivalent to that of applying fungicides. Oospore suspensions stored for 188 days or 379 days at 4℃ were as effective against A. cochlioides post-emergence damping-off as chemical control. Treating soil with PO oospores by mixing suspensions into the surface of soil in paper pot nurseries or by drenching seedlings 32 days before transplanting could control Aphanomyces root rot in the field without additional applications. The control effect conferred by PO suspensions was also demonstrated in vitro. A polymerase chain reaction (PCR) assay used to detect PO indicated that this oomycete could colonize the rhizosphere of sugar beet plants cultivated in the field when applied before transplanting. These results suggest that PO has the potential to control both post-emergence damping-off and root rot caused by A. cochlioides.