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Background: Sclerotium rolfsii, the causal agent of peanut southern blight, has become increasingly prevalent and harmful in China, causing serious economic losses to the peanut industry. To effectively manage peanut southern blight, this study evaluated the bioactivity of the new‐generation sterol demethylation inhibitor (DMI) fungicide mefentrifluconazole against peanut S. rolfsii. Results: In this study, the DMI fungicide mefentrifluconazole exhibited excellent inhibitory activity against the mycelial growth of S. rolfsii, with a mean EC50 value of 0.21 ± 0.11 mg L−1 and a range of 0.02 to 0.55 mg L−1 for 261 isolates collected from Hebei, Henan and Shandong provinces. Mefentrifluconazole significantly reduced the biomass of mycelia and affected the morphology of hyphae. Although sclerotia were more tolerant to mefentrifluconazole than mycelial growth, mefentrifluconazole greatly inhibited the formation and germination of sclerotia. In addition, sclerotia produced by mefentrifluconazole‐treated mycelia were deficient in nutrients (e.g., protein, carbohydrate and lipid). These results indicated that mefentrifluconazole may reduce the population of S. rolfsii in the following year. In greenhouse experiments, mefentrifluconazole showed control efficacy and good persistence against peanut S. rolfsii. The preventative and curative activities of mefentrifluconazole at 200 mg L−1 against southern blight still reached 95.36% and 60.94%, respectively, after 9 days of application. No correlation was observed for the sensitivity of S. rolfsii to mefentrifluconazole and the tested DMI, quinone outside inhibitor and succinate dehydrogenase inhibitor fungicides. Conclusion: All data indicated that mefentrifluconazole could provide favorable control efficacy against S. rolfsii from peanuts and reduce the infection and population of S. rolfsii in the following year. © 2023 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Identifying the sources of fungal inoculum that induces epidemics is instrumental to managing crop health in a more efficient way by implementing prophylactic methods and by using better targeted biocontrol and fungicide applications. For some phytopathogenic fungi, this identification is hampered by the multiplicity of inoculum types. This is the case for Sclerotinia sclerotiorum, the agent of white mould, which can produce ascospores disseminated via the atmosphere, sclerotia stored in the soil and mycelium in plant debris of a large variety of hosts. The present study aims to assess the relative importance of airborne and soilborne inocula in white mould disease development and its persistence across two crop seasons. S. sclerotiorum isolates were collected from air, soil and carrot plants during two crop seasons in south‐western France and genotyped with 16 microsatellite markers. Among the 490 isolates, 162 clonal lineages were identified. The genetic characteristics did not differ significantly among isolates collected from air, soil and carrots. The epidemics of white mould on carrots were initiated either by airborne inoculum or by soilborne inoculum. It also appears that some isolates from airborne inoculum persisted from year to year. [ABSTRACT FROM AUTHOR]

The fungal pathogen, Sclerotinia sclerotiorum, causes significant disease in oil‐seed crops, and produces sclerotia, primarily serving as a survival structure, but also as means of dispersal. The aim of this study was to quantify sclerotia recovered from South African soybean and sunflower silos between 2012/2013 and 2020, for each crop respectively. Historic data were retrieved from a public database managed by the South African Grain Laboratories. A one‐way analysis of variance (ANOVA) and summary statistics were visualized to determine variation in percentage (mass per seed mass) and prevalence (percentage of positive seed lots) of sclerotia recovered. Sclerotia recoveries were mapped to determine regions and years which were below or above legislative and industry sclerotia thresholds. A total of 190 and 163 soybean and sunflower silos were sampled, respectively, where between 100 and 176 3‐kg sub‐samples per annum were included. Prevalence of sclerotia recovered ranged between 33.3% (2015) and 78.3% (2020) in soybean production regions and 9.1% (2013) and 95.0% (2020) in sunflower production regions. ANOVA indicated significant differences between reported years, for both crops, and variation in frequency of sclerotia with regard to policy thresholds. Sclerotia recovered may provide an indication of sclerotia retained in farm‐saved seed as well as sclerotia remaining on and in fields. South Africa is one of the few countries with national and industry policies in place to monitor and restrict sclerotia in seed. This practice should continue, with the addition of research, which is underway, to understand the risk associated with S. sclerotiorum to remain seed‐borne and potentially cause infections. [ABSTRACT FROM AUTHOR]

For eukaryotes like fungi to regulate biological responses to environmental stimuli, various signalling cascades are utilized, like the highly conserved mitogen‐activated protein kinase (MAPK) pathways. In the model fungus Aspergillus nidulans, a MAPK pathway known as the pheromone module regulates development and the production of secondary metabolites (SMs). This pathway consists five proteins, the three kinases SteC, MkkB and MpkB, the adaptor SteD and the scaffold HamE. In this study, homologs of these five pheromone module proteins have been identified in the plant and human pathogenic fungus Aspergillus flavus. We have shown that a tetrameric complex consisting of the three kinases and the SteD adaptor is assembled in this species. It was observed that this complex assembles in the cytoplasm and that MpkB translocates into the nucleus. Deletion of steC, mkkB, mpkB or steD results in abolishment of both asexual sporulation and sclerotia production. This complex is required for the positive regulation of aflatoxin production and negative regulation of various SMs, including leporin B and cyclopiazonic acid (CPA), likely via MpkB interactions in the nucleus. These data highlight the conservation of the pheromone module in Aspergillus species, signifying the importance of this pathway in regulating fungal development and secondary metabolism. [ABSTRACT FROM AUTHOR]

Sclerotial powder of a cultivated species of the Tiger Milk Mushroom, Lignosus cameronensis was analysed for its nutritional components and compared against species of the same genus, Lignosus rhinocerus and Lignosus tigris. All three species have been used by indigenous tribes in Peninsular Malaysia as medicinal mushrooms. Content of carbohydrate, fibre, mineral, amino acid, palatable index, fat, ash and moisture were determined. L. cameronensis sclerotial material consists of carbohydrate (79.7%), protein (12.4%) and dietary fibre (5.4%) with low fat (1.7%) and no free sugar. It has the highest content of total carbohydrate (791 g kg−1), energy value (3,700 kcal kg−1) and calcium (0.85 g kg−1). The crude protein content (123 g kg−1) is comparable to that of L. rhinocerus with its main amino acids consisting of glutamic acid, aspartic acid and leucine. The umami index is determined to be 0.27. The total essential amino acid (45 g kg−1) is comparable to that of L. tigris. The main mineral is potassium (1.51 g kg−1) and the Na/K ratio was <0.6. Heavy metals such as mercury, cadmium, lead and arsenic were absent. L. cameronensis has the highest amount of food energy, total carbohydrate and calcium compared to those of both L. rhinocerus and L. tigris. The essential amino acids comprised almost 40% of the total amino acid content, slightly more than that reported from sclerotial powder of the L. tigris. © 2019 IUBMB Life, 9999(9999):1–6, 2019 [ABSTRACT FROM AUTHOR]

Controlling Verticillium dahliae through irrigation systems should be an important measure within integrated management of verticillium wilt of olive in Spain. Pathogen content of water infested by V. dahliae conidia and sclerotia can be diminished following in vitro treatments with the disinfectants OX‐VIRIN and OX‐AGUA AL25. Three concentrations per disinfectant were assessed for their effectiveness under operational conditions of modern irrigated olive orchards. Sterilized potted soil was drip‐irrigated with conidia‐ or sclerotia‐containing water that was pumped from a storage tank and disinfected (or not, control) within the pipelines via metering pumps. The trial was carried out in autumn and spring for each type of propagule infesting the water. The inoculum dispensed through drippers and the total inoculum density accumulated in soil were estimated. Furthermore, the treated residual inoculum in soil was assessed for pathogenicity on olive plants. Conidial incorporation in soil was prevented by most disinfectant treatments in spring; while for sclerotia, prevention was observed only at the highest OX‐VIRIN (51.2 mL L−1; in both seasons) and OX‐AGUA AL25 (11.27 mL L−1; in autumn) concentration. The remaining disinfectant treatments reduced conidia and sclerotia accumulation in soil by over 99% and 95%, respectively. Season particularly impacted the efficacy of lower concentrations. Expression of symptoms was not observed in olive plants grown in previously treated soils. The infectivity of the residual inoculum present in some treated soils was prevented, markedly reduced or limited to the roots. These results provide a novel, interesting and feasible approach in the management of the disease. [ABSTRACT FROM AUTHOR]

BACKGROUND: Since the introduction of herbicide‐tolerant varieties of canola (Brassica napus L.) in 1993, global plantings have increased resulting in an increased incidence of Sclerotinia sclerotiorum (Lib.) de Bary infections. Developments in narrow windrow burning techniques to destroy the seed of multiple herbicide‐resistant weeds provide an opportunity to also intercept and heat‐treat the S. sclerotiorum inoculum source, termed sclerotia, before it re‐enters the soil to infect susceptible crop species in successive years. RESULTS: Preliminary kiln studies determined that a temperature of 264 °C for 10 s was needed to destroy S. sclerotiorum sclerotia viability (LT99) of sclerotia < 3 mm in diameter, whereas temperatures of 353 and 362 °C for the same duration were required to kill sclerotia (LT99) of 3–4 and > 4 mm in diameter respectively. In the field, temperatures > 500 °C were maintained in the centre of burning narrow windrows of canola residue for > 450 s and 300 °C was maintained consistently at either edge of the windrows for the same duration. The temperatures achieved when burning canola narrow windrows were sufficient to kill all sclerotia concentrated into the narrow windrow. CONCLUSION: As a technique, narrow windrow burning of canola residue provides the temperature and temperature durations required to kill S. sclerotiorum sclerotia, thus providing a non‐fungicidal control option as part of a wider integrated disease management approach. © 2018 Society of Chemical Industry Narrow windrow burning canola residue provides the temperature and required duration to kill Sclerotinia sclerotiorum sclerotia, providing a non‐fungicidal control option for sclerotinia stem rot in integrated disease management. [ABSTRACT FROM AUTHOR]

The soilborne fungus Sclerotinia sclerotiorum infects many important crop plants. Central to the success of this pathogen is the production of sclerotia, which enables survival in soil and constitutes the primary inoculum. This study aimed to determine how crop plant type and S. sclerotiorum isolate impact sclerotial production and germination and hence inoculum potential. Three S. sclerotiorum isolates (L6, L17, L44) were used to inoculate plants of bean, carrot, lettuce, oilseed rape (OSR) and potato, and the number and weight of sclerotia per plant quantified. Carpogenic germination of sclerotia collected from different hosts was also assessed for L6. Production of sclerotia was dependent on both crop plant type and S. sclerotiorum isolate, with OSR and lettuce supporting the greatest number (42–122) and weight (1.6–3.0 g) of sclerotia per plant. The largest sclerotia were produced on OSR (33–66 mg). The three S. sclerotiorum isolates exhibited a consistent pattern of sclerotial production irrespective of crop type; L6 produced large numbers of small sclerotia while L44 produced smaller numbers of large sclerotia, with L17 intermediate between the two. Germination rate and percentage was greatest for larger sclerotia (4.0–6.7 mm) and also varied between host plants. Combining sclerotial production data and typical field crop densities suggested that infected carrot and OSR could produce the greatest number (3944 m−2) and weight (73 g m−2) of S. sclerotiorum sclerotia, respectively, suggesting these crops potentially contribute a greater increase in inoculum. This information, once further validated in field trials, could be used to inform future crop rotation decisions. [ABSTRACT FROM AUTHOR]

Sclerotinia sclerotiorum is a devastating necrotrophic plant pathogen with a worldwide distribution. Cell wall-degrading enzymes and oxalic acid are important to the virulence of this pathogen. Here, we report a novel secretory protein, Ss-Rhs1, which is essential for the virulence of S. sclerotiorum. Ss-Rhs1 is believed to contain a typical signal peptide at the N-terminal and eight rearrangement hotspot (Rhs) repeats. Ss-Rhs1 exhibited a high level of expression at the initial stage of sclerotial development, as well as during the hyphal infection process. Targeted silencing of Ss-Rhs1 resulted in abnormal colony morphology and reduced virulence on host plants. Microscopic observations indicated that Ss-Rhs1-silenced strains exhibited reduced efficiency in compound appressoria formation. [ABSTRACT FROM AUTHOR]

For efficient integrated management of verticillium wilt in olive ( VWO), it is important to establish whether irrigation treatments (with Verticillium dahliae-free water) that mitigate the disease in V. dahliae-infested soil, also reduce the levels of more and less persistent propagules of the pathogen in the soil. Effects of irrigation on VWO and V. dahliae propagules were evaluated under natural environmental conditions. Potted plants were irrigated (pathogen-free water) to two ranges of soil water content ( RWC; high and low) at three surface drip-irrigation frequencies (daily, weekly, and daily during some periods and otherwise weekly). VWO and total inoculum density (ID), density of less persistent micropropagules (MpD) and more persistent sclerotia in wet soil (SwD), and sclerotia density for air-dried soil (SdD) were monitored. A logistic model (multiple sigmoid) of disease incidence revealed the lowest parameter values in treatments irrigated daily. Daily frequency of irrigation showed significantly lower disease incidence (39.2%) and disease intensity index (43.9%) and MpD (88.0%) values as areas compared with other frequencies, regardless of the RWC. High RWC significantly reduced (70.8-84.9%) ID, SwD and SdD as areas, but significantly increased (18.0%) the incidence of infected plants (IIP), regardless of the irrigation frequency. The disease incidence was not correlated with temperature. Daily irrigation to low RWC mitigated the VWO and the IIP, kept soil to the lowest MpD and resulted in the lowest SdD level at the end of the trial. Results suggested that less persistent propagules could have played a part in the disease development. [ABSTRACT FROM AUTHOR]

This study aimed at investigating the biosorption of copper(II) from aqueous solutions by sclerotiogenic Aspergillus oryzae G15. Potentiometric titration analysis results indicated that carboxyl group was mainly responsible for Cu(II) adsorption. Sclerotia were a better biosorbent than mycelia, which could be ascribed to the higher amount of carboxyl sites exposed after differentiation. Langmuir isotherm model fitted well the absorption process of mycelia and sclerotia with the maximum theoretical sorption capacities of 35.34 and 73.53 mg/g, respectively. Scanning electron microscopy coupled with energy dispersive X-ray analysis confirmed that there was surface biosorption of Cu(II) on the adsorbents. Based on the fourier transform infrared spectroscopy analyses results, it could be proposed that the increased sorption capacity of sclerotia was due to increased functional groups related to the biosorption process. Cu(Il)-loaded biosorbents could be regenerated and reused, which indicated that A. oryzae G15 could be considered as an alternative for removing Cu (II) from wastewater. [ABSTRACT FROM AUTHOR]

Sheath blight disease in rice has caused major crop losses worldwide. Managing the causal agent of disease Rhizoctonia solani Kühn is difficult because of its broad host range and formation of sclerotia which can survive in harsh environmental conditions; therefore developing innovative disease management methods without application of hazardous chemicals has been considered as the main concern to maintain sustainable agriculture. This presented research has revealed the negative impact of silver nanoparticles (SNPs) on R. solani and disease progress both in vitro and in vivo. The adverse effects of the SNPs on R. solani are significantly dependent on the quantity of SNPs, sprayed at different concentrations in vitro. The highest inhibition level against sclerotia formation and mycelia growth are 92 and 85%, respectively, at a SNPs concentration of 50 ppm. In vivo glasshouse experiments also showed that SNPs at the same concentration favourably affects both the fresh and dry weight of rice plants with a remarkable suppressive effect on the lesion development in leaves. [ABSTRACT FROM AUTHOR]

We used a proteomic analysis to identify cell wall proteins released from Sclerotinia sclerotiorum hyphal and sclerotial cell walls via a trifluoromethanesulfonic acid (TFMS) digestion. Cell walls from hyphae grown in Vogel's glucose medium (a synthetic medium lacking plant materials), from hyphae grown in potato dextrose broth and from sclerotia produced on potato dextrose agar were used in the analysis. Under the conditions used, TFMS digests the glycosidic linkages in the cell walls to release intact cell wall proteins. The analysis identified 24 glycosylphosphatidylinositol (GPI)-anchored cell wall proteins and 30 non-GPI-anchored cell wall proteins. We found that the cell walls contained an array of cell wall biosynthetic enzymes similar to those found in the cell walls of other fungi. When comparing the proteins in hyphal cell walls grown in potato dextrose broth with those in hyphal cell walls grown in the absence of plant material, it was found that a core group of cell wall biosynthetic proteins and some proteins associated with pathogenicity (secreted cellulases, pectin lyases, glucosidases and proteases) were expressed in both types of hyphae. The hyphae grown in potato dextrose broth contained a number of additional proteins (laccases, oxalate decarboxylase, peroxidase, polysaccharide deacetylase and several proteins unique to Sclerotinia and Botrytis) that might facilitate growth on a plant host. A comparison of the proteins in the sclerotial cell wall with the proteins in the hyphal cell wall demonstrated that sclerotia formation is not marked by a major shift in the composition of cell wall protein. We found that the S. sclerotiorum cell walls contained 11 cell wall proteins that were encoded only in Sclerotinia and Botrytis genomes. [ABSTRACT FROM AUTHOR]

Penicillium thomii Q1 strain was able to form abundant orange, sand-shaped sclerotia in which carotenoids were accumulated. The aim of this work was to determine the effects of copper-induced oxidative stress on the sclerotial differentiation, biosynthesis of some endogenous antioxidants, and the activities of some antioxidative enzymes of Q1 strain. The results showed that the oxidative stress induced by copper was clearly dependent on the CuSO4 concentrations in media, and characterized by the initiation of lipid peroxidation. Under the copper-induced oxidative stress conditions, the time of exudates initiation, sclerotial initiation and sclerotial maturation of Q1 strain were advanced in 1-2 days. The analytical results of sclerotial biomass, carotenoids, and ascorbate contents showed that copper-induced oxidative stress favored the sclerotial differentiation and biosynthesis of carotenoids and ascorbate. The oxidative stress induced by a lower amount of CuSO4 in media could enhance significantly the superoxide dismutase and catalase activities of Q1 strain. [ABSTRACT FROM AUTHOR]

Morels are wild edible ascomycetous mushrooms that are highly prized because of their medicinal and nutritional qualities. Ligninolytic enzymes are considered as one of the most important enzymes in fungi due to their involvement in fruiting body formation during artificial cultivation on different substrates. In the life cycle of morels, sclerotia are the intermediate stage to form a fruiting body from mycelia. We have studied the production of ligninolytic enzymes by Morchella crassipes MR8 growing on different substrates and during sclerotia formation. This fungus is able to produce ligninolytic enzymes such as laccase (Lac), lignin peroxidase (LiP), and manganese-dependent peroxidase (MnP) when grown on different substrates. Maximum Lac activity was observed when grown in wheat grains whereas maximum activities of MnP and LiP were observed when grown in rice straw. Laccase enzyme was produced in high titers during sclerotia formation and maturation when grown in combinations of soil and substrates. A large number of sclerotia was observed in soil and wheat grains, along with high titers of laccase. Cellulase activity was observed to be constant during sclerotia formation and maturation. The present study results suggest that laccase enzyme might play an important role in sclerotia formation in morels. [ABSTRACT FROM AUTHOR]

Sclerotia produced by a single isolate of Rhizoctonia solani AG3 PT were buried in small plot experiments to investigate the effects of sclerotial production method, soil type and burial depth on sclerotial viability in field soil. The factor with the greatest effect on sclerotial viability, defined as the percentage of sclerotia germinating on agar following retrieval, in all experiments was the duration of burial. After 18 months, on average across all experiments, 20% of retrieved sclerotia were viable. A comparison between sclerotia produced in vitro on malt yeast extract agar and in vivo using micropropagated tubers in field soil found no significant differences between the two production methods on sclerotial viability. Burial in field soil at 20-cm depth was found to significantly reduce sclerotial viability to 50% compared to 60% at 5 cm. In two pot experiments, amending the growing medium and soil with increasing inoculum densities of R. solani was found to increase stem number, stem canker and black scurf severity regardless of whether this soil-borne inoculum was derived from mycelium or sclerotia. Black scurf incidence and severity were assessed 30-32 days posthaulm destruction and found to be similar for a range of sclerotial soil-borne inoculum densities (1.0 × 10−1 g/kg d.w. soil to 6 × 10−3 g/kg d.w. soil). The significance of these findings in relation to pathogen survival, detection in soil and disease development is discussed. [ABSTRACT FROM AUTHOR]

Studies were conducted to determine the effects of soil moisture (9, 16 or 24% w/w) and temperature (5, 15, 20 or 25°C) on the control of sclerotia of Sclerotinia sclerotiorum by five fungal agents in sterile and natural field soil. All five biocontrol agents were effective in reducing the survival of sclerotia of S. sclerotiorum in sterile soil under dry (9% moisture) or wet (24% moisture) conditions at 20°C, but only Coniothyrium minitans was effective in natural soil. Coniothyrium minitans was the most effective in reducing sclerotial viability at the temperature range of 15–25°C. Trichoderma virens was effective against sclerotia of S. sclerotiorum to a lesser extent than C. minitans, and in non-autoclaved soil, it performed best at 25°C. Although Epicoccum purpurascens, Talaromyces flavus and Trichothecium roseum were effective against sclerotia of S. sclerotiorum in some instances, they were less effective than C. minitans and T. virens. Sclerotia of S. sclerotiorum conditioned for myceliogenic germination were more vulnerable to attack by the biocontrol agents than dormant sclerotia. The implications are discussed with respect to enhancement of biological control of crop diseases caused by S. sclerotiorum in different geographic regions. [ABSTRACT FROM AUTHOR]

The effects of substrate composition and temperature on mycelial growth and sclerotium production in Grifola umbellate (Pers.) Pilát were investigated in the present study. The induction of sclerotia of G. umbellate was affected greatly by the type of medium, as well as the type of carbon source. Malt-extract agar was able to induce the production of sclerotia. The production of sclerotia was also observed when the carbon source in the GPC agar medium (glucose 20 g/L, peptone 6 g/L, corn steep liquor 10 g/L, and agar 15 g/L) was replaced with glycerol or mannitol. Altering the composition of the GPC medium with milk powder, thiamine hydrochloride, extract of Armillaria mellea, active clay, diatomite, kaolin, or arginine did not induce the production of sclerotia. A temperature range of 18–25°C was suitable for both mycelial growth and sclerotium formation. Glycerol significantly induced slerotium formation on nutrient supplemented with sawdust substrates in bottle culture. 24S-Polyporusterone A and polyporusterone B were assayed in samples of natural and cultured sclerotia. Both natural and cultured sclerotia contained 24S-polyporusterone A and polyporusterone B. (Managing editor: Ya-Qin Han) [ABSTRACT FROM AUTHOR]

Two isolates of Trichoderma viride (L4 and S17A) were assessed for biological control of Allium white rot (AWR) with different onion accessions and cultivars, alone and in combination with a tebuconazole-based seed treatment or composted onion waste. In glasshouse tests, 23 new bulb-onion accessions from previous work to detect resistance to Sclerotium cepivorum showed no differences in susceptibility to AWR but, when combined with S17A, disease was reduced by up to two-thirds over all accessions. Trichoderma viride L4 and S17A also reduced the proportion of infected plants for five commercial bulb-onion cultivars and one advanced breeding line by at least one-third. Further glasshouse tests using a salad-onion cultivar showed that L4, S17A, tebuconazole or composted onion waste controlled AWR and at least halved the proportion of diseased plants. Combination treatments of T. viride with either tebuconazole or compost enhanced control and, in some treatments, disease was almost eliminated. In field trials, control of AWR by S17A was significant for 17 out of 18 individual or mixed bulb-onion accessions, with disease reduced overall by more than half. In another field experiment, S17A failed significantly to reduce AWR for two out of three commercial bulb-onion cultivars, while tebuconazole reduced the final proportion of AWR-infected plants over all cultivars from 0·47 to 0·09. Combining S17A and tebuconazole resulted in a similar level of AWR to using tebuconazole alone. The use of T. viride in an integrated strategy with other treatments to enhance control of S. cepivorum is discussed. [ABSTRACT FROM AUTHOR]

The effects ofConiothyrium minitansinoculum quality and an 8-week interval between inoculum application and crop planting on sclerotinia (Sclerotinia sclerotiorum) disease in three successive lettuce crops were investigated in a glasshouse trial. Spore suspensions of three isolates ofC. minitans(Conio, IVT1 and Contans) applied at 108 CFU m−2 and a standard Conio maizemeal–perlite application (06 L m−2, 1011 CFU m−2) were assessed for their ability to controlS. sclerotiorum. Only the maizemeal–perlite inoculum (isolate Conio) consistently reduced sclerotinia disease. In the third lettuce crop only, isolates IVT1 and Contans formulated by Prophyta and isolate IVT as an oil–water formulation, all applied as spore suspensions, reduced disease at harvest compared with the untreated control. Recovery, viability andC. minitansinfection of sclerotia buried during the 8-week period prior to each of the three lettuce crops, and of sclerotia formed on the crop, were tested. Only the maizemeal–perlite inoculum (isolate Conio) reduced the recovery of sclerotia buried in soil for weeks between inoculum application and crop planting, reducing their viability and increasing infection byC. minitans. Eight weeks was sufficient to enableC. minitansto infect sclerotia ofS. sclerotiorum, and may account for disease control. After harvest of the second and third crops, maizemeal–perlite treatment (isolate Conio) reduced the number and viability of sclerotia recovered on the soil surface and increased infection byC. minitanscompared with spore-suspension treatments. The effect of inoculum concentration and the influence of soil temperature (varying with time of year) on infection of sclerotia byC. minitansare discussed. [ABSTRACT FROM AUTHOR]

The effects of different inocula of the mycoparasiteConiothyrium minitanson carpogenic germination of sclerotia ofSclerotinia sclerotiorumat different times of year were assessed. A series of three glasshouse box bioassays was used to compare the effect of five spore-suspension inocula ofC. minitans, including three different isolates (Conio, IVT1 and Contans), with a standard maizemeal–perlite inoculum. Apothecial production, as well as viability andC. minitansinfection ofS. sclerotiorumsclerotia buried in treated soil, were assessed. Maizemeal–perlite inoculum at 107 CFU per cm3 soil reduced sclerotial germination and apothecial production in all three box bioassays, decreasing sclerotial recovery and viability in the second bioassay and increasingC. minitansinfection of sclerotia in the first bioassay. Spore-suspension inocula applied at a lower concentration (104 CFU per cm3 soil) were inconsistent in their effects on sclerotial germination in the three box bioassays. Temperature was an important factor influencing apothecial production. Sclerotial germination was delayed or inhibited when bioassays were made in the summer. High temperatures also inhibited infection of sclerotia byC. minitans.Coniothyrium minitanssurvived these high temperatures, however, and infected the sclerotia once the temperature decreased to a lower level. Inoculum level ofC. minitanswas an important factor in reducing apothecial production by sclerotia. The effects of temperature on both carpogenic germination of sclerotia and parasitism of sclerotia byC. minitansare discussed. [ABSTRACT FROM AUTHOR]

Summary • The asexual ectomycorrhizal fungus Cenococcum geophilum , known for its wide host and habitat range, has been suggested to provide isolate-dependant drought protection to fine roots. However, little is known about its genetic structure at the fine scale. • Genetic diversity and population structure of C. geophilum at the regional and stand scales was surveyed in five beech (Fagus silvatica ) forests in northeastern France. The stands were selected for their contrasting climatic and edaphic features to assess the effect of environmental factors on population structure. • The genetic diversity of C. geophilum was estimated using RAPD, PCR/RFLP of the rDNA internal transcribed spacer (ITS) and PCR/RFLP and sequencing of an anonymous sequence characterized amplified region (SCAR) on ectomycorrhizas and sclerotia-derived mycelial cultures. • A high degree of genetic diversity was observed between and within beech stands in C. geophilum populations. These results suggest the occurrence of a high rate of mitotic or meiotic recombination and an effect of stand features on population structure. [ABSTRACT FROM AUTHOR]

Rhizoctonia solani produces ascorbic acid at levels dependent on its developmental stage and its ability to differentiate and form sclerotia. It was found that oxidized exceeded reduced ascorbic acid by a maximum of fourfold in the undifferentiated mycelia, and 2·5-fold in the differentiated mycelia and sclerotia. Ascorbic acid profiles were very distinctive between differentiating and nondifferentiating R. solani isolates. In the nondifferentiating isolate the ratio of reduced : oxidized ascorbic acid was constant throughout growth, while in the differentiating isolate it increased 1·7-fold and decreased 1·3-fold in the middle and at the end of sclerotial differentiation, respectively, compared with the undifferentiated stage. The differentiation-associated marker of oxidative stress – lipid peroxidation – was 2·8-fold higher in colonies of the differentiating isolate before they differentiated than in same-day colonies of the same age of the nondifferentiating isolate. In the differentiating isolate, exogenous ascorbic acid up to 8 mg mL-1 caused a dose-dependent inhibition of up to 100% of fully developed sclerotia and a delay of 3·5 days in formation of sclerotial initials, apparently acting as an antioxidant and lowering lipid peroxidation to levels similar to those in the nondifferentiating isolate. The data from this study support the hypothesis that oxidative stress induces differentiation in sclerotium-producing plant pathogenic fungi. [ABSTRACT FROM AUTHOR]

The rate of conidiogenic germination of Botrytis squamosa was highest at 16°C and the greatest numbers of conidia per sclerotium (up to 5 × 104) were produced at temperatures of 5–10°C. At temperatures above 20°C, the percentage of sclerotia producing conidia declined rapidly. Decreasing water potential reduced the rate at which conidia were produced and also resulted in fewer conidia produced per sclerotium. However, conidia were produced at water potentials as low as -2 MPa, at which sclerotial germination was at least 60%. A simulation model that included effects of both temperature and water potential was developed from laboratory and field data obtained for conidial production in sclerotia exposed for periods of 1, 2, 3 or 4 weeks during an entire year. There was good agreement between conidiogenic germination predicted by the model and conidial production observed in onion plots artificially inoculated with sclerotia. Temperature and water potential were therefore considered to be the principal microclimatic factors affecting conidial production by B. squamosa. The role of sclerotia in the context of UK onion production is discussed. [ABSTRACT FROM AUTHOR]

Sclerotia of Sclerotinia minor Jaggar have the ability to regenerate a new rind when the old rind is damaged before or after maturity. Regeneration involves growth of a completely new rind to cut off the exposed damaged surface, New, more or less spherical rind and cortical cells form by outgrowth of existing medullary hyphae. The new rind cells become pigmented over several days and new cortical cells contain reserves when the new rind has become fully pigmented. This process is most rapid in immature sclerotia but even in mature sclerotia, a new rind is fully regenerated within 8 d. Intact mature sclerotia exclude the apoplastic tracer sulforhodamine G but when the rind is damaged they become leaky to the fluorochrome. Regeneration of a new rind reduces permeability to sulforhodamine but the initial impermeable state is not fully regained, even when regeneration is complete. Sclerotia that have been damaged in the field, despite regeneration, might be more susceptible to external influences than those in which the rind has remained intact. [ABSTRACT FROM AUTHOR]

Intact mature sclerotia of Sclerotium rolfsii Sacc. and Sclerotium cepivorum Berk. produced in culture are impermeable to the apoplastic tracer sulphorhodamine G. Both of these species produce sclerotia with rinds. Some movement of sulphorhodamine into sclerotia of Rhizoctonia solani Kühn, which have no rind, occurred but the fluorochrome was arrested after permeation of at most the outer five layers of cells. In all cases, low permeability depended on an intact outer layer, and when sclerotia of each species were bisected to provide direct access of sulphorhodamine to all tissue layers, the fluorochrome permeated the cell walls and extracellular matrix (where present) of man cells within the sclerotium. A marked reduction in permeability of intact sclerotia occurs at maturity in a number of species and might be important in long-term survival. [ABSTRACT FROM AUTHOR]

Four different fluorescent dyes Acridine Orange (AO), Fluorescein Diacetate (FDA), Calco-fluor "White M2R (CW), and Europium (III) Thenoyltrifluoroacetonate, 3-Hydrate (Eu(TTA)3) were tested to distinguish rapidly between dead and living sclerotia from Sclerotinia trifoliorum. FDA, 0.01% diluted in phosphate buffer, had the shortest staining period and was easy to handle. It is especially suitable to test large numbers of sclerotia for viability. Furthermore the preparation of the samples for the staining procedure is described in this paper. [ABSTRACT FROM AUTHOR]

The sclerotia of Sclerotium rolfsii Sacc. survived in natural soil for 225 days under controlled moisture at 50% water holding capacity (WHC) after which there was a progressive reduction in the population of viable sclerotia. At 390 days only 48% were recovered. Sclerotia survived well at moisture contents up to 75% WHC but at 100% the population declined rapidly and none were recovered after 60 days. The contents of the sclerotia were found to lyse without germination leaving hollow rinds. Such lysis was found to be favoured between 25 and 40 °C. At and below 20 °C no such lysis was recovered and more than 80% sclerotia were recovered even after 60 days. [ABSTRACT FROM AUTHOR]

The effect of light on uredospore germination and germ tube growth of Phakopsora pachyrhizi was studied. Frequency of uredospore germination was only partially reduced by high light intensity (> 1,9 X 104 mW X m2). In uredospores unilaterally irradiated with polychromatic light germ tubes always emerged from the shadowed side. Already developed germ tubes showed a negative photo- tropic response. Both effects were inducible by low light intensities. Negative phototropism of germ tubes was a blue light effect. Light of 441 nm was more effective than that of 422 nm or 372 nm. Red light (> 600 nm) was ineffective, green light (513 nm) induced medium responses. In half-side illumination studies longitudinal halves of germ tube tips and spores were irradiated under a microscope. The tips of the germ tubes bent into the illuminating beam. In half-side illumination studies germ tubes always emerged from the illuminated spore halves. Under unilateral illumination liquid paraffin reversed this light "polarization" of spores and the negative phototropism of germ tubes. These results suggest that during unilateral illumination spores and germ tube tips act as a lens focussing the light on the wall farthest away from the light source. There, in uredospores emergence of germ tubes is stimulated and in germ tubes growth is inhibited. As a consequence, under unilateral illumination germ tubes emerge at the shadowed side of the spores and grow away from the light. [ABSTRACT FROM AUTHOR]

Aflatoxin is a toxic, carcinogenic mycotoxin primarily produced by Aspergillus parasiticus and Aspergillus flavus. Previous studies have predicted the existence of more than 20 genes in the gene cluster involved in aflatoxin biosynthesis. Among these genes, aflK encodes versicolorin B synthase, which converts versiconal to versicolorin B. Past research has investigated aflK in A. parasiticus, but few studies have characterized aflK in the animal, plant, and human pathogen A. flavus. To understand the potential role of aflK in A. flavus, its function was investigated here for the first time using gene replacement and gene complementation strategies. The aflK deletion-mutant ΔaflK exhibited a significant decrease in sclerotial production and aflatoxin biosynthesis compared with wild-type and the complementation strain ΔaflK::aflK. ΔaflK did not affect the ability of A. flavus to infect seeds, but downregulated aflatoxin production after seed infection. This is the first report of a relationship between aflK and sclerotial production in A. flavus, and our findings indicate that aflK regulates aflatoxin formation., (© 2017 The Authors. MicrobiologyOpen published by John Wiley & Sons Ltd.)

During 1985 60% of Claviceps purpurea sclerotia collected from Triticale heads were colonized by Fusarium acuminatum Ell. et Ev. and F. heterosporum Nees. [ABSTRACT FROM AUTHOR]