Germination Of Sclerotia Research Articles

Biocontrol effects of Penicillium griseofulvum against monkshood (Aconitum carmichaelii Debx.) root diseases caused by Sclerotium rolfsiii and Fusarium spp.

The aims of this study were to investigate the biocontrol effects of Penicillium griseofulvum strain CF3 and its mechanisms against soil-borne root pathogens (Fusarium oxysporum and Sclerotium rolfsii) of the medical plant Aconitum carmichaelii Debx. The effects of P. griseofulvum strain CF3 were evaluated with regard to the hyphal growth of S. rolfsii and F. oxysporum, the sclerotial formation and germination of S. rolfsii and its expression of sclerotia-formation-related genes. A field experiment was conducted to explore how strain CF3 controls the severity of soil-borne diseases, promotes the growth of A. carmichaelii plants and mediates shifts in the culturable rhizosphere microbial populations. The results showed that treatment with a cell-free culture filtrate of strain CF3 considerably inhibited the hyphal growth of both S. rolfsii and F. oxysporum, in addition to limiting the sclerotial formation and germination of S. rolfsii. Three genes related to sclerotial formation (ArsclR, ArnsdD1 and ArnsdD2) were predicted in S. rolfsii and their expression was found suppressed by the CF3 treatment. Field application of the CF3 biocontrol agent in a powder form (1·9×1010 conidia per gram of substrate) reduced soil-borne disease severity by 15·0%. The shoot and root growth of A. carmichaelii plants was promoted by 61·6 and 83·1% respectively, as the biocontrol strain massively colonized the rhizosphere soil. The CF3 treatment also markedly reduced the density of some known species harmful to plants while increasing the density of some beneficial species in the rhizosphere soil. Genes related to sclerotia formation of S. rolfsii are predicted for the first time and their expression patterns in the presence of P. griseofulvum strain CF3 are evaluated. This comprehensive study provides a candidate fungal biocontrol strain and reveals its potential mechanisms against S. rolfsii and F. oxysporum in A. carmichaelii plants.

Rolled–crimped cereal rye residue suppresses white mold in no-till soybean and dry bean

AbstractWhite mold caused by the fungus,Sclerotinia sclerotiorumis a devastating disease of soybean (Glycine max) and other leguminous crops, including dry bean (Phaseolus vulgaris). Previous research has demonstrated that no-till planting soybean into rolled–crimped cereal rye residue can enhance weed management, improve soil health and reduce labor requirements in organic production. However, there are limited data on the effects of cereal rye residue on white mold suppression in no-till planted soybean and dry bean. Two field trials were conducted in 2016–2017 (Year 1) and repeated in 2017–2018 (Year 2) to evaluate the potential of cereal rye cover crop residue to suppress white mold in these crops. In each trial (soybean and dry bean), the experimental design was a randomized complete block with two treatments: (1) rolled–crimped cereal rye residue and (2) no cover crop control. Treatment effects on plant population, biomass and yield components varied between the main crops. Compared with the control treatment, cereal rye residue reduced the incidence of white mold in soybean in both years and in dry bean in Year 2. The reduction in white mold in cereal rye residue plots was due to a combination of (1) decreased sclerotial germination (no stipes formed) and (2) increased nonfunctional sclerotial germination defined here as sclerotia that germinated but produced stipes without the expanded cup where asci containing ascospores are formed. Weed density and biomass were lower in cereal rye residue plots in soybean and dry bean, except in Year 1 in soybean when weed biomass was low in both treatments. Our findings indicate that cereal rye residue could help organic and conventional farmers manage white mold in no-till planted soybean and dry bean. Germination of sclerotia resulting in nonfunctional apothecia could potentially exhaust soilborne inoculum in the upper soil profile and reduce infections in subsequent crops.

Management of Congo grass cover crop affects timing of Sclerotinia sclerotiorum carpogenic germination and decay of soybean stem rot

The effects of cover crop management on the carpogenic germination of Sclerotinia sclerotiorum sclerotia and stem rot disease of soybean were investigated during three seasons (2008/2009 to 2010/2011) in a commercial farm of Goias State, Brazil. Congo grass (Urochloa ruziziensis) annually grown during the fall at different densities (150, 300, 450 and 600 units of pure live seeds) was evaluated as cover crop and compared with a spontaneous weeds treatment. The germination of sclerotia was evaluated during cover crop growth in the spring season and in the summer, during soybean flowering. In general, apothecia density, disease incidence and disease severity index assessed at the 5.2 and 5.5 stages decreased with the increase of cover crop density. Trichoderma harzianum doses did not affect disease variables Soybean yield was not affected by any treatment. Principal component analysis clustered grass-soybean treatments apart from the spontaneous weeds-soybean sequence in all seasons. Carpogenic germination under the Congo grass canopy was negatively associated with apothecia density and disease during soybean growth. Mulching with Congo grass stimulates early carpogenic germination of S. sclerotiorum, enhancing soil disinfestation rather quickly. Adjustments in soybean crop stand are suggested to match improved disease management with higher soybean yields.

Antagonistic activity of a novel antifungalmycin N2 from Streptomyces sp. N2 and its biocontrol efficacy against Rhizoctonia solani.

Antifungalmycin N2 (3-methyl-3,5-amino-4-vinyl-2-pyrone, C6H7O2N) is a novel bioactive substance produced by Streptomyces sp. N2. In this present work, the antagonistic activity of antifungalmycin N2 and its biocontrol efficacy on Rhizoctonia solani were carried out to evaluate its potential as a biocontrol agent against fungal plant diseases. By using potato dextrose agar media for in vitro cultivation of phytopathogenic fungi, the results showed that antifungalmycin N2 not only displayed broad-spectrum antifungal activities against various plant pathogenic fungi, but also had a strong antagonism to the sclerotial germination of R. solani. In a detached leaf assay, it was found that antifungalmycin N2 could effectively protect the rice leaves form the infection of R. solani, resulting in a significantly reduced sheath blight severity on the surfaces of rice leaves. In the pot experiments, the results also revealed that significantly lower sheath blight infections occurred in the tissues of the treated rice plants, which further confirmed that antifungalmycin N2 had a favorable biocontrol efficacy on rice sheath blight. In conclusion, the above results indicated that the novel antifungalmycin N2 was one of promising biocontrol agents for plant disease control.

Reduction of Stromatinia cepivora inocula and control of white rot disease in onion and garlic crops by repeated soil applications with sclerotial germination stimulants

The effect of soil-applied Allium crop products on the Stromatinia cepivora viability and the incidence of white rot in subsequent onion and garlic crops were evaluated in this work. The tested products were onion powder, garlic powder, onion oil, garlic oil and Allium waste (onion and garlic) that are described as sclerotial germination stimulants. Under in vitro conditions, data revealed that more than 80% of the sclerotia died in the soil treated with sclerotial germination stimulants. Under greenhouse conditions, soil-artificially infested with sclerotia of S. cepivora and treated with sclerotial germination stimulants for 6-months before cultivation, significantly reduced the incidence of white rot on onion and garlic. Onion oil, garlic oil and Allium waste were the most effective treatments, decreasing disease incidence by 78.6% in onion and 80.0% in garlic. Under field conditions, sclerotial germination stimulants were incorporated into the soil in commercial fields naturally infested with S. cepivora. Two fields were chosen based on differential sclerotial density. Within 6 months after treatment, more than 70% of the sclerotia died in the plots treated with sclerotial germination stimulants. In subsequent onion and garlic crops planted approximately one year after soil treatment, sclerotial germination stimulants were more effective than the control in reducing white rot symptoms coupled with low inoculum density (45.9 sclerotia/kg of soil). Reduction of white rot disease was accompanied by increased of growth and bulbs yield of onion and garlic plants. Despite the efficacy of sclerotial germination stimulants to reduce populations of viable sclerotia in soil with a high inoculum density (594.7 sclerotia/kg of soil), the pathogen caused substantial white rot and yield losses in subsequent onion and garlic crops planted approximately one year after soil treatment.

Effects of pH and Aeration on Sclerotium rolfsii sacc. Mycelial Growth, Sclerotial Production and Germination

Sclerotium rolfsii is one of the devastating soilborne fungus responsible for significant plant losses. The effects of pH and aeration on pathogen mycelial growth, sclerotial production and germination were investigated for three Tunisian isolates. Optimal mycelial growth occurred at pH 6 for Sr2 and Sr3 isolates and at pH 6-7 for Sr1. Dry mycelial growth was optimum at pH values ranging between 4 and 7. Sclerotial initiation started on the 3rd day of incubation at all pH values tested and mature sclerotia were formed after 6 to 12 days. Optimal sclerotial production was noted at pH 5. The dry weight of 100 sclerotia varied depending on isolates and pH and occurred at pH range 4-7. At pH 9, mycelial growth, sclerotial production and dry weight of 100 sclerotia were restricted. The optimum sclerotial germination, noted after 24 h of incubation, varied depending on isolates and pH and occurred at pH 4-9. Mycelial growth was optimum in aerated plates with a significant isolates x aeration treatments interaction. Sclerotial initiation occurred at the 3rd day of incubation and mature sclerotia were observed after 6-9 days. Sclerotial development was very slow in completely sealed plates and dark sclerotia were produced only after 15 days of incubation. The highest sclerotial yields were noted in aerated plates. The highest dry weight of 100 sclerotia for Sr1 isolate was recorded in ½ sealed, no sealed and completely sealed plates, while for Sr2, it was noted in ½ and ⅔ sealed plates. For Sr3, the maximum dry weight of 100 sclerotia was recorded in ½, ⅔ and completely sealed plates. Germination of S. rolfsii sclerotia, after 24 h of incubation, did not vary significantly depending on aeration treatments and ranged from 90 to 100% for all isolates.

Study on antifungal activity of silver/bentonite nanomaterials on soybean phytopathogenic fungi

In the present study, silver nanoparticles were synthesized by chemical reduction method route into the lamellar space of bentonite (Ag/CTS/Bentonite). Silver nitrate (AgNO3) was taken as a metal precursor, sodium borohydride (NaBH4) as a reducing agent, reduction of Ag+ ions and the subsequent formation of Ag nanoparticles, chitosan as a natural polymeric stabilizer and was sticked silver nanoparticles to the surface of bentonite particles, respectively. Manipulating the size and shape of Ag/CTS/Bentonite nanomaterial was characterized using transmission electron microscopy (TEM), spherical silver nanoparticles, as depicted by TEM, were found to have a wide particle size distribution from 5 nm to 90 nm. Meanwhile, the X-Ray flourescence (XRF) spectrum indicated the presence of silver on bentonite particles. Antifungal activity of the synthesized Ag/CTS/Bentonite nanomaterial was investigated against crop pathogenic fungi (Fusarium oxysporium (F. oxysporium) and Rhizoctonia solani (R. solani)) isolated from infected soybean plant in Bac Ninh province by the Plant Protection Research Institute. The assessment of fungicidal activity of the Ag/CTS/Bentonite nanomaterial showed that this product exhibited strong antifungal activity towards soybean pathogenic fungi. At highest nanosilver concentration of the Ag/CTS/Bentonite nanocomposite (400 ppm) sclerotial germination of F. oxysporum was almost inhibited, after 7 days the inhibition effect on sclerotial germination attained 66.70%. For the case of R. solani, after 2 days at 400 ppm silver nanoparticles concentration the inhibition effect on sclerotial germination attained 92.82%. The obtained results suggested that the synthesized Ag/CTS/Bentonite nanomaterial acts as an effective antifungal agent. Thus, it could be used in developing novel antifungal agents for potential applications in agriculture.

Sclerotium rolfsii causes stem rot on Ixeridium dentatum in Korea

Stem rot was observed on Ixeridium dentatum in Jinan-gun and Dangjin-gun, Korea during the growing seasons of 2016 and 2017. The first symptom was water-soaked lesions on the basal parts of stems. Lower leaves became wilted and blighted before the plants eventually died. White cottony mycelial mats and brown spherical or irregular sclerotia formed on the basal stem and adjacent soil surfaces. The optimal temperature for in vitro colony growth and sclerotia germination were 30 °C and 25 °C, respectively. The in vitro and morphological characteristics of the fungus were identical with those described for Sclerotium rolfsii. Phylogenetic analysis based on the internal transcribed spacer (ITS) region revealed that two isolates isolated from I. dentatum formed a monophyletic group with reference isolates of S. rolfsii. Koch’s postulates were satisfied for the same two S. rolfsii isolates, thereby confirming that the pathogen causes stem rot of I. detatum in Korea.

The pre-rRNA processing factor Nop53 regulates fungal development and pathogenesis via mediating production of reactive oxygen species.

Botrytis cinerea is a necrotrophic plant fungal pathogen that annually causes enormous economic losses worldwide. The ribosome is an organelle forcellular protein biosynthesis. However, little isknown about how the ribosome operates as a machine to mediate microbial pathogenesis. Here, we demonstrate that Nop53, a late-acting factor for 60S ribosomal subunit maturation, is crucial for the pathogen's development and virulence. BcNop53 is functionally equivalent to yeast nop53p. Complementation of BcNOP53 completely restored the growth defect of the yeast Δnop53 mutant. BcNop53 is located in nuclei and disruption of BcNOP53 also dramatically impaired pathogen growth. Deletion of BcNOP53 blocked infection structure formation and abolished virulence of the pathogen, possibly due to reduced production of reactive oxygen species. Moreover, loss of BcNOP53 impaired pathogen conidiation and stress adaptation, altered conidial and sclerotial morphology, retarded conidium and sclerotium germination as well as reduced the activities of cell-wall degradation-associated enzymes. Sclerotium production was, however, increased. Complementation with the wild-type BcNOP53 allele rescued defects found in the ΔBcnop53 mutant. Our work establishes a systematic elucidation of Nop53 in regulating microbial development and pathogenesis, provides novel insights into ribosomal processes that regulate fungal pathogenesis, and may open up new targets for addressing fungal diseases.

Inoculum potential of Sclerotinia sclerotiorum sclerotia depends on isolate and host plant

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.

Anaerobic Soil Disinfestation Reduces Germination and Affects Colonization of Sclerotium rolfsii Sclerotia.

Growth chamber and field studies were conducted with organic amendment mixtures of carbon (C) and nitrogen (N) at C:N ratios 10:1, 20:1, 30:1, and 40:1 and amendment rates of C at 2, 4, 6, and 8 mg/g of soil (C:N ratio 30:1) to evaluate anaerobic soil disinfestation (ASD) effects on germination and colonization of Sclerotium rolfsii. In the growth chamber, sclerotial germination was reduced in all ASD treatments regardless of C:N ratio (0.6 to 8.5% germination) or amendment rate (7.5 to 46%) as compared with nonamended controls (21 to 36% and 61 to 96%, respectively). ASD treatment increased Trichoderma spp. colonization of sclerotia, with consistently higher colonization in ASD treatments with amendment rates of C at 2 or 4 mg/g of soil (>87% colonization) compared with nonamended controls (<50% colonization). In the 2014 field study, sclerotial germination was reduced by 24 to 30% in ASD treatments when compared with the nonamended control. Sclerotial colonization by Trichoderma spp. was predominant; however, other potential mycoparasites (i.e., Aspergillus spp., Fusarium spp., zygomycetes, and other fungi) were present in the field study. Amendment C:N ratios in the range of 10:1 to 40:1 were equally effective in reducing sclerotial germination and enhancing colonization by potentially beneficial mycoparasites of sclerotia.

Effect of Temperatures and Culture Media on Sclerotium rolfsii Mycelial Growth, Sclerotial Formation and Germination

Sclerotium rolfsii is a serious soilborne phytopathogenic fungus causing serious yield loss in crops of high economic importance. In this study, the effects of temperatures and culture media were evaluated on S. rolfsii mycelial growth, sclerotial production and germination. The three isolates tested grew over a range of temperatures from 10°C to 35°C but not at 5°C and 40°C. Radial growth and dry mycelium production were highest at 30°C. Sclerotial initiation started on the 3rd day after incubation at 30°C and 35°C, and mature sclerotia were observed after 15 and 6 days of incubation, respectively. Optimal sclerotial production and the dry weight of 100 sclerotia varied depending on isolates and temperatures and occurred at 25°C-35°C. No mature sclerotia were produced at 5°C, 10°C, 15°C and 40°C. Sclerotial germination, noted after 24 h of incubation, was 96%-100% at 25°C-35°C, declined at 15°C-20°C, and was totally inhibited at 5°C, 10°C and 40°C even after 72 h of incubation. For all S. rolfsii isolates, optimal radial growth occurred on OAT medium followed by CZA, MYEA and PDA. When grown on PDA and OAT media, S. rolfsii developed cottony colonies with abundant mycelium whereas on WA and CZA pathogen growth was thin and scanty. Colonies formed on the other media developed sparse and flat mycelia. For sclerotial formation, WA and CZA were the most suitable culture media but no dark brown sclerotia were observed on NA and YDA. The highest sclerotial formation was observed on PDA and CZA. The highest sclerotium weight was produced by Sr3 isolate on PDA whereas for Sr1 and Sr2 isolates, sclerotial weights were significantly comparable on PDA, MYEA and CZA. Sclerotial germination was optimal on all tested media except NA. The significance of these findings on S. rolfsii biology is discussed.

Effect of nutrient status, temperature and PH on mycelial growth, sclerotial production and germination of Rhizoctonia Solani Isolated from paddy fields

Rhizoctonia solani Kuhn, is one of the most important pathogen of rice causing sheath blight disease, which accounts for heavy yield losses in all the major rice growing areas of the world including India. In the present investigation the effect of different culture media, carbon and nitrogen sources, temperature and pH on mycelial growth, sclerotia production and germination of Rhizoctonia solani (anastomosis groups AG1-IA from rice and AG3 from potato) were studied. Among the five culture media including potato dextrose agar (PDA), malt yeast extract agar (MYA), water agar (WA), oat meal agar (OMA) and soil extract agar (SEA), PDA medium supported maximum mycelial growth and sclerotium yield. The maximum mycelial growth and sclerotia formation was observed in D-glucose as carbon source while the maximum mycelial growth and sclerotia formation was recorded in potassium nitrate as nitrogen source. Different range of temperatures i.e. 10, 15, 20, 25, 30 and 35°C were tested and the maximum hyphal growth was measured at 25°C temperature. Mycelial growth of all isolates occurred between pH 4.0 and 9.0, with an optimum of pH 5.6. Sclerotium germination for all the AG1-IA isolates was optimum between 20 and 30°C on all the media tested, with a pH optimum between pH 5.0 and 6.0.

Characterization of mechanisms underlying degradation of sclerotia of Sclerotinia sclerotiorum by Aspergillus aculeatus Asp-4 using a combined qRT-PCR and proteomic approach

BackgroundThe biological control agent Aspergillus aculeatus Asp-4 colonizes and degrades sclerotia of Sclerotinia sclerotiorum resulting in reduced germination and disease caused by this important plant pathogen. Molecular mechanisms of mycoparasites underlying colonization, degradation, and reduction of germination of sclerotia of this and other important plant pathogens remain poorly understood.ResultsAn RNA-Seq screen of Asp-4 growing on autoclaved, ground sclerotia of S. sclerotiorum for 48 h identified 997 up-regulated and 777 down-regulated genes relative to this mycoparasite growing on potato dextrose agar (PDA) for 48 h. qRT-PCR time course experiments characterized expression dynamics of select genes encoding enzymes functioning in degradation of sclerotial components and management of environmental conditions, including environmental stress. This analysis suggested co-temporal up-regulation of genes functioning in these two processes. Proteomic analysis of Asp-4 growing on this sclerotial material for 48 h identified 26 up-regulated and 6 down-regulated proteins relative to the PDA control. Certain proteins with increased abundance had putative functions in degradation of polymeric components of sclerotia and the mitigation of environmental stress.ConclusionsOur results suggest co-temporal up-regulation of genes involved in degradation of sclerotial compounds and mitigation of environmental stress. This study furthers the analysis of mycoparasitism of sclerotial pathogens by providing the basis for molecular characterization of a previously uncharacterized mycoparasite-sclerotial interaction.

Management of southern blight on tomato with SDHI fungicides

Southern blight, caused by the soilborne basidiomycete fungus Athelia rolfsii (formerly Sclerotium rolfsii) is a persistent disease affecting tomato throughout the southern United States and other countries. Post-transplant applications of succinate-dehydrogenase inhibitor (SDHI) or quinone-outside inhibitor (QoI) fungicides may be effective alternatives to broad-spectrum fumigation to manage this disease. In vitro, fluxapyroxad + pyraclostrobin applied directly to dormant sclerotia or to tomato stems inoculated with nontreated sclerotia reduced sclerotial germination and colony diameter. Penthiopyrad applied to tomato stems also reduced sclerotial germination and colony diameter. In 2015 and 2016, pyraclostrobin, penthiopyrad, and fluxapyroxad + pyraclostrobin were applied twice post-transplanting and quintozene was applied once at transplanting to tomato in the field. Fluxapyroxad + pyraclostrobin and quintozene reduced southern blight compared to the nonsprayed control in both years, whereas efficacy of pyraclostrobin and penthiopyrad varied. Quintozene, however, stunted 43–75% of the plants. Fruit number and weight did not differ among treatments in either year. Fluxapyroxad + pyraclostrobin or penthiopyrad followed by pyraclostrobin can be applied to reduce incidence of southern blight on tomato.

Mechanism of in vitro antagonism of phytopathogenic Scelrotium rolfsii by actinomycetes

Sclerotium rolfsii (Sr), a soil-borne fungal pathogen, causes disease in a wide range of crops. Recently, we identified five actinomycetes (Streptomyces globisporus subsp. globisporus, S. globisporus, S. flavotricini, S. pactum, and S. senoensis) showing significant inhibitory effects on plant pathogens. In this study, the effects of the five actinomycetes for the biocontrol of Sr were investigated using the plate culture method and microscopy examination. Two actinomycetes with higher inhibitory effect were subsequently examined for the inhibition of sclerotial germination of Sr in unsterile soil in vitro. The cell-free cultures of five actinomycetes mediated significant inhibition of hyphal growth and sclerotial formation and germination of Sr. All actinomycete strains exhibited the ability to produce extracellular cell wall degrading enzymes in the culture conditions. The crude enzyme suspensions of S. flavotricini and S. pactum hydrolyzed the cell wall of Sr. At a dose of 1 g per kilogram soil, the solid formulations of S. flavotricini and S. senoensis prevented germination of 24% and 68% of sclerotia, respectively. Our results provide evidence of effective strains for the biocontrol of Sr, in addition to a further understanding of the underlying mechanism.

Evaluation of Pongamia pinnata Products against the Sclerotium rolfsii Extracted from Chickpea

This study was conducted to investigate antifungal properties of Pongamia pinnata products. Pongamia pinnata seed oils and leaf diffusates contain products that show fungi-static effect against Scelotium rolfssi on Chickpea. This study shows comparison between antifungal effects of Pongame seed oils and Leaves, as both of these potentially inhibit Sclerotial production and germination of S. rolfsii. It was noticed that ingredients of leaves were changed when autoclaved. It also showed that there were some ingredients that were altered in terms of composition when heated. These agents were thought to be proteins and carbohydrates. Similarly, ingredients of seed oil also undergo change in composition when autoclaved. Extract showed insignificant difference about 20% (v/v) in inhibiting concentrations when used before autoclaving, while there was a significant difference among various concentrations after autoclaving. This significantly increased inhibition was present in Sclerotial production, germination and growth of mycelia. Overall, leaf extract was more effective than seed oil extract.

Efficacy of Antagonists on mycelium growth and carpogenic germination of sclerotia of Sclerotinia sclerotiorum on Indian mustard

Sclerotinia sclerotiorum (Lib.) de Bary is a soil borne pathogen capable of infecting more than 400 host plants worldwide. It is a major pathogen that plays a crucial role in reducing the yield in economically important crops. The capability of sclerotia to survive for more than 4 years becomes very difficult to manage the crop from the infection of Sclerotinia rot fungus. Stem rot of indian mustard [Brassica juncea (L.) Czern and Cross] caused by Sclerotinia sclerotiorum is potentially a serious threat in many mustard growing areas in India. Treatments of seeds and foliar spray with of fungicides applied at regular intervals are effective in reducing infection, but uses of chemicals are hazardous, harmful for beneficial micro-organisms. Biological control of plant pathogens offers an exciting opportunity to manage plant diseases. In the present study, the efficacy of four bio-agents, viz., Coniothyrium minitans, Aspergilus nidulans, Trichoderma harzianum, and Pseudomonas chlororaphis were evaluated for the control of stem rot of Indian mustard. Results on bio-efficacy of different bioagents, when evaluated under glass house condition, the Coniothyrium minitans was the most effective agent and caused highest reduction (64.7 %) in carpogenic germination of sclerotia followed by Aspergilus nidulans (52.5 %) and Trichoderma harzianum (48.8 %), over control while Pseudomonas chlororaphis (48.3 %) was at par with T. harzianum. All the bioagents showed significant reduction effective in controlling the disease. Similar results were achieved when bioagents tested on dual inoculated plates.

Biological control of Sclerotinia disease by Aspergillus sp. on oilseed rape in the field

ABSTRACTSclerotinia sclerotiorum causes serious yield losses to many crops worldwide. Aspergillus sp. Asp-4, previously shown to inhibit germination of sclerotia of S. sclerotiorum in vitro and in the field, was evaluated in field trials for suppression of this pathogen on oilseed rape. Spray application of Asp-4 to the soil prior to sowing rice in a rice–oilseed rape rotation resulted in a significant reduction in incidence of Sclerotinia stem rot on oilseed rape compared with the non-treated control in two field trials. This application of Asp-4 also resulted in a significant reduction in germination of sclerotia relative to the non-treated control in these field trials, suggesting that this reduction in sclerotial germination led to disease control. Microscopic examination demonstrated that Asp-4 could effectively colonise external and internal portions of sclerotia of S. sclerotiorum in vitro. Incubation of Asp-4 with sterile sclerotial material induced production of β-glucanase and chitinase activities by this isolate; β-glucanase and chitinase being potentially capable of degrading the glucan and chitin polymeric components of sclerotia. Incubation of Asp-4 with sterile sclerotial material also resulted in a significant reduction in dry weight of this sclerotial material relative to the non-treated control in 96 h in vitro experiments. Experiments reported here indicate that Aspergillus sp. Asp-4 has promise as a biological control agent for S. sclerotiorum on oilseed rape. Experiments reported here suggest that disease control results from inhibition of germination of sclerotial resting structures due to mycoparasitic colonisation by Asp-4.

Antifungal activity of Ziziphora clinopodioides Lam. essential oil against Sclerotinia sclerotiorum on rapeseed plants (Brassica campestris L.)

The present study aimed to determine the in vitro and in vivo effects of Ziziphora clinopodioides Lam. essential oil (ZCEO) against Sclerotinia sclerotiorum on rapeseed plants. Gas chromatography-mass spectrometry (GC-MS) detected 21 compounds that represented 98.3% of the total amount of extracted oil, which mainly comprised pulegone (53.5%), isomenthone (10.4%), and carvone (5.7%). The mycelial growth of S. sclerotiorum was completely inhibited at essential oil concentrations of 1.25 and 0.15 μl ml−1 under contact and vapor phase conditions, respectively. Under contact phase, the germination of sclerotial was inhibited at the concentration of 1.00 μl ml−1. The essential oil concentration of 0.15 μl ml−1 in the vapor phase showed a strong inhibitory effect on sclerotial germination. Sclerotinia sclerotiorum growth on detached rapeseed leaves and potted rapeseed plants were dose dependently inhibited by the essential oil. Considerable morphological changes were also observed in the fungal hyphae and sclerotia. Both in vitro and in vivo results indicated ZCEO can effectively inhibit the growth of S. sclerotiorum. Thus, ZCEO could be used for crop protection.