Carpogenic Germination Of Sclerotia Research Articles

Inhibitory effect of Fungastop and Bion against carrot soft rot caused by Sclerotinia sclerotiorum

This study was conducted to assess likely inhibitory effects of Fungastop™ and Acibenzolar-S-Methyl (Bion®) against carrot rot caused by Sclerotinia sclerotiorum during postharvest phase. The results showed that Fungastop was able to markedly decrease mycelial growth and sclerotia formation of three isolates of the pathogen. In addition, Fungastop significantly reduced myceliogenic and carpogenic germination of sclerotia in the three tested isolates of S. sclerotiorum. Fungastop showed high antifungal efficacy against carrot rot in vivo as carrots were inoculated with the pathogen 2.5 h after treatment with Bion and Fungastop. However inhibitory effect of Bion against the disease was higher than Fungastop over time. The enzymatic tests revealed that Bion was able to significantly enhance levels of enzyme activities related to disease resistance including β-N-acetyl hexosaminidase, endochitinase, chitin 1,4-β-chitobiosidase and β −1,3-glucanase six days after treatment. In addition, activities of phenylalanine ammonia lyase and peroxidase were markedly increased four days after treatment. Bion showed higher effect in increasing enzyme activities related to disease resistance than Fungastop. The treatment with Fungastop and Bion enhanced relative conductivity of S. sclerotiorum mycelia over 160 min compared with control. The treatment with Fungastop increased the cell membrane permeability of mycelia more than Bion.

Bioactivity, physiological characteristics and efficacy of the SDHI fungicide pydiflumetofen against Sclerotinia sclerotiorum

Sclerotinia sclerotiorum, which can cause Sclerotinia stem rot, is a devastating plant pathogen. This study aimed to assess the potential of pydiflumetofen, a new-generation succinate dehydrogenase inhibitor (SDHI) fungicide, to control Sclerotinia stem rot. Pydiflumetofen exhibited favorable bioactivity in suppressing mycelial growth, sclerotial production and morphological changes, and the myceliogenic and carpogenic germination of sclerotia. Treatment with pydiflumetofen increased the cell membrane permeability of S. sclerotiorum and decreased oxalic acid production. In addition, inoculation tests demonstrated that the protective activity of 40 μg/mL pydiflumetofen against the fungus was better than its curative activity. Under natural infection conditions, the spraying of pydiflumetofen at 200 g a.i. ha−1 significantly reduced the incidence and severity of Sclerotinia stem rot. In addition, the sensitivity baseline to pydiflumetofen was established using 171 isolates collected from various crops in China. The results showed that the frequency distribution of the EC50 values of pydiflumetofen was a unimodal curve with a mean EC50 value of 0.0095 ± 0.0005 μg/mL. This study confirmed the favorable bioactivity of pydiflumetofen against S. sclerotiorum at various developmental stages and its high effectiveness under natural infection conditions, which indicates that pydiflumetofen is a promising tool for the management of Sclerotinia stem rot.

Inhibitory efficacy of different essential oils against storage carrot rot with antifungal and resistance‐inducing potential

AbstractThe inhibitory effects of essential oils (EOs) derived from coriander, lavender, geranium, thyme, savoury and eucalyptus were assessed against Sclerotinia sclerotiorum, the causal agent of carrot white mould. All EOs showed antifungal activity against the pathogen in vitro and in vivo. In addition, all EOs markedly increased 6‐methoxymellein in the treated carrots. The EOs of thyme and savoury were found to be more effective than other tested EOs. The enzymatic tests showed that thyme and savoury EOs were more able than lavender EO to significantly increase the level of chitinases, peroxidases, β‐1,3‐glucanases, polyphenol oxidase, peroxidase and phenylalanine ammonia‐lyase in the treated carrots, indicating that the EOs of thyme and savoury have potential to be considered as effective inducers of resistance against carrot white mould. In this study, all EOs inhibited myceliogenic and carpogenic germination of sclerotia at concentrations 1 and 10 µl/ml sterile distilled water, respectively. After gas chromatography/mass spectrometry, major component in the thyme EO was found to be thymol (39.15%) followed by p‐cymene (13.85%) and carvacrol (10.36%), while in savoury EO were carvacrol (41.9%), γ‐terpinene (17.38) and p‐cymene (11.25%).

The GATA-type IVb zinc-finger transcription factor SsNsd1 regulates asexual-sexual development and appressoria formation in Sclerotinia sclerotiorum.

The sclerotium, a multicellular structure composed of the compact aggregation of vegetative hyphae, is critical for the long-term survival and sexual reproduction of the plant-pathogenic fungus Sclerotinia sclerotiorum. The development and carpogenic germination of sclerotia are regulated by integrating signals from both environmental and endogenous processes. Here, we report the regulatory functions of the S.sclerotiorum GATA-type IVb zinc-finger transcription factor SsNsd1 in these processes. SsNsd1 is orthologous to the Aspergillus nidulans NsdD (never in sexual development) and the Neurospora crassa SUB-1 (submerged protoperithecia-1) proteins. Ssnsd1 gene transcript accumulation remains relatively low, but variable, during vegetative mycelial growth and multicellular development. Ssnsd1 deletion mutants (Δnsd1-KOs) produce phialides and phialospores (spermatia) excessively in vegetative hyphae and promiscuously within the interior medulla of sclerotia. In contrast, phialospore development occurs only on the sclerotium surface in the wild-type. Loss of SsNsd1 function affects sclerotium structural integrity and disrupts ascogonia formation during conditioning for carpogenic germination. As a consequence, apothecium development is abolished. The Ssnsd1 deletion mutants are also defective in the transition from hyphae to compound appressorium formation, resulting in a loss of pathogenicity on unwounded hosts. In sum, our results demonstrate that SsNsd1 functions in a regulatory role similar to its ascomycete orthologues in regulating sexual and asexual development. Further, SsNsd1 appears to have evolved as a regulator of pre-penetration infectious development required for the successful infection of its many hosts.

Efficacy of UV-C radiation in inducing systemic acquired resistance against storage carrot rot caused by Sclerotinia sclerotiorum

This research was carried out to assess inhibitory effect of UV-C (0.88kJm−2) against four isolates of Sclerotinia sclerotiorum, causal agent of carrot rot, in vitro and in vivo. A bank of seven germicidal tubes was used to produce UV-C radiation with peak emission at 254nm. The carrot roots were subjected to UV-C irradiation for five min. The tubes were located 40cm above the roots. In order to be exposed to UV radiation on all sides, the carrot roots were rotated five times at the interval of one min. Based on the results, UV radiation was able to significantly increase levels of pathogenesis-related proteins (chitinases, peroxidases, β-1,3-glucanases) as well as polyphenoloxidase, phenylalanine ammonia-lyase and 6-methoxymellein (6-m) in carrot roots. The levels of enzymes and 6-m were found to be higher in the whole treated carrots than half treated carrots in most of treatments. Despite increase of systemic acquired resistance (SAR) related enzymes in half treated carrots, the results of in vivo tests showed that UV-C irradiation can not reduce severity of carrot rot after 15d. In addition, UV-C radiation for 5min markedly decreased myceliogenic and carpogenic germination of sclerotia in four isolates. This study showed that UV-C cannot be considered as abiotic inducer of SAR.

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.

Volatiles from biofumigant plants have a direct effect on carpogenic germination of sclerotia and mycelial growth of Sclerotinia sclerotiorum

Aims Sclerotia of Sclerotinia sclerotiorum survive in soil and germinate to produce apothecia which release airborne ascospores. Current control methods rely predominantly on the use of fungicides to kill ascospores. The aim of this research was to identify potential biofumigation treatments which suppress sclerotial germination, providing a potential alternative and long-term approach to disease management. Methods Microcosm and in vitro experiments were conducted using dried and milled plant material from six different biofumigant crop plants to determine effects on carpogenic germination of sclerotia and mycelial growth of S. sclerotiorum. Results All biofumigant plants significantly reduced germination of S. sclerotiorum sclerotia in the microcosm experiments, but were less effective against larger sclerotia. In vitro experiments showed a direct effect of biofumigant volatiles on both the mycelial growth of S. sclerotiorum, and carpogenic germination of sclerotia, where the most effective treatment was B. juncea ‘Vittasso’. Conclusions It was clear from this study that biofumigant crop plants have potential as part of an integrated disease management system for control of S. sclerotiorum. The microcosm experiments described here provide a straightforward and reliable screening method for evaluating different biofumigants for activity.

Carpogenic germination of sclerotia of Sclerotinia minor and ascosporic infection of pyrethrum flowers

Carpogenic germination of sclerotia and infection of flowers by ascospores of Sclerotinia minor is rare and seldom documented in most hosts. During 2007–2009, S. minor isolates were obtained from surface-sterilized pyrethrum flowers collected from fields in Australia. The isolation frequency of S. minor from flowers in 2007, 2008 and 2009 was 15.8%, 5% and 1.4%, respectively. During these years, the prevalence of S. minor in flowers amongst pyrethrum fields varied between 10.3% and 60%. Sclerotia with apothecia, consistent in size with S. minor, were collected in one field. Colonies from individual ascospores from this isolate were identified as S. minor. A subsample of 10 S. minor isolates was selected for further studies. Phylogenetic analysis based on the internal transcribed spacer region grouped these isolates with S. minor, and distinct from published sequences of other Sclerotinia spp. Species-specific primers developed previously to differentiate the four major Sclerotinia spp. (S. sclerotiorum, S. minor, S. homoeocarpa and S. trifoliorum) were used to confirm identity. Of the 10 S. minor isolates, eight were able to carpogenically germinate in vitro. Pathogenicity of S. minor to flowers was confirmed in the greenhouse using ascospores. This study is one of the few instances documenting the ability of S. minor to infect floral tissues and the first documentation of S. minor causing flower disease of pyrethrum. These findings serve as a scaffold for further investigations into the mechanisms of flower infection by S. minor and have implications for the management of the Sclerotinia disease complex affecting pyrethrum in Australia.

Extratos de plantas de cobertura no desenvolvimento de Sclerotinia sclerotiorum

Extratos vegetais podem interferir no ciclo de vida dos fitopatógenos por promover ou inibir o desenvolvimento. Com base nessa propriedade, este trabalho foi realizado com o objetivo de estudar o efeito dos extratos aquosos das plantas de cobertura crotalária (Crotalaria juncea), braquiária (Brachiaria ruziziensis), capim-mombaça (Panicum maximum cv. mombaça), milheto (Pennisetum glaucum), feijão-guandu-anão (Cajanus cajan) e estilosantes (Stylosanthes capitata x Stylosanthes macrocephala) sobre o crescimento micelial, germinação carpogênica e micelial dos escleródios e germinação dos ascósporos do fungo Sclerotinia sclerotiorum. As etapas do experimento foram desenvolvidas em casa de vegetação, câmaras de crescimento e laboratório. As concentrações dos extratos utilizadas foram de 1%, 5%, 10% e 25%. Para verificar a influência dos extratos sobre a germinação micelial e carpogênica dos escleródios, foi utilizada somente a concentração de 25%. Os resultados sobre o crescimento micelial mostraram que o extrato da planta de Stylosanthes sp. inibiu o desenvolvimento do patógeno apenas na concentração de 25%. Para a germinação micelial dos escleródios, verificou-se que os extratos induziram a germinação 12 horas após a instalação do experimento, exceto o Stylosanthes sp. Na germinação dos ascósporos, apenas o extrato de Stylosanthes sp. impediu a germinação.

Forecasting Sclerotinia Disease on Lettuce: A Predictive Model for Carpogenic Germination of Sclerotinia sclerotiorum Sclerotia

ABSTRACT A predictive model for production of apothecia by carpogenic germination of sclerotia is presented for Sclerotinia sclerotiorum. The model is based on the assumption that a conditioning phase must be completed before a subsequent germination phase can occur. Experiments involving transfer of sclerotia from one temperature regime to another allowed temperature-dependent rates to be derived for conditioning and germination for two S. sclerotiorum isolates. Although the response of each isolate to temperature was slightly different, sclerotia were fully conditioned after 2 to 6 days at 5 degrees C in soil but took up to 80 days at 15 degrees C. Subsequent germination took more than 200 days at 5 degrees C and 33 to 52 days at 20 degrees C. Upper temperature thresholds for conditioning and germination were 20 and 25 degrees C, respectively. A predictive model for production of apothecia derived from these data was successful in simulating the germination of multiple burials of sclerotia in the field when a soil water potential threshold of between -4.0 and -12.25 kilopascals (kPa) was imposed. The use of a germination model as part of a disease forecasting system for Sclerotinia disease in lettuce is discussed.

Effects of soil moisture, organic matter and grass mulching on the carpogenic germination of sclerotia and infection of bean by Sclerotinia sclerotiorum

Microplot experiments were carried out during the autumn and winter of 1995 to determine the effects of soil moisture and levels of organic matter on the carpogenic germination of Sclerotinia sclerotiorum and subsequent infection of Phaseolus vulgaris. Soil moisture treatments were established by irrigation to field capacity: (a) when soil had dried to − 25 KPa, (b) when soil had dried to − 54 KPa, and (c) eight days after the soil had dried to − 54 KPa. Three levels of organic matter were established by mixing compost and yellow‐red latosol in the following proportions (by volume): (a) 0% compost and 100% soil, (b) 50% compost and 50% soil, and (c) 100% compost and 0% soil. More apothecia and diseased plants were observed in the plots with higher moisture levels. Drier treatments resulted in a reduction in number (in the winter experiment) or elimination (in the autumn experiment) of apothecia. Other experiments were designed to examine the effect of grass mulching and organic matter levels on the carpogenic germination of S. sclerotiorum. In one experiment, grass mulching was compared with no mulching, and in another, the effects of different depths of mulch on the soil surface (0, 1.5, 3, 6 and 9 cm) were examined. Fewer apothecia were formed in mulched soil and the effect was most pronounced with 6 and 9 cm of mulch. The highest level of mulch (9 cm) impaired the vigour and yield of bean plants. In these experiments, carpogenic germination was increased by high soil organic matter content. Control of soil moisture and grass mulching may reduce the production of apothecia of S. sclerotiorum even in soils rich in organic matter.

Variation within isolates of Typhula incarnata from localities differing in winter climate

Isolates ofTyphula incarnata, a snow mold fungus, were collected from four localities with different winter climates. Their ecological traits such as mycelial growth rate, sclerotium size, carpogenic germination of sclerotia, and aggressiveness were compared between populations in order to reveal infraspecific differentiation associated with climatic differences. Population variability was evident only in sclerotium germination: isolates from more snowy localities germinated faster than those from less snowy localities.T. incarnata is regarded as a versatile pathogen with no specialized forms in contrast withT. ishikariensis. The germination rate of sclerotia is considered very critical in the life history ofT. incarnata.

The effects of herbicides and mycoparasites at different moisture levels on carpogenic germination in Sclerotinia sclerotiorum

Two similar inclined boxes were constructed differing in several aspects from one developed earlier to regulate soil moisture potential. Each box had six 10-cm wide compartments with a perforated plastic cover. Boxes were placed in a room held at 10°C with a RH of 90%. The differential perforations in the plastic that covered the soil surface regulated evaporation which in turn regulated soil moisture. One box was used to carry out experiments on five herbicides at different matric potentials while the other box was used to test five mycoparasites. The herbicides chlorsulfuron, cyanazine, metribuzin, triallate and trifluralin significantly reduced the carpogenic germination of sclerotia of Sclerotinia sclerotiorum. Among five mycoparasites, Coniothyrium minitans completely inhibited germination. Penicillium sp., Sporidesmium sclerotivorum and Teratosperma oligocladium reduced germination in one of the two tests. The influence of soil moisture on carpogenic germination was significant in all tests. There were interactions between herbicides and moisture and also between mycoparasites and moisture. However, soil moisture did not have a marked effect on the efficacy of herbicides and mycoparasites.

Effect of sucrose concentration on sclerotia production and subsequent apothecial formation by Sclerotinia sclerotiorum

The number, range of individual and total fresh weight of sclerotia produced by an isolate of Sclerotinia sclerotiorum increased linearly with sucrose concentration. Mean weight of sclerotia had a log-normal distribution with respect to sucrose concentration and increased to a maximum at 3 and 5% w/v sucrose. Without any pretreatment, carpogenic germination of sclerotia began between 2–7 wk on moist filter paper under the same environmental conditions used for sclerotium production. Apothecial production increased with time, maximal production taking place after 6–10 wk from sclerotia from low sucrose concentrations. Formation was slower from sclerotia from higher sucrose levels and none were formed on sclerotia produced at 3 and 5% sucrose. Carpogenic germination was restricted mainly to sclerotia less than 10 mg. Production of a single apothecium per sclerotium was more frequent than multiple apothecia production.