Inhibition Of Conidial Germination Research Articles

Biofabricated silver nanoparticles act as a strong fungicide against Bipolaris sorokiniana causing spot blotch disease in wheat.

The present study is focused on the extracellular synthesis of silver nanoparticles (AgNPs) using culture supernatant of an agriculturally important bacterium, Serratia sp. BHU-S4 and demonstrates its effective application for the management of spot blotch disease in wheat. The biosynthesis of AgNPs by Serratia sp. BHU-S4 (denoted as bsAgNPs) was monitored by UV–visible spectrum that showed the surface plasmon resonance (SPR) peak at 410 nm, an important characteristic of AgNPs. Furthermore, the structural, morphological, elemental, functional and thermal characterization of bsAgNPs was carried out using the X-ray diffraction (XRD), electron and atomic microscopies, energy dispersive X-ray (EDAX) spectrometer, FTIR spectroscopy and thermogravimetric analyzer (TGA), respectively. The bsAgNPs were spherical in shape with size range of ∼10 to 20 nm. The XRD and EDAX analysis confirmed successful biosynthesis and crystalline nature of AgNPs. The bsAgNPs exhibited strong antifungal activity against Bipolaris sorokiniana, the spot blotch pathogen of wheat. Interestingly, 2, 4 and 10 µg/ml concentrations of bsAgNPs accounted for complete inhibition of conidial germination, whereas in the absence of bsAgNPs, conidial germination was 100%. A detached leaf bioassay revealed prominent conidial germination on wheat leaves infected with B. sorokiniana conidial suspension alone, while the germination of conidia was totally inhibited when the leaves were treated with bsAgNPs. The results were further authenticated under green house conditions, where application of bsAgNPs significantly reduced B. sorokiniana infection in wheat plants. Histochemical staining revealed a significant role of bsAgNPs treatment in inducing lignin deposition in vascular bundles. In summary, our findings represent the efficient application of bsAgNPs in plant disease management, indicating the exciting possibilities of nanofungicide employing agriculturally important bacteria.

Studies on the potential role of root exudates in the interaction between musk melon roots and Fusarium oxysporum f. sp. melonis

The interactions of resistant (Bingo, Giusto, Sweetness) and susceptible (Cantalupo di Charantais, Harper, Retato degli Ortolani) muskmelon cultivars with Fusarium oxysporum f. sp. melonis races 0, 1, 2 (FOM0, FOM1, FOM2) were studied through the effects of root exudates (REs), released by 14 and 21 days old hydroponic plantlets, on the percentage of germinated conidia. REs caused a moderate promotion or inhibition of conidial germination or did not cause any effect. The observed patterns mostly depended on pathogen race, plant cultivar and plant age: among the races, only FOM2 conidial germination was reduced by almost all REs but never totally; among the cultivars, none affected FOM0 conidial germination at any plant age. FOM1 conidial germination was either not affected or enhanced, depending on plant age. REs from Bingo and Retato degli Ortolani were also tested for their effects on FOM2 hyphal growth, number and length of germ hyphae and for root callose deposition after FOM2 challenge. Inhibitory effects of REs on the formation of germ hyphae by conidia of FOM2 were not noted. In case of the macroconidia the number increased. The length of germ hyphae was increased in both macro and microconidia and more pronounced with REs from cultivar Bingo. REs from Bingo and Retato degli Ortolani enhanced hyphal growth of FOM2. Fluorescence microscopy showed that FOM2 infection of roots caused callose deposition in root cortical cells in the resistant cultivar Bingo, but not in the susceptible Retato degli Ortolani. In conclusion, under our experimental conditions, REs appeared to be only partially involved in plant-pathogen interaction, whereas callose deposition in the roots of the resistant cultivar Bingo was elicited after inoculation with FOM2.

Effects of Ozone Gas Exposure on Toxigenic Fungi Species from Fusarium, Aspergillus, and Penicillium Genera

The antifungal properties of ozone (O3) gas exposure towards toxigenic fungi were evaluated in laboratory-scale treatments trials. O3 gas was utilized at a concentration of 60 μmol/mol at different times of exposure, which efficiently inhibited the fungi colonies growth, especially F. graminearum and P. citrinum. At the concentration applied, O3 gas exposure was able to inhibit conidia germination, caused hyphae morphological alterations that led to hyphae death and ROS production of all fungi tested. O3 action can be related to cell metabolism alterations, leading to apoptosis and oxidative stress, showing to be effective on controlling toxigenic fungal development which is one of the main problems regarding food contamination.

Evaluation of entomopathogenic fungus against Alternaria porri (Ellis) causing purple blotch disease of onion

Biological control through the use of antagonistic micro-organisms is a potential and non-chemical means of managing plant diseases. Alternaria porri causes purple blotch disease mostly in onion. In this study, three different entomopathogenic fungi, viz. Beauveria bassiana, Metarhizium anisopliae and Verticillium lecanii, were tested against A. porri. All the three entomopathogenic fungi showed inhibitory effect against A. porri subjected to in vitro studies under dual culture technique, spore (conidial) germination, food poisoning (mycelia germination) and seed germination. The percentage inhibition of mycelial growth (PIMG) of A. porri (69.24, 56.17, and 45.81%) and the percentage inhibition of conidial germination (CG) (97.81, 42.11, and 67.69%) were observed for B. bassiana, V. lecanii and M. anisopliae, respectively. Seed germination index was found to be maximum with M. anisopliae (5557 ± 107.7) and B. bassiana (4390 ± 129.9). B. bassiana exhibited efficient antagonism against A. porri showing the highest PIMG and CG with moderate seed germination index. Microscopic examination showed the disintegrated edge of conidia which had turned black and also stopped the growth of germ tube. Hence, these entomopathogenic fungi were found to be more effective antagonistic organisms and also moderately promote seed vigour index (4390 ± 129.9) as well as plant growth. The present study indicated that the entomopathogenic fungi evaluated have shown significant inhibition of A. porri. Thus, there is a possibility of exploiting them in the management of the disease.

In-vitro studies of some selected botanicals and baubiofungicide on mycelial growth and conidial germination of Cercospora arachidicola and Cercosporidium personatum

Efforts have been made to assess some plant extracts namely, Lycopersicon esculentum, Tagetus patula, Achras sapota, Azadirachta indica, Datura metel, Cymbopogon citrates, Polyalthia longifolia, Allium sativum and Allium cepa in vitro for the management of leaf spot (tikka) disease of groundnut cultivar Dhaka-1 caused by Cercospora arachidicola and Cercosporidium personatum. Results indicated that all the tested plant extracts and BAUBiofungicide suppressed the growth of mycelium and inhibition of conidial germination of C. arachidicola and C. personatum. Among the treatments, the leaf extracts of L. esculentum showed the most effective followed by leaf extract of D. metel, A. indica and BAU-Biofungicide in case of mycelial growth and conidial germination. Other plant extracts also had inhibitory effects. In case of conidial germination and germination inhibition, the least effective plant extract was C. citrates. Leaf extract of A. sapota was the least effective in case of mycelial growth. DOI: http://dx.doi.org/10.3329/ijarit.v3i2.17842 Int. J. Agril. Res. Innov. & Tech. 3 (2): 36-40, December, 2013

Atividade "in vitro" de extratos de Pycnoporus sanguineus e Lentinus crinitus sobre o fitopatógeno Fusarium sp

O controle alternativo de doenças de plantas tem como objetivo minimizar o impacto ambiental através da utilização de produtos naturais. Assim, este trabalho teve como objetivo avaliar a atividade in vitro de extrato aquoso e hidroalcoólico de Pycnoporus sanguineus e Lentinus crinitus contra Fusarium sp., conhecido por causar doenças das culturas. Os fungos foram coletados em áreas urbanas e rurais de Parintins-AM, e testados em diferentes concentrações de extratos, sendo avaliadas a inibição de crescimento micelial, a inibição da germinação de conídios e a inibição da germinação de esclerócios. Os melhores resultados de inibição do crescimento micelial foram obtidos com extratos hidroalcoólicos frios. Extratos de P. sanguineus obtidos em solvente hidroalcoólico frio e extrato aquoso ultrassônico e extrato de L. crinitus de solvente hidroalcoólico frio, inibiram mais de 92% da esporulação de conídios. Extratos aquosos quentes inibiram a germinação de escleródios, bem como o extrato de P. sanguineus hidroalcoólico frio. O consórcio dos fungos inibiram a germinação de escleródios em 1000 µg mL-1.

Leaf spot and dieback of Buxus caused by Cylindrocladium buxicola

Leaf blight symptoms were observed on potted box plants (Buxus sempervirens cv. Suffruticosa and B. microphylla) in a nursery in South Moravia in August 2010. These symptoms were suggestive of box blight on Buxus spp. Characteristics of the visual symptoms, microscopic features, and identification of the isolates using DNA sequencing are described. The causal agent was isolated and identified as Cylindrocladium buxicola Henricot by means of morphological, cultural, and molecular characters. The effect of five commercial fungicides on C. buxicola in vitro was studied. The most effective fungicides (kresoxim-methyl, azoxystrobin, and mancozeb) inhibited conidia germination and mycelial growth (kresoxim-methyl, myclobutanil, and penconazole) of C. buxicola more than 96%.  

Effects of sugar and amino acid supplementation on Aureobasidium pullulans NRRL 58536 antifungal activity against four Aspergillus species

Cultured cell extracts from ten tropical strains of Aureobasidium pullulans were screened for antifungal activity against four pathogenic Aspergillus species (Aspergillus flavus, Aspergillus niger, Aspergillus fumigatus, and Aspergillus terreus) using the well diffusion and conidial germination inhibition assays. The crude cell extract from A. pullulans NRRL 58536 resulted in the greatest fungicidal activity against all four Aspergillus species and so was selected for further investigation into enhancing the production of antifungal activity through optimization of the culture medium, carbon source (sucrose and glucose) and amino acid (phenylalanine, proline, and leucine) supplementation. Sucrose did not support the production of any detectable antifungal activity, while glucose did with the greatest antifungal activity against all four Aspergillus species being produced in cells grown in medium containing 2.5% (w/v) glucose. With respect to the amino acid supplements, variable trends between the different Aspergillus species and amino acid combinations were observed, with the greatest antifungal activities being obtained when grown with phenylalanine plus leucine supplementation for activity against A. flavus, proline plus leucine for A. terreus, and phenylalanine plus proline and leucine for A. niger and A. fumigatus. Thin layer chromatography, spectrophotometry, high-performance liquid chromatography, (1)H-nuclear magnetic resonance, and MALDI-TOF mass spectrometry analyses were all consistent with the main component of the A. pullulans NRRL 58536 extracts being aureobasidins.

Evaluation of DMI fungicides against species of Diplodia and Neofusicoccum associated with Botryosphaeria canker of grapevine

C. Torres, B.A. Latorre, P. Undurraga, and X. Besoain. 2013. Evaluation of DMI fungicides against species of Diplodia and Neofusicoccum associated with Botryosphaeria canker of grapevine. Cien. Inv. Agr. 40(1):131-138. The Botryosphaeriaceae species have been widely studied and are considered a serious problem to the production of grapes worldwide. To aid in the development of control strategies for these fungi, in vitro experiments were conducted to evaluate the effectiveness of demethylation inhibiting (DMI) fungicides against Diplodia seriata, D. mutila, Neofusicoccum australe and N. parvum isolated from grapevine (Vitis vinifera). Fungicidal effectiveness was evaluated over a range of increasing concentrations using measurements of both the inhibition of conidial germination and the effects on mycelial growth. The effective concentrations (EC) necessary to inhibit conidial germination and mycelial growth by 50% (EC 50 ) and 90% (EC 90 ) were estimated by linear regression analysis between x = log 10 of the fungicidal concentration and y = the Probit value of the inhibition percentage. The results demonstrate that tebuconazole, myclobutanil, prochloraz and prochloraz plus epoxiconazole exhibit considerable in vitro activity against D. mutila, D. seriata, N. australe and N. parvum. These DMI compounds were able to arrest conidial germination and inhibit mycelial growth. The EC 50 values obtained for conidial germination were generally higher than the EC 50 values obtained for mycelial growth, suggesting that mycelia are more sensitive to the DMI compounds than are conidia. However, the effectiveness of these DMI compounds in the vineyard must be studied before any final conclusions can be reached.

Evaluation of the Use of Ammonium Bicarbonate and Oregano (Origanum vulgare ssp. hirtum) Extract on the Control of Apple Scab

AbstractIn vitro experiments showed that ammonium bicarbonate and aqueous extracts of oregano were effective in inhibiting conidia germination and germ‐tube elongation of Venturia inaequalis. Complete inhibition was achieved by 1% ammonium bicarbonate, 2% oregano extract and 0.01% synthetic fungicide difenoconazole. Two orchard experiments were conducted on the highly susceptible cv. Mutsu to apple scab to investigate the efficacy of ammonium bicarbonate alone or in combination with an aqueous extract of oregano for the control of apple scab. In 2008 and 2009, except for the applications of 1% aqueous extract of oregano, the applications of ammonium bicarbonate (0.5 and 1%) and difenoconazole (0.01%) to trees at 10‐day intervals significantly reduced disease incidence and severity on leaves and fruit compared to the water‐treated control. In both years, the efficacy of 0.5 and 1% ammonium bicarbonate in inhibiting both disease incidence and severity on leaves and fruit was equally effective in all monthly assessments from June to September. Combining 0.5 and 1% ammonium bicarbonate with 1% aqueous extract of oregano did not significantly improve the efficacy of stand‐alone applications of treatments in the final assessment in 2008 and 2009. All treatments were neither phytotoxic to leaves and fruit nor did they adversely affect quality parameters of fruit including physiological disorders and taste both at harvest and after storage. These results indicate that ammonium bicarbonate treatment may be applied as an alternative chemical for the control of apple scab.

Suitability of Nano-sulphur for Biorational Management of Powdery mildew of Okra (Abelmoschus esculentus Moench) caused by Erysiphe cichoracearum

New nano-sulphur synthesized at IARI and three other commercial products namely commercial sulphur (Merck), commercial nano-sulphur (M K Impex, Canada) and Sulphur 80 WP (Corel Insecticide) were evaluated in vitro for fungicidal efficacy at 1000 ppm against Erysiphe cichoracearum of okra. All the sulphur fungicides significantly reduced the germination of conidia of E. cichoracearum as compared to control. Least conidial germination was recorded in IARI nano-sulphur (4.56%) followed by Canadian nanosulphur (14.17%), Merck sulphur (15.53%), sulphur 80 WP (15.97%) and control (23.09%). Non-germinated conidia count was also high in case of IARI nanosulphur followed by Canadian nano-sulphur, Merck sulphur and Sulphur 80WP. Apart from inhibition of conidial germination, cleistothecial appendages were also disrupted in contact with nano-sulphur and the cleistothecia became sterile. The study proved that IARI nano-sulphur is more effective than the commercial formulations and could be applied at lower amount for controlling powdery mildew disease for its better efficacy.

Role of Different Microbial-origin Bioactive Antifungal Compounds Against Alternaria spp. Causing Leaf Blight of Mustard

Trichoderma harzianum, T. viride, T. virens and Aspergillus niger were isolated from mustard leaf surface. Efficacy of their conidial suspension and culture filtrates was evaluated. In dual culture test, T. viride caused maximum inhibition of radial growth of A. brassicae (74%) and A. brassicicola (77%). Highest concentration (3:1) of T. viride culture filtrates caused 60 and 54% inhibition of radial growth of A. brassicae and A. brassicicola, respectively. The culture filtrates of T. viride at their highest concentration (3:1) caused 71 and 69% inhibition of conidial germination of A. brassicae and A. brassicicola, respectively. In field trial foliar spray of 1x107 conidia mL-1 of biological control agents was done on mustard plants 24 h after artificial inoculation by A. brassicae conidial suspension (1x105 conidia mL-1. Viability of BCAs was recorded up to 30 days in phylloplane of mustard at relative humidity between 80-90% and temperatures between 20-25°C. T. viride proved to be most effective as its conidial suspension caused up to 76 and 68% reduction in disease intensity on leaves and pods, respectively. Whereas, its culture filtrate caused 45 and 36% reduction in disease severity on leaves and pods, respectively. These results suggested that T. viride can be used to control Alternaria blight disease of mustard.

Sensitivity of the entomopathogenic fungus Beauveria bassiana (Bals.‐Criv.) Vuill. to selected herbicides

The in vitro effect of six commonly used herbicides viz., amidosulfuron, dicamba, metribuzin, pyridate, S-metolachlor and tembotrione on mycelial growth of entomopathogenic fungus Beauveriabassiana (ATCC 74040) was investigated. Mycelial growthrates at 15 and 25°C were evaluated on PDA plates containing 100, 75, 50, 25, 12.5, 6.25 and 0% of the recommended application rate of each selected herbicide. The tested herbicides were classified in 4 scoring categories based on reduction of mycelial growth in toxicity tests. All six herbicides had a fungistatic effect of varying intensities, dependent on their rate in medium, on B. bassiana. The present study showed that B. bassiana is sensitive to all tested herbicides, particularly at recommended as well as lower field rates. Metribuzin, S-metolachlor and tembotrione had a strong fungistatic effect on mycelial growth even at rates 25 and 12.5%.Pyridate was slightly harmful, depending on the rate and temperature. Dicamba and amidosulfuron had slight effect on mycelial growth. Sporulation and conidial germination of B. bassiana were significantly inhibited by all tested herbicides. Amidosulfuron and dicamba, both at 100% rate, had the lowest inhibitory effect on sporulation, i.e. 24% and 44%, respectively. Other herbicides in test showed much higher inhibitory effect on sporulation (69-95%). With exception of dicamba with 33% of conidial germination inhibition all other herbicides in test inhibited conidial germination for 70-100%. At 200% dosage, inhibition rates even increased. Of all tested herbicides, amidosulfuron and dicamba showed the least adverse effects and are therefore probably compatible with B. bassiana in the field.

Antifungal activity and ultrastructural alterations in Pseudocercospora griseola treated with essential oils

Pseudocercospora griseola, the etiologic agent of angular leaf spot of common bean (Phaseolus vulgaris), is an important disease in all bean-producing regions worldwide and may cause extremely high yield losses. The control of this disease is made more difficult by the pathogen's genetic variability and the inefficiency of fungicides. In this study, of 26 essential oils tested at different concentrations, 25 demonstrated efficiency in affecting the germination of strains 63-31 and 63-63 of the pathogen, reaching inhibition levels of between 80% and 100%. Cymbopogon citratus and Cymbopogon martinii inhibited conidia germination at all concentrations; Eugenia caryophyllata, Cinnamomum sp., Thymus vulgaris, Matricaria recutita, Cordia verbenacea, Origanum vulgare, Cymbopogon nardus, at 0.1 and 0.5%; and Zingiber officinale, Mentha arvensis, Chamaecyparis pisifera, Lavandula officinalis, Ocimum basilicum, Pimpinella anisum, Ocimum selloi, Baccharis dracunculifolia, Laurus nobilis, Citrus sinensis, Melaleuca alternifolia and Eucalyptus globulus, at 0.5%. The main constituents identified were cinnamaldehyde in Cinnamomum sp.; eugenol in E. caryophyllata; trans-β-farnesene in M. recutita; pulegone in C. verbenacea; thymol in T. vulgaris; geranial and neral in C. citratus, and geraniol in C. martini. Through transmission electron microscopy (TEM), it was verified that C. citratus, C. martini and E. caryophyllata presented direct fungitoxic action on P. griseola, causing severe damage to the cellular ultrastructure of the conidia, invalidating germination. These results indicated that essential oils are a promising alternative strategy for the control of angular leaf spot in bean, representing less risk to human health and the environment.

In vitro and in vivo evaluation of microbial-enriched compost tea on the development of powdery mildew on melon

This study evaluated the effects of microbial-enriched compost tea (CT) on the conidial germination of Golovinomyces cichoracearum DC. and development of powdery mildew on melons in a time-dependent manner. In vitro conidial germination was significantly reduced by 94 % and 85 % upon treatment with Daconil® (fungicide) or microbial-enriched CT, respectively, 96 h after incubation (hai). Morphological analysis under light microscopy demonstrated that conidia co-incubated with microbial-enriched CT at 48 hai appeared ruptured, which contributed to higher inhibition of conidial germination, increased cell permeability and leakage of cellular contents. These observations may be explained by antibiosis. Moreover, different application time of microbial-enriched CT on melons significantly affected disease development. There was a delay in disease development by 12 days in plants treated with Daconil®, microbial-enriched CT applied 24 h after inoculation and microbial-enriched CT applied simultaneously with inoculation when compared to the control treatment. Curative application of microbial-enriched CT (24 h after inoculation) delayed the onset of disease, and the efficiency of inhibition was comparable to a fungicidal spray (Daconil®). Hence, microbial-enriched CT may be used to inhibit the development of powdery mildew on melons, thus reducing the dependency on chemical fertilisers.

Effect of Zataria multiflora essential oil on Alternaria alternata in vitro and in an assay on tomato fruits

The present study aimed to evaluate the effects of Zataria multiflora essential oil at different concentrations (0, 100, 200, 300 and 500 ppm) on the growth rate and morphogenesis of Alternaria alternata in in vitro and in vivo conditions. The antifungal activity of the oil was tested by the poisoned food technique (PF) and volatile activity assay (VA). The mycelial growth of the test fungus was completely inhibited at oil concentrations of 500 and 200 ppm in PF and VA assessments, respectively. Determination of conidial germination in the presence of the oil was also carried out and it was found that the oil caused 100% inhibition of conidial germination at the level of 300 ppm. Light Microscopy (LM) showed morphogenic changes in the test fungus with 300 ppm of the oil. These changes included a significant decrease and loss of conidiation, severely collapsed and squashed hyphae, a decreased hyphal diameter and granulation of cytoplasm. The treatment with the oil also resulted in highly lobate and bulbous anomalous structures at the hyphal tips. GC-MS evaluations of the essential oil revealed that the latter consisted of 14 compounds of which carvacrol was the major component. In vivo Z. multiflora oil at 500 ppm effectively reduced the percentage of decayed tomatoes. Findings of the current study suggest that essential oils could be used as an alternative for chemicals for control of postharvest phytopathogenic fungi on fruits or vegetables.

Pyraclostrobin sensitivity of baseline and fungicide exposed isolates of Pyrenophora tritici-repentis

Tan spot, caused by Pyrenophora tritici-repentis, is an important disease of wheat (Triticum aestivum L.) in the United States (U.S). Wheat growers sometimes rely on fungicide applications to manage foliar diseases. Pyraclostrobin is one of the recommended quinone outside inhibitor (QoI) fungicides and is commonly used to manage tan spot on wheat. Although P. tritici-repentis isolates has been reported as insensitive to QoI fungicides in Europe, little is known regarding the sensitivity of the P. tritici-repentis population to fungicides in the U.S. Twenty-eight isolates collected prior to 1997 and 136 isolates collected from pyraclostrobin treated fields in North Dakota were collected in 2007 and 2009 to determine if P. tritici-repentis isolates can use alternative respiration in the presence or absence of salicylhydroxamic acid (SHAM) in vitro and to determine the effective fungicide concentration that inhibited conidia germination by 50% (EC50). Six of 10 baseline isolates of P. tritici-repentis assayed had significantly higher (P ≤ 0.05) EC50 values when SHAM was not added to agar medium amended with pyraclostrobin, confirming that the fungus can utilize alternative respiration to overcome QoI toxicity in vitro. EC50 values of the baseline isolates ranged from 0.0012 to 0.0024 μg/ml (mean EC50 value of 0.0017 μg/ml and standard deviation is ±0.00039 μg/ml) while EC50 values of the 136 fungicide exposed isolates ranged from 0.0013 μg/ml to 0.0027 μg/ml (mean EC50 value of 0.0017 μg/ml and standard deviation is ±0.00030). These results indicate that the field exposed isolates have not shifted to reduced sensitivity to pyraclostrobin and that the baseline sensitivity values can be useful for a fungicide resistance monitoring program for P. tritici-repentis in the U.S.

FUNGITOXIC SPECTRUM OF AMALAB-A AGAINST FUNGAL PATHOGENS IN RICE UNDER IN-VITRO

ABSTRACT Through the present study a botanically derived product Amalab-a was developed by combining Aegle marmelos leaf extract with a formulating agent (coded A+) and tested against three fungal pathogens of rice viz. Helminthosporium oryzae , Curvularia lunata and Fusarium moniliforme. Product registered complete inhibition of conidial germination at 0.01% in H.oryzae, C. lunata and F.moniliforme and mycelial growth inhibition at 1% in H.oryzae, F.moniliforme and at 0.1% in C. lunata whereas the extract alone could not at the same concentration. The shelf-life test displayed greater fungitoxic effect against all the three tested pathogens and retained its fungitoxicity upto 0.01% concentration till 12 months storage period. This formulated product has therefore improved the efficacy and shelf-life of this botanical product compared to the unformulated botanical extracttested under in-vitro, hence possesses greater potential for its integration against rice brown spot and grain discolouration control strategy but needs to be tested under in-vivo.

In vitro effect of pesticides on the germination, vegetative growth, and conidial production of two strains of Metarhizium anisopliae

Entomopathogenic fungi are widely used as biological control agents against a broad range of insect and arachnid pests. However, the control efficacy of entomopathogenic fungi is variable because of unfavourable and fluctuating environmental conditions and intrinsic factors. One strategy to enhance entomopathogenic fungi efficacy is a combined use of entomopathogenic fungi and low dosages of pesticides. These sub-lethal dosages of chemicals can increase the control efficiency of entomopathogenic fungi but only if they do not affect the fungi. Adverse effects could include the inhibition of germination and/or vegetative growth as well as conidiogenesis.The present study investigated the in vitro effects of different concentrations of fipronil, permethrin, imidacloprid, NeemAzal, and amitraz as potential candidates for combined applications on two strains of the entomopathogenic fungus Metarhizium anisopliae (MA). MA was inoculated on a medium amended with five different concentrations (0.32–200ppm) of the abovementioned pesticides. The germination, vegetative growth, and sporulation were evaluated. The results showed, according to a physiology parameter compatibility classification, that all pesticides were compatible with both tested MA strains. Only fipronil in the higher dose rates of 40 and 200ppm was close to moderately toxic to MA-7. Furthermore, only higher concentrations of the pesticides caused a slight inhibition (about 15%) of conidial germination and a reduction in colony size. Sporulation was reduced at most by approximately 50% by 40 or 200ppm of fipronil or amitraz, respectively.Therefore, it is possible to use the tested pesticides in combination with either strain of MA for an integrated pest management approach. Studies on the effect of these combinations on target organisms are in progress.

Effects of volatile substances of Streptomyces globisporus JK-1 on control of Botrytis cinerea on tomato fruit

Volatile substances produced by Streptomyces globisporus JK-1 grown on autoclaved wheat seed inhibited Botrytis cinerea growth and development both on media and in inoculated tomato fruit. The volatiles suppressed mycelial growth of various plant pathogens in vitro, especially that of B. cinerea and Sclerotinia sclerotiorum. Conidial germination and sporulation of B. cinerea were also suppressed. Disease incidence and severity on wound-inoculated tomato fruit (Lycopersicon esculentum) were inhibited when fumigated with 120g wheat seed culture of S. globisporus JK-1 per liter of airspace in treatment containers. Suppression of the infection process of B. cinerea on tomato fruit was observed via scanning microscopy, showing inhibition of conidial germination and of appressorial formation on tomato fruit, as well as abnormal morphology of appressoria and conidia. The viability of the conidia obtained from the volatile-treated and non-treated disease lesions was tested with the vital stains fluorescein diacetate (FDA) and propidium iodide (PI). Conidia fumigated with 30, 60 or 120g/L wheat seed culture of S. globisporus JK-1 at 20°C for 6days showed 46.0%, 69.8%, or 80.9% reduction in viability, respectively. Transmission electron microscopy of fumigated and untreated B. cinerea showed excessive vesiculation or thickened cell walls in exposed conidia and increased vesiculation or strong retraction of plasma membrane in exposed hyphae. These results provide a better understanding of the mode of action of volatiles from JK-1 on B. cinerea. The inhibition growth of B. cinerea both in vitro and in vivo showed that volatiles from S. globisporus JK-1 have the potential for control of postharvest grey mold of tomato fruits through fumigant action.