Field evaluations of systemic fungicides and derivatives of dithiocarbamic acid for the control of clubroot

Strains of Botrytis cinerea and Mucor mucedo germinated and grew over the range 0.25^°C. There were differences in germination rates and growth rates between strains of B. cinerea at any given temperature. Five of the benomyl-resistant strains germinated and grew more slowly than any of the other benomyl-resistant or benomyl-sensitive strains of B. cinerea tested. Strains of Rhizopus stolonifer and R. sexualis germinated and grew between 5 and 25^°C, and although some spores germinated at 2^°C, subsequent growth of the germ tubes and growth from a mycelial inoculum did not occur. Neither species germinated or grew at o^°C. The effect of temperature on mycelial growth in vitro was consistent with the ability of the strains of the four species to infect strawberry fruits.     

Using combinations of biocontrol agents to control Botrytis cinerea on strawberry leaves under fluctuating temperatures

Experiments were conducted with Botrytis cinerea on strawberry leaves to investigate where combinations of commercially available biological control agents (BCAs) might control B. cinerea more effectively than individual BCAs. Specifically, we studied the persistence of biocontrol activities, spread of BCAs among leaves, and biocontrol efficacy in relation to application regimes: mixed versus single BCA, pre-versus post-inoculation application, and sequential versus simultaneous application. Three BCA products (Sentinel, Serenade and Trianum) were used for this study. Overall, Serenade did not significantly reduce sporulation of B. cinerea on strawberry leaf discs whereas Sentinel and Trianum gave a similar and significant biocontrol efficacy. Biocontrol efficacy remained almost unchanged 10 days after application at 20/20°C (day/night) or 24/16°C temperature regimes. In contrast, reduced biocontrol efficacy at 26/14°C suggests BCA survival was reduced under these conditions. Incidence of B. cinerea sporulation on leaf discs was ca. 60% higher on leaves that emerged after the BCA application than on leaves directly exposed to BCA, indicating insufficient amount of the BCA had managed to spread to new leaves. Combinations of BCAs, whether applied simultaneously or sequentially (48 h apart), did not improve disease control over the most effective BCA within the combination applied alone. This indicated possible antagonism or interference between the BCAs. Results suggested that there was significant antagonism for most combinations of the three BCAs tested and the degree of antagonism increased as the time from BCA application to pathogen introduction lengthened.     

Biological control of strawberry crown rot,root rot and grey mould by the beneficial fungus Aureobasidium pullulans

Utilization of biocontrol agents is a sustainable approach to reduce plant diseases caused by fungal pathogens. In the present study, we tested the effect of the candidate biocontrol fungus Aureobasidium pullulans (De Bary) G. Armaud on strawberry under in vitro and in vivo conditions to control crown rot, root rot and grey mould caused by Phytophthora cactorum (Lebert and Cohn) and Botrytis cinerea Pers, respectively. A dual plate confrontation assay showed that mycelial growth of P. cactorum and B. cinerea was reduced by 33–48% when challenged by A. pullulans as compared with control treatments. Likewise, detached leaf and fruit assays showed that A. pullulans significantly reduced necrotic lesion size on leaves and disease severity on fruits caused by P. cactorum and B. cinerea. In addition, greenhouse experiments with whole plants revealed enhanced biocontrol efficacy against root rot and grey mould when treated with A. pullulans either in combination with the pathogen or pre-treated with A. pullulans followed by inoculation of the pathogens. Our results demonstrate that A. pullulans is an effective biocontrol agent to control strawberry diseases caused by fungal pathogens and can be an effective alternative to chemical-based fungicides.

     

Influence of Temperature, Wetness Duration, and Leaf Type on the Quantification of Monocyclic Parameters of Bean Rust

Monocyclic parameters of bean rust (Uromyces phaseoli var. typical) were quantified in growth chambers, on rwo bean cultivars for three temperatures (17, 21, and 25 °C), two types of leaves (unifoliolate and trifoiiolate leaves), and nine leaf wetness periods (0, 4, 7, 10, 13, 16, 19, 22, and 25 hrs). The expression of disease was greatly influenced by past-inoculation temperatures. The incubation and latent periods were shortest at 21 °C for both cultivars and leaf types. For both cultivars, trifoiiolate leaves were more susceptible than unifoliolate leaves. A wetness period of at least four hours was required for disease to occur. The maximum disease efficiency for both cultivars occurred with 22 hrs of leaf wetness at 17 °C. The disease efficiencies for temperatures of 17–29 °C and leaf wetness periods of 0–25 hrs were adequately described by a response-surface model. Because of the great influence of temperature and leaf wetness on infection, bean rust is unlikely to occur at high temperatures (> 25°C) and short leaf wetness periods (< 7 hrs).     

UV-B radiation reduces biocontrol ability of Clonostachys rosea against Botrytis cinerea

There is a lack of information comparing UV-B radiation conidial sensitivity of the biocontrol agent Clonostachys rosea (Cr) and its target pathogen, Botrytis cinerea (Bc). We investigated the interactions in vitro and on strawberry leaf discs between previously selected Cr and Bc strains tolerant to UV-B radiation. Strawberry leaf discs inoculated with Bc, Cr, or combinations of both fungi were exposed to UV-B doses (2.9, 5.9, and 8.9?kJ?m^?2). Incidence and sporulation of both fungi were evaluated, and the Area Under Incidence Progress Curve (AUIPC) and Area Under Sporulation Progress Curve (AUSPC) were calculated. AUIPC and AUSPC of Cr on leaf discs were negatively correlated to increased UV-B. When inoculated alone on leaf discs, Bc was not affected by UV-B, but when inoculated with Cr the incidence and sporulation of Bc were positively correlated to UV-B radiation dose. In the absence of UV-B, Cr reduced incidence and sporulation of Bc. However, the ability of Cr to control Bc was reduced by 20% to 50% with increasing UV-B radiation. Increasing the applied concentration of Cr conidia 10-fold partially overcame the deleterious effects of UV-B on the ability of the biocontrol agent to reduce Bc sporulation in strawberry leaves. The selection of antagonists must fulfil many requirements; besides being active against the specific targeted plant pathogens, they must be cost-effective and have ecological characteristics suitable for the desired use conditions. We suggest that UV-B exposure must be taken into account during the development of bio-fungicides based on Cr.     

Presence of Transposons and Mycoviruses in Botrytis cinerea Isolates Collected from a German Grapevine Growing Region

Transposons and infection of fungal strains with mycoviruses can have significant effects on distinctive phenotypic traits of phytopathogenic fungi such as mycelial growth and sporulation, pathogenicity or fungicide resistance. Two transposable elements (TE), Boty and Flipper, are known to be associated with the ubiquitous fungus Botrytis cinerea. In addition, the presence of two types of ssRNAsRNA viruses, BVX and BVF, has been reported in B. cinerea. In this study, we assessed the genetic diversity of B. cinerea isolates, all sampled within a small‐sized German viticultural area (‘Rheingau’) by examining and classifying them according to the presence of TEs and mycoviruses. A subset of the isolates was further analysed with microsatellite markers to determine the origin of particular isolates with or without one or both mycoviruses. Virtually all isolates (98%) sampled in two different years (2008 and 2010) were screened positive for the presence of a transposon. Presence of one or both B. cinerea mycoviruses was confirmed for 37% of the analysed isolates sampled in 2010, representing the first record of B. cinerea mycoviruses in German isolates. Assignment on individual B. cinerea isolates to different genetic groups was independent of the presence or absence of a mycovirus or a transposable element, respectively. Furthermore, we found no correlation between the presence of either a mycovirus or a transposable element and different viticultural management practices, soil properties or levels of nitrogen fertilization applied to the respective vineyards. However, mycelial growth of B. cinerea strains containing mycovirus BVF was significantly reduced at lower temperatures.     

Patterns of leaf surface wetness for montane and subalpine plants

The frequency and duration of water on leaf surfaces have important consequences for plant growth and photosynthetic gas exchange. The objective of the present study was to compare the frequency and duration of leaf wetness under natural field conditions among species and to identify variation in structural features of leaves that may reduce surface wetness. During June–September 1992 in the central Rocky Mountains (USA), natural leaf wetting due to rain and dewfall was observed on 79 of 89 nights in open meadow habitats compared to only 29 of 89 nights in the understorey. Dew formation occurred at relative humidities that were often well below 100% because of radiational heat exchange with cold night skies and low wind speeds (< 0.5 m s^?1). A survey of 50 subalpine/montane species showed that structural characteristics associated with the occurrence and duration of leaf surface wetness differed among species and habitats. Both adaxial and abaxial surfaces accumulated moisture during rain and dewfall events. Leaf surfaces of open-meadow species were less wettable (P= 0.008), and had lower droplet retention (P= 0.015) and more stomata P= 0.017) than adjacent understorey species. Also, leaf trichomes reduced the area of leaf surface covered by moisture. Ecophysiological importance is suggested by the high frequency of leaf wetting events in open microsites, influences on growth and gas exchange, and correspondence between leaf surface wettability and habitat.     

Screening of bacteria for the suppression of Botrytis cinerea and Rhizoctonia solani on lettuce (Lactuca sativa) using leaf disc bioassays

Two leaf disc bioassays were developed for screening bacteria as putative biological control agents of Botrytis cinerea and Rhizoctonia solani on lettuce. Aerobic spore and non‐spore forming bacteria were isolated from the phylloplane, rhizoplane and rhizosphere of symptom‐free lettuce plants grown in the presence and absence of chitin or composted bark soil amendments. Bacteria, previously isolated from other plants, were also included in the primary screen initially against B. cinerea. One hundred and twenty‐seven of 700 isolates reduced botrytis rotting of lettuce leaves by more than 50% in the primary screen. Following a secondary screen against B. cinerea, the lead 50 isolates were also tested for suppression of R. solani infection. Four isolates significantly reduced both botrytis and rhizoctonia leaf rotting. Eleven and five isolates gave control of botrytis and rhizoctonia, respectively, equal to that given by the standard fungicides Rovral WP (iprodione) and Basilex (tolclofos methyl). The two most effective isolates against B. cinerea and R. solani were both identified as Bacillus subtilis. Use of soil amendments did not increase the proportion of efficacious isolates recovered. Effective isolates were originally recovered from roots of oilseed rape and lettuce leaves. In general, it was found that bacteria which controlled one disease effectively did not control the second disease nearly as well. The bioassay protocols developed in this study were used successfully in screening a large number of bacterial isolates in a short time.     

Ability of the antagonistic yeast Cryptococcus albidus to control Botrytis cinerea in strawberry

The yeast Cryptococcus albidus, originally isolated from mature strawberry fruits, was tested for antagonistic activity against Botrytis cinerea, the causal agent of grey mould in strawberries. Conidial germination and germ tube growth of conidia of B. cinerea were inhibited by a cell suspension of the antagonist in aqueous strawberry fruit pulp suspension (1%) after 6 and 24 hours of incubation. Application of a cell suspension (1 × 10⁶ cells/ml) on detached strawberry leaf disks incubated at 10°C reduced incidence and conidiophore density of B. cinerea by 86 and 99%, respectively, but effectiveness was reduced at higher temperatures. Treatments with C. albidus during bloom of strawberries reduced incidence of grey mould on ripe strawberry fruits after harvest by 33, 28 and 21% in three years of field trials. The effectiveness of the yeast was increased when formulation substances (alginate, xanthan and cellulose) were added to the cell suspension.     

Isolation of bioactive antibiotic peptides from Bacillus brevis and Bacillus polymyxa against Botrytis grey mould in strawberry

Abstract

Grey mould caused by Botrytis cinerea is a devastating disease that results in extensive yield losses to strawberry. Bacillus brevis (Brevibacillus brevis) and Bacillus polymyxa (Paenibacillus polymyxa), which showed strong antifungal activity against B. cinerea, were isolated from the phyllosphere of strawberry plants. The advantage of using these bacteria is that the biochemistry and physiology of production of antibiotic peptides antimicrobial substances is well documented. A study was conducted to assess the activity of both Bacilli and their antibiotic peptides produced against B. cinerea in strawberry plants in vitro and in vivo. In vitro bioassay, both Bacilli have strongly inhibited pathogen germination, growth and extra-cellular enzyme production. Bacillus brevis was generally the most effective in reducing Botrytis growth. Gramicidin S and polymyxin B peptide antibiotics were extracted from culture filtrate of B. brevis and B. polymyxa, respectively, purified by silica thin chromatography and identified by high performance liquid chromatography. Germination, growth rate and production of extra-cellular enzymes were more sensitive to both antibiotics. Gramicidin S was the most active against B. cinerea with a minimal inhibitory concentration of 15 μmol/l. Polymyxin B also showed activity against B. cinerea at 25 μmol/l. Under controlled conditions (18 – 22°C, 90% relative humidity and 12 h photoperiod), strawberry plants were sprayed with pathogens (10⁵ spores/ml), antagonists (from 10⁵ to 10⁸ cells/ml) and antibiotic peptides (0 – 30 μmol/l) for reducing grey mould. Disease incidence was decreased in the presence of B. brevis. Both antibiotic peptides inhibited Botrytis growth that was observed by scanning electron microscopy. The plant leaves adsorbed significant amounts of antibiotics which reached from 46.1 to 67.5% of the original solution. Under natural field conditions, these biocontrol and antibiotic peptides at different concentrations were evaluated in 2003/2004 and 2004/2005 seasons against Botrytis grey mould. Treating plants with B. brevis exhibited a significant high activity against the development of Botrytis disease on strawberry. Gramicidin S showed a strong potential in reducing disease incidence, followed by polymyxin B, and acted as a fungicide to the pathogen growth. Inhibition of B. cinerea by both Bacilli was similar to equivalent levels of their antibiotics produced. In addition, these treatments significantly reduced the development of Botrytis and increased fruit yield. It can be suggested that B. brevis and B. polymyxa may be considered as potential biocontrol agents against Botrytis grey mould on strawberry based on the production of antifungal peptides. Therefore, gramicidin S and polymyxin B products are considered as biocontrol agents and may play a significant role in the future for practical applications in strawberry management systems.     

Effect of extracts from in vitro-grown shoots of <Emphasis Type="Italic">Quillaja saponaria</Emphasis> Mol. on <Emphasis Type="Italic">Botrytis cinerea</Emphasis> Pers.

The ethanolic and aqueous extracts from in vitro shoots of Quillaja saponaria Mol. (Quillay) were studied for their antifungal activity against the phytopathogenic fungus Botrytis cinerea Pers. These extracts reduced conidial germination and mycelial growth of B. cinerea, ethanolic extracts being more active than aqueous extracts. In addition, the damage areas produced by this fungus on tomato leaves and strawberry fruits pre-treated with quillay extracts were diminished. The fungitoxic effect of in vitro-grown quillay extract was similar to those obtained with commercial fungicides of both natural (BC-1000) and synthetic (iprodione–dicarboximide) origin. On the other hand, the antifungal action of quillay extracts obtained from adult trees naturally grown was only slightly superior to the fungitoxic activity of the extract from in vitro plants. HPLC analysis of the extract showed that it contained saponins and some phenolic compounds such as chlorogenic, caffeic, vanillic, and salicylic acids, and scopoletin, which have been identified as antifungal agents on phytopathogenic fungi. The results obtained in this work, suggests that extracts of in vitro-grown quillay have an important protective effect against B. cinerea and support the use of an in vitro culture system as a biotechnological alternative to obtain environmental safe antifungal quillay extracts to control B. cinerea, contributing to the preservation of this indigenous Chilean species.     

Baseline sensitivity of Botrytis cinerea to fluazinam and cross‐resistance

Grey mould, caused by the fungus Botrytis cinerea Pers ex Fr., is a very destructive and important disease worldwide. Fluazinam is a phenylpyridinamine fungicide with broad‐spectrum activities. The baseline sensitivity of B. cinerea to fluazinam is yet to be established in Henan Province, China. In this study, a total of 117 field isolates of B. cinerea were collected from 49 commercial greenhouses in different locations of Henan Province, in 2016, and the sensitivities of these isolates to fluazinam were determined based on mycelial growth. The effective concentration for 50% (EC₅₀) values ranged from 0.0038 to 0.0441 μg/ml, and the mean EC₅₀ value was 0.0201 ± 0.0081 μg/ml for mycelial growth. The frequency distribution range presented a unimodal curve. To define the cross‐resistance relationships, the linear correlation coefficients of the EC₅₀ values between fluazinam and carbendazim, procymidone, pyrimethanil or boscalid were analysed. The results showed that no correlation was observed between fluazinam and the other tested fungicides. These results provide important information to growers for the prevention and control of grey mould.     

Septoria Leaf Spot of Stevia rebaudiana in Canada and Methods for Screening for Resistance

The herb Stevia rebaudiana is a potential source of low-calorie sweeteners. In 1995, a severe leaf spot and blight was observed in stevia production fields and research plots in the provinces of Ontario and British Columbia, Canada. The disease was characterized by angular, shiny, olive-grey lesions that rapidly coalesced and were often surrounded by a chlorotic halo. Leaves quickly became necrotic and often dropped off the plant. The disease progressed upwards in the foliage during the growing season. A Septoria sp. was isolated from diseased leaves. Ten isolates (five from each of the two provinces) of the Septoria sp. were compared with respect to conidial size. Across isolates, conidia lengths and widths overlapped (grand means for length and width were 71.4 μm and 1.4 μm, respectively). Conidiogenesis was holoblastic. Morphological characteristics and disease symptoms were similar to those of Septoria steviae, previously reported only from Japan. It was concluded that the Canadian isolates belonged to S. steviae. Isolates from Canada did not differ significantly from one another with respect to effects of temperature on colony growth or germination of conidia. Optimum temperatures for these parameters were between 20 and 25°C. In field trials, the pathogen was shown to successfully over-winter in diseased leaf tissue. In order to develop procedures for identification of resistant germplasm and greenhouse screening of candidate fungicides, effects of leaf wetness period, inoculum concentration, and plant age on disease development were determined. Thirty-six hours of leaf wetness were required for consistent development of leaf spots. Inoculum concentrations of 5 × 10⁵ conidia/ml or more were required to produce high disease severities; 6-week-old plants were more susceptible than older plants. In the growth chamber, greenhouse, and field trials, germplasm selections with high levels of resistance to S. steviae were identified. This is the first report of resistance to this disease in S. rebaudiana.     

Brief in vitro study on Botrytis cinerea and Aspergillus carbonarius regarding growth and ochratoxin A

Aims: To evaluate the effect of Botrytis cinerea growth on ochratoxin A (OTA) production by Aspergillus carbonarius and degradation. Methods and Results: OTA‐producing A. carbonarius and B. cinerea were grown on grape‐like medium at 20°C for 7 days. Radii of colonies were daily recorded and OTA was analysed. In addition, each B. cinerea isolate was inoculated on grape‐like synthetic nutrient medium (SNM) paired with each A. carbonarius isolate at a distance of 45 mm. Botrytis cinerea isolates were also grown in OTA‐spiked SNM. Growth rates of B. cinerea and A. carbonarius were 20 and 7·5 mm day^?1, respectively. The growth of the colonies of each species stopped when they contacted each other in paired cultures. OTA production by A. carbonarius in the contact area was affected by B. cinerea, but no clear trend was observed. All B. cinerea isolates showed to degrade between 24·2% and 26·7% of OTA from spiked SNM. Conclusions: The ecological advantage of B. cinerea, in terms of growth rate, vs. OTA‐producing Aspergillus in some wine‐growing regions and its ability to degrade OTA may explain the low levels of this toxin in noble wines. Significance and Impact of the Study: At determinate conditions, the presence of B. cinerea in grapes with A. carbonarius may help in reducing OTA accumulation.     

Epiphytic bacteria antagonistic to Curvularia leaf spot of yam

Curvularia eragrostidis yam leaf spot is a serious concern among the northeast Brazilian yam growing areas. In order to study its biocontrol, bacterial isolates from the yam phylloplane were tested against the pathogen. They were evaluated with respect to the following parameters: (1) inhibition of C. eragrostidis mycelial growth by using paired culture and cellophane membrane methods, (2) inhibition of conidium germination by using a paired suspension test, (3) reduction of disease severity and, (4) persistence of antagonistic action, on plants under greenhouse conditions. From a total of 162 bacterial isolates, 39 showed antagonism to the pathogen in paired culture. The bacteria produced extracellular, nonvolatile, and diffusible metabolites in the membrane cellophane test. Seventeen isolates resulted in more than 75% inhibition of C. eragrostidis mycelial growth. Among them, IF-26 showed the greatest antagonism. The isolates IF-82, IF-88, and IF-109 inhibited pathogen conidial germination, with average inhibition levels of 99.2, 98.2 and 96.2%, respectively. Under greenhouse conditions the antagonists were applied at three different time intervals relative to C. eragrostidis inoculation: 3 days before, at the same time, and 3 days after. IF-82 and IF-88 applied at the same time as pathogen inoculation both reduced disease severity 75%. IF-82 showed the best persistence of antagonistic action, with an average of 96.3%. IF-82, identified as Bacillus subtilis, was the best biocontrol agent for the yam leaf spot disease in this study.Correspondence to: Sami J. Michereff     

Purple non-sulfur bacteria technology: a promising and potential approach for wastewater treatment and bioresources recovery

Botrytis cinerea, the causal agent of gray mold is one of the major devastating fungal pathogens that occurs in strawberry cultivation and leads to massive losses. Due to the rapid emergence of resistant strains in recent years, an ecofriendly disease management strategy needs to be developed to control this aggressive pathogen. Bacillus velezensis CE 100 exhibited strong antagonistic activity with 53.05% against B. cinerea by dual culture method. In the present study, 50% of culture filtrate supplemented into PDA medium absolutely inhibited mycelial growth of B. cinerea whereas the highest concentration (960 mg/L) of different crude extracts including ethyl acetate, chloroform, and n-butanol crude extracts of B. velezensis CE 100, strongly inhibited mycelial growth of B. cinerea with the highest inhibition of 79.26%, 70.21% and 69.59% respectively, resulting in severe damage to hyphal structures with bulging and swellings. Hence, the antifungal compound responsible was progressively separated from ethyl acetate crude extract using medium pressure liquid chromatography. The purified compound was identified as methyl hippurate by nuclear magnetic resonance and mass spectrometry. The inhibitory effect of methyl hippurate on both spore germination and mycelial growth of B. cinerea was revealed by its dose-dependent pattern. The spore germination rate was completely restricted at a concentration of 3 mg/mL of methyl hippurate whereas no mycelial growth was observed in agar medium supplemented with 4 mg/mL and 6 mg/mL of methyl hippurate by poisoned food method. Microscopic imaging revealed that the morphologies of spores were severely altered by long-time exposure to methyl hippurate at concentrations of 1 mg/mL, 2 mg/mL and 3 mg/mL and hyphae of B. cinerea were severely deformed by exposure to methyl hippurate at concentrations of 2 mg/mL, 4 mg/mL and 6 mg/mL. No significant inhibition on tomato seed germination was observed in treatments with methyl hippurate (2 mg/mL) for both 6 h and 12 h soaking period as compared to the controls. Based on these results, B. velezensis CE 100 could be considered a potential agent for development of environmentally friendly disease control strategies as a consequence of the synergetic interactions of diverse crude metabolites and methyl hippurate.

     

Biological control of Botrytis cinerea on tomato using naturally occurring fungal antagonists

Abstract

In order to evaluate the potential of naturally occurring filamentous fungi having potential as biocontrol agents effective against grey mould and post-harvest fruit rot caused by Botrytis cinerea on tomato, fungal saprophytes were isolated. They were obtained from leaves, fruits and flowers belonging to different species of cultivated and spontaneous Solanaceous plants collected at the horticultural area of La Plata, Argentina. Of 300 isolates screened for inhibition of B. cinerea using the dual culture technique on agar plate, 12 strains inhibited strongly mycelial growth of the pathogen. Among the antagonists one isolate of Epicoccun nigrum (126), four of Trichoderma harzianum (110, 118, 248 and 252) and four isolates of Fusarium spp. decreased the spore germination of B. cinerea between 30 and 70%. These isolates were probed on tomato fruits to evaluate their biocontrol activity against post-harvest grey mould. In growth chamber tests, E. nigrum (27), F. equiseti (22, 105) and T. harzianum (118, 252) reduced the diameter of fruit lesions by 50 – 90% and were selected for further biocontrol assays of tomato plants in the greenhouse. Although there were not significant differences between the treatments and the control, F. equiseti (105), E. nigrum (27) and T. harzianum (118) reduced by 20, 22 and 22 respectively the disease on whole plants. The targeted application of isolates of E. nigrum, T. harzianum and F. equiseti provides a promising alternative to the use of fungicide spray to control B. cinerea on tomatoes.     

Effect of volatile substances of Streptomyces platensis F-1 on control of plant fungal diseases

Headspace volatile substances (VS) produced by Streptomyces platensis F-1 were preliminarily identified using GC–MS. The effects of VS released by S. platensis F-1 on the control of leaf blight/seedling blight of rice caused by Rhizoctonia solani, leaf blight of oilseed rape caused by Sclerotinia sclerotiorum and fruit rot of strawberry caused by Botrytis cinerea, as well as on the growth of these three pathogenic fungi, were investigated. Results showed that sixteen volatile compounds were tentatively identified in 1-week-old cultures of S. platensis F-1 grown on autoclaved wheat seeds. They could be chemically grouped into alcohols, esters, acids, alkanes, ketones and alkenes. The most abundant composition in volatiles of S. platensis F-1 is geosmin, an earthy-muddy–smelling compound. Two antifungal compounds, phenylethyl alcohol and (+)-epi-bicyclesesquiphellandrene, were detected in the volatile profile of S. platensis F-1. Consistent fumigation of healthy tissues of rice, oilseed rape and strawberry to VS of S. platensis effectively reduced the incidence and/or the severity of leaf blight/seedling blight of rice (R. solani), leaf blight of oilseed rape (S. sclerotiorum) and fruit rot of strawberry (B. cinerea). A significant (P < 0.05) suppression of the mycelial growth of R. solani, S. sclerotiorum and B. cinerea by the VS of S. platensis was observed. The potential of using VS of S. platensis F-1 as a biofumigant to control plant fungal diseases is discussed.     

Antimicrobial activities of extracts of Cyperus rotundus L. rhizomes against some bacterial and fungal pathogens of strawberry and tomato

Antimicrobial activities of rhizome extracts of Cyperus rotundus were investigated on selected plant pathogenic bacteria and fungi. Ethyl acetate and hexane extracts showed antibacterial activity against three isolates of Clavibacter michiganensis subsp. michiganensis at concentrations of 900 and 1000 μg/ml. However, Gram-negative bacterial pathogens of tomato; Pseudomonas syringae pv. tomato and Ralstonia solanacearum were not inhibited from the extracts. Ethyl acetate extracts at 100 μg/ml inhibited mycelial growth and spore germination of the two strawberry isolates of Botrytis cinerea; however, no significant inhibition was found in tomato fungal pathogen, Fusarium oxysporum f. sp. radicis lycopersici. Minimum inhibitory concentrations were determined as 0.0625 and 0.125 mg/ml against C. michiganensis subsp. michiganensis for ethyl acetate and hexane extracts of rhizomes, respectively. This study shows the potentials of extracts of C. rotundus rhizomes as antimicrobial agents that are effective against the tested plant pathogenic bacteria and fungi.     

Antifungal Vapour‐phase Activity of a Combination of Allyl Isothiocyanate and Ethyl Isothiocyanate Against Botrytis cinerea and Penicillium expansum Infection on Apples

The potential use of allyl isothiocyanate (AITC) and ethyl isothiocyanate (EITC), singly and in combination, was tested in in vitro and in vivo trials for their effect on Penicillium expansum Link and Botrytis cinerea Persl. infection on apple when used as a fumigant. A 3 : 1 ratio of AITC : EITC was more efficient at reducing in vitro spore germination of P. expansum and B. cinerea than were other combinations or either AITC or EITC alone. The optimized combination showed the lowest EC₅₀ values, at 0.08 and 0.14 μg/ml air, for P. expansum conidial germination and mycelial growth, respectively, and 0.07 and 0.12 μg/ml air for B. cinerea conidial germination and mycelial growth, respectively. In in vivo trials, artificially infected apples were exposed for 4 days to an ITC‐enriched atmosphere. Among the ITCs tested, AITC, EITC and their combinations reduced incidence by more than 85% after 3–4 days of apple incubation at 20°C. Although further studies are necessary to evaluate any detrimental effects on apple quality, the evidence from this study supports the use of fumigation based on ITCs, and in particular a 3 : 1 combination of AITC and EITC, for control of postharvest mildew in apple fruit.