Influence of environmental conditions in a glasshouse on conidia ofBotrytis cinerea and on post-harvest infection of rose flowers

Quantification and horizontal distribution of air-borne inoculum ofBotrytis cinerea in a rose crop in a glasshouse of 300 m² was studied in 1991 and 1992. Conidia ofB. cinerea were caught in spore traps consisting of an agar medium selective forB. cinerea in Petri dishes placed within the crop, at flower height 1 m above the ground. Spore catches were counted as colonies, after incubation. Lesions due to conidial infection were counted on petals of rose flowers, also after incubation. Relative humidity (RH) and temperature within the glasshouse and global radiation and windspeed outside were recorded during the experiments. The horizontal distribution ofB. cinerea in a rose crop grown under glass was fairly uniform in both years. In 1991 a clear seasonal pattern in the number of colonies could not be found. In 1992 the number of colonies were high in August, September and October. The number of lesions on rose flowers showed a distinct pattern in both years. In August, September and October many lesions were counted whereas in the other months few lesions appeared. In linear regression analysis, variation in numbers of colonies (spore catches) could not be explained by environmental factors recorded during the experiments. Linear regression accounted for 76 and 63% of the variation in the number of lesions on rose flowers in 1991 and 1992, in terms of relative humidity (positively correlated), global radiation outside the glasshouse (negatively correlated) and, numbers of colonies on spore traps (positively correlated). The results in the rose crop suggest that RH, global radiation and spore density in glasshouses are important variables in regulating the numbers of lesions during storage and transport. The numbers of spores in glasshouses are dependent on the production system. A glasshouse with a system resulting in wet dead tissue on the ground give higher amount of spores in the glasshouse air and through that high numbers of lesions on flowers. On roses outside the glasshouses very high numbers of lesions were counted sometimes, mostly during and after rain showers, as a result of rain-deposition of spores onto the flowers.     

Effects of temperature,vapour pressure deficit and radiation on infectivity of conidia ofBotrytis cinerea and on susceptibility of gerbera petals

The effect of vapour pressure deficit, temperature and radiation on the postharvest susceptibility of gerbera flowers toB. cinerea, on the water relations of gerbera flowers and on the lesion formation after conidial infection ofB. cinerea was studied. The temperature range in whichB. cinerea could germinate and growin vitro is 5–30 °C. In climate chamber experiments flowers had more lesions ofB. cinerea at temperatures of 20 and 25 °C than at 10 and 15°C. At 15, 20 and 25°C the infectivity ofB. cinerea conidia was negatively affected during a storage-period of 7 days. At a vapour pressure deficit (VPD) of 200 Pa significantly more conidia ofB. cinerea were infective than at 800 Pa. At a VPD of 800 Pa the susceptibility of gerbera flowers forB. cinerea was not significantly different than at 200 Pa. High radiation levels in glasshouses in spring and summer negatively influenced the infectivity of conidia ofB. cinerea on the flower surface, but did not affect the susceptibility of gerbera flowers forB. cinerea. In spring and early summer conidia lost their infectivity at high radiation levels, high temperatures and high levels of VPD. In summer gerbera flowers could be more susceptible toB. cinerea because of high temperatures in glasshouses, but the negative effect of radiation on the conidia ofB. cinerea seemed to overrule the temperature effect. Thus, the numbers of lesions in spring and summer can be low compared with the numbers in other seasons, although the numbers ofB. cinerea colonies on spore traps can be high. The effect of temperature on the susceptibility of gerbera flowers can probably be explained by changes of water status in the petals. At higher temperatures the number of lesions and the turgor (=water potential—osmotic potential) in the petals increased. Temperatures <10°C during lesion formation (RH>95% and VPD<50 Pa) had a temporary negative effect on the number of lesions. After 3 days of incubation the numbers of lesions were about equal (30 lesions/cm²) from 5 to 20°C. At 30°C no lesion formation was observed even after 3 days.     

Effects of temperature,relative humidity and age of conidia on the incidence of spotting on gerbera flowers caused by Botrytis cinerea

In recent years, spotting of ray florets of gerbera flowers has become an important problem. This type of small necrotic lesions may occur before, but especially shortly after harvesting the flowers.Botrytis cinerea was easily isolated from such lesions. Inoculation withB. cinerea only gave typical necrotic lesions, when dry conidia were dusted on the flowers with a short period of high rh after inoculation. At 18–25 °C a high rh for at least 5 hours was necessary. Rotting of ray florets and receptacles byB. cinerea occurred when inoculated flowers were kept wet for a few days. Spots consist of one to several necrotic, usually epidermal cells. A single conidium could give rise to a necrotic lesion after germination. Germination of conidia and lesion formation occurred between 4 and 25 °C; at 30 °C, germination and lesion formation did not occur. Between 18 and 25 °C, many lesions became visible within 1 day after inoculation; at 4 °C it took 2 to 3 days before lesions could be seen. If kept dry, conidia ofB. cinerea remained ungerminated on ray florets of gerbera flowers and could be removed from the ray florets. Within 1 day at high rh, germination occurred and lesions were produced. Conidia ofB. cinerea, stored dry, were able to survive much longer than the lifetime of a gerbera flower. Even after storage at room temperature for up to 14 months, some conidia were able to germinate in vitro and on ray florets and induce the formation of lesions. Addition of gerbera pollen diffusate stimulated germination and lesion formation.     

Influence of environmental conditions on dispersal of Botrytis cinerea conidia and on post-harvest infection of gerbera flowers grown under glass

Dispersal of Botrytis cinerea in a gerbera crop grown in two glasshouses 30 km apart was studied over a period of 18 months, in 1988 and 1989. Conidia were caught in spore traps consisting of agar in petri dishes exposed at different heights in the crop in each glasshouse. No seasonal patterns could be identified in the spore catches, assessed as colonies on the agar traps after incubation. The number of lesions caused by conidial infection of gerbera flowers following incubation, however, showed a distinct pattern. In spring and early summer few lesions were recorded whereas at other times of the year many lesions appeared. In linear regression analysis, variation in numbers of colonies (spore catches) could not be explained by environmental factors recorded during the experiments. Linear regression accounted for 77% and 81% of the variation in the number of lesions on flowers in the two glasshouses, in terms of relative humidity (postively correlated), global radiation outside the glasshouse (negatively correlated) and age of the crop (positively correlated). Despite differences in the systems by which the gerbera crop was produced and in the spore catches, the numbers of lesions on gerbera flowers in the two glasshouses were significantly correlated though not significantly different from each other.     

A selective medium for Botrytis cinerea to be used in a spore-trap

A selective medium has been developed for the use in spore-traps to study the dispersion ofB. cinerea on gerbera grown in glasshouses.Samenvatting Een selectief medium voorB. cinerea is, ontwikkeld voor het gebruik in sporevangers. Deze sporevangers werden gebruikt bij het bestuderen van de ontwikkeling vanB. cinerea in gerbera geteeld onder glas.     

Epidemiology of Grey Mould in Annual Waiting-bed Production of Strawberry

The epidemiology of Botrytis cinerea was studied in five annual strawberry crops using waiting-bed transplants, a system widely adopted in the Netherlands. On dead leaves of transplants the incidence of B. cinerea varied from 26.7% to 52.6%, but the leaf area with potential sporulation was low (3.5–15.6%). During each crop cycle, the availability of necrotic leaf substrate for spore production of B. cinerea was generally low and varied between seasons and with the quality of transplants. B. cinerea sporulated on a maximum of 15.5 cm² of leaf area per plant, measured as potential sporulation. The aerial concentration of B. cinerea conidia in untreated plots did not differ from the concentration in plots where all dead leaves had been removed, nor from the concentration at 25–50 m distance from the strawberry plots. B. cinerea incidence on flowers ranged from 5% to 96%, but no correlation was found with the potential spore production on necrotic leaves. Grey mould at harvest varied from 1.4% to 11.3% and was correlated with the average precipitation during the harvesting period but not with B. cinerea incidence on flowers. Post-harvest grey mould ranged from 2.1% to 32.6% and was correlated with petal colonisation by B. cinerea. The results suggest that in the annual cropping system with waiting-bed transplants, necrotic leaves are not a significant source of B. cinerea inoculum, unlike in other strawberry production systems. Therefore, control measures of grey mould in this annual system should focus on protection of flowers and young developing fruits, and not on the reduction of inoculum production on leaf debris.     

Periodicity and gradients in dispersal ofAlternaria linicola in linseed crops

Conidia ofAlternaria linicola produced on infected linseed crops were mainly dispersed by wind. The numbers of conidia in the air above linseed crops collected by a Burkard spore sampler were greatest between 1200 h and 1300 h, when the relative humidity was lowest. Although numbers of conidia collected decreased with increasing height within and above the crop canopy, air-borneA. linicola conidia were present up to 80 cm above the crop canopy. Conidia ofA. linicola were transported by wind up to at least 40 m downwind from an artificial line inoculum source, but their numbers decreased with increasing distance from the source. In 1991, 1992, and 1993, the dispersal ofA. linicola conidia above linseed crops followed a seasonal periodicity which was influenced by weather conditions and cultural practices. The greatest numbers of conidia were collected during July, August and early September and coincided with periods favourable for sporulation and with an increase in the incidence of the disease in the senescent crop. Air-borneA. linicola conidia produced on point or line inoculum sources (naturally infected linseed stem debris) were responsible for the spread of the disease in linseed crops. In 1992 and 1993, the disease was first detected downwind from the sources, but by the end of the growing seasons, it had spread in all directions and up to 20 m and 60 m from the sources, respectively. Disease gradients were initially steep near the inoculum sources but they became flatter with time due to the secondary spread of the disease.     

The Effect of Treatment With Ulocladium Atrum on Botrytis Cinerea-attack of Geranium (Pelargonium Zonale) Stock Plants and Cuttings

In two successive seasons, the effect of treatment of geranium stock plants with the competitive saprophytic fungus Ulocladium atrum as a biocontrol agent against Botrytis cinerea was compared to a fungicide treatment with Euparene M. B. cinerea incidence and severity on the stock plants, B. cinerea spore load in the air around stock plants and death of cuttings due to B. cinerea were scored. B. cinerea incidence and severity were much stronger in the second than the first experiment. This was quantitatively expressed by higher numbers of conidia of B. cinerea monitored in the second than the first year, both on necrotic (a maximum for the control of 27.5 × 10⁶ spores per sample - all necrotic leaves of five plants - in experiment 1 against 86 × 10⁶ in experiment 2) and green leaves, but numbers of conidia of B. cinerea recovered from the air were only slightly different. The death rate of cuttings was moderate in the first and extremely high in the second experiment. For the fungicide treatment, maximum sample values of 7% and 76% of 6-week old cuttings were killed in the first and the second experiment respectively. Treatment with U. atrum was effective in reducing all parameters studied. With the exception of the spore load of B. cinerea in the air and the success of cuttings, the effect of U. atrum varied from as good as the fungicide to half as effective. In the first trial, only Euparene M reduced spore load in the air, in the second trial only U. atrum consistently did so. In the first trial U. atrum reduced death of 4-week old cuttings, though less than fungicide (1.2, 20 and 38% killed with fungicide treatment, U. atrum treatment and control respectively). In the second trial only the fungicide reduced loss of cuttings. The impact of the data on the integration of U. atrum in a control system of B. cinerea in geranium is discussed.     

Relations between glasshouse climate and dry weight of petals,epicuticular wax,cuticle, pre-harvest flowering period and susceptibility toBotrytis cinerea of gerbera and rose flowers

Studies were conducted on the effects of seasonal levels of relative humidity, temperature, and total radiation, on dry weight of petals, on fresh weight of epicuticular wax and of cuticle of petals, on numbers ofBotrytis cinerea lesions in petals, and on preharvest flowering periods in gerbera and rose. No temporal relationships or significant correlations were found among dry weight of petals, weight of wax and cuticle of petals, and numbers of lesions on the petals. Temperature, relative humidity and total radiation did not correlate significantly with dry weight of petals, or with fresh weights of wax and cuticle of petals, except for a positive correlation between relative humidity and cuticle weight in the gerbera cultivar Delphi. No relation was found between weight of epicuticular wax and cuticle of petals and susceptibility of gerbera and rose petals toB. cinerea. The thickness of wax and cuticle on flowers did not seem to be an important factor influencing the susceptibility of flowers toB. cinerea. The seasonal pattern in number of lesions produced on the flowers byB. cinerea was related to the effects of relative humidity and radiation on infectivity of conidia of the pathogen on the flower surface but not to the effects on the susceptibility of flowers.     

Effect of interrupted leaf wetness periods on suppression of sporulation ofBotrytis allii andB. cinerea by antagonists on dead onion leaves

Saprophytic antagonists were evaluated for suppression of sporulation ofBotrytis allii andB. cinerea on artificially killed segments of onion leaves that were pre-inoculated with the pathogens. During incubation of the antagonisttreated leaf segments in moist chambers, periods of leaf wetness and leaf dryness were alternated to simulate conditions in the field. Interruption of humid conditions with dry periods had a differential effect on antagonists.Alternaria alternata, Chaetomium globosum, Ulocladium atrum andU. chartarum suppressed sporulation ofB. allii almost completely under continuously wet conditions, and when the leaf wetness periods were interrupted with drying periods of 9h imposed 16, 40, and 64 h after the antagonists were applied. When leaf wetness was interrupted 16 h after antagonist application, the number of conidia ofB. allii produced cm^–2 leaf surface after eight days was under the detection limit of 5.2 × 10³ conidia on leaves treated with these antagonists compared to 3.7 × 10⁵ conidia on leaves that were not treated. On the other hand,Gliocladium roseum, G. catenulatum andSesquicillium candelabrum, all highly efficient under continuously wet conditions, were of low to moderate efficiency when leaf wetness periods had been interrupted 16 h after application of the antagonists. The antagonists showed the same differentiation and sensitivity to interrupted wetness periods when tested withB. cinerea.     

Development ofClonostachys rosea and interactions withBotrytis cinerea in rose leaves and residues

The effect of microclimate variables on development ofClonostachys rosea and biocontrol ofBotrytis cinerea was investigated on rose leaves and crop residues. C.rosea established and sporulated abundantly on inoculated leaflets incubated for 7–35 days at 10°, 20° and 30°C and then placed on paraquat—chloramphenical agar (PCA) for 15 days at 20°C. On leaflets kept at 10°C, the sporulation after incubation on PCA increased from 60% to 93% on samples taken 7 to 21 days after inoculation, but decreased to 45% on material sampled after 35 days. A similar pattern was observed on leaves incubated at either 20° or 30°C. The sporulation ofC. rosea on leaf disks on PCA was not affected when the onset of high humidity occurred 0, 4, 8, 12 or 16 h after inoculation. However, sporulation was reduced to 54–58% on leaflets kept for 20–24 h under dry conditions after inoculation and before being placed on PCA. The fungus sporulated on 68–74% of the surface of leaf disks kept for up to 24 h at high humidity after inoculation, but decreased to 40–51% if the high humidity period before transferral to PCA was prolonged to 36–48 h. The growth ofC. rosea on leaflets was reduced at low inoculum concentrations (10³ and 10⁴ conidia/ml) because of competition with indigenous microorganisms, but at higher concentrations (10⁵ and 10⁶ conidia/ml) the indigenous fungi were inhibited. Regardless of the time of application ofC. rosea in relation toB. cinerea, the pathogen’s sporulation was reduced by more than 99%. The antagonist was able to parasitize hyphae and conidiophores ofB. cinerea in the leaf residues. AsC. rosea exhibited flexibility in association with rose leaves under a wide range of microclimatic conditions, and in reducingB. cinerea sporulation on rose leaves and residues, it can be expected to suppress the pathogen effectively in rose production systems.     

Relationship between Concentrations of Botrytis Cinerea Conidia in Air, Environmental Conditions, and the Incidence of Grey Mould in Strawberry Flowers and Fruits

Atmospheric concentrations of Botrytis cinerea conidia were monitored for two seasons in a strawberry crop in Moguer (Huelva, southwestern Spain). Concentrations of conidia were estimated using a Burkard volumetric spore sampler. A diurnal pattern of conidial release was observed. Airborne conidial concentration was significantly and positively correlated with the average solar radiation and mean temperature, and negatively with rainfall and relative humidity. Among the weather variables considered, solar radiation showed the most consistent results in the regression analysis, explaining over 40% of airborne conidial concentration variability. Correlation between Botrytis fruit rot incidence and accumulated number of conidia over seven days was significant and positive. Two regression models containing three variables explained over 62 and 52% of the fruit rot incidence variability. A positive but non-significant correlation was established between B. cinerea incidence in flowers and airborne conidial concentration. It was not possible to fit a consistent regression model to relate flower infection incidence to conidial concentration or weather variables.     

Acute ozone exposure predispose Phaseolus vulgaris beans to botrytis cinerea

The impact of ozone in predisposingPhaseolus vulgaris toBotrytis cinerea has been investigated. One day after 8 h exposures to 0, 120, 180 and 270 g ozone m^–3, primary and trifoliate leaves of four bean cultivars were detached and inoculated with conidia suspended in water or in an inorganic phosphate (Pi) solution. Visible ozone injury increased with increasing ozone concentrations in all cultivars. Primary leaves were more sensitive than trifoliate leaves. Conidia suspended in Pi solution caused lesions on healthy leaves, whereas conidia in water did not. Ozone-injured leaves of all cultivars showed lesions byB. cinerea after inoculations in water. The number of lesions was significantly correlated with ozone injury for primary leaves. After Pi inoculations, the number of lesions on the ozone-sensitive cultivars also increased with increasing ozone concentrations. However, the ozone-tolerant cultivar Groffy showed first a decrease in the Pistimulated infection at the lowest ozone dosages. The trifoliate leaves of all cultivars were less predisposed to the fungus than the primary leaves. The results indicate that realistic concentrations of ozone enhance the predisposition of bean leaves toB. cinerea. The rate of enhancement depends on the level of ozone-induced injury which was influenced by cultivar, leaf and ozone concentrations.Samenvatting De invloed van ozon op de vatbaarheid van boon voorBotrytis cinerea werd onderzocht. Een dag na de blootstelling van vier bonecultivars gedurende 8 uur aan 0, 120, 180 en 260 g ozon m^–3, werden primaire en drietallige bladeren geïnoculeerd met conidiën in water of in een anorganische fosfaatoplossing (Pi). Zichtbare beschadiging door ozon nam met de concentratie toe in alle cultivars. De primaire bladeren waren gevoeliger dan de drietallige. In tegenstelling tot conidiën in water, verooraakten conidiën in de Pi-oplossing lesies op gezonde bladeren. Bij ozonbeschadiging vertoonden bladeren van alle cultivars lesies doorB. cinerea na inoculatie in water. Voor primaire bladeren was het aantal lesies significant gecorreleard met de bladbeschadiging. Na Pi-inoculatie nam bij de ozongevoelige cultivars het aantal lesies ook toe met de concentratie ozon. Echter, de ozontolerante cultivar Groffy vertoonde eerst een afname in de door Pi gestimuleerde infectie bij de laagste ozonconcentratie. De door ozon verhoogde vatbaarheid van drietallige bladeren was minder dan die van primaire bladeren. De resultaten tonen aan dat realistische concentraties van ozon boon vatbaarder maken voorB. cinerea. Deze stijging in vatbaarheid is afhankelijk van het niveau van de ozonbeschadiging die wordt beïnvloed door cultivar, soort blad en ozonconcentratie.     

Natural occurrence of and inoculation experiments withConidiobolus coronatus andConidiobolus sp. in glasshouse populations ofBemisia tabaci

Bemisia tabaci (Gennadius), the sweetpotato whitefly, has only one known entomophthoralean pathogen,Erynia radicans (Entomophthoraceae). Two new pathogens have been isolated recently from a glasshouse population of this pest:Conidiobolus coronatus and another, undescribed species ofConidiobolus (Entomophthorales: Ancylistaceae). Artificial inoculation experiments revealed that eggs ofB. tabaci are practically immune to infection by either species. Second-instar larvae are highly resistant, only high doses of conidia causing between <1% and 4.6% mortality. Adults were found to be much more susceptible. Doses of 60 conidia/mm² ofC. coronatus caused average mortalities ofca 95%. The maximum mortality of adults caused byConidiobolus sp. was much lower,ca 30%, at a dose of 210 conidia/mm². The incubation period (inoculation to death) for both species, under our experimental conditions, is very short: 18–24 h forC. coronatus and 30 h forConidiobolus sp. Both fungi produced loricoconidia (conidia metamorphosed into resting spores) on cotton leaves and other dry surfaces. This ability allowedConidiobolus sp. to remain viable for 17–21 days on cotton leaves, in glasshouse conditions and in the absence of hosts, whileC. coronatus persisted for 10–14 days.     

Effects of triazole fungicides on sterol biosynthesis during spore germination of Botrytis cinerea,Venturia inaequalis and Puccinia graminis f. sp. tritici

With three plant pathogens,Botrytis cinerea, Venturia inaequalis and Puccinia graminis f. sp.tritici, the time course of sterol biosynthesis during spore germination was examined by labeling experiments along with the question whether this pathway could be inhibited by triazole fungicides. Conidia ofB. cinerea andV. inaequalis are able to synthesize sterols immediately after the beginning of the germination process when the germ tubes have not yet emerged. On the contrary uredospores ofP. graminis start sterol biosynthesis after 6 to 8 h germination time almost at the end of the germ tube phase, indicating that sterol reserves of the spores are likely to be used for the germ tube growth.The sterol C-14 demethylation appeared to be the rate limiting step within the sterol biosynthetic pathway: the half life of 24-methylenedihydrolanosterol was less than 1 h forB. cinerea. It was more than 1 h forV. inaequalis and 3 h forP. graminis. Independent of these differences in the time course of sterol biosynthesis and in the C-14 demethylation rate, the synthesis of sterols in germinating spores was strongly inhibited by triazole fungicides in all three pathogens examined. In contrast toP. graminis, this inhibition could be demonstrated withB. cinerea andV. inaequalis even in ungerminated conidia, indicating that the fungicides were rapidly taken up and reached their target within 1 or 2 h. These results are discussed along with the question whether spore germination can be used as a bioassay for the estimation of sensitivities of triazole fungicides.     

Use of sclerotia of<Emphasis Type="Italic">Sclerotinia sclerotiorum</Emphasis> for efficient production of conidia of<Emphasis Type="Italic">Coniothyrium minitans</Emphasis> in liquid culture

A study was conducted to determine the feasibility of using sclerotia ofSclerotinia sclerotiorum for producing conidia ofConiothyrium minitans in liquid culture. The medium (SST) was made of water containing 2.0, 1.5, 1.0 or 0.5% (w/v) ground sclerotia ofS. sclerotiorum and 100 μgl ⁻¹ thiamine hydrochloride (HCl). One ml of conidial suspension (2 × 10⁷ conidia ml⁻¹) ofC. minitans LRC 2534 was inoculated into 100 ml of SST medium or control (thiamine HCl in water) and incubated at 20 ± 2°C on a shaker at 200 rpm. Subsamples were removed periodically and examined under a compound microscope. Conidia in the SST media germinated within 24 h, developed into branched hyphae within 48 h, produced pycnidia after 3–4 days, and the pycnidia released mature conidia after 7 days. Production of conidia varied with the concentration of sclerotia in the SST medium. It was lower (3.6 × 10⁶ conidia ml⁻¹) at 0.5% but higher (1.2 × 10⁸ conidia ml⁻¹) at 2%. The new conidia were viable and the colonies developing from them showed the original morphological characteristics. It was concluded that using SST liquid medium as a substrate for mass production of conidia ofC. minitans has potential for use in commercial development of this mycoparasite as a biocontrol product. http:www.phytoparasitica.org posting Jan. 23, 2007.     

Control of infection and sporulation ofBotrytis cinerea on bean and tomato by saprophytic bacteria and fungi

Sixty isolates of saprophytic microorganisms were screened for their ability to reduce the severity of grey mould (Botrytis cinerea) infection and sporulation. Isolates of the bacteriaXanthomonas maltophilia, Bacillus pumilus, Lactobacillus sp., andPseudomonas sp. and the fungusGliocladium catenulatum reduced germination of conidia of the pathogen and controlled disease on bean and tomato plants. Their activity under growth room conditions was good, consistent, and similar to the activity of the known biocontrol agent,Trichoderma harzianum T39 (non-formulated). Although the tested isolates may for nutrients with the germinating conidia ofB. cinerea, resistance induced in the host by live or dead cells were also found to be involved. Inhibitory compounds were not detected on treated leaves. Sporulation ofB. cinerea after its establishment on leaves was also reduced by the above mentioned isolates and byPenicillium sp.,Arthrinium montagnei, Ar. phaeospermum, Sesquicillium candelabrum, Chaetomium globosum, Alternaria alternata, Ulocladium atrum, andT. viride. These sporulation-inhibiting fungi did not reduce the infection of leaves byB. cinerea. Most of these selected fungi and bacteria were capable of reducing lesion expansion.     

Synthesis of 2-amino-6-oxocyclohexenylsulfonamides and their activity against Botrytis cinerea

BACKGROUND: With the objective of exploring the fungicidal activity of 2‐oxocyclohexylsulfonamides (2), a series of novel 2‐amino‐6‐oxocyclohexenylsulfonamides (6 to 23) were synthesised, and their fungicidal activities against Botrytis cinerea Pers. were evaluated in vitro and in vivo. RESULTS: The compounds were characterised by IR, ¹H NMR and elemental analysis. Bioassay results of mycelial growth showed that compounds 6 to 23 had a moderate antifungal activity against B. cinerea. N‐(2‐methylphenyl)‐2‐(2‐methylphenylamino)‐4,4‐dimethyl‐6‐oxocyclohexenylsulfonamide (13) and N‐(2‐chlorophenyl)‐2‐(2‐chlorophenylamino)‐6‐oxocyclohexenylsulfonamide (21) showed best antifungal activities, with EC₅₀ values of 8.05 and 10.56 µg mL^?1 respectively. Commercial fungicide procymidone provided an EC₅₀ value of 0.63 µg mL^?1. The conidial germination assay showed that most of compounds 6 to 23 possessed excellent inhibition of spore germination and germ‐tube elongation of conidia of B. cinerea. For in vivo control of B. cinerea colonising cucumber leaves, the compound N‐cyclohexyl‐2‐(cyclohexylamino)‐4,4‐dimethyl‐6‐oxocyclohexenylsulfonamide (19) showed a better control effect than the commercial fungicide procymidone. CONCLUSION: The present work demonstrated that 2‐amino‐6‐oxocyclohexenylsulfonamides can be used as possible new lead compounds for further developing novel fungicides against B. cinerea. Copyright © 2011 Society of Chemical Industry     

Effect of Inoculum Rates and Sources of Coniothyrium minitans on Control of Sclerotinia sclerotiorum Disease in Glasshouse Lettuce

Coniothyrium minitans isolate Conio grew on both maizemeal-perlite and ground maizemeal-perlite, producing high numbers (1.6×10⁷ conidiag^–1 inoculum) of germinable conidia. Coniothyrium minitans isolate Conio applied as a preplanting soil incorporation of maizemeal-perlite inoculum at full application rate (0.6lm^–2; 10¹¹ colony forming units (cfu)m^–2) significantly reduced Sclerotinia disease in a sequence of three lettuce crops grown in a glasshouse. No reduction in disease was achieved with any of the reduced rate treatments (10⁸cfum^–2) of a range of C. minitans isolates (Conio ground maizemeal-perlite at reduced rate, Conio and IVT1 spore suspensions derived from maizemeal-perlite, IVT1 spore suspension derived from oats and Contans® WG spore suspension). After harvest of the second and third crops, C. minitans maizemeal-perlite at full rate reduced the number and viability of sclerotia recovered on the soil surface and increased infection by C. minitans compared with spore suspension and reduced rate maizemeal-perlite inocula. Coniothyrium minitans was recovered from the soil throughout the trial, between 10⁵ and 10⁷cfucm^–3 in maizemeal-perlite inoculum full rate treated plots and 10¹–10⁴cfu cm^–3 in all other inoculum treated plots.Pot bioassays were set up corresponding to the inoculum used in the glasshouse, with the addition of Conio ground maizemeal-perlite at a rate corresponding to the full rate maizemeal-perlite. Coniothyrium minitans maizemeal-perlite and ground maizemeal-perlite at full rate significantly decreased carpogenic germination, recovery and viability of sclerotia and increased infection of sclerotia by C. minitans in comparison with spore suspension treatments, reflecting results of the glasshouse trials. Additionally, reduced maizemeal-perlite treatment also decreased apothecial production, recovery and viability of sclerotia compared with the spore suspension treatment, despite being applied at similar rates. Simultaneous infection of sclerotia by several isolates of C. minitans was demonstrated. Inoculum level in terms of colony forming unitscm^–3 of soil appears to be a key factor in both control of Sclerotinia disease and in reducing apothecial production by sclerotia.     

Survival of dicarboximide-resistant strains ofBotrytis cinerea in plant debris during summer in Israel

Survival- ofBotrytis cinerea was monitored during two summer seasons. Mycelium and conidia were found dead on the surface of plant debris within 2 months of incubation, whereas a high level of viability was detected in thallus of the pathogen which was 1–2 mm inside the dry host tissue. Of the 148 samples of infected senescing cucumber female fruits, 8% survived seven warm months; half of these isolates ofB. cinerea were resistant to dicarboximides (5 (μ/ml iprodione). Of the stems of cucumber infected withB. cinerea in winter, 18% yielded the pathogen at the beginning of the following winter; 15% of the surviving isolates were resistant to dicarboximides. Cucumber seedlings artificially infected byB. cinerea did not yield the pathogen longer than 9 weeks after establishment of infection, even when incubated in the shade. Plant debris with symptoms of gray mold were kept in the shade during the summer; at the beginning of winter it was possible to establish infection ofB. cinerea from the dry debris.