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.     

Microscopical studies of the infection of gerbara flowers byBotrytis cinerea

The formation of lesions on ray florets of gerbera flowers caused by single conidia ofBotrytis cinerea was studied in two cultivars infected by two isolates of the pathogen. No differences in reaction after inoculation with conidia of either isolate were seen on either cultivar. The conidia produced usually one germ tube not longer than 10 m, but conidia with five germ tubes were also seen. Direct penetration of germ tubes through the upper cuticle of ray florets was observed. No appressoria or other specialised structures were observed before penetration, and degradation of the cuticle did not occur. Germination of conidia and subsequent flower infection was dependent on the availability of free water, but not on the addition of external nutrients.Between 18 to 25°C, fungal development usually stopped after cuticle penetration, two to four cells around the site of penetration becoming necrotic. This number did not increase when inoculated flowers were subsequently placed at 4°C, conditions conductive for the formation of spreading lesions. When flowers were incubated constantly at 4°C, lesions became visible 3 days after inoculation as a group of 10 to 14 cells. Initially from a vesicle-like structure, mycelium spread subcuticularly or in the lumen of epidermal cells resulting in the death of 40 to 50 cells at 18 days after inoculation. Ungerminated conidia and conidial germlings which has not yet penetrated the cuticle did not cause any visible symptoms in underlying epidermal cells.     

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.     

Horizontal and vertical distribution of airborne conidia of Botrytis cinerea in a gerbera crop grown under glass

The horizontal and vertical distribution of airborne conidia ofBotrytis cinerea in a gerbera crop in two glasshouses (100 m² and 350 m²) was studied during 18 months in 1988 and 1989. Conidia ofB. cinerea were caught in simple spore traps consisting of agar in Petri dishes placed in a regular pattern at three different heights in the glasshouse and counted as colonies, after incubation. Lesions due to conidial infection were counted on gerbera petals. The horizontal and vertical distribution of conidia ofB. cinerea in a gerbera crop grown under glass was fairly uniform in both distinct glass-houses. Conidia ofB. cinerea trapped in a glasshouse can originate from sources inside and outside the glasshouse. No significant interaction was found between location and time for the colony counts and for the log transformed (ln(N+1)) lesion counts. The results of this study suggest that spore trapping at one height and at a limited number of locations and dates is sufficient for efficient monitoring ofB. cinerea in a glasshouse.     

Influence of environmental factors on conidial germination and survival of Sphaeropsis pyriputrescens

Sphaeropsis pyriputrescens is the cause of Sphaeropsis rot in apples and pears. In this study, effects of temperature, wetness duration, relative humidity (RH), dryness, and interrupted wetness duration on conidial germination of the fungus were evaluated. Conidial germination and germ tube elongation occurred at temperatures from 0°C to 30°C. The optimum temperature for germination and germ tube elongation appeared to be 20°C, at which a minimum wetness period of 5 h was required. Conidia germinated at RH as low as 92% after 36 h at 20°C, but not at 88.5% RH. The effect of dry periods on germination depended on RH. Conidial germination at 85% RH was higher than that at 25% RH within a 4-h dry period, after which time no difference was observed. Less than 10% conidia germinated after a 10-day dry period at both 20°C and 28°C. Conidial germination decreased as the wetness duration prior to dryness increased. Conidia wetted for 6 h prior to dryness died within a 1-h dry period. After a 12-h dry period, no or few conidia germinated at 25% RH, whereas 3% to 10% of the conidia germinated at 85% RH and no further decrease was observed as the dry period increased. The results contribute to our understanding of conditions required for conidial germination of S. pyriputrescens and infection of fruit leading to Sphaeropsis rot.     

Studies on red light-induced resistance of broad bean to Botrytis cinerea: I. Possible production of suppressor and elicitor by germinating spores of pathogen

When detached broad bean leaves were preinoculated with virulent strain B304 of Botrytis cinerea 24 h before a challenge inoculation with strain B304, lesion formation by B304 was significantly inhibited in red light but not in the dark. In leaves that were preinoculated with avirulent strain 021 and then challenged by B304, however, lesion formation was not inhibited even under red light. Such differences in lesion formation after the challenge inoculation with an avirulent strain were also observed with lesions caused by Alternaria alternata, a nonpathogen of broad bean and by avirulent strain 021R in the presence of germination fluid from spores of strains B304 and 021R. These results suggest the possibility that virulent B. cinerea produced a suppressor involved in induced susceptibility and an elicitor involved in resistance induced by red light during spore germination.     

Appearance of a new leaf rot disease on common ice plant

An unknown disease abruptly appeared on hydroponic cultures of common ice plant (Mesembryanthemum crystallinum) in the greenhouse, causing catastrophic damage. Although the symptoms of the plant were unlike typical Botrytis lesions on leaves and stems of other plants, fungi isolated from the necrotic lesions on the plant were similar to genus Botrytis in terms of conidial shape, colony color and nature. A representative isolate, Ice-2, caused similar symptoms on the host plants after inoculation with conidia, and the same fungus was isolated from the lesions. The conidia and conidiophores of Ice-2 were morphologically similar to those of B. cinerea but not to those of B. allii, B. fabae or B. squamosa. The tested Botrytis fungi grew at temperatures between 5 and 30°C. Ice-2 grew faster than the others at the lower end of the temperature range. Ice-2 was also more virulent than B. cinerea (Bay-1) in artificial inoculations, especially on common ice plant leaves. The glyceraldehyde-3-phosphate dehydrogenase gene (G3PDH) sequence of Ice-2 was determined and compared with those from four Botrytis species. The gene sequence of Ice-2 appeared to be identical to that of B. cinerea. In leaf tests on common ice plant and kidney bean, the diseases caused by Ice-2 and Bay-1 were controlled equally well by the primary Botrytis fungicides. Based on the results of the present studies, Ice-2 is thought to be Botrytis cinerea Person: Fries.     

Production of <Emphasis Type="Italic">Guignardia bidwellii</Emphasis> conidia on grape leaf lesions is influenced by repeated washing events and by alternation of dry and wet periods

The ascomycete Guignardia bidwellii is an economically important pathogen in many grapevine-growing areas. Primary infections are caused by ascospores and conidia produced in mummified berries and in cane lesions. Secondary infections are caused by the conidia produced by pycnidia formed in leaf lesions and, in later season, in rotted berries. Environment-controlled experiments were conducted to study the production dynamics of G. bidwellii conidia on grape leaf lesions as influenced by: i) repeated washing events, and ii) alternate dry and wet periods. Under optimal environmental conditions (25 °C, 100 % relative humidity), production of conidia declined over washings and was almost completely depleted after four washings. When pycnidia were kept in a low humidity environment (average of 54 % relative humidity) between two successive washings, the production of conidia progressively diminished as the time between washings increased, with few conidia being still produced after 87 days. This decline in conidial production was faster at 29 °C than at 20 °C. This information is relevant in that it determines the potential of black-rot lesions to produce conidia along the grape-growing season and, therefore, their contribution to epidemic development.     

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.     

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.     

Effect of microclimate and nutrients on development of cucumber gray mold (Botrytis cinerea)

Infection of young parthenocarpic cucumber fruits byBotrytis cinerea begins in the petals. Removing petals or washing nutrients from the flower significantly reduced infection. Germination of conidia occurred at relative humidity (r.h.) above 92%, but when water deposition on artificial surfaces was prevented, germination did not occur even at 98% r.h. Germination of conidia on petals is promoted by deposition of an aqueous film not visible on the petal surface by the bare eye (but demonstrable by CoCl₂). Provided there is a film of water on the surface of the host, germination and the infection process occur at a wide range of temperatures up to 25 °C. Pre-exposure of cucumber plants at temperatures as high as 30 °C or as low as 8 °C, prior to their infection and incubation under conditions conducive to gray mold, resulted in greater severity of the disease on young fruits or leaves as compared with plants previously incubated at 10-25 °C. The relevance of these results to cultural control of gray mold is discussed.     

Laboratory shelf-life of oil-formulated conidia of the locust and grasshopper fungal pathogen Metarhizium flavoviridae Gams & Rozsypal,in mixtures with the pyrethroid insecticide lambda-cyhalothrin

The addition of 20 ppm lambda-cyhalothrin pyrethroid insecticide to Metarhizium flavoviridae (Fungi: Deuteromycetes) dry conidia in oil kept germination above 80% for 2 and 12 months at temperatures of approximately 30 and 8°C respectively. At 30°C, conidia in oil alone maintained viability for only a few weeks, but this was doubled at 8°C. Even dry conidia retained good viability for only 5 months at the higher temperature. The extended viability of conidia given by adding the pyrethroid to the oil formulation is regarded as very valuable for areas where the fungus is to be used against locusts and grasshoppers.     

Histology of waxflower (Chamelaucium spp.) flower infection by Botrytis cinerea

Botrytis cinerea infects waxflower (Chamelaucium spp.) flowers and can induce them to abscise from their petioles before disease becomes evident. Botrytis cinerea infection of flowers was studied on two waxflower cultivars by light and electron microscopy. Pot‐grown waxflower flowers were harvested, inoculated with aqueous suspensions of B. cinerea conidia, incubated at 20–22°C and >95% RH and examined within 96 h post‐inoculation (hpi). Conidial germination on petals started 4 hpi, penetration via germ tube tips was 6 hpi and protoappressoria were formed 8 hpi. Germination on petals approximately doubled every 4–6 h to 18 hpi. Conidial germination was ca. 50% at 22–24 hpi. Botrytis cinerea infected most waxflower flower organs, including petals, anthers and filaments, stigma and hypanthium, within 24 hpi. Hyaline and lobate appressoria were observed 36 hpi. Infection cushions on stamen bases were formed 36 hpi by saprophytic hyphae that originated from anthers. This infection process can give rise to tan‐coloured symptoms typical of botrytis disease that radiate from this part of the flower. Subcuticular hyphae were present at high density near stamen bases and evidently resulted from multiple penetrations from single infection cushions. The subcuticular hyphae grew within the hypanthium and towards the centre of the floral tube. When flower abscission occurred, floral tube tissues close to the abscission zone remained uninfected. This observation infers possible transmission of a signal (e.g. ethylene) upon B. cinerea infection. Thus, B. cinerea causes flower abscission apparently as a defence response.     

Control of post‐harvest decay of apples by pre‐harvest and post‐harvest application of ammonium molybdate

Ammonium molybdate was tested as a potential fungicide for use in apples (cv Golden Delicious) against blue and grey mould, important post‐harvest diseases of pome fruits. In tests in vivo at 20 °C, ammonium molybdate (15 mM ) reduced lesion diameters of Penicillium expansum, Botrytis cinerea and Rhizopus stolonifer by 84%, 88% and 100% respectively. When apples treated with ammonium molybdate were stored at 1 °C for three months, a significant reduction in severity and incidence of P expansum and B cinerea was observed in both years of study (1998 and 1999). In the second year of the experiment the reduction in disease severity was greater than 88% for both pathogens, and the level of control was similar to, or greater than, that observed with the fungicide imazalil. When ammonium molybdate was applied as a pre‐harvest treatment, a significant reduction in blue mould decay was observed after three months in cold storage. In vitro, ammonium molybdate greatly inhibited spore germination of P expansum and B cinerea, although better inhibition was obtained against grey mould. Ammonium dimolybdate, sodium molybdate and potassium molybdate were also tested in vitro in comparison with ammonium molybdate as inhibitors of spore germination, but only ammonium molybdate inhibited spore germination by more than 50%. © 2001 Society of Chemical Industry     

Genetic and phenotypic characterization of Botrytis calthae

Botrytis calthae is a necrotrophic plant pathogen, closely related to the ubiquitous broad host range fungus Botrytis cinerea, but highly host specific. Botrytis isolates from lesions of Caltha palustris grown at different locations were classified with genetic markers as either B. calthae or Botrytis pseudocinerea, or less frequently as B. cinerea. A PCR‐based identification of B. calthae was developed. Seven haplotypes of B. calthae could be distinguished. Compared to B. cinerea, mycelium growth of B. calthae was similar, but conidiation less abundant, and sclerotia formation was only partially repressed by light. Conidia of B. calthae germinated more slowly, and showed a highly acidic optimum (pH 2·5) compared to B. cinerea conidia (pH 5·3). All B. calthae isolates were sensitive to common anti‐Botrytis fungicides, but showed partial resistance to the succinate dehydrogenase inhibitors boscalid, fluopyram and carboxin. Infection experiments revealed a weak capability of B. calthae to induce necrotic lesions on plants that are hosts for B. cinerea. On C. palustris leaves, B. calthae induced similar lesions to B. cinerea. These data provide a basis for comparative molecular investigation of the physiology and host specificity of B. calthae and closely related Botrytis species.     

Mechanisms involved in the biological control ofBotrytis cinerea incited diseases

Mechanisms involved in the biological suppression of infection and inoculum potential ofBotrytis cinerea are numerous and variable and the involvement of two or more mechanisms has been demonstrated in several systems. Reported combinations include antibiosis with enzyme degradation ofB. cinerea cell walls; competition for nutrients followed by interference with pathogenicity enzymes of the pathogen or with induced resistance; and alteration of plant surface wettability combined with antibiosis. Since germinatingB. cinerea conidia are dependent on the presence of nutrients, competition for nutrients is regarded as important in systems where biocontrol is involved. Conidial viability and germination capacity are also potentially affected by the presence of antibiotics produced by biocontrol agents and present in the phyllosphere. Slower in action are mechanisms involving induced resistance in the host plant and production of hydrolytic enzymes that degradeB. cinerea cell walls. The latter has been demonstrated much more convincinglyin vitro than in the phyllosphere. Biocontrol in established lesions and reduction of sporulation on necrotic plant tissues is a means to minimize the pathogen inoculum.Abbreviations BCA bio-control agent - Bc Botrytis cinerea - PG polygalacturonase - PL Pectin lyase - PME Pectin methyl esterase - PR pathogenesis related - VPD vapour pressure deficit     

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.     

Spotting of tomato fruits caused by Botrytis cinerea

Botrytis spot or ghost spot on tomato fruits occurs after penetration of germ tubes ofB. cinerea into epidermal cells. A few days after the penetration a halo appears around the infected necrotic cells. These symptoms can be reproduced by inoculating young fruits with a few dry conidia. When many conidia alight on the epidermis of the fruit, scab-like symptoms develop, while under conditions of high humidity, blisters can be formed on the fruit surface before the fungus spreads through the fruit parenchyma. Under conditions of low humidity, necrotic areas are formed.In the necrotic cells, developed after inoculation with many or with a few conidia, no mycelium could be found by the histological methods so far used. However,B. cinera can be reisolated, implying that theBotrytis spot is a latent infection by the fungus. No renewed growth takes place when the fruit is fully ripe.Samenvatting Botrytis-stip op tomatevruchten ontstaat na binnendringen van kiembuizen vanB. cinerea in epidermiscellen van een jonge vrucht. Enkele dagen na de infectie treden celdelingen op in het onderliggende parenchymweefsel. De geïnfecteerde cel en enkele aangrenzende cellen sterven af, terwijl rondom dit necrotische plekje een zilverwit gekleurde ring ontstaat. Worden veel conidiën bijeen op een vruchtwand gebracht, dan krijgt de epidermis binnen 24 uur een schurftig uiterlijk. Blijft de luchtvochtigheid na de inoculatie hoog, dan kunnen daarentegen kleinere en grotere blaasjes in de vruchtwand ontstaan. Deze barsten na enkele dagen open, terwojl mycelium zich door de vrucht verbreidt. Daalt de luchtvochtigheid circa 16 uur na de inoculatie, dan blijft de aantasting beperkt tot de epidermis. Hoewel in het necrotische weefsel geen mycelium vanB. cinerea kon worden aangetoond, blijkt herisolatie van de schimmel gemakkelijk te zijn. Ook uitBotrytis-stippen van uit de praktijk afkomstige vruchten kanB. cinerea geïsoleerd worden. Dit betekent, dat het hier om een latente infectie gaat, waarbij evenwel geen hernieuwde groei plaats vindt als de vrucht geheel rijp is.     

Potential distribution of citrus black spot in the United States based on climatic conditions

Citrus black spot (CBS), caused by Phyllosticta citricarpa McAlp Van der Aa, was recently detected in southern Florida in the US. In addition to infected plant propagation materials, movement of infected citrus fruit poses a concern for potential spread of the disease out of the current quarantine zone, because lesions with pycnidia and conidia could develop after harvest. The conditions conducive for mycelial growth and development of pycnidia and conidia are not well known. Therefore, effects of temperature and relative humidity on growth and conidial production of P. citricarpa were determined and used as parameter inputs in CLIMEX to predict potential establishment of CBS in North America. Colony growth and conidial production in vitro were optimal at 27 °C, whereas there was no growth below 4 °C and above 37 °C. On fruit, lesion development and conidial production were observed at 4 °C, though at a low rate, indicating a greater versatility of the fungus on fruit. More full pycnidia were produced on the CBS lesions at 91 % RH compared to 84 %. Input parameters for CBS risk in CLIMEX obtained from literature, which reflected conditions for infection in spring/summer in Florida, predicted potential establishment in Florida but not in California. However, altering the parameter values to account for survival of the pathogen in leaf litter in winter predicted potential establishment in California as well as Florida. Thus, P. citricarpa could possibly establish beyond Florida if this organism is transported outside of the current quarantine zone to other citrus production areas.     

Effect of mint oil against <Emphasis Type="Italic">Botrytis cinerea</Emphasis> on table grapes and its possible mechanism of action

This paper assessed the antifungal effects of sage oil, lavender oil, mint oil, and tea tree oil on the postharvest fungal pathogen, Botrytis cinerea, which causes gray molds. The change of morphology, physiological, and biochemical characteristics about fungal hyphae and conidia were determined. As results show, all four oils can effectively inhibit the growth of B.cinerea and the antifungal effects are dose dependent. The best antifungal effect has been found from mint oil. According to in vitro studies, volatile vapor worked better than direct contact. With volatile vapor, the growth of B.cinerea was inhibited completely at 2 for all four oils. Mint oil at 500 μL/L and its volatile vapor at 25 could inhibit both conidia germination and disease incidence significantly in vivo. Observations by using scanning electron microscope and transmission electron microscope revealed that, mint oil could destroy the ultrastructure of hyphae and conidia, resulting in markedly shriveling and crinkling of the hyphae and conidia. It could also thicken and disrupt cell wall, causing cellular nucleic acids and proteins divulged with the damage of the cell wall. The chemical composition analysis of mint oil using GC/MS revealed that its main components were cyclohexanol, cyclohexanone, and some alkenes and alkanes. The majority of the components were effective antifungal agents. The content of volatile cyclohexanol and cyclohexanone were found to be 39.79% and 22.24% respectively.