Antagonism of Nutrient-Activated Conidia of Trichoderma harzianum (atroviride) P1 Against Botrytis cinerea

ABSTRACT The effect of preliminary nutrient activation on the ability of conidia of the antagonist Trichoderma harzianum (atroviride) P1 to suppress Botrytis cinerea was investigated in laboratory, greenhouse, and field trials. Preliminary nutrient activation at 21 degrees C accelerated subsequent germination of the antagonist at temperatures from 9 to 21 degrees C; at >/=18 degrees C, the germination time of preactivated T. harzianum P1 conidia did not differ significantly from that of B. cinerea. When coinoculated with B. cinerea, concentrated inocula of preactivated but ungerminated T. harzianum P1 conidia reduced in vitro germination of the pathogen by >/=87% at 12 to 25 degrees C; initially quiescent conidia achieved this level of suppression only at 25 degrees C. Application of quiescent T. harzianum P1 conidia to detached strawberry flowers in moist chambers reduced infection by B. cinerea by >/=85% at 24 degrees C, but only by 35% at 12 degrees C. Preactivated conidia reduced infection by >/=60% at 12 degrees C. Both quiescent and preactivated conidia significantly reduced latent infection in greenhouse-grown strawberries at a mean temperature of 19 degrees C, whereas only preactivated conidia were effective in the field at a mean temperature of 14 degrees C on the day of treatment application. An antagonistic mechanism based on initiation of germination in sufficiently concentrated inocula suggests that at suboptimal temperatures the efficacy of Trichoderma antagonists might be improved by conidia activation prior to application.     

Biological Control of Botrytis cinerea in Cyclamen with Ulocladium atrum and Gliocladium roseum Under Commercial Growing Conditions

ABSTRACT The effect of treatments with conidial suspensions of Ulocladium atrum and Gliocladium roseum on leaf rot of cyclamen caused by Botrytis cinerea was investigated under commercial greenhouse conditions. Spraying U. atrum (1 x 10(6) conidia per ml) or G. roseum (2 x 10(6) conidia per ml and 1 x 10(7) conidia per ml) at intervals of 2 to 3 weeks during the production period and spraying U. atrum (1 x 10(6) conidia per ml) at intervals of 4 to 6 weeks resulted in a significant reduction of natural infections of petioles by B. cinerea. U. atrum or G. roseum (1 x 10(7)conidia per ml) was as effective as the standard fungicide program. B. cinerea colonized senesced leaves within the plant canopy and infected adjacent petioles and leaves later. The antagonists colonized senesced leaves and reduced B. cinerea development on these leaves. Thus, the inoculum potential on petioles adjacent to necrotic leaf tissues was reduced. The fate of U. atrum conidia on surfaces of green cyclamen leaves during a 70-day period after application was studied. The number of conidia per square centimeter of leaf surface remained relatively constant during the entire experiment. Sixty percent of the conidia sampled during the experiments retained the ability to germinate. When green leaves were removed from the plants to induce senescence and subsequently were incubated in a moist chamber, U. atrum colonized the dead leaves. Senesced leaves also were colonized by other naturally occurring fungi including B. cinerea. On leaves treated with U. atrum from all sampling dates, sporulation of B. cinerea was significantly less as compared with the untreated control. Our results indicate that early applications of U. atrum before canopy closure may be sufficient to achieve commercially satisfactory control of Botrytis leaf rot in cyclamen.     

两种季铵盐阳离子表面活性剂对番茄灰霉病菌的毒理效应

为探讨季铵盐阳离子表面活性剂1227和C8-10对番茄灰霉病菌Botrytis cinerea的毒理效应,运用电子显微镜、氧电极、紫外-可见分光光度计等测定了1227、C8-10对番茄灰霉病菌分生孢子萌发、细胞壁结构、呼吸作用和三种细胞壁降解酶的影响,并在番茄叶片活体上接种经药剂处理的番茄灰霉病菌,观察药剂对其侵染活性的影响.结果显示,两种季铵盐阳离子表面活性剂5μg/mL处理可使分生孢子芽管变短变粗、基部明显膨大,显著抑制聚甲基半乳糖醛酸酶、多聚半乳糖醛酸酶和羧甲基纤维素酶的活性,并可显著影响番茄灰霉病菌在番茄活体叶片上的侵染活性;40μg/mL处理可导致菌体细胞壁表面出现多处破损、细胞内含物聚集等现象;100μg/mL处理显著抑制分生孢子的呼吸作用;250μg/mL和1 000μg/mL处理对病原菌菌丝呼吸产生破坏作用.说明两种季铵盐杀菌剂高剂量能够破坏菌体细胞壁结构,导致番茄灰霉病菌呼吸完全停止和死亡,而低剂量可以抑制细胞胞壁降解酶的活性,降低其致病力.     

Spatial and temporal variation of reactive oxygen species and antioxidant enzymes in o-hydroxyethylorutin-treated tomato leaves inoculated with Botrytis cinerea

Pretreatment of detached tomato leaves with o -hydroxyethylorutin reduced the percentage leaf area affected, and delayed the appearance of necrosis, following inoculation with conidial suspensions in droplets of the grey mould fungus Botrytis cinerea . o -Hydroxyethylorutin delayed, but did not inhibit, in vitro germination of conidia, although overall percentage germination was reduced compared with water controls. Both the reactive oxygen species (ROS) – superoxide anions and hydrogen peroxide – increased twice as much in o -hydroxyethylorutin-treated leaf tissue 2 and 6 h postinoculation with B. cinerea conidia in tissues under inoculation drops, as well as in surrounding tissues, whereas in plants not pretreated with the compound ROS generation was noticed later, and only in tissues under inoculation drops. Compared with these compounds, changes in the levels of hydroxyl radicals, lipid peroxidation and the activity of the enzymes superoxide dismutase, guaiacol peroxidase, ascorbate peroxidase and catalase were largely unchanged. In stimulating ROS in inoculated tomato tissue, B. cinerea appeared to be affected directly pre- and postinfection, but indirect effects increasing host resistance cannot be excluded.     

A Laboratory Simulation for Vectoring of Trichosporon pullulans by Conidia of Botrytis cinerea

ABSTRACT A mechanism that could contribute to the suppression of Botrytis cinerea during pathogen sporulation was examined in this study. Yeasts capable of binding to B. cinerea were formulated with a cellulose carrier and applied to sporulating colonies of the pathogen. The particles from this yeast/cellulose product attached to B. cinerea conidia in the sporulating colony. Inoculum from treated colonies was harvested and applied to tomato stem tissue to test for subsequent pathogenicity. Disease development from inoculum obtained from cultures that had been treated with Trichosporon pullulans was significantly retarded (P = 0.0001) compared with cellulose-only controls. However, between 5 and 11% of conidia applied were attached to yeast cells. The removal of conidia not attached to yeast resulted in inoculum composed of >90% of conidia attached to yeast, and from this inoculum, disease development was significantly retarded (P < 0.05). When inoculum from treated B. cinerea colonies was applied to nutrient limiting agar and then incubated, the B. cinerea conidia germinated, and yeast cells infested the new hyphal growth. Constraints of the formulation of the yeast used in this study, and the implications of this vectoring approach for the suppression of B. cinerea during pathogen sporulation are discussed.     

Combinations of Fungicides with Phylloplane Yeasts for Improved Control of Botrytis cinerea on Geranium Seedlings

ABSTRACT Control of Botrytis cinerea on geranium seedlings was evaluated in treatments with phylloplane yeasts in combination with 10 fungicides used to manage Botrytis blight of ornamental plants. Rhodotorula glutinis PM4 significantly reduced the development of lesions caused by B. cinerea on geranium cotyledons; however, yeast biocontrol efficacy was highly variable between trials. Treatment with the yeast in combination with azoxystrobin or trifloxystrobin at one tenth the labeled rate (7.5 mug a.i. ml(-1)) or the full labeled rate (7.5 mug a.i. ml(-1)) reduced lesion development, compared to treatment with the yeast or the fungicide alone. Vinclozolin at half the labeled rate or the full labeled rate (250 or 500 mug a.i. ml(-1)), in combination with R. glutinis PM4, significantly reduced the development of lesions caused by an isolate of B. cinerea resistant to vinclozolin. Copper hydroxide and iprodione at one-tenth the labeled rates, with or without yeast, were highly effective in limiting lesion development. Mancozeb did not increase the biocontrol efficacy of the yeast, and thiophanate-methyl negatively affected the yeast efficacy. Improved disease control was observed in treatments with vinclozolin at the labeled rate and R. glutinis PM4 at cell densities of 5 x 10(5) and 1 x 10(6) cells ml(-1), but not 1 x 10(5) cells ml(-1), on seedlings co-inoculated with B. cinerea in a suspension containing 1 x 10(5) conidia ml(-1). Disease control improved in treatments with combinations of vinclozolin and eight other isolates of R. glutinis, two isolates of R. graminis, and two isolates of R. mucilaginosa. Biocontrol was not observed in treatments with two isolates of R. minuta. The combination of yeast and vinclozolin significantly reduced the germination of conidia of B. cinerea and the growth of R. glutinis PM4 in vitro. All combinations of R. glutinis PM4 with azoxystrobin, trifloxystrobin, or vinclozolin provided highly effective and consistent disease control not observed in treatments with the fungicides alone or the yeast alone.     

The Role of Trichoderma harzianum Protease in the Biocontrol of Botrytis cinerea

The role of protease of Trichoderma harzianum in the biocontrol of Botrytis cinerea was examined. Two isolates of T. harzianum were compared for their ability to produce protease in liquid culture medium and on the surface of bean leaves. The biocontrol agent T. harziaum T39 produced 58mU/ml of protease and T. harzianum NCIM1185 produced 54mU/ml on the 5th day of growth in liquid culture medium. On bean leaves, combinations of B. cinerea and T. harzianum isolates were examined for the synthesis of protease. The protease activities were 0.9 and 0.6mU/ml for T. harzianum T39 and NCIM1185, respectively, and 0.5mU/ml for B. cinerea alone after 48h of incubation. In the presence of T. harzianum T39 culture liquid containing protease, a 55% reduction in B. cinerea germination and a 80% reduction in the germ tube length were observed after 17h of incubation in vitro. When T. harzianum isolates were added to B. cinerea on bean leaves, increased synthesis of protease was observed (1.0 and 1.2mU/ml for T39 and NCIM1185, respectively). In the presence of T. harzianum NCIM1185 protease, although the rate of germination was reduced, B. cinerea attained 98% germination after 17h of incubation. The hydrolytic enzymes produced by B. cinerea, endo-polygalacturonase (PG) and exoPG were partially deactivated by protease from the T. harzianum isolates. Carboxymethyl cellulase was deactivated only by protease of NCIM1185. On the surface of bean leaves, the protease (obtained from liquid culture medium of T. harzianum isolates) resulted in 56–100% reduction of disease severity. The culture liquid containing protease synthesized on the surface of bean leaves treated with B. cinerea and with T. harzianum was collected and added to fresh leaves infected by B. cinerea. There was 56–100% and 30–75% reduction of disease severity with liquid droplet collected from the leaves treated with T. harzianum T39 and NCIM1185, respectively. Increased control of disease was obtained by combining the conidia of T. harzianum isolates with protease obtained from culture media. Protease inhibitors, trans-epoxysuccinyl-L-leucylamido-(4-guanidino)butane (E64), antipain hydrochloride, and a mixture of inhibitors, but not pepstatin A, fully or partially nullified the biocontrol effect of T39. T39 was found to be a poor producer of chitinase and -1,3-glucanase in vitro. These enzymes were not detected on leaves treated with T39. Involvement of protease in biocontrol of B. cinerea is suggested.     

Virus-induced changes in the response of faba bean to infection by Botrytis

Prior infection of faba bean with the viruses bean yellow mosaic and bean leaf roll increased host susceptibility to subsequent infection by Botrytis fabae and B. cinerea. Cell necrosis beneath inoculum droplets, rate and extent of lesion spread and sporulation of B. fabae were all increased on detached leaves from virus-infected compared with healthy plants. Changes were most marked in young leaves showing conspicuous symptoms of systemic virus infection and in plants virus-infected for at least 2-4 weeks. Localized lesions produced by B. cinerea or a low concentration of B. fabae conidia (10³ spores/ ml) showed increased cell necrosis but were not transformed into aggressive, spreading lesions on virus-infected leaves.     

Botrytis cinerea Infection of Grape Flowers: Light and Electron Microscopical Studies of Infection Sites

ABSTRACT Specific floral organs including the calyptra, stigma, and receptacle area of glasshouse-grown grapevines (Vitis vinifera cv. Cabernet Sauvignon) were inoculated with aqueous suspensions of Botrytis cinerea conidia, and the initial steps involved in colonization and infection of the host tissues were studied for several days postinoculation using light microscopy as well as scanning and transmission electron microscopy. Conidia germinated on all floral organs examined and became attached to the host surface within 48 h after inoculation. However, in all cases the vast majority of conidia accumulated in a channel-like gap between the ovary and the calyx that extended in a narrowing fashion into the flower interior where the ovary joined the receptacle. Very few conidial germ tubes were detected in the style following inoculation of the stigma, and no evidence for their growth toward the ovaries could be found. In contrast, hyphae were more abundant in the receptacle area, regardless of the site of inoculation. Tips of the calyx became necrotic and mycelium formed in the gap between ovary and calyx within 72 h following inoculation, providing a major point of colonization and infection. B. cinerea colonized dehiscent calyptras within 72 h of inoculation, providing a potential source of inoculum from calyptras that remained stuck in the cluster. The results suggest that the grape flower's receptacle area is the predominant site of infection for B. cinerea, although a minor portion of infections may also occur through the stigma and style.     

Differences Between Ascospores and Conidia of Didymella rabiei in Spore Germination and Infection of Chickpea

ABSTRACT Studies were performed to compare the germination and infection of ascospores and conidia of Didymella rabiei under different temperature and moisture conditions. Germination of ascospores and conidia on cover glasses coated with water agar began after 2 h, with maximum germination (>95%) occurring in 6 h at 20 degrees C. No germination occurred at 0 and 35 degrees C. Ascospores germinated more rapidly than conidia at all temperatures. Germination declined rapidly as the water potential varied from 0 to -4 MPa, although some germination occurred at -6 MPa at 20 and 25 degrees C. Ascospores germinated over a wider range of water potentials than conidia and their germ tubes were longer than those of conidia at most water potentials and temperatures. The optimum temperature for infection and disease development by both ascospores and conidia was around 20 degrees C. Disease severity was higher when ascospores were discharged directly onto plant surfaces from naturally infested chickpea debris compared with aqueous suspensions of ascospores and conidia sprayed onto plants Disease severity increased as the length of the wetness period increased. When dry periods of 6 to 48 h occurred immediately after inoculation, disease severity decreased, except for the shorter periods which had the opposite effect. Disease severity was higher with ascospore inoculum when no dry periods occurred after inoculation.     

Characterization of an Exo-beta-1,3-Glucanase Produced by Pichia anomala Strain K, Antagonist of Botrytis cinerea on Apples

ABSTRACT The exo-beta-1,3-glucanase (EC 3.2.1.58) activity of Pichia anomala strain K, an antagonistic yeast of Botrytis cinerea on postharvest apples, was studied in a synthetic medium supplemented with laminarin, a cell wall preparation (CWP) of B. cinerea, or glucose. The highest enzyme activity was detected in culture media containing a CWP of B. cinerea as the sole carbon source, whereas the lowest activity was observed in culture media supplemented with glucose. Exoglc1, an exo-beta-1,3-glucanase, was purified to homogeneity from culture filtrates of strain K containing a CWP. The molecular mass of exoglc1 was estimated to be under 15 kDa. Optimum activity of exoglc1 was recorded at 50 degrees C and pH 5.5. The exoglc1 K(m) value was estimated at 22.4 mg/ml. Exoglc1 showed in vitro a stronger inhibitory effect on germ tube growth of B. cinerea than on conidia germination and caused morphological changes such as leakage of cytoplasm and cell swelling. Exo-beta-1,3-glucanase activity was detected on apples treated with strain K and was similar to exoglc1 on the basis of activity on native gel. Moreover, the addition of a CWP to a suspension of P. anomala stimulated both in situ exo-beta-1,3-glucanase activity and protective activity against the pathogen, strengthening the hypothesis that exo-beta-1,3-glucanase activity is one of the mechanisms of action involved in the suppression of B. cinerea by P. anomala strain K.     

Impact of alternative respiration and target-site mutations on responses of germinating conidia of Magnaporthe grisea to Qo-inhibiting fungicides

Qo-inhibiting fungicides act as respiration inhibitors by binding to the Qo center of cytochrome b. Sensitivities of fungi to Qo inhibitors can be influenced by the induction of alternative respiration or by mutational changes of the cytochrome b target site. Previous studies on both mechanisms in Magnaporthe grisea (Hebert) Barr were focused on the mycelial stage of the pathogen. The present study describes the expression and impact of both resistance mechanisms during the stage of conidia germination. In the absence of a host, alternative respiration provided a >500-fold rescue from azoxystrobin during the germination of conidia derived from four wild-type isolates of M. grisea. This rescue potential during conidia gemination was substantially more pronounced than for mycelial growth. However, the pronounced effectiveness of alternative respiration during conidia germination was not apparent when barley leaves were protected with azoxystrobin prior to inoculation with conidia. In a comparison of a wild-type strain and an alternative respiration-deficient mutant, azoxystrobin efficacies in suppressing symptom development differed by a factor of two, with full disease control achieved for both genotypes at 1 microg ml(-1) azoxystrobin. In contrast, conidia derived from two QoI-resistant target site mutants were highly resistant to azoxystrobin and trifloxystrobin and fully capable of infecting leaf surfaces protected with 10 microg ml(-1) of azoxystrobin. Both target-site mutants had emerged spontaneously in the presence of high azoxystrobin doses when residual mycelial growth was supported by alternative respiration. The effective silencing of alternative respiration in protective applications of Qo-inhibiting fungicides might constitute a strategy of slowing the emergence of highly resistant target site mutants.     

Bioassays of glucosinolate-derived isothiocyanates against postharvest pear pathogens

The present study assayed the effect of six isothiocyanates (ITCs), produced by the enzymatic hydrolysis of glucosinolates, on fungal pathogens of pear. Sample pear fruits were artificially inoculated through induced wounds with conidial suspensions of Botrytis cinerea Rhizopus stolonifer Monilinia laxa Mucor piriformis or Penicillium expansum and were then treated with ITCs. Of the six ITCs tested, the ITC from glucoraphenin showed the highest effectiveness after 6 days at 20°C, against M. laxa B. cinerea and M. piriformis . The effectiveness of the ITC from glucoraphenin against M. laxa was assayed in two further trials to test the effect of ITC concentration on different concentrations of inoculum and to determine the duration of the curative effect of this ITC. ITC concentration directly affected fungus control capacity. The highest ITC concentration (3.6 mg mL⁻¹) afforded pathogen control at the highest level of pathogen concentration (10⁶ conidia mL⁻¹) after 6 days at 20°C. Its curative effect was evident up to 40 h after inoculation.     

Reduced sensitivity of Botrytis cinerea to two sterol biosynthesis-inhibiting fungicides: fenetrazole and fenethanil

Isolates of Botrytis cinerea having reduced sensitivity to the sterol biosynthesis-inhibiting (SBI) fungicides fenetrazole and fenethanil were obtained from one out of four sites from which isolates were tested. Reduced sensitivity was associated with poor disease control by fenetrazole, which had been applied with dichlofluanid. Conidial germination and hyphal growth of B. cinerea from the four sites were tested in vitro on media amended with the fungicides. Following fenetrazole or fenethanil treatment, at the site where control had failed, populations of B. cinerea were detected with higher EC₅₀ and EC₉₀ values than at the three other sites. Germination of conidia of B. cinerea was markedly inhibited by 1.0 μg/ml fenetrazole and 0.5–1.0 μg/ml fenethanil. The frequency of isolates insensitive to 1.0 μg/ml fenetrazole or to 0.5 μg/ml fenethanil was 3.4 and 1.8 times higher, respectively, at the site where control had failed, compared with another site where SBI fungicides had never been applied to control grey mould. Grey mould caused by selected isolates of B. cinerea which expressed the phenotype of low sensitivity to SBI fungicides in leaves of tomato, pepper and Senecio cineraria was not controlled by either fenetrazole or fenethanil (1 .5–3.0 μg/ml). However, up to 100% disease reduction was obtained when leaves infected by sensitive isolates were treated with the fungicides.     

Improved Control of Postharvest Decay of Pears by the Combination of Candida sake (CPA-1) and Ammonium Molybdate

ABSTRACT The potential enhancement of Candida sake (CPA-1) by ammonium molybdate to control blue and gray mold caused by Penicillium expansum and Botrytis cinerea, respectively, on Blanquilla pears was investigated. In laboratory trials, improved control of blue and gray molds was obtained with the application of ammonium molybdate (1, 5, 10, and 15 mM) alone or in combination with C. sake at 2 x 10(6) or 2 x 10(7) CFU ml(-1) on Blanquilla pears stored at 20 degrees C. In semicommercial trials at 1 degrees C for 5 months, the efficacy of C. sake at 2 x 10(6) CFU ml(-1) on reducing P. expansum and B. cinerea decay was enhanced more than 88% with the addition of ammonium molybdate 5 mM in the 1999-2000 season. In two seasons, the performance C. sake at 2 x 10(6) CFU ml(-1) plus ammonium molybdate was similar to or greater than that of C. sake at 2 x 10(7) CFU ml(-1). Similar control of blue mold was obtained on pears stored under low oxygen conditions. The preharvest application of ammonium molybdate did not reduce postharvest blue mold decay. The population of C. sake on pear wounds significantly decreased in the presence of ammonium molybdate 1 and 5 mM at 20 and 1 degrees C.     

Fungal development and plant response in detached onion, onion bulb scales and leaves inoculated with Botrytis allii, B. cinerea, B. fabae and B. squamosa

Fungal development and plant responses were examined in detached leaves and mid-bulb scales of Allum cepa. Following inoculation with suspensions of 105 conidia/ml distilled water Botrytis squamosa consistently produced spreading lesions in leaves and bulb scales. B. allii produced spreading lesions at most sites in bulbs but was very inconsistent in its infection of leaves; lesions were often confined to inoculation sites. Limited lesions were usually produced by B. cinerea but R. fabae failed to produce symptoms at most sites. Extensive colonization by B. allii and B. tauamosa required rapid penetration and totally necrotrophic fungal growth. During development of a spreading lesion, plant cell walls became very swollen around intramural hyphae and wall swelling appeared to precede epidermal cell death. Resistance to colonization was due to poor germination, failure to produce distinct infection hyphae (associated with accumulation of deposits of granular reaction material [RM] in underlying live cells) or restriction of infection ryphae amongst small groups of dead cells (limited lesion formation). Only B. fabae germinated poorly, and germ-tubes produced often failed to attempt penetration but grew over the leaf or bulb scale surface. Reducing numbers of conidia increased the frequency of sites associated with RM accumulation; granular deposits being particularly common at sites inoculated with low numbers of B. allii conidia. Electron microscopy revealed that RM granules were osmiophilic aggregates formed between the plasma membrane and epidermal cell wall. In the absence of RM, growth of avirulent species was restricted within the swollen walls of dead epidermal cells. Results ae compared with those from studies on tulip and broad bean leaves.     

枯草芽孢杆菌BS-208和BS-209菌株防治番茄灰霉病研究

为开发防治番茄灰霉病Botrytis cinerea的生防细菌,进行了枯草芽孢杆菌Bacillus subtilis BS-208和BS-209菌株对番茄灰霉病的温室和田间防治试验,并测定了两菌株对番茄灰霉病菌的抑制作用。结果表明:BS-208菌株分泌物对番茄灰霉病菌菌丝生长的抑制率为44%以上;BS-208和BS-209菌株的发酵液在经稀释10倍后,对番茄灰霉病菌分生孢子萌发的抑制率可达90%以上。经温室盆栽试验测定,以BS-208和BS-209菌株发酵液和菌体处理后24和48 h接种病菌,防效均达75%以上,好于0 h接种的防效,但分泌物滤液防治效果较差。两年的田间试验结果表明,BS-208和BS-209制剂对番茄灰霉病均具有良好的防治效果,其防效随浓度加大而提高,以800倍液的防效最好,两菌株制剂800倍液连续3次施药后防效均达到74%以上,并且BS-208菌株的防效略高于BS-209菌株。     

Botrytis cinerea Infection in Grape Flowers: Defense Reaction, Latency, and Disease Expression

ABSTRACT Inflorescences of field-grown grapevines (Vitis vinifera L. cv. Gamay) were inoculated with a Botrytis cinerea conidia suspension or dried conidia at different stages during bloom in moist weather. Approximately 10% of the conidia germinated within 72 h, resulting in two to three times more latent infections than uninoculated controls in pea-size (7 mm in diameter) berries. In surface-sterilized pea-size berries, latent B. cinerea was present predominantly in the receptacle area. After veraison, latent B. cinerea also was found in the style and, in mature berries, latent colonies were distributed throughout the pulp. Inoculation at full bloom led to the highest disease severity (66%) at harvest, compared with 38% in controls. Stilbene stress metabolites in the flowers were measured by high-performance liquid chromatography. Resveratrol accumulated mainly after pre-bloom and full-bloom inoculation, but did not prevent infection. Piceid levels did not change following inoculation, while epsilon-viniferin was found in necrotic tissues only, and pterostilbene and alphaviniferin were not detected at all. B. cinerea conidia suspensions also were applied to various locations on flowers of pot-grown cvs. Pinot Noir and Chardonnay. Inoculation of the receptacle area, but not that of the stigma and ovary, resulted in latent infections. Stilbene synthesis was similar to the field results, with resveratrol accumulating mainly in the calyptra and receptacle area. Constitutive soluble phenolic compounds (mainly derivatives of quercetin and hydroxy-cinnamic acid) were present at high concentrations in the calyptra but at low levels in the receptacle area. These experiments confirmed bloom as a critical time for B. cinerea infection in grapes and suggest that the most likely site of infection is the receptacle area or cap scar exposed at anthesis. Stilbenes may have a limited role in inhibition of flower infection and latency in susceptible grape cultivars, and epsilon-viniferin may be a by-product rather than a deterrent of infection.     

Strawberry Plant Extracts Stimulate Secondary Conidiation by Colletotrichum acutatum on Symptomless Leaves

ABSTRACT Conidial suspensions of Colletotrichum acutatum were prepared in 1:27, 1:45, and 1:81 (wt/vol) dilutions of an extract of strawberry (cv. Tristar) flowers or leaves in water. Strawberry leaves and plastic coverslips were sprayed with the conidial suspensions, incubated at 25 degrees C and continuous wetness for 48 h, and the number of conidia and appressoria were counted. In another experiment, leaves and coverslips were sprayed with a conidial suspension in water, incubated for 72 h to establish C. acutatum populations, and placed in a growth chamber under dry conditions for up to 6 weeks. At each sampling time, leaves and coverslips were sprayed with flower extracts, leaf extracts, or water, incubated for 48 h at 25 degrees C and continuous wetness, and the number of conidia and appressoria were counted. Flower extracts significantly (P 相似文献   

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