Purification and Biological Characterization of Host-Specific SV-Toxins from Stemphylium vesicarium Causing Brown Spot of European Pear

ABSTRACT Culture filtrates of a pathogenic isolate (IT37) of Stemphylium vesicarium, causing brown spot of European pear, induced veinal necrosis only on pear leaves susceptible to the pathogen. Two host-specific toxins, SV-toxins I and II, were purified from culture filtrates of IT37 by successively using Amberlite XAD-2 resin adsorption, cellulose thin-layer chromatography, and high-performance liquid chromatography under three different sets of conditions. Susceptible cultivars showed veinal necrosis at a SV-toxin I concentration of 0.01 to 0.1 mug/ml, whereas resistant cultivars were insensitive to the toxin at 1,000 mug/ml. SV-toxins I and II caused a dose-dependent increase in electrolyte loss from susceptible leaf tissues. No increase in electrolyte loss was detected in leaf tissues from resistant cultivars. The results of physiological studies indicated that SV-toxins appear to have an early effect on plasma membranes of susceptible leaves. Spores of a nonpathogenic isolate induced necrotic lesions on susceptible leaves in the presence of a small amount of toxin. SV-toxins were detected in intercellular fluids obtained from diseased leaves after inoculation with the pathogen. The results indicate that SV-toxins I and II produced by S. vesicarium can be characterized as host-specific toxins.     

Relationships between Weather Variables, Airborne Spore Concentrations and Severity of Leaf Blight of Garlic Caused by Stemphylium vesicarium in Spain

Ascospores and conidia released into the air were recorded around plots on which garlic debris infected by Stemphylium vesicarium were fixed onto the soil surface. Symptoms in garlic trap plots located in the vicinity of infected debris, started in March and developed during April–May to reach disease incidence close to 100%, final disease severity values being lower in 1993 and 1995 than in 1994 and 1996. Whereas daily concentrations of ascospores were rather erratic, with 30% of captures between 0 and 6 h, conidia showed a daily periodicity with highest concentrations between 12 and 18 h, with a pronounced peak between 14 and 16 h, and lowest values at night. Ascospore release occurred mainly in February and March. It coincided with rainfall periods, 14 h with vapour pressure deficit 5 mb and solar radiation <145 W m^–2 on the current day of the capture. In contrast, greatest captures of conidia started in late April and were prevalent in May, and were associated with rainfall in days previous to the capture in which rather high temperature occurred and solar radiation was 109–345 W m^–2. Among the weather variables considered, rainfall appeared directly related to the aerial concentration of ascospores and conidia. The role of relative humidity seemed essential when rainfall did not occur. There was a relationship between conidia concentration in the air and number of hours with temperature in the range 12–21 °C. Ascospore production was not essential for infections to take place, since primary infection from conidia may occur and disease can develop from them readily.     

Development of Pleospora allii on Garlic Debris Infected by Stemphylium vesicarium

Pseudothecia of Pleospora allii developed best on garlic leaf debris infected by Stemphylium vesicarium incubated at low temperature (5–10°C) and relative humidity (RH) close to saturation. RH of less than 96% prevented the formation of pseudothecia, while an incubation temperature of 15–20°C led to the early degeneration of pseudothecia. Under natural conditions, colonization by pseudothecia of unburied garlic leaf debris varied between seasons from 6.0 to 15.5 pseudothecia/mm2, whereas lower colonization levels were recorded when samples were buried. Pseudothecial maturity was reached 1–4mo after the deposition of garlic debris on the soil surface and 15 days after the burial of residues. In the later case, pseudothecia degenerated with degradation of the plant debris. Ascospore release, which required rainfall or dew periods, occurred between late January and late April depending upon the year. A high correlation was found between pseudothecia maturation and four meteorological variables. Two of which, i.e. the number of hours with RH98% and with a mean temperature of 4.5–10.5°C, and the accumulated rainfall, explained most variability (adjusted R2=0.82–0.98 depending upon the year). A multiple regression equation relating the pseudothecia maturity index with these two variables could be used to forecast the epidemic onset of Stemphylium leaf spots in Southern Spain. Temporal progress of pseudothecia maturation was best fitted by a monomolecular model.     

Brown Leaf Spot on Lantana spp. Caused by Pseudocercospora guianensis

Brown leaf spot of Lantana camara L. and L. montevidensis Briq. caused by Pseudocercospora guianensis (Stevens et Solheim) Deighton was found in Shizuoka, Chiba, Kagoshima and Okinawa Prefectures. Pathogenicity of isolates from the leaf spots was examined, and a taxonomic study as well as identification of the causal fungus was carried out. Similar leaf spots appeared on 7 to 25 days after inoculation with the isolates on Lantana spp., and the same fungus was re-isolated from the inoculated leaves. Two hitherto known Pseudocercospora species on Lantana, P. guianensis and P. formosana, were considered to be variations within one species, and we identified the causal fungus as P. guianensis due to priority. Received 25 September 2000/ Accepted in revised form 20 May 2001     

Brown spot of pear,an emerging disease in Argentina: identification and pathogenicity characterization of Argentinean Stemphylium vesicarium isolates

European Journal of Plant Pathology - Recently, a new plant disease was detected in the rural area of the High Valley of Río Negro, in Northern Patagonia, Argentina, called “Brown Spot...     

Aetiology of leaf spot of garlic and onion caused by Stemphylium vesicarium in Spain

Surveys between 1989 and 1993 in the major garlic production areas of Spain identified a new leaf spot disease, characterized by white and purple lesions followed by extensive necrosis. Isolation and pathogenicity tests with fungal isolates taken from these spots indicated that Stemphylium vesicarium was the causal agent. Pseudothecia of the teleomorph stage, Pleospora sp., were found on leaf debris from affected plants. Inoculation of garlic and onion plants with residues carrying mature pseudothecia, or with ascospore suspensions obtained from the pseudothecia, resulted in the development of white and purple leaf spots. Wetness periods longer than 24 h were required for symptom development under controlled conditions. Isolates of S. vesicarium from garlic, onion and asparagus caused disease in all three hosts. In garlic, cv. Blanco de Vallelado was most susceptible, while lines B4P17 and B6P1, and cvs Iberose and Golourose were less susceptible to the disease.     

Infection of onion leaves by Alternaria porri and Stemphylium vesicarium and disease development in controlled environments

Infection of onion by Alternaria porri and Stemphylium vesicarium was investigated under a range of controlled temperatures (4–25°C) and leaf wetness periods (0–24 h). Conidia of A. porri and S. vesicarium germinated within 2 h when incubated at 4°C. Terminal and intercalary appressoria were produced at similar frequencies at or above 10°C. The maximum number of appressoria was produced after 24 h at 25°C. Penetration of leaves by both pathogens was via the epidermis and stomata, but the frequency of stomatal penetration exceeded that of epidermal penetration. There was a strong correlation ( R ² > 90%) between appressorium formation and total penetrations at all temperatures. Infection of onion leaves occurred after 16 h of leaf wetness at 15°C and 8 h of leaf wetness at 10–25°C, and infection increased with increasing leaf wetness duration to 24 h at all temperatures. Interruption of a single or double leaf wetness period by a dry period of 4–24 h had little effect on lesion numbers. Conidia of A. porri and S. vesicarium separately or in mixtures caused similar numbers of lesions. Alternaria porri and S. vesicarium are both potentially important pathogens in winter-grown Allium crops and purple leaf blotch symptoms were considered to be a complex caused by both pathogens.     

木霉几丁质酶对烟草赤星病菌的作用

以指形管培养法分别测定几丁质酶粗酶液和纯化的几丁质酶混合液(2种几丁质酶)对烟草赤星病菌孢子萌发的抑制作用。结果表明,较高浓度(25 2U)几丁质酶粗酶液在48h内强烈抑制孢子萌发和芽管伸长,或致芽管畸形和细胞壁破裂;几丁质酶混合液对赤星病菌的孢子萌发也表现出明显的抑制作用,但在相同或相近酶活性条件下,纯化的几丁质酶混合液(9 4U)和粗酶液(12 6U)对赤星病菌孢子萌发的抑制率(处理24h时)分别为46%和84 3%,前者明显低于后者。采用孢子液悬滴法接种烟苗(K 326)叶片测定木霉几丁质酶对赤星病菌致病性的影响。结果表明,几丁质酶粗酶液浓度越高,对孢子萌发抑制时间越长,抑制率越高;其浓度为4 9、9 8、19 5U/ml的抑制率7d时分别为36 8%、56 2%和57 6%。     

Effect of Relative Humidity on Sporulation of Fusarium oxysporum in Various Formulations and Effect of Water on Spore Movement Through Soil

ABSTRACT Fusarium oxysporum f. sp. erythroxyli is being investigated as a mycoherbicide for the narcotic plant coca. Sporulation of the fungus in seven formulations containing different organic substrates and movement of its propagules through soil were studied. The formulations were a granular wheat flour/kaolin (pesta); an extruded wheat and rice flour (C-6); and five alginate pellet products containing corn cobs, soybean hull fiber, canola meal, rice flour, or rice flour plus canola oil. Formulations were incubated at 25 degrees C for 6 weeks in desiccators with various salt solutions to provide nine relative humidities (RH), ranging from 100% (pure deionized water) to 0% (anhydrous (CaSO(4)). Hyphae of F. oxysporum f. sp. erythroxyli grew out of alginate pellets with canola meal, rice, and rice plus canola oil as early as 24 h at 100% constant RH. Alginate pellets of rice plus canola oil and granular C-6 and pesta formulations consistently produced more microconidia, macroconidia, and CFU than the other four formulations at all RH tested. The C-6 formulation produced more propagules than the other formulations at low RH (<53%). Canola meal pellets produced more spores than three other formulations when exposed to fluctuating RH (100 to 75%). The effect of percolating water on spore movement through soil was studied using a plant-pathogenic isolate of F. oxysporum f. sp. niveum. To determine the effect of water percolation on propagule movement, formulations were placed on soil columns and artificial rain was applied. In general, 10-fold fewer CFU were recovered at a 8- to 10-cm depth compared with a 0- to 2-cm depth.     

Effect of Modified Atmosphere for Control of Black Spot, Caused by Alternaria alternata, on Stored Persimmon Fruits

ABSTRACT Modified atmosphere packaging (MAP) of persimmon fruit resulted in the accumulation of acetaldehyde to a level of 80 mug/ml; ethanol to a level of 900 mug/ml; and CO(2) up to 30%. When fruits were stored at -1 degrees C for 4 months in such atmospheres, the incidence of black spot disease, caused by Alternaria alternata, was reduced. The effects of each of these gases were examined to determine their individual involvement in the inhibition of Alternaria development during storage. When A. alternata, grown at 20 degrees C on potato dextrose agar or inoculated in persimmon fruit, was exposed for 24 h to different levels of each volatile, acetaldehyde was the most fungistatic but only at concentrations higher than those that accumulated under MAP; CO(2) was moderately inhibitory at concentrations from 10 to 60%, whereas ethanol had no effect. Similar inhibitory effects were obtained with acetaldehyde at 620 mug/ml or 30% CO(2) when in vitro cultures of A. alternata and infected fruits were exposed for up to 2 weeks at 20 degrees C, but 1,000 mug of ethanol per ml had only a transitory inhibitory effect under these conditions. Based on analysis of the effect of concentration versus time for each gas accumulating in MAP, we suggest that the increasing concentration of CO(2) during storage is the principal factor in the inhibition of black spot disease development.     

Alternaria Leaf Spot on Three Species of Pelargonium Caused by Alternaria alternata in Japan

A new disease of pelargonium (Pelargonium domesticum Bailey), ivy geranium (P. peltatum (L.) L'Hér. ex Ait.) and scented geranium (P. graveolens L'Hér.), primarily causing brown spots on leaves, was found in Kawasaki-shi in Kanagawa Prefecture and Tachikawa-shi in Tokyo. An Alternaria sp. was consistently isolated from these diseased leaves, and the isolates were pathogenic to their host leaves. Based on morphological characteristics, the causal fungus in all three cases was identified as Alternaria alternata (Fr.) Keissler. Because Alternaria leaf spot of geranium by A. alternata has already been reported, the pathogenicity of isolates from four groups of genus Pelargonium was investigated. The isolates from scented geranium were pathogenic only to their original host, but the isolates from pelargonium, ivy geranium and geranium were pathogenic to all groups of pelargonium. This is the first report of this disease on pelargonium, ivy geranium and scented geranium caused by A. alternata in Japan. We propose the names for these diseases as Alternaria leaf spot of pelargonium (kappan-byo), Alternaria leaf spot of ivy geranium (kappan-byo) and Alternaria leaf spot of scented geranium (kappan-byo). Received 11 December 2000/ Accepted in revised form 19 July 2001     

New Leaf Spot Disease of Cymbidium Species Caused by Fusarium subglutinans and Fusarium proliferatum

Fusarium species were consistently isolated from yellow, swollen spots with reddishbrown centers and small black spots on leaves of Cymbidium plants in the greenhouse. Fusarium subglutinans caused the yellow spots and Fusarium proliferatum caused either the yellow or the black spots. We propose the name “yellow spot” for the new disease. To denote differences in their pathogenicity to orchid plants, we designate the population causing yellow spot as race Y and that causing black spot as race B of F. proliferatum. Received 29 October 1999/ Accepted in revised form 10 March 2000     

Spore Release of Bremia lactucae on Lettuce Is Affected by Timing of Light Initiation and Decrease in Relative Humidity

ABSTRACT A suction-impaction mini-spore trap was developed to study the effect of light initiation and decreasing relative humidity (RH) on spore release of Bremia lactucae in a controlled environment. Three light periods (from 0400 to 1600, 0600 to 1800, and 0800 to 2000 h, circadian time) at a constant RH of 99 to 100% were used for studying the effect of light initiation on spore release. Few spores were released during the dark periods. Spore release increased sharply after the initiation of the three light periods, reached a maximum 1 to 2 h after light initiation, and then declined until only a few spores could be detected. The effect of reduction in RH on spore release was studied by comparing decreases in RH 2 h before and 2 h after light initiation at 0800 h. When RH decreased from 100 to 94% 2 h before light initiation, spore release increased within 1 h, followed by a second increase after light initiation. When RH decreased 2 h after light initiation, spore release continued to increase after the initial increase after light initiation, reached a maximum 1 h after the reduction in RH, and then declined. The results suggest that both light initiation and reduction in RH can trigger spore release and that these factors have separate effects on spore release of Bremia lactucae.     

Sporulation of Bremia lactucae Affected by Temperature, Relative Humidity, and Wind in Controlled Conditions

ABSTRACT The effects of temperature (5 to 25 degrees C), relative humidity (81 to 100%), wind speed (0 to 1.0 m s(-1)), and their interactions on sporulation of Bremia lactucae on lettuce cotyledons were investigated in controlled conditions. Sporulation was affected significantly (P < 0.0001) by temperature, with an optimum at 15 degrees C, and by relative humidity (RH), with sporulation increasing markedly at RH >/= 90%. There was a significant effect of exposure time in relation to temperature (P = 0.0007) but not to RH. In separate experiments, both RH and wind speed significantly (P < 0.0001) affected the number of cotyledons with sporulation and the number of sporangia produced per cotyledon. No sporulation was observed at wind speeds of >0.5 m s(-1), regardless of RH. In still air, the number of sporangiophores produced per cotyledon increased linearly with RH from 81 to 100% (P = 0.0001, r = 0.98). Histological observations indicated that sporulation may be affected by stomatal aperture in response to RH, as more closed stomata and correspondingly fewer sporangiophores were present at lower RH. These results are important for understanding the mechanism of RH effects on sporulation and for predicting conditions conducive to downy mildew development.     

Effects of Temperature and Wetness Duration on Infection of Peanut Cultivars by Cercospora arachidicola

ABSTRACT The effects of temperature and duration of wetness (relative humidity >/=95%) on infection of three peanut cultivars by Cercospora arachidicola were determined under controlled conditions. Plants of the Spanish cv. Spanco and the runner cvs. Florunner and Okrun were exposed to constant temperatures of 18 to 30 degrees C during 12-h periods of wetness each day that totaled 12 to 84 h following inoculation of leaves with conidia. Severity of disease, measured by either lesion density (number per leaf) or lesion size (diameter), was greatest for 'Spanco', intermediate for 'Florunner', and lowest for 'Okrun' in each of two experiments. Lesion density was evaluated further because it was an indicator of both the occurrence and degree of infection. Nonlinear regression analysis was employed to evaluate the combined effects of temperature (T) and wetness duration (W) on lesion density (Y). In the regression model, the Weibull function characterized the monotonic increase of Y with respect to W, while a hyperbolic function characterized the unimodal response of Y with respect to T. Parameters for the intrinsic rate of change with respect to W (b), the intrinsic rate of change with respect to T (f), the optimal value of T (g), and the upper limit (e) when T is optimum (T = g) were estimated for each cultivar and experiment. The effect of cultivar was characterized primarily by differences in the upper limit parameter e. In each experiment, e was greatest for 'Spanco', intermediate for 'Florunner', and least for 'Okrun'. The effect of cultivar on b followed a pattern similar to that for e in experiment 1, but not in experiment 2. Differences among cultivars for estimates of f and g were small and inconsistent. Estimates for g were precise for each cultivar and experiment and fell within the range of 22.3 to 23.2 degrees C. Cultivar responses to T and W were further evaluated using data pooled over the two experiments. Parameter e was estimated for each cultivar, but common values of b, f, and g were estimated. At e = 22.8 degrees C, lesion density approached an upper limit of 96, 17, and 6 lesions per leaf for the cvs. Spanco, Florunner, and Okrun, respectively. These fitted values approximated the observed values of 86, 25, and 9 lesions per leaf for the respective cultivars. Cultivars varied in their response to W at a given T. At 22.8 degrees C, one lesion per leaf was expected following 26, 30, and 36 h of wetness for 'Spanco', 'Florunner', and 'Okrun', respectively. If temperature was increased to 28 degrees C, one lesion per leaf was expected following 36, 44, and 54 h of wetness for the respective cultivars.     

Influence of Light, Relative Humidity, and Maturity of Populations on Discharge of Ascospores of Venturia inaequalis

ABSTRACT Ascospore release in 20 populations of Venturia inaequalis was generally suppressed in wind tunnel tests during darkness and simulated rain, but the following relieved this suppression: (i) exposure to low relative humidity during simulated rain and (ii) protracted incubation of leaf samples and the consequent senescence of the pathogen population. No counterpart to (i) was observed under orchard conditions. Although V. inaequalis also released a high percentage of ascospores during darkness in field studies under simulated rain late in the season of ascospore release, this phenomenon has not been reported for natural rain events. A threshold value of 0.5 muW/cm(2) at 725 nm was identified as the minimum stimulatory light intensity. Ascospore release increased with increasing light intensity from 0.5 to 5.2 muW/cm(2) at 725 nm. There was also an intrinsic increase in ascospore release as duration of rain increased. In orchards, the combined impact of both processes is probably responsible for a delay in reaching peak ascospore release at several hours after sunrise. Ascospore release during darkness will generally constitute a small proportion of the total available supply of primary inoculum. Significant ascospore release, and therefore infection periods, can be assumed to begin shortly after sunrise, when rain begins at night in orchards with low potential ascospore dose (PAD). A PAD level of 1,000 ascospores per m(2) of orchard floor per season is suggested as a threshold, above which the night-released ascospores should not be ignored.     

Effect of Strawberry Density on the Spread of Anthracnose Caused by Colletotrichum acutatum

ABSTRACT Spread of strawberry anthracnose, resulting from the rain splash dispersal of Colletotrichum acutatum conidia, was determined in field plots by assessing fruit disease incidence at a range of distances from an introduced point source of infected fruit with sporulating lesions. Four within-row plant densities were established in replicated plots in each of 2 years. A generalized linear model with a logit link function and binomial distribution for incidence was used to quantify the effects of distance and side of the row relative to the inoculum source, plant density treatment, and their interactions on disease incidence. At all assessment times, there was a significant (P 相似文献   

夏季北极涛动与亚洲中部干湿状况关系研究

利用NCEP/NCAR全球再分析资料和NOAA北极涛动指数资料,采用相关分析、谱分析、小波分析等,对北极涛动(AO)与亚洲中部干旱区(ACA)的干湿变化关系进行分析.研究认为:夏季北极涛动指数和ACA相对湿度场存在显著反相关,尤其表现在年代际尺度上;两者都于20世纪70年代初发生显著突变,2年准周期贯穿过去50年,但5年左右的周期在70年代中期以后表现显著.结果表明:AO突变前后,ACA海平面高度场、对流低层风场都具有显著变化,但ACA东半部和西半部受作用的亚系统并不一致,认为夏季ACA干湿状况突变及其周期特点转变的主要原因之一是AO突变引起环流场变化所致.     

Effect of Film-forming Polymers on Control of Lily Leaf Blight Caused by Botrytis elliptica

The effectiveness of film-forming polyelectrolytes for the control of lily leaf blight caused by Botrytis elliptica was evaluated using laboratory a leaf disk assay, greenhouse tests and field trials. Among the six polyelectrolytes, 400ppm FO4240SH, FO4490SH and FO4550SH reduced the disease severity of lily leaf blight in leaf-disk tests. Both FO4240SH and FO4490SH also suppressed sporulation of the pathogen on leaf disks. In greenhouse tests, the number and size of lesions on leaves of Lilium oriental hybrid cv. Star Gazer were markedly reduced by FO4490SH and FO4550SH. Field trials showed that the effectiveness of FO4490SH was similar or better than that of procymidone on the reduction of lily leaf blight disease severity. The polymers had no harmful effects on the lily plants. The cationic polyelectrolytes FO4240SH, FO4490SH and FO4550SH reduced the percentage of conidial germination, inhibited germ-tube growth, and also suppressed the esterase production by germ tubes of B. elliptica. All the above evidence indicates that the disease control achieved with polyelectrolytes is due, at least in part, to the reduction of esterase secretion by B. elliptica.