准噶尔盆地东南缘绿洲-荒漠交错带土壤甲螨群落结构

为了查明准噶尔盆地东南缘绿洲-荒漠交错带土壤甲螨群落特征,2011年4月、7月、9月、11月中旬对该交错带的自然林、灌木林、防护林、荒草原、耕地、菜瓜地和荒漠等7种不同生境进行调查。结果表明:该区域共捕获土壤甲螨成体3767头,28科36属43种,其中覆盖头甲螨、萨勒盖头甲螨、新疆尖棱甲螨和普通尖棱甲螨为优势种,截合若甲螨、长单翼甲螨属、白上罗甲螨大洋亚种为亚优势种,优势种和亚优势种占总数的72.45%。7种不同生境土壤甲螨群落组成和数量分布均有明显的差异(P<0.05),在自然林种类(30种)和个体数(1001头)最多,而在菜瓜地种类(9种)最少,荒漠个体数(118头)最少。不同生境土壤甲螨的个体数具有明显季节变化差异(P<0.05),秋季数量最高、冬季次之、夏季其次、春季最低。MGP分析结果表明,该交错区土壤甲螨群落均属于O型,但G群的种类明显高于M群和P群。甲螨的群落异质性高,各生境间的多样性指数(H)有一定的差异,其中防护林最高,而菜瓜地最低。生境间相似性分析表明,自然林、灌木林、防护林生境之间是中等相似(0.50～0.70),荒漠和荒草原与其他生境间为中等不相似(0.25～0.50)或极不相似(0.00～0.25)。研究表明气候、植被和土壤差异是影响土壤甲螨群落的主要因素。     

Production and Germination of Conidia of Trichoderma stromaticum, a Mycoparasite of Crinipellis perniciosa on Cacao

ABSTRACT Growth characteristics of the fungus Trichoderma stromaticum, a mycoparasite on the mycelium and fruiting bodies of Crinipellis perniciosa, the causal agent of witches'-broom disease of cacao, were evaluated under controlled environmental conditions. The ability of T. stromaticum to produce conidia and germinate on dry brooms was evaluated at three constant temperatures (20, 25, and 30 degrees C) and two constant relative humidities (75 and 100%). T. stromaticum produced abundant conidia on brooms at 100% relative humidity and incubation temperatures of 20 and 25 degrees C, but none at 30 degrees C. Sporulation of T. stromaticum was not observed at 75% relative humidity at any temperature. At 100% relative humidity and either at 20 or 25 degrees C, treatment of brooms with T. stromaticum suppressed C. perniciosa within 7 days. In contrast, at 30 degrees C, treatment with T. stromaticum had no effect on the pathogen in brooms maintained at either 75 or 100% relative humidity. Mycelium of C. perniciosa grew from brooms at all temperatures at 100% relative humidity. Conidial germination on broom tissue approximated 80% at temperatures from 20 to 30 degrees C. Results suggest that applying T. stromaticum under high-moisture conditions when the air temperature is below 30 degrees C may enhance the establishment of this mycoparasite in cacao plantations.     

Variations in acaricidal effect of wettable sulfur on Tetranychus urticae (Acari:Tetranychidae): effect of temperature,humidity and life stage

Under laboratory conditions, the acaricidal effect of wettable sulfur is influenced by climatic conditions and the stage of development of Tetranychus urticae. Its ovicidal effect results from the combined action of temperature and relative humidity (RH). Wettable sulfur becomes effective at 27.5 degrees C and 75% RH. Beyond this threshold, the acaricidal effect increases with rising temperature or humidity, to become complete at a temperature of 35 degrees C and 90% RH. Within the range of temperatures and humidities 20 degrees C/30% RH and 35 degrees C/90% RH the mortality of immatures (from protonymphs to teleiochrysalis) was total. Under similar experimental conditions, females usually died before the end of the experiment. Temperature and relative humidity increased the adulticidal potential of wettable sulfur. The fecundity of the sulfur-treated females and the viability of their progeny was found to depend on temperature and RH. According to the same climatic conditions, eggs were less susceptible than females, which were in turn less susceptible than juvenile stages.     

Effect of Microclimate on Leveillula taurica Powdery Mildew of Sweet Pepper

ABSTRACT Sweet pepper-Leveillula taurica microclimate relations were studied under controlled conditions and in commercial greenhouses. Conidial germination occurred at 10 to 37 degrees C and was optimal at 20 degrees C. Conidial viability declined as temperatures increased to 40 degrees C for 6 h. Leaf colonization was optimal at 15 to 25 degrees C. Severe leaf infections occurred at 15 to 20 degrees C and conidiation was suppressed at 20 to 25 degrees C. Highest germination rates were observed at 75 to 85% relative humidity (RH). Severity of leaf coverage by symptoms was high for plants which were subjected to longer periods of temperatures between 10 to 15 degrees C and daytime RH between 85 to 95%, and positively correlated with nighttime RH. Disease severity was negatively correlated with lengthy periods of temperatures >25 degrees C, day and night average temperatures, and average daytime RH. Conversely, leaf shedding was relatively high under conditions characterized by long periods of temperatures >20 degrees C and <13 degrees C, and positively correlated with average daytime temperatures and periods of RH <75%. Increasing nighttime temperatures by heating and daytime temperatures by closing the greenhouse side walls reduced disease in two commercial greenhouse experiments. A midseason shift from a cooler greenhouse climate to warm daytime climate halted epidemic development. Flower number and yield were reduced in infected crops.     

Growth and pathogenicity of isolates of the fungus Metarhizium anisopliae against the parasitic mite, Psoroptes ovis: effects of temperature and formulation

Psoroptes mites (Acari: Psoroptidae) are important ectoparasites of mammals, and are of particular economic significance as the agents of mange in sheep. To be effective against mites, putative fungal biocontrol agents must be able to operate at the relatively high temperatures and humidities found at the sheep skin surface. To consider this, the growth rates of different isolates of the entomopathogenic fungus Metarhizium anisopliae (Metschnikoff) Sorokin (Deuteromycotina: Hyphomycetes) were compared and the pathogenicity of these isolates against Psoroptes derived from rabbits (Psoroptes ovis Hering, syn P cuniculi) were evaluated at temperatures between 28 degrees C and 40 degrees C, and when formulated in either Tween 80 or silicone oil. For this study four multi-conidia, arthropod-derived, isolates of M anisopliae were used: from the USA, France, Denmark and Brazil. One single-conidia culture derived from the US isolate was also included in the investigation. Fungal growth was higher at the lower temperatures and none of the isolates grew at 40 degrees C. The growth of the US and single-conidia isolate declined markedly with temperature. In contrast, the Danish, French and Brazilian isolates grew almost as well at 32 degrees C and 35 degrees C as at 28 degrees C and 30 degrees C. The French and Brazilian isolates showed some growth at 37.5 degrees C but the Danish and US isolates did not. The number of fatal infections which resulted from exposure of mites to the fungal isolates was also strongly influenced by temperature. At 30 degrees C all isolates gave between 70 and 90% infection. The number of infections declined with increasing temperature and no infections were seen at 40 degrees C. However, the French and Danish isolates of M anisopliae gave higher numbers of infections than the other isolates at elevated temperatures. When formulated in silicone oil, significantly higher levels of infection were obtained than when formulated in Tween 80, even at the relatively high temperature of 37.5 degrees C. It is suggested that high-temperature adapted isolates of M anisopliae formulated in silicone oil offer good candidates as control agents under the conditions found at the sheep skin surface.     

Germination of Ascospores of Gibberella zeae after exposure to various levels of relative humidity and temperature

Fusarium head blight (FHB) is one of the most important cereal diseases in the world and has caused major losses to the grain industry. The principal pathogen causing FHB in North America is Gibberella zeae (anamorph Fusarium graminearum). Information on survival and the conditions under which ascospores remain viable once released from perithecia may assist in refining disease forecasting models. This study measured germination of ascospores after exposure to different temperatures, 15, 20, and 30 degrees C, and levels of relative humidity (RH), 30, 60, and 90% for 4, 24, or 48 h periods. Viability was tested by germination on water agar. Germination rates fell with increasing temperatures at all observation times and at all humidity levels. At 15 and 20 degrees C after 48 h, germination ranged from 74 to 85%, and 52 to 72%, respectively. At 30 degrees C, germination ranged from 36 to 59% after 24 h and from 13 to 47% after 48 h. Germination was highest at 90% RH, except at 30 degrees C after 48 h, and lowest at 60% RH. Successful germination, even under extreme conditions, suggests that ascospores are sufficiently robust to constitute a source of inoculum under most environmental conditions encountered during the growing season.     

Cucumber mosaic virus Establishes Systemic Infection at Increased Temperature Following Viral Entrance Into the Phloem Pathway of Tetragonia expansa

ABSTRACT A potential regulatory site for Cucumber mosaic virus (CMV, pepo strain) movement necessary to establish systemic infection was identified through immunological and hybridization studies on Tetragonia expansa, which was systemically infected by CMV at 36 degrees C but not at 24 degrees C. In inoculated leaves, cell-to-cell movement of CMV was enhanced at 36 degrees C compared with that observed at 24 degrees C. CMV was distributed in the phloem cells of minor veins as well as epidermal and mesophyll cells at both 36 and 24 degrees C. CMV was detected in the petioles of inoculated leaves, stems, and petioles of uninoculated upper leaves at 36 degrees C, whereas CMV was detected only in the petioles of inoculated leaves and in stems at 24 degrees C. CMV moved into the phloem and was transported to the stem within 24 h postinoculation (hpi) at 36 degrees C. However, it did not accumulate in the petioles of the upper leaves until 36 hpi. In petioles of inoculated leaves at 24 degrees C, CMV was detected in the external phloem but not in the internal phloem. From these results, we conclude that systemic infection is established after viral entrance into the phloem pathway in T. expansa at 36 degrees C.     

Influence of Nutrient and Environmental Factors on Conidial Germination of Potebniamyces pyri

ABSTRACT Potebniamyces pyri is the causal agent of Phacidiopycnis rot, a postharvest disease of pears. Infection of fruit occurs in the orchard, and symptoms develop during storage. Conidial germination of P. pyri in response to nutrient, temperature, wetness duration, relative humidity (RH), and pH was determined in vitro. Conidia germinated by either budding or developing germ tubes in various concentrations of pear juice solutions. The mode of conidial germination was nutrient-dependent. Low nutrient levels favored budding, whereas high nutrient levels favored germ tube development. Conidia germinated at 0 to 30 degrees C but not at 35 degrees C, with optimum temperature between 20 and 25 degrees C. Wetness durations of 4 to 5 h and 6 to 8 h at optimum temperature were required for budding and developing germ tubes, respectively, and 20 to 24 h of wetness was required to reach germination peaks. Regardless of temperature, conidia germinated primarily by budding in 10% pear juice. Secondary conidia, produced by budding of conidia, initially increased their dimensions and later germinated at 0 to 25 degrees C in the same manner as mother conidia. No germination of secondary conidia occurred at 30 degrees C. Germ tubes from conidia elongated at 0 to 25 degrees C but not at 30 degrees C. No germination occurred at 相似文献   

Conidial germination, infection structure formation, and early colony development of powdery mildew on poinsettia

ABSTRACT Powdery mildew disease on poinsettias (Euphorbia pulcherrima) growing in commercial greenhouses was first observed in the United States in 1990 and has become an economically significant problem for poinsettia growers in the Midwest and northern United States since 1992. The temporal development of infection structures produced by conidial germ tubes of the pathogen (Oidium sp.) and the effect of high temperature on their development were investigated using poinsettia leaf disks placed in humidity chambers. Observations were made using light microscopy and scanning electron microscopy. At 20 degrees C (85% relative humidity), conidia germinated and formed an appressorium within 6 h of inoculation. Germination over time followed a monomolecular curve (r(2) = 0.77, P 相似文献   

Influence of Environmental Conditions on Spore Production and Budding in Taphrina deformans, the Causal Agent of Peach Leaf Curl

ABSTRACT Environment-controlled studies were carried out to determine the growth of Taphrina deformans under different conditions of temperature, humidity, and nutrient availability similar to those found on plant surfaces during the peach-growing season. Both ascospores and blastospores were able to bud at all temperatures tested (5 to 37 degrees C), with the optimum at 14 and 21 degrees C, respectively. Temperature <20 degrees C favored ascospore production and release, with the optimum at 10 degrees C. Budding was approximately two-and-a-half times higher in a film of water than on a dry substrate, with 100% relative humidity and blastospores also maintained a certain budding ability at lower humidity levels (minimum tested = 47%). Both spore types did not bud after approximately 50 to 55 h in the absence of external nutrients. In the presence of a periodically renewed carbon source, such as simple sugars, at concentrations that typically are present on peach plant surfaces, the fungus maintained its budding capability over time. Results showed that T. deformans is able to bud profusely under a wide range of environmental conditions that occur on peach tree surfaces. This work supports the hypothesis that T. deformans is a part of the normal epiphytic mycoflora of peach trees throughout the entire growing season.     

Response of two fungi in the apple sooty blotch complex to temperature and relative humidity

ABSTRACT Peltaster fructicola and Leptodontium elatius, two of the causal fungi of apple sooty blotch, responded differently to temperature and relative humidity in vitro. Conidia of L. elatius germinated from 12 to 32 degrees C at relative humidities >/=97%, whereas conidia of P. fructicola germinated from 12 to 24 degrees C at relative humidities >/=95%. Germination of conidia of L. elatius was optimum at 32 degrees C and 99% relative humidity compared with 24 degrees C and 97 or 99% relative humidity for P. fructicola. When L. elatius and P. fructicola were grown in Parafilm culture, sporulation was greatest at relative humidities of 97 to 99%. In agar culture, mycelia of L. elatius expanded radially from 12 to 32 degrees C, and that of P. fructicola at 12 to 28 degrees C. Mycelia of P. fructicola did not survive exposure for 7 days or more to temperatures >/=32 degrees C. Mycelial growth was inhibited at relative humidities <95% for both fungi and no growth occurred at 88% relative humidity. Conidia of P. fructicola were more sensitive to air drying than were those of L. elatius. Conidial viability of P. fructicola was reduced significantly after 8 h of air drying and nearly completely inhibited after 12 h. Conidia of L. elatius required 24 h of air drying before a significant reduction in conidial viability was observed. These results support the hypothesis that environmental factors influence the temporal and geographical distributions of the fungi associated with the apple sooty blotch disease.     

Early development of Khawia sinensis Hsü, 1935 (Cestoda: Caryophyllidea), a carp parasite

The development of the tapeworm Khawia sinensis parasitizing carp (Cyprinus carpio L.) has been studied from the release of cestode eggs into water to the formation of infective procercoids in the intermediate host under laboratory conditions. The rate of embryonal development is greatly influenced by the water temperature. While at 5 degrees C the development of oncospheres was not recorded, at 10-12 degrees C, 15 degrees C, 20-22 degrees C, and 23-24 degrees C oncospheres were fully formed after 57, 42, 21 and 16 days, respectively. Infectivity of oncospheres was confirmed by successful experimental infection of the intermediate hosts: Tubifex tubifex and Limnodrilus udekemiamus (Oligochaeta: Tubificidae). Fully formed procercoids infective for the definitive host were found in the intermediate host from 52 days of development at 20-22 degrees C. From the third week of development in the intermediate host, most of the parasite larvae were located in the anterior part of the tubificid body, mainly between 8th and 15th segments.     

Effects of humidity on the development of grapevine powdery mildew

ABSTRACT The effects of humidity on powdery mildew development on grape seedlings and the germination of Uncinula necator conidia in vitro were examined. Studies were conducted at an optimum temperature of 25 +/- 2 degrees C. Disease on foliage was markedly affected by humidity levels in the test range of 39 to 98% relative humidity (RH), corresponding to vapor pressure deficits (VPD) of 1,914 to 61 Pa. Incidence and severity increased with increasing humidity to an optimum near 85% RH, and then appeared to plateau or decrease marginally at higher values. Conidial density and chain length also were proportional to humidity, but were influenced less strongly. There was a strong, positive linear relationship between humidity level and frequency of conidium germination with RH treatments of 相似文献   

Influence of concentration, temperature and humidity on the toxicity of phosphine to the strongly phosphine-resistant psocid Liposcelis bostrychophila Badonnel (Psocoptera: Liposcelididae)

BACKGROUND: The psocid Liposcelis bostrychophila Badonnel, is a widespread, significant pest of stored commodities, has developed strong resistance to phosphine, the major grain disinfestant. The aim was to develop effective fumigation protocols to control this resistant pest. RESULTS: Time to population extinction of all life stages (TPE) in days was evaluated at a series of phosphine concentrations and temperatures at two relative humidities. Regression analysis showed that temperature, concentration and relative humidity all contributed significantly to describing TPE (P<0.001, R(2)=0.95), with temperature being the dominant variable, accounting for 74.4% of the variation. Irrespective of phosphine concentration, TPE was longer at lower temperatures and high humidity (70% RH) and shorter at higher temperatures and low humidity (55% RH). At any concentration of phosphine, a combination of higher temperature and lower humidity provides the shortest fumigation period to control resistant L. bostrychophila. For example, 19 and 11 days of fumigation are required at 15 degrees C and 70% RH at 0.1 and 1.0 mg L(-1) of phosphine respectively, whereas only 4 and 2 days are required at 35 degrees C and 55% RH for the same respective concentrations. CONCLUSIONS: The developed fumigation protocols will provide industry with flexibility in application of phosphine.     

Conditions for development of powdery mildew of tomato caused by Oidium neolycopersici

Oidium neolycopersici causes severe powdery mildew on all aerial parts of tomato, excluding the fruit. The objective of the present work was to examine factors that influence the development of O. neolycopersici on tomato and to identify potential methods for managing tomato powdery mildew. Under controlled conditions, the highest rates of conidial germination were observed at 25 degrees C, 99% relative humidity (RH) and minimal light, and the lowest on leaves adjacent to fruits. Optimal conditions for appressoria formation were 25 degrees C, RH ranging from 33 to 99%, and 1,750 lux light intensity. More conidia were formed at 20 degrees C, 70 to 85% RH, and 5,150 lux light intensity than at 16 and 26 degrees C, 99% RH, and 480 to 1,750 lux, respectively. Conidia survived and remained capable of germination for over four months when initially incubated at lower temperatures and higher RH, as compared with their fast decline under more extreme summer shade conditions. In growth chamber experiments, disease did not develop at 28 degrees C. Within the range of 70 to 99% RH, disease was less severe under the higher RH than the drier conditions. Disease was also less severe at lower light intensities. Data collected in three commercial-like greenhouse experiments involving various climate regimes were used to draw correlations regarding the effects of temperature and RH on the development of epidemics. Severity of powdery mildew was positively correlated with the duration of the range 15 to 25 degrees C, 1 to 4 weeks before disease evaluation (BDE), RH levels of 60 to 90% at 2 to 4 weeks BDE, and RH of 50 to 60% during the week BDE. Conversely, disease was negatively correlated with the duration of temperatures in the low and high ranges (5 to 15 degrees C and 35 to 40 degrees C) at 1 to 4 weeks BDE, with the duration of RH levels of 40% and below at 1 to 4 weeks BDE, and with 50 to 60% RH during the third week BDE. High (90 to 100%) RH was also negatively correlated with disease severity. These results suggest that the combination of high temperatures and low RH may help reduce O. neolycopersici powdery mildew severity in greenhouse tomatoes.     

Finite dose diffusion studies: III. Effects of temperature, humidity and deposit manipulation on NAA penetration through isolated tomato fruit cuticles

Effects of temperature, humidity, rewetting and removal of deposits on penetration of NAA [2-(1-naphthyl)acetic acid] through isolated tomato (Lycopersicon esculentum Mill) fruit cuticles were studied using a finite dose diffusion system. In this system, an aqueous 5-microliter droplet (0.1 mM NAA in 20 mM citric acid buffer) is applied to the outer surface of a cuticle, which is mounted in a glass diffusion half-cell. The cell wall surface is in contact with a receiver solution (20 mM citrate). Penetration is monitored by repeated sampling of the receiver solution. Droplets appeared dry on visual inspection within 1 h of application, but significant NAA penetration continued after droplet drying. Maximum rates of NAA penetration increased exponentially as temperature was increased (from 5 degrees to 35 degrees C), the energy of activation averaging 153 (+/- 11.6)kJ mol-1. At 35 degrees C, penetration reached a plateau within 10 h of application (at 91.1 (+/- 1.0)% of dose applied) while at 5 degrees C penetration after 800 h reached only 30.2 (+/- 7.5)%. Increasing relative humidity from 20 to 80% increased maximum rates [from 1.0 (+/- 0.21) to 2.7 (+/- 0.80)% h-1] and penetration at 120 h after application [from 36.8 (+/- 2.1) to 64.3 (+/- 3.7)%]. Rewetting deposits at 120, 240 and 360 h after application resulted in increased NAA penetration. However, amounts and rates of NAA penetration progressively decreased with each subsequent rewetting. Removal of deposits by cellulose acetate stripping at various times after droplet application resulted in a rapid decrease in NAA penetration. NAA penetration following deposit removal was always less than 6.1% of the amount of NAA applied and averaged 0.5 (+/- 0.2)% when deposits were removed immediately after droplet drying.     

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.     

Quantitative Models for Describing Temperature and Moisture Effects on Sporulation of Phomopsis amygdali on Peach

ABSTRACT Twigs with constriction cankers were pruned from a Prunus persica 'Jerseyglo' orchard and placed in incubators under high humidity (>95%) at constant temperatures of -6, 1, 10, 17, 24, 31, 38, and 45 degrees C. Cankers were removed for observation after 2, 6, 24, 48, 72, and 96 h incubation. Sporulation was expressed as the percentage of pycnidia producing cirri and the number of conidia per pycnidium or canker. The experiment was first performed during 1998 to 1999 and then repeated in 1999 to 2000 and 2000 to 2001. Sporulation was modeled by fitting the Richards function to each dependent variable with duration of high relative humidity as the independent variable. The asymptote and rate parameters of the Richards model were expressed as Gaussian and quadratic functions of temperature, respectively. Models created from the first two experimental repetitions were validated by statistical comparison to those created independently from the third repetition. When models were fit to the pooled data, temperature and moisture described 69 to 80% of the variation in sporulation. The models specified a temperature ranging from 0 to 37 degrees C (optimum temperatures for cirri formation and conidia production range from 19 to 20 and 22 to 23 degrees C, respectively), and the majority of sporulation occurred between 16 and 48 h from initiation of the high humidity period. These results show that the environmental criteria for sporulation coincide with those that prolong the susceptibility of infection courts during fall and spring.     

Effect of surface material on electrostatic charging of houseflies (Musca domestica L)

Houseflies (Musca domestica L) accumulated electrostatic charges when walking over clean, uncharged dielectric surfaces. The charges elicited on a walking housefly by a range of materials were quantified, allowing a triboelectric series to be determined relative to M domestica. This ranged from surfaces that charged individuals positively, e.g. Correx (corrugated polypropylene) [.1 (+/- 4.2)pC], to those that applied a negative charge, e.g. clear cast acrylic [-14.9 (+/- 2.9)pC]. Maximum positive and negative charges accumulated by individual M domestica were +73 and -27 pC. Replicate measurements on the same fly and surface showed little variation. Variation between individuals was not related to sex and was not consistent between surfaces. Different materials charged M domestica significantly differently and individual flies had significantly different charging properties. Variation in temperature between 21.3 degrees C and 24.7 degrees C and humidity between 24% and 41% RH significantly affected charge accumulated by M domestica on some surfaces, although further experimentation is needed to confirm this. The implications of this work are discussed in relation to insect trap design and pollination biology.