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1.
ABSTRACT To determine how exposure to heat effects their survival, oospores of Aphanomyces cochlioides isolate C22 were exposed in water to 35, 40, 45, or 50 degrees C for prescribed times and then examined for viability. The Weibull model was modified to represent the effects of temperature on survival of oospores. The final fitted model gave lethal doses for 50% of the oospores of 251, 49.8, 9.8, and 1.9 h at 35, 40, 45, and 50 degrees C, respectively. To determine if alternating high and low temperatures resulted in (i) recovery from heat damage during low temperature periods, (ii) increased susceptibility to heat damage, or (iii) if effects of heat damage were cumulative, oospores were examined after each of four 24-h cycles at 45 degrees C for 4 h and 21 degrees C for 20 h. Survival of oospores exposed to alternating high and low temperatures fit the cumulative effects model. Significant variability in heat tolerance among five isolates was observed (P< 0.001) but model parameters successfully accommodated this variability (R(2) = 0.96, P < 0.001). This research shows that under wet conditions, there are predictable patterns to mortality for A. cochlioides oospores exposed to continuous or fluctuating high temperatures. 相似文献
2.
Brooks AJ de Muro MA Burree E Moore D Taylor MA Wall R 《Pest management science》2004,60(10):1043-1049
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. 相似文献
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The acute and sublethal toxicities of novaluron, a novel chitin synthesis inhibitor, to a laboratory-reared insecticide-susceptible strain of Colorado potato beetle, Leptinotarsa decemlineata (Say), were determined. Novaluron exhibited excellent residual (120 h LC(50) = 0.42 mg litre(-1)) and good direct contact (120 h LC(50) = 27 mg litre(-1)) activity against second-instar larvae (L2). Hatch of eggs exposed by direct contact to novaluron solutions > or =100 mg litre(-1) was significantly reduced, as was the ability of emerged first-instar larvae to moult. L2 from eggs exposed to > or =100 mg litre(-1) novaluron weighed significantly less (P < 0.0001) than those from untreated eggs. However, L2 from eggs treated with 1 mg litre(-1) novaluron weighed significantly more (P < or = 0.05) than those from untreated eggs, suggesting novaluron can have a hormetic effect on L decemlineata larval development. Leptinotarsa decemlineata mating pairs fed foliage treated with novaluron at 25 or 75 g AI ha(-1) produced approximately 25% fewer egg masses and eggs per mass. Hatch of eggs on treated foliage was almost completely suppressed, and longevity of male beetles was reduced by approximately 50% when fed foliage treated with novaluron at 75 g AI ha(-1). 相似文献
5.
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. 相似文献
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The thermal sensitivity of Erwinia amylovora was determined at 45° C and 50°C. In vitro assays with eight differetit strains showed that thermal death times did not exceed 70min at 45° C and 50min at 50° C (95% confidence interval). Heat treatments of naturally infected apple and pear shoots were performed using a moist and a dry heat procedure. When shoots were wrapped in wet cotton cloths (wet heat) and maintained in an incubator, no bacterial growth could be detected after an incubation of 5 h at 45° C. When shoots were sealed in polyethylene bags and immersed in water (dry heat), no Erwinia amytovora could be isolated after an immersion of 3 h at 45° C. Incubation at 50°C for 1 –2h in either condition did not eradicate the pathogen entirely. The failure rate of grafts using budwoods treated at the effective time-temperature combinations did not exceed 25%.
The present investigations showed that the use of thermotherapy techniques for controlling Erwinia amylovora in propagation material of apple and pear might be possible. 相似文献
The present investigations showed that the use of thermotherapy techniques for controlling Erwinia amylovora in propagation material of apple and pear might be possible. 相似文献
7.
ABSTRACT Experiments to identify the factors affecting survival of Bremia lactucae sporangia after deposition on lettuce leaves were conducted in growth chambers and outdoors under ambient conditions. Lettuce seedlings at the four-leaf stage were inoculated with B. lactucae sporangia under dry conditions. Sporangia deposited on lettuce seedlings were incubated at different temperature and relative humidity (RH) combinations, exposed to 100, 50, 25, and 0% sunlight in the second experiment, and exposed to different artificial lights in wavelength ranges of UVA (315 to 400 nm), UVB (280 to 315 nm), or fluorescent light in the third experiment. After exposure for 0 to 48 h in the first experiment and 0 to 12 h in the second and third experiments, seedlings in two pots were sampled for each treatment, and sporangia were washed from 15 leaves excised from the sampled seedlings. Germination of sporangia was determined in water after incubation in the dark at 15 degrees C for 24 h. The sampled seedlings with remaining leaves were first transferred to optimal conditions for infection (24 h), for the development of downy mildew, and then assessed for disease after 9 days. Sporangia survived much longer at 23 degrees C (>12 h) than at 31 degrees C (2 to 5 h), regardless of RH (33 to 76%). Germination percentage was significantly reduced after exposure to 50 and 100% sunlight. UVB significantly reduced sporangium viability, while fluorescent light and UVA had no effect relative to incubation in the dark. Infection of seedlings followed a pattern similar to germination of sporangia. Solar radiation is the dominant factor determining survival of B. lactucae sporangia, while temperature and RH have small, insignificant effects in coastal areas of California. This suggests that infections by sporangia that survived a day are probable only on cloudy days or on leaves that are highly shaded. 相似文献
8.
Kirk WW 《Phytopathology》2003,93(11):1400-1406
ABSTRACT Mycelium of Phytophthora infestans, the causal agent of potato late blight, can initiate crop infections over successive years by overwintering in infected potato tubers that survive as seed in fields or within cull piles. This study used four different genotypes of P. infestans to evaluate the influence of freezing temperatures on survival of mycelium in vitro. Sporangium-free mycelium of P. infestans US1, US8, US11, and US14 growing on rye agar plates was exposed to temperatures ranging from -20 and 0 degrees C (experiment A) for different periods up to 24 h and from -5 and 0 degrees C (experiment B) for periods up to 5 days. Cultures were incubated at 12 degrees C after exposure, and survival of the cultures was estimated after 28 days by a digital image analysis technique that measured the average reflectance intensity (ARI) of images of the mycelium of temperature-treated cultures. The ARI values of treated cultures were compared with the growth of mycelium in negative controls (mycelium not present) and positive controls (mycelium exposed to 12 degrees C for an equivalent period), and determination of recovery was based on statistical differences from the controls. There were significant differences in ARI values among genotypes, temperature treatment, and exposure periods in all experiments. An index of recovery was calculated for each genotype at all treatment temperatures and exposure periods for both experiments. In experiment A, exposure of mycelium of P. infestans (all genotypes) to -20 and -10 degrees C proved lethal for exposure periods of more than 1 h. All genotypes showed some degree of recovery up to 24-h exposure at -5 and -3 degrees C. In both experiments, exposure of mycelium of P. infestans to 0 degrees C was not lethal to any genotype tested for any exposure period. In experiment B, all of the genotypes survived exposure up to 3 days at -3 degrees C to some degree, but at -5 degrees C, exposure of 1 day was lethal to all genotypes. Tolerance of freezing temperatures by mycelium of P. infestans may be an ecologically important survival mechanism and the increased tolerance of US8 and US14 may explain their predominance in cooler climates such as north-central United States. 相似文献
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The effect of phosphine at exposure periods of 24, 48 and 120 h on hatching and mortality of 0- to 1-day-old eggs of susceptible (TN6) and resistant (FC10) strains of Rhyzopertha dominica of field origin was investigated. The fumigant affected hatching in both the strains. In a 48-h exposure at 27 (+/- 2) degrees C, the LD99 doses for the eggs of TN6 and FC10 were 0.56 and 3.25 mg litre-1, respectively. Significant reduction in hatching was observed in treated batches with progressive increase of phosphine dose in the first 2-3 days. On subsequent days the numbers hatching were often similar to those in controls, and sometimes exceeded control hatch, especially following a 5-day exposure. A critical change in the order of susceptibility of egg and adult stages of the two strains was noticed. In 48-h exposures, eggs of the susceptible strain were more tolerant than their adults, whilst the reverse was true in the resistant strain. 相似文献
11.
T Scholz 《Folia parasitologica》1991,38(1):39-55
A part of the life cycle of Proteocephalus neglectus La Rue, 1911, a parasite of trout, starting from release of eggs from mature parasites into water, to the early phase of development in the definitive host, was studied under experimental conditions. Special regard has been paid to development in the intermediate host, copepod Cyclops strenuus. Some oncospheres in eggs kept in water at 5 and 10 degrees C remained infective for 20-25 days. The percentage of infected copepods depended on the length of their contact with parasite eggs. Cestode larvae (cercoscoleces) were formed in the intermediate host on days 8-10 p.i. at the temperatures of 21-22 degrees C, on days 18-21 at 15 degrees C, on days 24-28 at 10 degrees C, and on days 59-65 at 6 degrees C. Most larvae, including infective cercoscoleces, were localized in the cephalothorax of the intermediate host, particularly in its first segment. This localization did not change during their development. The infectivity of cercoscoleces was verified by experimental infection of Salmo gairdneri fry. The development of the cestode in this definitive host was observed for 17 days after infection at 10 degrees C. The finding of P. neglectus cereoscoleces in fish of the families Cottidae and Cyprinidae on day 2 after experimental infection indicates that these larvae can survive for a short time in atypical fish hosts. 相似文献
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ABSTRACT The effect of variable temperature on the infection severity of Podosphaera macularis was investigated. Potted 'Symphony' hop plants were inoculated and exposed to different temperature regimes that included supraconducive temperatures (30 to 42 degrees C) for varying periods of time (2 to 9 h). Infection severity (lesions per cm(2) of leaf area) was calculated 7 to 10 days after inoculation. Immediately exposing inoculated plants to 30 degrees C for as little as 2 h significantly (P 相似文献
13.
BACKGROUND: Novaluron is a benzoylphenyl urea chitin synthesis inhibitor that combines good activity against larval stages of the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), with low mammalian toxicity. Previous studies suggest that it has deleterious sublethal effects on adults. RESULTS: Continuous exposure of adult Colorado potato beetles to novaluron-treated foliage as both ovipositional and feeding substrate did not affect their survivorship or the number of eggs produced, but viable larvae hatched only from the eggs that were laid on the first day of the experiment. Viability was restored after adult beetles spent 48-96 hours on untreated leaves. In a separate experiment, direct exposure to novaluron of eggs laid by unexposed beetles also reduced the number of larvae hatching. CONCLUSIONS: Results confirm a negative effect of novaluron on the number of progeny produced by the Colorado potato beetle. Direct toxicity did not explain all of the reduction in egg hatch observed, suggesting that novaluron probably acted on reproductive adults as well as on eggs after they were deposited. 相似文献
14.
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. 相似文献
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ABSTRACT Strains of Pantoea agglomerans (synanamorph Erwinia herbicola) suppressed the development of basal kernel blight of barley, caused by Pseudomonas syringae pv. syringae, when applied to heads prior to the Pseudomonas syringae pv. syringae infection window at the soft dough stage of kernel development. Field experiments in 1994 and 1995 revealed 45 to 74% kernel blight disease reduction, whereas glasshouse studies resulted in 50 to 100% disease control depending on the isolate used and barley cultivar screened. The efficacy of biocontrol strains was affected by time and rate of application. Percentage of kernels infected decreased significantly when P. agglomerans was applied before pathogen inoculation, but not when coinoculated. A single P. agglomerans application 3 days prior to the pathogen inoculation was sufficient to provide control since populations of about 10(7) CFU per kernel were established consistently, while Pseudomonas syringae pv. syringae populations dropped 100-fold to 2.0 x 10(4) CFU per kernel. An application to the flag leaf at EC 49 (before heading) also reduced kernel infection percentages significantly. Basal blight decreased with increasing concentrations (10(3) to 10(7) CFU/ml) of P. agglomerans, with 10(7) CFU/ml providing the best control. For long-term preservation and marketability, the survival of bacterial antagonists in several wettable powder formulations was tested. Over all formulations tested, the survival declined between 10- to >100-fold over a period of 1.5 years (r = -0.7; P = 0.000). Although not significant, storage of most formulations at 4 degrees C was better for viability (90 to 93% survival) than was storage at 22 degrees C (73 to 79%). However, long-term preservation had no adverse effect on biocontrol efficacy. 相似文献
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ABSTRACT Sporangia germination of Phytophthora infestans isolates belonging to three clonal lineages (US-1, -7, and -8) was assessed at temperatures ranging from 10 to 25 degrees C. At 10 degrees C there were no significant differences in germination percents among US-1, -7, and -8. At 18 or 20 degrees C US-7 and -8 had significantly lower germination percents than US-1. At 21, 24, or 25 degrees C all clonal lineages had low germination percents. Sporangia of the US-7 and -8 lineages germinated more quickly at 15 degrees C (P = 0.001) during the first 2 h than did the US-1 lineage. The incubation period (IP), lesion area (LA), and sporulation per unit of lesion area (SPU) of the isolates were assessed on inoculated detached leaflets of susceptible potato cv. Norchip kept at 10, 15, 20, or 25 degrees C. In general, IP declined exponentially and LA increased exponentially with increasing temperatures. SPU had a quadratic shape, with the maximum at 15 degrees C. Averaged over all temperatures, the US-7 lineage had the shortest IP (59.3 h compared to 66.4 h for US-1 [P = 0.012] and 71.7 h for US-8 [P = 0.026]). Again, averaged over all temperatures, the US-8 lineage had a larger LA (P = 0.030) than US-1. There was no significant difference between US-7 and -1 for LA. There were no significant differences among lineages in terms of SPU. These results indicate that clonal lineages differ from each other in epidemiological attributes, but the differences can be complex. 相似文献
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The activity of diflubenzuron against eggs ofLobesia botrana Den. & Schiff. was assayed with a dipping procedure, at 22° and 27° C. The compound was much more active at 27°C (LC-50 = 0.0072%) than at 22°C (LC-50 = 0.195%). 相似文献
18.
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. 相似文献
19.
Cadle-Davidson L Schindelbeck RR van Es HM Gray SM Bergstrom GC 《Phytopathology》2003,93(9):1131-1136
ABSTRACT An air pressure cell, a laboratory tool that precisely controls soil matric potential, was utilized in a novel approach to investigate the epidemiology and management of soilborne disease. Matric potentials of -1, -5, -20, and -40 kPa were established in cores of field soil infested with Wheat soilborne mosaic virus (WSBMV) and its presumed vector Polymyxa graminis. Equilibrated soil cores were planted to wheat (Triticum aestivum), and after intervals of growth under controlled environment, virus transmission was assessed by serological detection of the virus in washed roots. Transmission occurred at all but the driest soil matric potential tested, -40 kPa, in which only pores with a diameter of 7.4 mum or less were water-filled, possibly obstructing movement of P. graminis zoospores. By starting plants at -40 kPa for 10.5 days and then watering them to conducive matric potential, we found that WSBMV transmission occurred between 12 to 24 h at 15 degrees C, and within 36 h at 20 degrees C. No significant transmission occurred within 96 h at 6.5 degrees C. In contrast, transmission of Wheat spindle streak mosaic virus (WSSMV) did not occur at 15 degrees C (the only transmission temperature tested), suggesting either that WSSMV is unable to establish infection at 15 degrees C or that a different vector is involved. The air pressure cell is a novel tool with many potential applications in research on the epidemiology and management of soilborne pathogens. Applications of the precise environmental control attained through the use of air pressure cells range from assessing the effects of cultural practices on soilborne inoculum to standardized virulence assays for soilborne pathogens to preliminary screens of host resistance and pesticide efficacy. 相似文献
20.
庚醛与桉叶油醇组合对马铃薯块茎蛾产卵选择的影响 总被引：3，自引：0，他引：3
马铃薯块茎蛾(Phthorimaea operculella)是世界上为害马铃薯最严重的害虫之一,本研究利用桉叶油醇与庚醛驱避-引诱组合对其产卵行为进行调控,以探究最佳驱避-引诱组合规律及影响因素。在室内条件(27±1℃,L∥D=14h∥10h,RH:50%~70%)测定了桉叶油醇与庚醛单组分及两种组分驱避-引诱组合对马铃薯块茎蛾产卵选择的影响。桉叶油醇在6~12mg/L浓度范围内对马铃薯块茎蛾表现为产卵引诱作用,在18~30mg/L浓度范围内则表现为产卵驱避作用;庚醛在6~30mg/L浓度范围内对马铃薯块茎蛾表现为产卵驱避效果。将对马铃薯块茎蛾产卵行为引诱效果较好的桉叶油醇(3,6,12 mg/L)与驱避效果较好的庚醛(12,18,24mg/L)进行引诱-驱避组合,12mg/L庚醛与3mg/L桉叶油醇push-pull组合效果最好,push-pull效应达36.6%。对马铃薯块茎蛾产卵行为调控最佳的驱避-引诱组合为最低驱避浓度(12mg/L庚醛)与最低引诱(3mg/L桉叶油醇)浓度组合。产卵选择指数和push-pull效应与交配率、单雌产卵量不具有相关性,但是浓度变化可以导致交配率和单雌产卵量的变化。 相似文献