Effects of leaf wetness duration and temperature on infection efficiency, latent period, and rate of pustule appearance of rust in alfalfa

ABSTRACT Dew and growth chamber tests were conducted on the alfalfa cultivar Ranger to determine the effect of duration of leaf wetness and temperature on several components of the alfalfa rust (Uromyces striatus) monocycle. Duration of leaf wetness and temperature both had significant effects on pustule development. Infection efficiency (number of alfalfa rust pustules per leaf) increased linearly as duration of leaf wetness was increased from 4 to 24 h after inoculation. There was an inverse linear relationship between temperature and infection efficiency as indicated by the slope (-5.73) of the regression line relating the number of pustules per leaf to increasing temperatures between 17.5 and 28 degrees C. Infection efficiency was approximately 20 times greater at 17.5 degrees C than at 28 degrees C. Inoculated alfalfa plants exposed to constant temperatures of 15, 18, 21, 24, 27, or 30 degrees C after an initial 24-h leaf wetness period (19 degrees C) did not significantly affect infection efficiency (P 相似文献   

不同湿润持续时间及叶片温度对温室黄瓜霜霉病发生的影响

为探明不同湿润持续时间及叶片温度与黄瓜霜霉病发生的关系,通过观察不同湿润条件下黄瓜霜霉病的初显症时间,计算逐日显症率及累积显症率,并利用热红外成像仪对显症后叶片温度进行连续监测。结果显示,不同湿润持续时间对黄瓜霜霉病的初显症时间、逐日显症率产生影响。叶片湿润持续4 h,黄瓜霜霉病在接种后7.00 d显症;叶片湿润持续12 h,黄瓜霜霉病初显症时间最早,仅为3.25 d。叶片湿润持续时间不同,黄瓜霜霉病初显症时的叶片温度存在显著差异。回归分析表明,初显症时间与最大温差呈显著正相关,与平均温度呈显著负相关。叶片湿润持续4、6 h的病斑出现高峰在显症后第2、3天,逐日显症率分别是37.50%和41.18%,比叶片湿润持续10、12 h的早。显症后期,湿润持续时间4、6、8、10、12 h的病斑累积显症率分别是87.94%、93.71%、90.25%、84.24%和88.36%,差异不显著。表明接种黄瓜霜霉菌Pseudoperonospora cubensis后叶片湿润持续时间越长,潜育期越短,叶片最大温差越小,叶片平均温度越大。     

Impact of Diurnal Periodicity, Temperature, and Light on Sporulation of Bremia lactucae

ABSTRACT We evaluated direct and interactive effects of light quality and intensity, temperature and light, diurnal rhythms, and timing of high relative humidity during long day lengths on sporulation of Bremia lactucae, the causal agent of lettuce downy mildew, using inoculated lettuce seedlings and detached cotyledons. Suppression of sporulation by light was strongly dependent upon temperature and there was little suppression at 相似文献   

Influence of Environmental Conditions on Infection of Peach Shoots by Taphrina deformans

ABSTRACT The effect of weather conditions on the infection of peach shoots by Taphrina deformans was investigated both under orchard conditions and in controlled-environment experiments. Leaf curl incidence and severity were related to rainfall, length of wet periods, and temperature during wetness and during the incubation period, as well as to the development stage of shoots. Surface wetness was more important than rainfall for infection to occur. Minimum rainfall for infection was 3 mm, with a wet period of at least 12.5 h; higher amounts of rainfall did not cause infection when the wet period they triggered was shorter. Wet periods initiated by dew or fog were too short for infection to occur. Infection occurred only when air temperature was <16 degrees C during the wet period and <19 degrees C during incubation. Logistic equations relating relative disease incidence and either duration of wetness or temperature were developed under controlled-environment conditions, with asymptotes at >/=48 h of wetness and 相似文献   

避雨栽培对葡萄霜霉病发生的影响与葡萄冠层微气象因子的关系

系统比较了云南省石林县(‘红地球’)和弥勒县(‘水晶葡萄’)葡萄园采用避雨栽培和露天栽培对葡萄霜霉病Plasmoparaviticola(Berk.Curtis)Berl.de Toni.的防治效果,监测了田间葡萄园内避雨栽培和露天栽培处理中葡萄霜霉病的发生流行与植株冠层气象因子的变化情况,并结合适宜葡萄霜霉病病害循环的温度、相对湿度、叶面持露时间及田间葡萄植株冠层微气象因子的变化对避雨栽培有效防治葡萄霜霉病的气象原理进行了分析。结果表明,避雨处理可有效控制葡萄霜霉病的发生和危害,石林县和弥勒县两地葡萄园的防治效果分别达到97.84%和66.29%。弥勒县‘水晶葡萄’对霜霉病的抗性较强,霜霉病发生较轻,但在避雨栽培条件下霜霉病的病情指数也显著低于对照。植株冠层微气象因子变化分析表明,避雨栽培可以减少决定霜霉病菌能否成功侵染的叶面水膜持续时间,创造不适宜霜霉病菌萌发和侵入的条件,还可以显著减低棚内植株冠层适宜孢子囊产生的相对湿度的持续时间,减少霜霉病菌的侵染菌量,从而有效地控制了霜霉病的发生和危害。     

Development of ZWIPERO, A Model Forecasting Sporulation and Infection Periods of Onion Downy Mildew based on Meteorological Data

The weather-based forecasting model ZWIPERO was developed by the German Weather Service and determines the risk of sporulation and infection of Peronospora destructor quantitatively based on actual as well as predicted weather data (temperature, relative humidity, leaf wetness, precipitation). The model allows precise planning of disease monitoring and infection-related application of fungicides. ZWIPERO is a more complex mathematical model than the previously published models for downy mildew. In order to operate ZWIPERO independently of the actual field location and season, the time of sunrise and sunset of the location are exactly determined by a subroutine. Another subroutine provides simulated microclimatic input variables based on local production data as well as actual and hourly predicted (up to 4 days) standard weather data. Starting at the time of 'sunrise + 7 h', ZWIPERO calculates the number of sporangia produced, the time of onset of sporangia release, as well as the number of infections possible and the number of sporangia which may survive the day for each 24-h time step. Field evaluations of sporulation periods of downy mildew showed that the simulated micrometeorological input variables are reliable. As the actual plant development, the susceptibility and the disease incidence in the field are not taken into account, ZWIPERO has to be considered primarily as a decision support system for extension services and growers.     

Effects of leaf wetness and temperature on late leaf-spot infection of groundnut

Experiments are described to quantify the effects of temperature and leaf wetness duration on infection of groundnut by Phaeoisariopsis personata. Temperature response curves for conidial germination and infection were similar, with optima close to 20°C and minimum and maximum temperatures of about 8°C and 34 C, respectively. The effect of temperature on infection between 15°C and 26°C was slight. Lesions developed only if the leaf wetness period exceeded about 20 h, and the total wetness period necessary for maximum infection exceeded 160 h. The number of lesions resulting from a fixed amount of inoculum was several times greater if leaves were exposed to alternate wet and dry periods (intermittent wetness), compared with continuous wetness. With intermittent wetness the length of the dry period had little effect on the number of lesions, providing it exceeded 2 h. The response curve relating total wetness periods to lesion density was an exponential asymptote.     

Ascospore Release and Infection of Apple Leaves by Conidia and Ascospores of Venturia inaequalis at Low Temperatures

ABSTRACT Mills' infection period table describes the number of hours of continuous leaf wetness required at temperatures from 6 to 25 degrees C for infection of apple leaves by ascospores of Venturia inaequalis and reports that conidia require approximately two-thirds the duration of leaf wetness required by ascospores at any given temperature. Mills' table also provides a general guideline that more than 2 days of wetting is required for leaf infection by ascospores below 6 degrees C. Although the table is widely used, infection times shorter than those in the table have been reported in lab and field studies. In 1989 a published revision of the table eliminated a potential source of error, the delay of ascospore release until dawn when rain begins at night, and shortened the times reported by Mills for ascospore infection by 3 h at all temperatures. Data to support the infection times below 6 degrees C were lacking, however. Our objective was to quantify the effects of low temperatures on ascospore discharge, ascospore infection, and infection by conidia. In two of three experiments at 1 degrees C, the initial release of ascospores occurred after 131 and 153 min. In the third experiment at 1 degrees C, no ascospores were detected during the first 6 h. The mean time required to exceed a cumulative catch of 1% was 143 min at 2 degrees C, 67 min at 4 degrees C, 56 min at 6 degrees C, and 40 min at 8 degrees C. At 4, 6, and 8 degrees C, the mean times required to exceed a cumulative catch of 5% were 103, 84, and 53 min, respectively. Infection of potted apple trees by ascospores at 2, 4, 6, and 8 degrees C required 35, 28, 18, and 13 h, respectively; substantially shorter times than previously were reported. In parallel inoculations of potted apple trees, conidia required approximately the same periods of leaf wetness as ascospores at temperatures from 2 to 8 degrees C, rather than the shorter times reported by Mills or the longer times reported in the revision of the Mills table. We propose the following revisions to infection period tables: (i) shorter minimum infection times for ascospores and conidia at or below 8 degrees C, and (ii) because both ascospores and conidia are often present simultaneously during the season of ascospore production and the required minimum infection times appear to be similar for both spore types, the adoption of a uniform set of criteria for ascosporic and conidial infection based on times required for infection by ascospores to be applied during the period prior to the exhaustion of the ascospore supply. Further revisions of infection times for ascospores may be warranted in view of the delay of ascospore discharge and the reduction of airborne ascospore doses at temperatures at or below 2 degrees C.     

Influence of Weather Conditions on Infection of Peach Fruit by Taphrina deformans

ABSTRACT The effect of environment on the infection of peach fruit by Taphrina deformans was investigated using orchard observations under natural conditions (in 2001 to 2004) or in trees managed in such a way to exclude rainfall. These conditions were then validated using pot-grown peach plants exposed to single infection events and independent orchard observations. Leaf curl incidence was related to rainfall, length of wet periods, and the temperature during wetness and during the incubation period, as well as to the developmental stage of flowers and fruit. Weather conditions before petal fall did not influence fruit infection. After petal fall, rainfall and the duration of the wet period triggered by rainfall played a key role in infection occurrence. The minimum rainfall required for infection was 12 mm, with at least 24 h of wetness interrupted by no more than 4 h. No infection occurred when temperature was >/=17 degrees C during the wet period or >19 degrees C during incubation. Disease symptoms appeared on fruit after approximately 3 weeks of incubation, which is equivalent to 240- to 290-degree-days (base 0 degrees C). The period for fruit infection was relatively short being from petal fall until air temperature remained greater than 16 degrees C. During this period, the incidence of fruit that developed symptoms was closely related to the number of favorable events and the total wetness duration during such events.     

Prediction of stem rust infection favorability, by means of degree-hour wetness duration, for perennial ryegrass seed crops

ABSTRACT A weather-based infection model for stem rust of perennial ryegrass seed crops was developed and tested using data from inoculated bioassay plants in a field environment with monitored weather. The model describes favorability of daily weather as a proportion (0.0 to 1.0) of the maximum possible infection level set by host and inoculum. Moisture duration and temperature are combined in one factor as wet degree-hours (DH(w)) (i.e., degree-hours > 2.0 degrees C summed only over time intervals when) moisture is present). Degree-hours are weighted as a function of temperature, based on observed rates of urediniospore germination. The pathogen Puccinia graminis subsp. graminicola requires favorable conditions of temperature and moisture during the night (dark period) and also at the beginning of the morning (light period), and both periods are included in the model. There is a correction factor for reduced favorability if the dark wet period is interrupted. The model is: proportion of maximum infection = 1 - e((-0.0031) (DHw Index)), where DH(w) Index is the product of interruption-adjusted overnight weighted DH(w) multiplied by morning (first 2 h after sunrise) weighted DH(w). The model can be run easily with measurements from automated dataloggers that record temperature and wetness readings at frequent time intervals. In tests with three independent data sets, the model accounted for 80% of the variance in log(observed infection level) across three orders of magnitude, and the regression lines for predicted and observed values were not significantly different from log(observed) = log(predicted). A simpler version of the model using nonweighted degree hours (>2.0 degrees C) was developed and tested. It performed nearly as well as the weighted-degree-hour model under conditions when temperatures from sunset to 2 h past sunrise were mostly between 4 and 20 degrees C, as is the case during the growing season in the major U.S. production region for cool-season grass seed. The infection model is intended for use in combination with measured or modeled estimates of inoculum level, to derive estimates of daily infection.     

Pathogenicity of <Emphasis Type="Italic">Mycochaetophora gentianae</Emphasis>, causal fungus of gentian brown leaf spot,as affected by host species,inoculum density,temperature, leaf wetness duration,and leaf position

When the influence of host species, inoculum density, temperature, leaf wetness duration, and leaf position on the incidence of gentian brown leaf spot caused by Mycochaetophora gentianae, was examined, the fungus severely infected all seven Gentiana triflora cultivars, but failed to infect two cultivars of G. scabra and an interspecific hybrid cultivar. Inoculum density correlated closely with disease incidence, and a minimum of 10² conidia/mL was enough to cause infection. In an analysis of variance, temperature and leaf wetness duration had a significant effect upon disease incidence, which increased with higher temperature (15–25°C) and longer duration of leaf wetness (36–72 h). No disease developed at temperatures lower than 10°C or when leaf wetness lasted <24 h. At 48-h leaf wetness, disease incidence was 0, 28, 77, and 85% at 10, 15, 20, and 25°C, respectively. Middle and lower leaves on the plant were more susceptible than upper leaves. In microscopic observations of inoculated leaves, >50% of conidia germinated at temperatures >15°C after 24-h leaf wetness. More appressoria formed at higher temperatures (15–25°C) with extended duration of leaf wetness (24–72 h). At 48-h leaf wetness, appressorium formation was 0, 8, 26, and 73% at 10, 15, 20, and 25°C, respectively. These results suggest that temperature and leaf wetness duration were important factors for infection of gentian leaves.     

沈阳地区葡萄霜霉病流行时间动态及其气象影响因子分析

 通过2012-2014年田间小区试验,对沈阳地区葡萄霜霉病自然发病情况进行了系统调查和对比分析,并对影响葡萄霜霉病流行动态的气象因素进行了相关性分析。结果表明,沈阳地区葡萄霜霉病的季节流行曲线是典型的单峰S形曲线。应用SPSS19.0软件分析,明确了Logistic模型能够反映沈阳地区葡萄霜霉病流行时间动态情况。同时,推导了病害流行阶段:指数增长期为7月上旬至7月下旬,该时期为最佳药剂防治时期;逻辑斯蒂增长期为7月下旬至8月下旬;衰退期为8月下旬至葡萄生育末期。不同生长季病害发生日期、流行阶段天数和最大病情指数虽各不相同,但与Logistic模型推导趋势基本一致。各个流行阶段病害的表观侵染速率表现为:始发期＞盛发期＞衰退期。始发期和盛发期的是决定整个生长季葡萄霜霉病流行程度的关键时期。气象因素对葡萄霜霉病的流行有明显影响,其中表观侵染速率与7 d平均相对湿度、7 d累计降雨量和7 d叶面湿润时数成显著正相关,而与7 d平均气温呈显著负相关,以上4个气象因素是影响沈阳地区葡萄霜霉病流行的主导因子。     

Epidemiology,prediction and control of onion downy mildew caused byPeronospora destructor

The effect of environmental factors on the development of each stage ofPeronospora destructor (Berk.) Caspary on onions is reviewed. For sporulation to take place, a period of light must precede the period of darkness and high humidity in which spores are formed. Spores are discharged when the relative humidity (RH) is increasing or decreasing, and over a wide range of temperatures. Their discharge is triggered by exposure to red-infrared radiation and by vibration of the leaf. Dissemination of spores follows a daily periodic cycle and spores can be blown by wind over long distances. Duration of spore survival depends on temperature, RH and, especially, the absence of strong radiation. The rate of spore germination is highest at 10°C and declines with the rise in temperature. Germ tubes develop in liquid water, and a continuous period of wetness is required for infection to be completed. Systemic infection is common in cooler climates, where necks of onion bulbs are slow to dry. The principal sources of downy mildew infection by wind-borne spores are systemically infected propagation material, onion volunteer plants, and neighboring older crops.     

Effects of temperature,inoculum concentration,leaf age,and continuous and interrupted wetness on infection of olive plants by Spilocaea oleagina

Experiments were conducted on olive plants in controlled environments to determine the effect of conidial concentration, leaf age, temperature, continuous and interrupted leaf wetness periods, and relative humidity (RH) during the drier periods that interrupted wet periods, on olive leaf spot (OLS) severity. As inoculum concentration increased from 1·0 × 10² to 2·5 × 10⁵ conidia mL^?1, the severity of OLS increased at all five temperatures (5, 10, 15, 20 and 25°C). A simple polynomial model satisfactorily described the relationship between the inoculum concentration at the upper asymptote (maximum number of lesions) and temperature. The results showed that for the three leaf age groups tested (2–4, 6–8 and 10–12 weeks old) OLS severity decreased significantly (P < 0·001) with increasing leaf age at the time of inoculation. Overall, temperature also affected (P < 0·001) OLS severity, with the lesion numbers increasing gradually from 5°C to a maximum at 15°C, and then declining to a minimum at 25°C. When nine leaf wetness periods (0, 6, 12, 18, 24, 36, 48, 72 and 96 h) were tested at the same temperatures, the numbers of lesions increased with increasing leaf wetness period at all temperatures tested. The minimum leaf wetness periods for infection at 5, 10, 15, 20 and 25°C were 18, 12, 12, 12 and 24 h, respectively. The wet periods during early infection processes were interrupted with drying periods (0, 3, 6, 12, 18 and 24 h) at two levels of RH (70 and 100%). The length of drying period had a significant (P < 0·001) effect on disease severity, the effect depending on the RH during the interruption. High RH (100%) resulted in greater disease severity than low RH (70%). A polynomial equation with linear and quadratic terms of temperature, wetness and leaf age was developed to describe the effects of temperature, wetness and leaf age on OLS infection, which could be incorporated as a forecasting component of an integrated system for the control of OLS.     

Effect of leaf wetness duration and temperature on infection of downy mildew (Peronospora sp.) of basil

Journal of Plant Diseases and Protection - The effect of leaf wetness duration and temperature on the development of downy mildew of basil, incited by Peronospora sp., was studied under controlled...     

Activity of carboxylic acid amide (CAA) fungicides against Bremia lactucae

Four carboxylic acid amide (CAA) fungicides, mandipropamid (MPD), dimethomorph (DMM), benthiavalicarb (BENT) and iprovalicarb (IPRO) were examined for their effects on various developmental stages of Bremia lactucae, the causal agent of downy mildew in lettuce, in vitro and in planta. Spore germination in vitro or on leaf surfaces was inhibited by all CAA fungicides (technical or formulated). MPD was more effective in suppressing germination than DMM or BENT, whereas IPRO was least effective. CAA induced no disruption of F-actin microfilament organisation in germinating spores of B. lactucae. CAA applied to germinating spores in vitro prevented further extension of the germ tubes. When applied to germinated spores on the leaf surface they prevented penetration. Preventive application of CAA to intact plants inhibited infection. MPD was more effective in suppressing infection than DMM or BENT, whereas IPRO was least effective. Curative application was effective at ≤3 h post-inoculation (hpi) but not at ≥18 hpi. CAA (except IPRO) applied to upper leaf surfaces inhibited spore germination on the lower surface and hence reduced infection. CAA suppressed sporulation of B. lactucae on floating leaf discs and when sprayed onto infected plants two days before onset of sporulation. BENT and DMM were more effective in suppressing sporulation than MPD or IPRO. Epidemics of downy mildew in shade-house grown lettuce were suppressed by CAA. A single spray applied to five-leaf plants before transplanting controlled the disease for 50 days. The results suggest that CAA are effective inhibitors of spore germination and therefore should be used as preventive agents against downy mildew of lettuce caused by B. lactucae.     

A temperature and leaf wetness duration-based model for prediction of gray leaf spot of perennial ryegrass turf

ABSTRACT Gray leaf spot is a serious disease of perennial ryegrass (Lolium perenne), causing severe epidemics in golf course fairways. The effects of temperature and leaf wetness duration on the development of gray leaf spot of perennial ryegrass turf were evaluated in controlled environment chambers. Six-week-old Legacy II ryegrass plants were inoculated with an aqueous conidial suspension of Pyricularia grisea (approximately 8 x 10(4) conidia per ml of water) and subjected to four different temperatures (20, 24, 28, and 32 degrees C) and 12 leaf wetness durations (3 to 36 h at 3-h intervals). Three days after inoculation, gray leaf spot developed on plants at all temperatures and leaf wetness durations. Disease incidence (percent leaf blades symptomatic) and severity (index 0 to 10; 0 = leaf blades asymptomatic, 10 = >90% leaf area necrotic) were assessed 7 days after inoculation. There were significant effects ( alpha = 0.0001) of temperature and leaf wetness duration on disease incidence and severity, and there were significant interactions ( alpha = 0.0001) between them. Among the four temperatures tested, 28 degrees C was most favorable to gray leaf spot development. Disease incidence and severity increased with increased leaf wetness duration at all temperatures. A shorter leaf wetness duration was required for disease development under warmer temperatures. Analysis of variance with orthogonal polynomial contrasts and regression analyses were used to determine the functional relationships among temperature and leaf wetness duration and gray leaf spot incidence and severity. Significant effects were included in a regression model that described the relationship. The polynomial model included linear, quadratic, and cubic terms for temperature and leaf wetness duration effects. The adjusted coefficients of determination for the fitted model for disease incidence and severity were 0.84 and 0.87, respectively. The predictive model may be used as part of an integrated gray leaf spot forecasting system for perennial ryegrass turf.     

PLASMO: a simulation model for control of Plasmopara viticola on grapevine1

The problem of protecting grapevine against diseases is an old one, but in the last few years new techniques have been developed to reduce cost to the farmer and damage to the ecosystem. These are based on mathematical models describing the state of the plant-parasite environment system. A model for forecasting development of grapevine downy mildew (Plasmopara viticola) is presented. The input variables are temperature, rainfall and leaf wetness (determining infection by sporangia), and RH and temperature (for incubation period). The model also takes into account the limited survival of spores. The output is expressed as %, disease progress. Field validation tests, performed in 1990, 1991 and 1992 in several vineyards in Toscana (central Italy) showed a good correlation between observed and simulated infections. The model allowed the number of treatments to be reduced without any increase in downy mildew damage. It could in future be integrated with grapevine growth and development simulation models in an expert system to determine infected tissue area and thus the economic damage threshold.     

Effects of leaf wetness duration, relative humidity, light and dark on infection and sporulation by Didymella rabiei on chickpea

No infection occurred at less than 95% relative humidity (r.h.) when chickpea plants were dried after inoculation with conidia of Didymella rabiei. Infection was significant when the dry leaves were exposed to 98% r.h. for 48 h. When inoculated plants were subjected to different leaf wetness periods, some infection occurred with 4 h wetness, and disease severity increased with wetness duration according to an exponential asymptote, with a maximum value after about 18 h. Germination of conidia and germ tube penetration increased linearly with increasing wetness periods when recorded 42 h after inoculation. With a 24-h wetness period, germination of conidia was first observed 12 h after inoculation and increased linearly with time up to 52 h (end of the experiment). Dry periods immediately after inoculation, followed by 24-h leaf wetness, reduced disease severity; as the dry period increased the severity decreased. Disease severity increased with increasing periods of darkness after inoculation. The number of pycnidia and the production of conidia on infected leaves increased only slightly with high r.h. (either in the light or in the dark), but large increases occurred over an 8-day period when the leaves were kept wet.