The sensitivity of the epidemic growth rate to weather variables, with an application to yellow rust on wheat

ABSTRACT We first show how to estimate the exponential epidemic growth rate, r, for different combinations of three weather variables. Then we derive a method to quantify the sensitivity of r to a weather variable as a function of the pathogen life cycle variables of latent period, basic reproductive number, and the mean and standard deviation of the sporulation curve. The method can be used to identify the most important weather variable and pathogen life cycle component in terms of epidemic progress. The method is applied to yellow rust, caused by Puccinia striiformis, on winter wheat. We conclude that the most important weather variable for the progress of yellow rust is temperature, followed by dew period and light quantity. By far, the most important pathogen life cycle component is the basic reproductive number, especially at low and high temperatures. This disagrees with the general view that latent period is the most important variable at low temperatures. We discuss explanations of this.     

The elasticity of the epidemic growth rate to observed weather patterns with an application to yellow rust

ABSTRACT We extend a previously developed method that quantifies the sensitivity of the exponential epidemic growth rate, r, to weather changes, through a pathogen's life cycle components (basic reproduction number, latent period, and mean and standard deviation of the spore production curve). Here a method is developed to study the elasticities of the system and subsequently the model is linked to observed weather patterns. This enables a direct comparison between the effects of different weather variables (temperature, surface wetness duration, and light quantity) under realistic weather scenarios. The three sites studied represent areas within the United Kingdom with contrasting climates. Yellow rust, caused by Puccinia striiformis, on winter wheat is studied as a key application. Our results show that temperature and more importantly changes in temperature through their effect on pathogen reproduction have the largest effect on r. The long latent period at low winter temperatures is not a key component in the epidemic development, which is contrary to general beliefs. The results combined with long term average yellow rust severity patterns show that it is winter survival and not summer survival that controls the eventual disease severity. The results also show that within the current United Kingdom spraying regime on wheat crops against yellow rust, the first spray should mainly affect the basic reproduction number, i.e., should be a protectant spray, whereas the second spray should also affect the latent period, i.e., should also have curative action.     

Effects of an Interaction Between Inoculum Density and Temperature on Germination of Puccinia allii Urediniospores and Leek Rust Progress

ABSTRACT Controlled environment experiments were conducted to study the effects of inoculum density, temperature, and their interaction on germination of Puccinia allii urediniospores and infection of leek leaves. Percent germination of P. allii urediniospores and percent branching of germ tubes increased with 3 density of urediniospores and approached a plateau for densities above approximately 20 spores cm(-2) of leaf area. Percent germination was highest at 12 to 21 degrees C, a wide-range temperature optimum. Branching occurred at temperatures ranging from 5 to 25 degrees C, but there were few germ tubes branching at 25 degrees C. P. allii successfully infected leek leaves at temperatures ranging from 7 to 22 degrees C. The number of pustules produced increased with urediniospore density on leek leaves. At low spore densities, pustule production was little affected by temperature; at higher spore densities, pustule production was greatest between 9 to 11 degrees C, and numbers of pustules decreased greatly with temperature increasing above this optimum. Latent period was affected by temperature, with latent period being shortet between 19 and 22 degrees C, and latent period increasing when temperature decreased. Latent periods became approximately 1.8 days shorter for every 10-fold increase in spore density. The rate of pustule production increased with increasing spore density on leaves and was greatest between 11 to 14 degrees C. Computer simulation of leek rust progress based on the found relationships suggested that at optimal temperatures the development of leek rust epidemics may be little affected by initial spore density and density caused by each pustule, but that at sub- and supra-optimal temperatures the development is greatly affected by these variables.     

Contribution of the life-history traits of a plant pathogen to the development of field epidemics

The pathogenicity-related traits of biotrophic plant pathogens are usually measured on the individual host plant, at the scale of a single pathogen life cycle, whereas epidemic development in the field encompasses a succession of cycles. It remains unclear which traits make the greatest contribution to pathogen fitness in the field and to epidemic severity. The objective of this study was to determine the contributions of elementary pathogenicity traits to epidemic development in field conditions. We challenged a set of wheat cultivars with three different leaf rust isolates, under both controlled and field conditions, in 3 consecutive years. Infection efficiency, latent period, lesion size, spore production per lesion and spore production capacity were measured in the greenhouse, whereas disease severity was measured in the field. Most, but not all, of the pathogenicity traits were related to each other. All traits contributed to epidemic development in the field, but to different extents. Surprisingly, lesion size and spore production per lesion were inversely correlated with epidemic severity. Conversely, there was a strong positive correlation between spore production capacity and pathogen fitness in the field, in accordance with the concept of propagule pressure as a strong determinant of invasion success. Severe epidemics were mostly associated with small lesions with a high spore production capacity, high infection efficiency and a short latent period.     

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   

The influence of silicon on components of resistance to blast in susceptible, partially resistant, and resistant cultivars of rice

ABSTRACT The application of silicon (Si) fertilizers reduces the severity of blast, caused by Magnaporthe grisea, in irrigated and upland rice; however, little research has been conducted to examine the epidemiological and etiological components of this reduction. Four cultivars of rice with differential susceptibilities to race IB-49 of M. grisea were fertilized with three rates of a calcium silicate fertilizer and inoculated with the pathogen to test the effects of Si on the following components of resistance to blast: incubation period, latent period, infection efficiency, lesion size, rate of lesion expansion, sporulation per lesion, and diseased leaf area. For each cultivar, the incubation period was lengthened by increased rates of Si, and the numbers of sporulating lesions, lesion size, rate of lesion expansion, diseased leaf area, and number of spores per lesion were reduced. Lesion size and sporulation per lesion were lowered by 30 to 45%, and the number of sporulating lesions per leaf and diseased leaf area were significantly reduced at the highest rate of Si. The net effect of Si on these components of resistance is an overall reduction in the production of conidia on plants infected with M. grisea, thereby slowing the epidemic rate of blast.     

Effects of temperature on the development of light leaf spot (Pyrenopeziza brassicae) on oilseed rape (Brassica napus)

The effects of temperature on the development of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape were investigated in controlled-environment experiments. The proportion of conidia which germinated on leaves, the growth rate of germ tubes, the severity of light leaf spot and the production of conidia increased with increasing temperature from 5 to 15 C. The time to 50% germination of conidia and the incubation and latent periods of light leaf spot lesions decreased when temperature increased from 5 to 15°C. At 20°C, however, light leaf spot severity and production of conidia were less and the incubation and latent periods were longer than at 15 C. There were differences between P brassicae isolates and oilseed rape cultivars in the severity of light leaf spot, the production of conidia and the length of the incubation period but not in the length of the latent period. The responses to temperature for lesion severity and incubation and latent periods appeared to be approximately linear over the temperature range 5-15°C and could be quantified using linear regression analysis.     

温度对伪钝绥螨实验种群的影响

本文研究了5个不同恒温条件下伪钝绥螨取食二斑叶螨时的发育和繁殖情况,并对该实验种群的生命参数进行了分析。结果表明,在19~31℃范围内,伪钝绥螨各螨态和整个未成熟期的发育历期随温度的升高而缩短,发育速率随温度的升高而加快;运用直线回归法计算出了伪钝绥螨各螨态的发育起点温度及有效积温。伪钝绥螨产卵期在22℃时最长,在31℃时最短;日均卵量随温度的升高而增大。伪钝绥螨净增殖率Ro在28℃时最高(60.256),在19℃时最低(4.174);内禀增长率rm和周限增长率λ皆是在31℃时最高,在19℃时最低;31℃时种群加倍时间t最短(2.79 d),19℃时最长(15.868 d)。     

Early development of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape (Brassica napus) in relation to temperature and leaf wetness.

In controlled environment experiments to study early development of light leaf spot, lesions developed with leaf wetness durations of 16 to 48 h after inoculation of oilseed rape with conidial suspensions of Pyrenopeziza brassicae at 12 or 18°C, but not with leaf wetness durations of 0 to 13h. The incubation period was 21 to 22 days at 12°C and 14 to 18 days at 18°C for leaf wetness durations of 16 to 48 h. The latent period was 21 to 23 days at 12°C and 18 to 19 days at 18°C, and the total number of lesions increased with increasing leaf wetness duration at both temperatures. In field experiments, light leaf spot always developed on oilseed rape with a leaf wetness duration of 48 h after inoculation in both 1990/1991 and 1991/1992, but the percentage leaf area affected was less on plants placed in an oilseed rape crop than on those placed in a glasshouse. Plants moved to an oilseed rape crop immediately after inoculation nearly always developed light leaf spot symptoms when they were inoculated between 19 October 1990 and 1 March 1991 or between 27 September 1991 and 14 February 1992, but plants inoculated between 31 August and 16 October 1990 or on 20 September 1991, when estimated leaf wetness duration was less than 16 h for several days after they were placed in crops, did not develop symptoms. The latent period of light leaf spot on plants transferred to the oilseed rape crop was 15 to 40 days, and there was an approximately linear relationship between 1 (latent period) and mean temperature during this period. The accumulated temperature during the latent period ranged from c. 150 to 250 day-degrees. The severity of lesions on these plants increased with increasing temperature from 5 to 15°C.     

Selective sieves in the epidemiology of Melampsora lini

The effects of various potential selective sieves operating at different stages in the epidemiological cycle of pathogen populations were examined in the context of a natural interaction between Melampsora lini and Linum marginale The establishment of self-sustaining pathogen populations in previously healthy host stands was significantly lowered only when the size of host populations was extremely low (1-3 plants). During the endemic phase of growth when interpustule competition was non-existent, differences in the latent period or size of individual pustules of 10 different pathogen isolates were minor compared to differences due to temperature. A competition experiment between two pathotypes of M. lini detected a marked shift in the relative frequency of the two pathotypes during the course of an epidemic lasting approximately five generations. Finally, the survival of two different pathotypes of the pathogen during off-season reductions in population size was significantly affected by site, year and pathotypic identity. Interactions between these variables were either marginal or non-existent. The net effect of the interplay of these genetic and ecological factors is to increase stochasticity and the potential for sustained differences between pathogen denies a feature expected when host pathogen co-evolution occurs at a metapopulation level.     

The effects of dispersal gradient and pathogen life cycle components on epidemic velocity in computer simulations

ABSTRACT The velocity of expansion of focal epidemics was studied using an updated version of the simulation model EPIMUL, with model parameters relevant to wheat stripe rust. The modified power law, the exponential model, and Lambert's general model were fit to primary disease gradient data from an artificially initiated field epidemic of stripe rust and employed to describe dispersal in simulations. The exponential model, which fit the field data poorly (R (2) = 0.728 to 0.776), yielded an epidemic that expanded as a traveling wave (i.e., at a constant velocity), after an initial buildup period. Both the modified power law and the Lambert model fit the field data well (R(2) = 0.962 to 0.988) and resulted in dispersive epidemic waves (velocities increased over time for the entire course of the epidemic). The field epidemic also expanded as a dispersive wave. Using parameters based on the field epidemic and modified power law dispersal as a baseline, life cycle components of the pathogen (lesion growth rate, latent period, infectious period, and multiplication rate) and dispersal gradient steepness were varied within biologically reasonable ranges for this disease to test their effect on dispersive wave epidemics. All components but the infectious period had a strong influence on epidemic velocity, but none changed the general pattern of velocity increasing over time.     

The effect of temperature and light intensity on growth and sporulation of Puccinia striiformis on wheat

Urediniospore production by Puccinia striiformis on wheat per unit leaf area infected was much lower at low light intensities than at high light intensities. The number of pustules per unit area of infected leaf and the daily sporulation rate per pustule increased linearly with increasing light over the range 10–50 W/m². Increasing temperature between 7 and 20°C shortened latent period and reduced the longevity of sporulating leaves. Colonization rate and the frequency of pustules per unit area of infected leaf increased between 7 and 15°C but declined markedly at 20°C. Spore production reached its peak earlier and declined more rapidly with increasing temperature between 7 and 15°C. this decline being less marked in the highly susceptible cultivar Maris Beacon than in the more resistant Maris Nimrod and Maris Huntsman.     

紫外线胁迫对红色型豌豆蚜生物学特性的影响

由于臭氧层消耗,南北半球中高纬度地区紫外线(UV-B)胁迫增强,为了探求增强的UV-B胁迫对红色型豌豆蚜生物学特性的影响,以期明确UV-B辐射在豌豆蚜种群演替和种下分化中的作用。本研究以40 W紫外线灯连续辐射处理红色型豌豆蚜8代,每代从初产若蚜开始每天处理1次,连续照射6d,分20、30、40、50和60min 5个处理,并设置白炽灯对照。结果显示,同一世代,随着UV-B辐射时间延长,豌豆蚜体长逐渐减短,体重逐渐减轻,净增殖率、内禀增长率、周限增长率逐渐减小,平均世代周期逐渐延长。同一UV-B辐射时间下,随着世代增加,豌豆蚜体长、体重、净增殖率、内禀增长率、周限增长率均呈先上升后显著下降的趋势,平均世代周期呈先下降后显著上升的趋势。至F8代,不同辐射时间下豌豆蚜平均体长为对照的42.58%~81.94%,平均体重为对照的33.77%~73.12%,净增殖率为对照的6.94%~46.55%,周限增长率为对照的77.00%~87.94%,平均世代周期为对照的1.20~1.38倍,内禀增长率降低,且50~60min处理下小于对照的1/2,种群数量增长放缓。以上说明长期UV-B胁迫对豌豆蚜的生长发育和种群增长最终都有抑制作用。     

Epidemic dynamics and patterns of plant diseases

ABSTRACT The general Kermack and McKendrick epidemic model (K&M) is derived with an appropriate terminology for plant diseases. The epidemic dynamics and patterns of special cases of the K&M model, such as the Vanderplank differential-delay equation; the compartmental healthy (H), latent (L), infectious (S), and postinfectious (R) model; and the K&M model with a delay-gamma-distributed sporulation curve were compared. The characteristics of the disease cycle are summarized by the basic reproductive number, R(0), and the normalized sporulation curve, i(tau). We show how R(0) and the normalized sporulation curve can be calculated from data in the literature. There are equivalences in the values of the basic reproductive number, R(0), the epidemic threshold, and the final disease level across the different models.However, they differ in expressions for the initial disease rate, r, and the initial infection, Q, because the values depend on the sporulation curve. Expressions for r and Q were obtained for each model and can be used to approximate the epidemic curve by the logistic equation.     

Effects of temperature on the latent period of the rose powdery mildew pathogen, Sphaerotheca pannosa

The effects of temperature on the length of the latent period of rose powdery mildew, caused by Sphaerotheca pannosa var . rosae , were studied. At constant temperatures over the range of 10–28°C, the length of the latent period ranged from 4 to 10 days. The relationship between temperature and the rate of fungal development during the latent period (expressed as the reciprocal of the latent period) was described by a nonlinear (thermodynamic) model. The resulting curve was asymmetrically bell-shaped with an optimum temperature of about 22°C. The latent period was further subdivided into two periods: incubation period (from inoculation to visible colonies) and postincubation period (from visible colonies to the first sign of conidiophores). The relationship between temperature and the rate of fungal development during the incubation period (expressed as the reciprocal of the incubation period) was also well described by a thermodynamic model. In contrast, the relationship between temperature and the rate of fungal development during the postincubation period (expressed as the reciprocal of the postincubation period) was approximately linear. The latent period under fluctuating temperatures was predicted using a two-stage integration scheme at a step of 24 min by first integrating the incubation rate and then the postincubation rate. The predicted length of the latent period agreed well with the observed values.     

Mummified fruit as a source of inoculum and disease dynamics of olive anthracnose caused by Colletotrichum spp

Anthracnose, caused by Colletotrichum spp., is a destructive disease of olive fruit worldwide. The objective of this study was to investigate the influence of agronomical and weather factors on inoculum production using detached olive fruit and on the development of epidemics in the field. The pathogen produced very large numbers of conidia on rotted (>1.87 × 10(8) conidia/fruit) or mummified (>2.16 × 10(4) conidia/fruit) fruit under optimal conditions. On mummified fruit, conidial production was highest on mummies incubated at 20 to 25°C and 96 h of wetness. Repeated washings of mummies reduced conidial production until it was very low after five washings. When mummies were placed in the tree canopy, conidial production was not reduced after 6 months (May to October); but, when they were held on the soil or buried in the soil, conidial production comparatively decreased up to 10,000 times. Anthracnose epidemics on susceptible 'Hojiblanca' and 'Picudo' during three seasons (2005-08) were influenced by rainfall, temperature, and fruit ripening, and had three main phases: the latent period (May to October); the onset of the epidemic, which coincided with the beginning of fruit ripening (early November); and disease development, which was predicted by the Weibull model (November to March). No epidemics developed on the susceptible cultivars during the driest season (2007-08) or on the resistant 'Picual' olive during any of the three seasons. These results provide the basis for a forecasting system of olive anthracnose which could greatly improve the management of this disease.     

不同温度下的豌豆蚜实验种群生命表研究

在6种温度(12、15、18、21、24℃和27℃)和相对湿度为80%的条件下,研究了温度对豌豆蚜发育和增殖的影响。组建了生命表,并统计出种群内禀增长率、净增殖率、世代平均周期、种群加倍时间和周限增长率等种群动态参数。结果表明,在试验温度范围内,豌豆蚜的发育历期随温度升高而缩短。种群的内禀增长率在24℃条件下最大(rm=0.281 0),相应的种群净增殖率(R0)、周限增长率(λ)、平均世代周期(T)和种群加倍时间(t)分别为17.030 9、1.324 5、10.089 3 d和2.466 7 d。     

小麦白粉病菌对温度不同敏感性菌株的寄生适合度研究

 利用离体叶片接种法,将12个对温度不同敏感性的小麦白粉病菌株分别在18℃和22℃条件下的流行组分（潜育期、侵染几率、单病斑累积产孢量和病斑日扩展面积）和寄生适合度进行了测定。结果表明,对温度不同敏感性菌株的流行组分在18℃和22℃条件下均存在显著性差异,且单病斑累积产孢量与病斑日扩展面积的相关性最高。各供试菌株在22℃条件下的寄生适合度均低于18℃条件下的寄生适合度。在两温度条件下,对温度低敏感性菌株平均寄生适合度高于对温度高敏感性菌株,特别是在较高温度下这种趋势更为明显。     

Effects of temperature and wetness duration on conidial infection, latent period and asexual sporulation of Pyrenopeziza brassicae on leaves of oilseed rape

Experiments in controlled environments were carried out to determine the effects of temperature and leaf wetness duration on infection of oilseed rape leaves by conidia of the light leaf spot pathogen, Pyrenopeziza brassicae . Visible spore pustules developed on leaves of cv. Bristol inoculated with P. brassicae conidia at temperatures from 4 to 20°C, but not at 24°C; spore pustules developed when the leaf wetness duration after inoculation was longer than or equal to approximately 6 h at 12–20°C, 10 h at 8°C, 16 h at 6°C or 24 h at 4°C. On leaves of cvs. Capricorn or Cobra, light leaf spot symptoms developed at 8 and 16°C when the leaf wetness duration after inoculation was greater than 3 or 24 h, respectively. The latent period (the time period from inoculation to first spore pustules) of P. brassicae on cv. Bristol was, on average, approximately 10 days at 16°C when leaf wetness duration was 24 h, and increased to approximately 12 days as temperature increased to 20°C and to 26 days as temperature decreased to 4°C. At 8°C, an increase in leaf wetness duration from 10 to 72 h decreased the latent period from approximately 25 to 16 days; at 6°C, an increase in leaf wetness duration from 16 to 72 h decreased the latent period from approximately 23 to 17 days. The numbers of conidia produced were greatest at 12–16°C, and decreased as temperature decreased to 8°C or increased to 20°C. At temperatures from 8 to 20°C, an increase in leaf wetness duration from 6 to 24 h increased the production of conidia. There were linear relationships between the number of conidia produced on a leaf and the proportion of the leaf area covered by 'lesions' (both log₁₀-transformed) at different temperatures.     

茶尺蠖核型多角体病毒对宿主种群的控制作用

室内试验表明,茶尺蠖核型多角体病毒对宿主种群具有明显的控制作用。宿主感染病毒后,其存活率、化蛹率、羽化率、生殖率、净生殖率(R_0)、内禀增长力(r_m)和周限增长率(λ)均低于或明显低于对照;平均世代长度(T)长于对照。饲毒组与对照组间的这种差异因饲毒浓度、饲毒虫龄和温度的不同而变化。免于病死蛹羽化所得雌成虫和对照间的产卵期、产卵量则无显著性差异。田间试验除表明具有明显的控制作用外,并显示一定的后效作用。