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1.
ABSTRACT The spatial pattern of hop powdery mildew was characterized using 3 years of disease incidence data collected in commercial hop yards in the Pacific Northwest. Yards were selected randomly from yards with a history of powdery mildew, and two to five rows were selected for sampling within each yard. The proportion of symptomatic leaves out of 10 was determined from each of N sampling units in a row. The binomial and the beta-binomial frequency distributions were fit to the N sampling units observed in each row and to SigmaN sampling units observed in each yard. Distributional analyses indicated that disease incidence was better characterized by the beta-binomial than the binomial distribution in 25 and 47% of the data sets at the row and yard scales, respectively, according to a log-likelihood ratio test. Median values of the beta-binomial parameter theta, a measure of small-scale aggregation, were near 0 at both sampling scales, indicating that disease incidence was close to being randomly distributed. The variability in disease incidence among rows sampled in the same yard generally increased with mean incidence at the yard scale. Spatial autocorrelation analysis, used to measure large-scale patterns of aggregation, indicated that disease incidence was not correlated between sampling units over several lag distances. Results of a covariance analysis showed that heterogeneity of disease incidence was not dependent upon cultivar, region, or time of year when sampling was conducted. A hierarchical analysis showed that disease incidence at the sampling unit scale (proportion of sampling units with one or more diseased leaves) increased as a saturation-type curve with respect to incidence at the leaf level and could be described by a binomial function modified to account for the effects of heterogeneity through an effective sample size. Use of these models permits sampling at the sampling unit scale while allowing inferences to be made at the leaf scale. Taken together, hop powdery mildew was nearly randomly distributed with no discernable foci, suggesting epidemics are initiated from a well-distributed or readily dispersible overwintering population. Implications for sampling are discussed. 相似文献
2.
Abstract Incidence and geographical distribution of downy mildew (Peronosclerospora sorghi) on maize (Zea mays) were determined in a systematic survey of 181 maize fields in the major maize‐growing regions and ecological zones of Nigeria. Downy mildew was observed in the forest and Guinea savanna ecologies, but no disease was detected in other ecologies. Highest levels of disease incidence (63%) were observed in the forest zone, and progressively less disease incidence was found at the southern and northern Guinea savanna zones. Spatial pattern analysis indicated an aggregation and randomness of infected plants in the northern Guinea savanna and the forest zone, respectively. Disease incidence was positively correlated with the presence of downy mildew infected sorghum plants and relative amount of sporulation on infected sorghum (Sorghum bicolor) but negatively correlated with plant age and cropping pattern. Relative sporulation on maize plants was negatively correlated with age of maize plants. Higher levels of disease incidence were observed when the previous crop was either maize or sorghum than when previous crops were cassava, okra, tomatoes, or rice. 相似文献
3.
Analysing disease incidence data from designed experiments by generalized linear mixed models 总被引：2，自引：0，他引：2
Piepho 《Plant pathology》1999,48(5):668-674
As a result of aggregation or clustering of sampling units, disease incidence data from designed experiments frequently show overdispersion relative to the binomial distribution. This paper discusses generalized linear mixed models (GLMM) suitable for analysing overdispersed disease incidence data. The methods are exemplified using data from a randomized complete block experiment on the incidence of downy mildew ( Plasmopara viticola ) of grape ( Vitis lambrusca ). Hints are given regarding implementation of the methods using the %GLIMMIX macro for the SAS system. 相似文献
4.
ABSTRACT Relationships between disease incidence measured at two levels in a spatial hierarchy are derived. These relationships are based on the properties of the binomial distribution, the beta-binomial distribution, and an empirical power-law relationship that relates observed variance to theoretical binomial variance of disease incidence. Data sets for demonstrating and testing these relationships are based on observations of the incidence of grape downy mildew, citrus tristeza, and citrus scab. Disease incidence at the higher of the two scales is shown to be an asymptotic function of incidence at the lower scale, the degree of aggregation at that scale, and the size of the sampling unit. For a random pattern, the relationship between incidence measured at two spatial scales does not depend on any unknown parameters. In that case, an equation for estimating an approximate variance of disease incidence at the lower of the two scales from incidence measurements made at the higher scale is derived for use in the context of sampling. It is further shown that the effect of aggregation of incidence at the lower of the two scales is to reduce the rate of increase of disease incidence at the higher scale. 相似文献
5.
Downy mildew, caused by Peronospora arborescens, has become the major disease affecting oilseed poppy (Papaver somniferum) since its first record in Tasmania in 1996. Two field trials conducted in 2000 and 2001 studied the progression and spatial distribution of downy mildew epiphytotics. The logistic and exponential models best described the progression of disease incidence and severity, respectively. Incidence and severity increased rapidly following canopy closure. In 2001, incidence increased from 0.16%, prior to canopy closure, to 100% at late flowering (40 days). Spatial analyses of epiphytotics were conducted by fitting the beta-binomial and binomial distributions, median runs analysis, and the spatial analysis by distance indices. All analyses demonstrated that the distribution of incidence and severity was strongly spatially aggregated from canopy closure until at least late flowering. These results suggest that secondary spread from a few primary infections is the major factor in epiphytotics. 相似文献
6.
To improve sampling efficiency and precision in the assessment of white mould (caused by Sclerotinia sclerotiorum) disease incidence on bean (Phaseolus vulgaris), the spatial characteristics of epidemics were characterized in 54 linear transects in 18 bean fields during 2008–2010 in northern Tasmania, Australia. The incidence of diseased pods and plants was assessed prior to harvest. Distributional and correlation‐based analyses indicated the incidence of diseased pods was characterized by a largely random pattern at the individual plant scale, with some patches of similar disease levels on pods occurring at a scale of 1·5 m or greater. Collectively, these results suggested epidemics may be dominated by localized sources of inoculum. Sequential sampling approaches were developed to estimate or classify disease incidence above or below provisional thresholds of 3, 5 and 15% incidence on pods near harvest. Achieving prespecified levels of precision by sequential estimation was possible only when disease incidence on pods was greater than approximately 4% and sampling was relatively intense (i.e. 10 pods evaluated on each of at least 64 plants). Using sequential classification, correct decisions on disease status were made in at least 95% of independent validation datasets after assessment of only 10·1–15 plants, depending on classification threshold and error rates. Outcomes of this research provide the basis for implementing more efficient sampling and management strategies for this disease in Australian fields. 相似文献
7.
Odile Carisse Catherine Meloche William W. Turechek 《European journal of plant pathology / European Foundation for Plant Pathology》2011,130(3):349-365
The spatial pattern of apple scab was characterized using 10 years of disease incidence and lesion density data collected
in managed orchards located in Quebec, Canada. Distributional analyses indicated that scab incidence was better characterized
by the beta-binomial than the binomial distribution in 53 and 65% of the data sets at the leaf and shoot scales, respectively.
Median values of the beta-binomial parameter θ, a measure of small-scale aggregation, were near 0 (0.003 and 0.028) at both
sampling scales, indicating that disease incidence was close to being randomly distributed (low degree of aggregation). For
lesion density, the negative binomial distribution fitted the data better than the Poisson distribution in 86% of the data
sets at the leaf scale. The median value of the index of dispersion k was 0.068, indicating that aggregation was present. For all apple scab measurements, the power law models provided a good
fit to the data. The estimated slope and intercept parameters were significantly greater than 1 and 0, respectively, suggesting
that spatial heterogeneity changed systematically with disease incidence. Results of a covariance analysis showed that spatial
heterogeneity of scab incidence at both scales and lesion density was not dependent upon shoot type but that spatial heterogeneity
of scab incidence and lesion density at the leaf scale was influenced by the sampling period. A hierarchical analysis showed
that scab incidence at the tree scale increased as a saturation-type curve with respect to incidence at the leaf or shoot
scales. A similar relationship was observed for incidences at the shoot and leaf scales. An effective sample size model based
on the binary power law parameters (Madden and Hughes, Phytopathology 89:770–781, 1999) gave the best fit to the leaf and shoot data, respectively. The incidence-lesion density relationship at both scales was
well described by a complementary log-log (CLL) and log transformation model ( Radj2 = 0.97 and Radj2 = 0.94 ) \left( {R_{{adj}}^2 = 0.97\,and\,R_{{adj}}^2 = 0.94} \right) , however, the models tended to underestimate lesion density. The information of the spatial relations of apple scab within
and between hierarchical scales acquired from this study can be used in developing and evaluating practical disease management
strategies and to improve apple scab assessments for fungicide or cultivar susceptibility trials. 相似文献
8.
Abstract The losses in yield due to sorghum downy mildew of maize induced by Peronoscleospora sorghi were assessed from 1982 to 1984 in the epidemic‐prone area of Nigeria. Plots of maize with different downy mildew incidences were obtained by planting seedlots containing different percentages of metalaxyl‐treated seeds. The losses in yield were directly proportional to the incidence of the disease. There was highly significant negative correlation between the incidence of downy mildew and grain yield. 相似文献
9.
BACKGROUND: The present study investigated the effect of chitosan seed priming on the induction of disease resistance in pearl millet against downy mildew disease caused by Sclerospora graminicola (Sacc.) Schroet. RESULTS: Pearl millet seeds were primed with chitosan at different concentrations: 0.5, 1.5, 2.5 and 3 g kg?1 seed. Of the different concentrations, 2.5 g kg?1 was found to be optimum, with enhanced seed germination of 99% and seedling vigour of 1782, whereas the untreated control recorded values of 87% and 1465 respectively. At optimum concentration, chitosan did not inhibit sporulation and release of zoospores from sporangia. Furthermore, pearl millet seedlings raised after seed treatment with chitosan showed an increased level of the defence‐related enzymes chitosanase and peroxidase as compared with the untreated pearl millet seedlings on downy mildew pathogen inoculation. The effect of chitosan in reducing downy mildew incidence was evaluated in both greenhouse and field conditions, in which respectively 79.08 and 75.8% disease protection was obtained. CONCLUSION: Chitosan was effective in protecting pearl millet plants against downy mildew under both greenhouse and field conditions by inducing resistance against the pathogen. Thus, chitosan formulation can be recommended for seed treatment in the management of downy mildew disease. Copyright © 2008 Society of Chemical Industry 相似文献
10.
弱光胁迫下黄瓜霜霉病抗性评价与分析 总被引：2，自引：2，他引：0
为明确弱光胁迫下黄瓜霜霉病田间发病规律及遗传特性,筛选抗霜霉病黄瓜品种,以15份黄瓜自交系为试材,在弱光条件下通过子叶接菌诱导寄主植株发病,同时结合田间发病率及病情指数调查进行复合抗性鉴定,进而筛选抗病组合,并对其分离世代进行抗性鉴定与遗传特征分析。结果表明,供试15份材料中共筛选出4个典型品系HB1、HB2、HB3和HB4,其病情指数分别是14.17、28.71、63.33和78.33,分别属于高抗、抗病、感病和高感病类型。这4个亲本的F1代及分离世代群体中霜霉病抗性与亲本抗性均存在正相关关系,抗性亲本的后代表现出较强的抗性;F2代群体病株分离现象比较明显,呈偏态分布,有明显的主基因+多基因存在特征,表明弱光胁迫下黄瓜霜霉病受主基因+多基因控制,主基因效应值较大。经田间抗病性鉴定分析,初步筛选出组合HB12、HB13和HB21为抗霜霉病组合,可用于后续抗病品种的选育。 相似文献
11.
水稻细菌性基腐病株的空间分布及其抽样研究 总被引：2，自引：0，他引：2
经五种聚集度指标测定和Taylor,Iwao法检验,细菌性基腐病株在一切密度下都呈聚集型,属一般负二项分布。病株空间结构以疏松个体群形式存在,个体群间是聚集的,个体群内是随机的。个体群平均大小为0.1~0.2m2。利用分布型参数K、α、β值,分析了病株聚集的原因;探讨了平均密度与k值的关系;确定了理论抽样数。比较几种顺序抽样方法,以平行线法效果最佳。依X=41.5032Pe1·2603关系可由病丛率来估计病株密度。 相似文献
12.
beta-Aminobutyric acid (BABA) treatment of pearl millet [Pennisetum glaucum (L) R Br] seeds influenced seedling vigour and protected the seedlings from downy mildew disease caused by the oomycetous biotropic fungus Sclerospora graminicola (Sacc) Schroet. Of the different concentrations of BABA tested, viz 25, 50, 75 and 100 mM, seeds treated with 50 mM for 6 h resulted in the maximum of 1428 seedling vigour and showed 23% disease incidence in comparison with the control which recorded a seedling vigour of 1260 and 98% disease incidence i.e. 75% protection from disease. Seeds treated with BABA when challenged for downy mildew disease using zoospores of S graminicola required 48 h after inducer treatment to develop maximum resistance. Durability of induced resistance was also tested in plants raised from seeds treated with the inducer and identified as resistant, by second challenge inoculation with the downy mildew pathogen at tillers and inflorescence axes. Reduced disease incidence of only 10 and 12% in these plants, compared with 71 and 76% disease in control plants inoculated at the tillers and inflorescence axes, respectively, suggested that resistance induced in seeds with BABA remained operative through vegetative and reproductive growth of pearl millet plants. Induction of resistance by seed treatment with BABA enhanced vegetative growth, viz height, fresh weight, leaf area and tillering, and reproductive growth, viz early flowering, number of productive ear heads and 1000 seed weight. Studies on induction of resistance in different cultivars of pearl millet with varying resistance reaction to downy mildew indicated that the protection offered by BABA is independent of the nature of cultivars used and not dependent on their constitutive resistance. 相似文献
13.
为明确不同栽培模式下葡萄霜霉病菌Plasmopara viticola的遗传结构、遗传多样性及遗传分化水平,于2014-2015年定期采集露地和避雨2种栽培模式下的葡萄霜霉病菌菌株,利用6对SSR引物对该病菌基因型、遗传多样性及遗传分化进行对比分析。结果表明,露地和避雨栽培模式下葡萄霜霉病菌群体的Nei’s基因多样性指数大于0.14,香农多样性指数大于0.31,2种栽培模式下群体具有丰富的遗传多样性,但避雨栽培模式可显著降低群体等位基因数和等位基因频率。露地栽培模式下该病菌群体的流行模式呈现中等水平无性繁殖,2年初侵染和再侵染对病害流行的贡献率分别约占26.1%和73.9%;避雨栽培模式下葡萄霜霉病菌群体的流行模式则呈现高等水平无性繁殖,初侵染和再侵染对病害流行的贡献率分别约占4.3%和95.7%。卵孢子的形成对于葡萄霜霉病菌种群遗传变异和有效越冬起着关键的作用。2014-2015年露地栽培模式下葡萄霜霉病菌群体的主效流行基因型对病害流行的贡献率分别为44.5%和51.8%;而其在避雨栽培模式下葡萄霜霉病菌群体的贡献率分别可达84.2%和87.1%。同一年份的露地和避雨栽培模式下葡萄霜霉病菌群体的主效基因型种类相同,2个群体间的等位基因频率呈现显著正相关性,且二者之间存在频繁的基因交流,推测避雨栽培模式下葡萄霜霉病的初侵染源自于避雨设施附近的露地栽培病株上再侵染形成的飞散传播孢子囊。 相似文献
14.
The development of systemic disease from primary inoculum sources of sorghum downy mildew was studied on field-grown maize in Thailand. Data were recorded five times, from the first appearance of disease until 5 weeks after plant emergence. The incidence of diseased plants decreased with increasing distance from the primary inoculum sources, and the slope of the gradient flattened as the epidemic progressed. The steepest gradient of disease incidence was observed downwind. The progress in time and spread in space of disease about primary foci is described by three non-linear models which fit the data equally well. However, the resulting gradients at wider distances are different. With two models the gradients decrease asymptotically to zero with increasing distance, whilst the other model leads to negative values above a certain distance. The rates of isopath movement of all models decrease with time, but the effect of distance on the isopathic rate is different; the rate can decrease, stay constant or increase with distance. 相似文献
15.
Moshe Reuveni 《European journal of plant pathology / European Foundation for Plant Pathology》2003,109(3):243-251
Benthiavalicarb is a new fungicide active against Oomycetes fungal plant pathogens. The present study shows that benthiavalicarb is effective for controlling the Oomycete fungal pathogen Plasmopara viticola, which causes downy mildew in grapevines. The fungicide did not affect zoospore discharge from sporangia of P. viticola, but strongly inhibited zoospore encystment, cystospore germination in vitro and mycelial growth, together with sporangial production in vivo. Benthiavalicarb showed strong prophylactic and local activity in intact plants or detached leaves and low translaminar activity. The compound was not translocated from leaf to leaf in either a acropetal or basipetal direction. Benthiavalicarb applied at 1, 3 and 6 days post-inoculation protected grapevine plants against downy mildew and inhibited sporulation of the pathogen. Similar results were obtained on leaf disks if benthiavalicarb was applied up to 96 h post-inoculation. Benthiavalicarb diminished the sporulation of P. viticola when applied to established disease in the tissue. Benthiavalicarb remained active on leaves for a period up to 28 days. Two foliar applications of benthiavalicarb, 2 weeks apart, to field-grown grapevines inhibited downy mildew development and were as effective as the standard metalaxyl-Cu treatment in controlling the disease. A formulated mixture of benthiavalicarb + Folpet was similar or superior in performance to metalaxyl-Cu and the new strobilurin trifloxystrobin in controlling downy mildew. The effectiveness of benthiavalicarb makes it well suited for integration into a control programme against downy mildew disease in vineyards, and as a component to delay resistance buildup. 相似文献
16.
ABSTRACT The relationships between disease incidence and colony density and between leaf and shoot disease incidences for apple powdery mildew were investigated over four seasons in order to derive a simple relationship for predicting density using incidence. The Neyman type A distribution generally provided a good fit to the observed number of colonies per leaf and shoot, and provided a significantly better fit than the Poisson distribution, indicating a degree of aggregation of mildew colonies. In general, Taylor's power-law satisfactorily described the observed variance-mean relationship for colony density; however, Taylor's power-law broke down at very high levels of mean density. Incidence of leaf infection could be determined based on average number of colonies per leaf assuming a fixed variance-mean relationship and a Neyman type A distribution for colony density. Regression models using the complemen- tary log-log transformation of incidence also provided accurate predictions of leaf (or shoot) disease incidence from colonies per leaf (or per shoot). Similar accuracies of these incidence-density models suggested that variance-mean ratio of colony density was more or less constant over time. Unlike the case with colony density, the number of mildewed leaves per shoot generally had a random pattern, as indicated by the good fit of the binomial distribution. Thus, it was possible to estimate the leaf incidence of the youngest unrolled leaves on a shoot using the shoot incidence. It is argued that the leaf incidence-density relationships developed in the present study may be used in making practical disease management decisions. 相似文献
17.
小麦白粉病田间分布型的初步研究 总被引：1，自引：1，他引：0
Al-sohaily 等研究丝黑穗病菌的生理分化指出,玉米丝黑穗病菌与高粱丝黑穗病菌应为2个不同的“变种”,分别命名为:Sphacelotheca reiliana var.Zeae 和 S.rei-(?)iana var.reiliana。国内的初步研究结果表明,来自不同地区的玉米丝黑穗病菌不存在明显的致病力差异。为探明高梁丝黑穗病菌的地区间差异性,深入研究病菌生理分化,为抗病育种提供依据,进行了此项试验,简报如下。 相似文献
18.
Lesion-count data on fruits/leaves from two regions of China and on leaves from controlled-environment studies were used to investigate incidence-density [incidence of leaves/fruits with lesion(s) and average number of lesions per leaf/fruit] and incidence-incidence [incidences of leaves and shoots with lesion(s)] relationships. Few of the datasets for the number of lesions per fruit/leaf could be fitted satisfactorily by a Poisson distribution. Three two-parameter distributions (negative binominal, Neyman type A and Polya-Aeppli) provided significantly better fit than the Poisson distribution, indicating a degree of aggregation in the number of lesions on a single leaf/fruit. However, many datasets could still not satisfactorily be fitted by these distributions. The dynamics of aggregation of lesions on leaves/fruits was well described by Taylor's power-law model. Regression models provided accurate predictions of the average number of lesions per leaf/fruit from the incidence of leaves or fruits with lesion(s). Nevertheless, the incidence-density relationship varied considerably between regions and between leaf and fruit scab. Field data also indicated that the number of scabbed leaves per shoot showed some degree of aggregation. The incidence of leaves with scab could be predicted accurately from the incidence of shoots with scab. The incidence-density relationships developed in this study could be used in making practical disease-management decisions when incidence of leaves with scab is less than 35%. 相似文献
19.
20.
ABSTRACT For aggregated or heterogeneous disease incidence, one can predict the proportion of sampling units diseased at a higher scale (e.g., plants) based on the proportion of diseased individuals and heterogeneity of diseased individuals at a lower scale (e.g., leaves) using a function derived from the beta-binomial distribution. Here, a simple approximation for the beta-binomial-based function is derived. This approximation has a functional form based on the binomial distribution, but with the number of individuals per sampling unit (n) replaced by a parameter (v) that has similar interpretation as, but is not the same as, the effective sample size (n(deff) ) often used in survey sampling. The value of v is inversely related to the degree of heterogeneity of disease and generally is intermediate between n(deff) and n in magnitude. The choice of v was determined iteratively by finding a parameter value that allowed the zero term (probability that a sampling unit is disease free) of the binomial distribution to equal the zero term of the beta-binomial. The approximation function was successfully tested on observations of Eutypa dieback of grapes collected over several years and with simulated data. Unlike the beta-binomial-based function, the approximation can be rearranged to predict incidence at the lower scale from observed incidence data at the higher scale, making group sampling for heterogeneous data a more practical proposition. 相似文献