Spatiotemporal distribution of tomato plants naturally infected with leaf mold in commercial greenhouses

The distribution of tomato plants infected by Passalora fulva, causal agent of leaf mold, was analyzed by using Taylor’s model and Iwao’s model to assess the patterns of spatial distribution within the greenhouses. In Taylor’s model, the sample variance (s ²) of diseased plants newly recognized at each observation increased only slightly with mean density (m). In Iwao’s model, the mean crowding (m*) of newly recognized diseased plants at each observation increased with m of diseased plants. The statistical analysis in this study suggests that new infections in greenhouses observed during this investigation tended to cluster around a diseased plant and that secondary infections occurred as independent cluster points.     

基于冗余分析的降香黄檀人工林叶部病害与土壤因子的关系研究

为了探讨降香黄檀人工林土壤因子与叶部病害发生的关系,对海南省13块降香黄檀人工纯林样地进行了病害调查和土壤因子的测定,运用冗余分析找到影响病害发生的主导因子,结果表明:土壤的pH、速效氮、全磷、速效钾是影响病害发生最主要的4个指标。对病害发生影响的土壤因子按其重要性依次为:pH速效氮全磷速效钾。在冗余分析的基础上,通过聚类分析将样地划分为轻度、中度、重度感病区3种不同类型,并通过单因素方差分析研究了4个主导因子在不同类型样地中的差异。结果表明,不同发病程度的样地与土壤因子相关性差异明显,总体表现为:发病严重的Ⅲ类样地土壤中的速效氮和全磷含量最高,平均值分别为82.08mg/kg、0.68g/kg,轻度感病的Ⅰ类样地土壤中的pH和速效钾含量最高,平均值分别为6.56、143.60mg/kg。     

Spatiotemporal distribution of barley and wheat plants naturally infected with bacterial black node in fields in western Japan

Bacterial black node caused by Pseudomonas syringae pv. syringae is the most serious bacterial disease of barley and wheat in Japan. The spatiotemporal distribution of barley and wheat plants infected with bacterial black node in fields in 2016–2017 was analyzed using Taylor’s model and Iwao’s model. In Taylor’s model, the sample variance (s ²) of the total and the newly diseased plants at each observation increased with mean plant density (m). In Iwao’s model, although the mean crowding (m*) of total and newly recognized diseased plants increased with m, Taylor’s model fit the data better than did Iwao’s model. Thus, bacterial black node could be explained as a colony expansion model.     

侵染甜椒的番茄黄化曲叶病毒的分子鉴定和全序列分析

<正>番茄黄化曲叶病毒(Tomato yellow leaf curl virus,TYLCV)在世界范围内可危害多种作物,造成植株矮化、叶片皱缩变形、局部黄化等症状。该病毒自1964年首次报道以来已蔓延至世界多地。在我国2006年上海首次报道该病毒[1],随后江苏、山东、安徽、北京、河北、天津等地相继报道,危害严重。TYLCV为双生病毒科(Geminiviridae)菜豆金色花叶病毒属(Begomovirus)成员,基因组为单组     

广西胜红蓟黄脉病样中发现多种菜豆金色花叶病毒属的病毒

 双生病毒科(Geminiviridae)病毒是一组植物单链DNA病毒,它的特点是病毒粒子形态为孪生颗粒状。双生病毒分为菜豆金色花叶病毒属(Begomovirus)、甜菜曲顶病毒属(Curtovirus)、玉米线条病毒属(Mastrevirus)和番茄伪曲顶病毒属(Topocuvirus)^[1]。     

An effective sample size for predicting plant disease incidence in a spatial hierarchy

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.     

Detection of corn stunt spiroplasma in vivo by ELISA using antisera to extracts from infected corn plants (Zea mays)

Antisera were raised in rabbits to extracts from healthy corn plants and from plants infected with corn stunt spiroplasma (CSS); they were prepared by partially purifying sap or tissue homogenates from whole stems by differential centrifugation and filtration. The titres of CSS-specific antibody in the antisera to diseased plant extracts (DPE) were monitored by spiroplasma deformation tests. After cross-absorption against healthy plant extracts, the DPE antisera detected cultured CSS at concentrations exceeding 10⁶ cells/ml, compared with less than 10⁵ cells/ml for homologous antiserum, and reacted more strongly against extracts from diseased than from healthy plants. A comparison of techniques for extracting diseased plant tissues showed that the reaction of stems and midribs against cultured CSS antiserum was two to three times stronger if the samples were lyophilized before extraction. When extracts from lyophilized tissues were used as test antigens the DPE antisera discriminated between diseased and healthy corn stems, midribs and roots as effectively as antiserum to cultured CSS. Preliminary attempts to detect CSS in its vector, Dalbulus maidis , were complicated by non-specific reactions of insect tissue extracts but concentrations equivalent to at least one CSS-infected insect/ml of sample were detected by antiserum to cultured CSS.     

A generalized linear modeling approach for characterizing disease incidence in a spatial hierarchy

ABSTRACT Several statistical models are introduced to quantify the effect of heterogeneity on disease incidence relationships in a three-scale spatial hierarchy: the sampling unit level (highest), the leaf scale (intermediate), and the leaflet scale (lowest). The models are an extension of the theory previously developed for a two-scale hierarchy and were tested using data collected from strawberry leaf blight epidemics. Disease incidence at the sampling-unit scale (proportion of sampling units with one or more diseased leaflets) increased as a saturation-type curve with increasing leaflet or leaf disease incidence (proportion of leaflets or leaves diseased) as predicted by the good fit of the beta-binomial distribution to the leaflet and leaf data. The relationship could be accurately described, without curve fitting, by several simple nonlinear models, in which the aggregation of disease was represented by a modified binomial function incorporating an effective sample size that was either constant or dependent on mean incidence. The relationship between incidence at the leaflet and leaf scales could be modeled based on the combined sampling-unit models for leaflets and leaves. By taking the complementary log-log (CLL) transformation of incidence, the equations could be expressed as generalized linear models, and curve fitting used to estimate the parameters. Generally, curve fitting gave slight to no improvement in the accuracy of the predictions of incidence. These models have broad applicability in sampling for disease incidence, and results can be used to interpret how diseased individuals at the lowest level in a hierarchy are arranged within sampling units.     

水稻稻曲病室内人工接种技术

为提高稻曲病人工接种的发病效果和稳定性,在温棚条件下采用水稻孕穗期注射接种法分别研究了稻曲病菌不同接种体、培养时间、接种浓度和接种时期的接种效果。采用病菌马铃薯蔗糖液体培养基（potato sucrose broth,PSB）作为接种体,其穗发病率为100%,明显好于病菌米糠培养液（23.33%）。病菌在PSB中培养5～7天接种效果较好,随病菌培养天数的延长,接种效果明显下降。接种的分生孢子浓度越低水稻病穗率和病粒数也越低。在水稻品种两优培九孕穗中后期,采用含分生孢子浓度为4×106个/mL的病菌PSB培养液注射接种,穗发病率达100%,平均病粒数35.1粒,最高达87粒。研究表明,温棚条件下建立的稻曲病人工接种技术能获得稳定的发病效果,并可区别水稻品种间的抗性差异。     

Detection and identification of the maize bushy stunt phytoplasma in corn plants in Brazil using PCR and RFLP

Plants of corn (Zea mays L.) exhibiting symptoms of stunting and leaf reddening were assayed for the presence of phytoplasma gene sequences through the use of phytoplasma rRNA and ribosomal protein gene and maize bushy stunt (MBS) phytoplasma-specific oligonucleotide primers in polymerase chain reactions (PCR). Polymorphisms in 16S rDNA amplified from diseased plants were those characteristic of phytoplasmas classified in the16S rRNA gene group 16SrI, subgroup IB, of which MBS phytoplasma is a member. Amplification of ribosomal protein (rp) gene sequences in PCR primed by phytoplasma-specific primers confirmed presence of a phytoplasma in the diseased plants. Restriction fragment length polymorphism (RFLP) patterns of the amplified phytoplasma rp gene sequences were similar or identical to those observed for a known strain of MBS phytoplasma. In separate PCR, an MBS-specific oligonucleotide pair primed amplification of a MBS-characteristic DNA from templates derived from the diseased corn. Our data provide the first firm evidence for the presence of maize bushy stunt phytoplasma in corn in Brazil.     

Intraspecific Variation in Phytophthora citrophthora from Citrus Trees in Eastern Corsica

Isolates of Phytophthora pathogenic to citrus crops on Eastern Corsica and associated with gummosis were identified by PCR-RFLP of internal transcribed spacers (ITS) sequences and characterized by the random amplified microsatellites (RAMS) technique. A sample of 114 isolates collected from diseased trunks and fruits, and from soil, were overwhelmingly Phytophthora citrophthora. Further analysis indicated that the P. citrophthora population was not homogeneous in citrus groves. There were two groups, with a few (4%) atypical isolates in two marginal groups. The major groups have been re-examined in the light of mating behaviour, RFLPs of mitochondrial DNA and sequence comparisons of ITS regions of rDNA. They were found distinct with all these criteria and perhaps constitute distinct taxa. The results indicate that important modifications occurred in the population structure of P. citrophthora over time in Corsican groves. These changes may have impact on the recent outbreaks of gummosis.     

基于小RNA深度测序和RT-PCR检测侵染广东省冬种马铃薯的病毒

为明确侵染广东省冬种马铃薯的病毒种类及优势病毒,结合小RNA深度测序技术及RTPCR检测方法,对采集于广东省冬种马铃薯7个主产区的189份疑似病样进行检测分析。结果表明,经小RNA深度测序技术检测马铃薯病毒病混合样,发现存在马铃薯Y病毒(Potato virus Y,PVY)、马铃薯S病毒(Potato virus S,PVS)和马铃薯卷叶病毒(Potato leaf-roll virus,PLRV)3种病毒。进一步设计3种病毒的特异性引物并利用国内已报道的其它5种马铃薯病毒的特异性引物进行RT-PCR检测,发现189份马铃薯病毒病疑似病样中仅检测到PVY、PVS和PLRV这3种病毒,检出率依次为75.13%、10.05%和4.76%,且3种病毒在马铃薯上还存在复合侵染,复合侵染率为14.19%,其中PVY在各马铃薯产区均可检测到。表明侵染广东省冬种马铃薯的病毒为PVY、PVS和PLRV,其中PVY是优势病毒。     

玉米疯顶病种子传播研究

连续3a对不同来源的玉米种子,利用显微镜镜检和试种观察植株发病显症的方法,检测其携带玉米疯顶病病菌状况。结果表明,病株病穗籽粒、病株健穗籽粒、病田健株籽粒都有较高的带菌率。因此,病菌随种子调运远距离传播是造成各地病害突发的主要原因。     

Identification of Neofabraea species causing bull's eye rot of apple in Poland and their direct detection in apple fruit using multiplex PCR

Based on partial sequence analysis of the β‐tubulin gene, 19 isolates of fungi causing bull's eye rot on apple in Poland were classified into species: Neofabraea alba, N. perennans and N. kienholzii. To the authors’ knowledge, the detection of N. kienholzii is the second in Europe and the first in Poland. Species affiliation of these fungi was confirmed by a new species‐specific multiplex PCR assay developed on the basis of previously published methods. The new protocol allowed for the specific identification of bull's eye rot‐causing species, both from pure cultures and directly from the skin of diseased or apparently healthy apples. In 550 samples of diseased fruits collected from nine cold storage rooms located in three regions of Poland, in 2011 and 2012, N. alba was detected as the predominant species causing bull's eye rot, occurring on average in 94% of the tested samples. Neofabraea perennans was found in a minority of apple samples, N. kienholzii was found only in two apple samples, while N. malicorticis was not detected in any sample tested. In tests on 120 apparently healthy fruits, only N. perennans was detected in a single sample. The results of genetic diversity analyses of bull's eye rot‐causing fungi based on the β‐tubulin gene sequence and an ISSR (inter‐simple sequence repeat) PCR assay with two primers were consistent, showing the expected segregation of tested isolates with respect to their species boundaries. However, the genetic distance between N. perennans and N. malicorticis was very low, as reported previously.     

Fine-tuning banana Xanthomonas wilt control options over the past decade in East and Central Africa

Xanthomonas wilt, caused by Xanthomonas campestris pv. musacearum has, since 2001, become the most important and widespread disease of Musa in East and Central Africa. Over the past decade, new research findings and especially feedback from small-scale farmers have helped in fine-tuning Xanthomonas wilt control options. During the initial years of the Xanthomonas wilt epidemic in East Africa, the complete uprooting of diseased mats and the burning or burying of plant debris was advocated as part of a control package which included the use of clean garden tools and early removal of male buds to prevent insect vector transmission. Uprooting a complete mat (i.e. the mother plant and a varying number of lateral shoots) is understandably time-consuming and labour intensive and becomes very cumbersome when a large number of diseased mats have to be removed. Recent research findings suggest that Xcm bacteria do not colonize all lateral shoots (i.e. incomplete systemicity occurs) and even when present that this does not necessarily lead to symptom expression and disease. This led to a new control method whereby only the visibly diseased plants within a mat are cut at soil level. The underlying idea is that the continued removal of only the diseased plants in a field will reduce the inoculum level and will bring down disease incidence to an acceptable level. This method is less labour intensive and takes a short time compared to the removal of a complete mat. However, single diseased stem removal needs to go hand in hand with prevention of new infections that can occur through the use of contaminated garden tools or through insect vector transmission. Novel transgenic approaches are also discussed. This paper presents an overview of past and ongoing research towards the development of a more practical and less demanding control strategy for Xanthomonas wilt.     

巢豆油壶菌与蚕豆相互作用下植物内源激素的动态

 蚕豆火肿病由巢豆油壶菌(Olpidium Viciae Kusano)引起,症状特点是病部产生小瘤状突起。我们对该病的组织病理学研究^［1］表明是一种增生型组织病变,病菌仅定殖在侵入叶、茎的表皮细胞内,病菌的侵染引起邻近侵染点的表皮细胞及其下的叶肉细胞或茎的皮层组织细胞转化为分生细胞,并不断分裂增生和细胞体积增大,导致蚕豆病组织发生畸形增生的病理解剖改变,是病部产生瘤状物的组织学机制。前人对一些增生型组织病变病害的研究结果发现是由于病组织内的内源激素水平改变所致^［2］。蚕豆火肿病这种增生型病变是否与内源激素水平改变有关？其变化特点怎样？至今尚未有研究报导。     

Role of rainfall in the development of coffee berry disease in Coffea arabica caused by Colletotrichum kahawae,in Cameroon

The development of coffee berry disease (CBD) epidemics (caused by Colletotrichum kahawae) in Cameroon was monitored over two successive years (2004 and 2005) on coffee trees protected from rainfall by transparent plastic sheets and on unprotected control trees. This work was done to assess how rain affected disease development when it did not fall directly onto the coffee trees and to determine the influence of primary inoculum on the severity of CBD. Weekly observations over the 2 years showed that there were 1·1% diseased berries on coffee trees completely protected from rainfall, compared with 45% diseased berries on unprotected coffee trees. Disease severity on unprotected trees during the 2 years of the experiment was estimated at 53% diseased berries, compared with 27% on trees only protected in the first year. These results confirmed rainfall as one of the key physical factors in the development of Arabica CBD. They also provided evidence of a subsequent effect of protecting coffee trees from rainfall in 2004 on the severity of CBD in 2005. This suggested some practices that might lead to very effective cultural control of CBD in regions where severe epidemics of the disease occur.     

Detection and identification of phytoplasmas in yellows-diseased weeds in Italy

Yellows-diseased plants of Crepis setosa (hawksbeard), Knautia arvensis (field scabious), Convolvulus arvensis (field bindweed), Picris echioides (bristly oxtongue), Echium vulgare (blueweed) and Calendula officinalis (pot marigold) collected in central and southern Italy were examined for phytoplasma infection by means of polymerase chain reaction (PCR) technology using universal phytoplasma primers directed to ribosomal sequences. The detected phytoplasmas were characterized and differentiated using restriction fragment length polymorphism analysis of PCR-amplified DNA. The phytoplasma detected in diseased pot marigold plants was identified as a member of the aster yellows group and proved indistinguishable from a strain of the American aster yellows phytoplasma. The phytoplasma identified in diseased field bindweed plants is a putative new type of the stolbur group that differed from the typical stolbur phytoplasma. Phytoplasmas detected in diseased hawksbeard, blueweed and field scabious plants are all putative new members of the sugarcane white leaf group while the phytoplasma detected in diseased bristly oxtongue plants represents a new member of the faba bean phyllody group. For hawksbeard and field scabious this is the first report on the occurrence of phytoplasma diseases, whereas phytoplasmas infecting bristly oxtongue and blueweed have never been characterized before.     

Armillaria Species Infesting Vineyards in Northwestern Spain

Twelve vineyards in northwestern Spain were studied to assess the incidence of white root rot during 1995 and 1997. In both years, diseased plant material was collected and the Armillaria species responsible was identified on the basis of compatibility testing. Subsequently, restriction fragment length polymorphism (RFLP) analysis of the intergenic spacer region of the nuclear ribosomal RNA gene cluster was used to identify Armillaria species in another 45 symptomatic samples submitted for diagnosis from this area. During 1995, 9 of the 12 vineyards showed white root rot, although in eight cases less than 2% of plants were affected; in the remaining vineyard 17% of plants were diseased. During 1997, 10 of the 12 vineyards were affected and three showed a marked increase in the number of plants with white root rot (to 43%, in the vineyard in which 17% were affected in 1995). The compatibility method detected Armillaria mellea in samples from 10 of the 12 vineyards, and Armillaria gallica in samples from two vineyards. RFLP–PCR analysis detected four restriction patterns corresponding to A. mellea, A. gallica and Armillaria cepistipes: patterns mel 1 (A. mellea, 71% of samples), mel 2 (A. mellea, 18%), gal 1 (A. gallica, 9%), and cep 1 (A. cepistipes, 2%, i.e. a single sample). This is the first report of A. gallica and A. cepistipes infecting Vitis spp. The presence of these two Armillaria species may be related to the fact that the vineyards from which they were isolated were located on cleared forestry sites.     

Spatiotemporal distribution of tomato plants naturally infected with bacterial canker in greenhouses

The distribution of plants with tomato bacterial canker within a greenhouse was analyzed using Morisita’s binomial index of dispersion, I _B , to assess spatial distribution patterns. The distribution patterns of diseased plants were similar in four commercial greenhouses. The degree of clustering of added together diseased plants based on the I _B index did not increase with time, but the statistical significance of the cluster distribution did increase, suggesting that new independent cluster points had formed during the investigation. Therefore, a scattered pattern of potentially or apparently diseased plants caused by primary inoculum from residual plants in the soil emerged with time.