Durability of Resistance and Cost of Virulence

A seasonal model, where a growing season is defined as the time between sowing and harvest and alternates with an inter-crop period, was derived to study the effects of the ‘cost of virulence’ and cropping ratio on durability of resistance. We assumed a single strain of virulent pathogen, a single strain of avirulent pathogen and two cultivars (one resistant and one susceptible) and studied two measures of durability of resistance (‘take-over time’ and ‘usefulness time’). Take-over time is defined as the time needed for the virulent strain of the pathogen to reach a preset threshold and predominate over the previous pathogen population. Usefulness time is the time needed before the estimated gain in green canopy area duration per plant through the use of the resistant cultivar becomes negligible. The model suggested that, although it could take several seasons before the virulent strain of the pathogen predominated over the previous pathogen population, the usefulness time of the resistant cultivar was always much shorter. Furthermore, increasing selection for the virulent strain of the pathogen (through increasing the cropping ratio of the resistant cultivar) caused the virulent strain of the pathogen to invade the system more rapidly. Cost of virulence, reflecting differences in pathogen infection rates between the four possible combinations of cultivar/pathogen strain, significantly affected durability of resistance, with the dynamics of the virulent and avirulent strains ranging from a case where the virulent strain of the pathogen died out to a case where the virulent strain of the pathogen invaded the resident pathogen population. An intermediate state, where the system reached equilibrium and the virulent strain of the pathogen neither became predominant nor died out, was defined as ‘coexistence’ of both strains of the pathogen. Occurrence of coexistence was directly related to the cost of virulence since it did not occur when virulence of the pathogen did not have a fitness cost. Two methods to include cost of virulence in the model gave similar results in relation to the two measures of durability of resistance studied.     

Use of a Nitrate-Nonutilizing Mutant and Selective Media to Examine Population Dynamics of Fusarium oxysporum f. sp. spinaciae in Soil

ABSTRACT Determining the population density of the spinach wilt pathogen Fusarium oxysporum f. sp. spinaciae in soil with conventional Fusarium-selective media is quite difficult because nonpathogenic strains of F. oxysporum also grow on those media and are indistinguishable from the pathogen. Therefore, a nitrate-nonutilizing (nit) mutant of the pathogen and corresponding selective media were tested in an experimental approach to determine the population density of the pathogen. Colony forming units of the pathogen were countable after soil-dilution plating onto nit mutant-selective media MMCPA, CMP, and CGMBP. Colony forming units of wild-type Fusarium spp. were countable using a wildtype Fusarium-selective medium, GMBP. By combining nit mutant- and wild-type-selective media, the population densities of pathogenic and nonpathogenic F. oxysporum in the same soil could be measured selectively. This method was useful in studying population dynamics of the pathogen after different soil treatments. Soil disinfested with hot water or chloropicrin was amended with the nit mutant pathogen, and subsequent changes in population densities of the pathogen were compared with those in nontreated field soil. The pathogen rapidly proliferated in disinfested soil and wilt developed faster than in nontreated soil. When a nonpathogenic isolate of F. oxysporum was added at high density to sterilized soil prior to the pathogen, growth of the pathogen was greatly suppressed. Nonpathogenic F. oxysporum could not, however, reduce the density of preexisting pathogen.     

玉米灰斑病菌的可溶性蛋白质及同工酶多态性

利用聚丙烯酰胺凝胶电泳技术,对采自北方玉米主产区的23个玉米灰斑病菌菌株进行可溶性蛋白质和同工酶电泳图谱分析及聚类分析,从蛋白质和酶学的多态性水平上分析玉米灰斑病菌的生理分化特征.研究表明,玉米灰斑病菌在可溶性蛋白质和SOD、MDH、PPO、POD、EST、CAT等的同工酶谱存在差异,不同菌株之间某些同工酶谱带数和同一迁移率谱带的亮度和色泽差异非常显著,说明菌株间的多态性可在同工酶水平上得到反映.研究还发现,来自不同地区的菌株同工酶谱带无明显的变化规律,反映出病菌同工酶的变异与地理位置关系不密切,也表明该病菌可能具有较广泛的地域适应性.     

广东省番石榴褐斑病的病原分离及鉴定

In order to clarify the pathogen causing brown spot of Psidium guajava Linn., and provide a theore-tical basis for effective prevention and treatment of the disease, the pathogen of the brown spot of Psidium guajava Linn. was isolated and identified by molecular and morphological methods. The pathogen was obtained by tissue separation method, and the pathogenicity of the pathogen was determined by Koch′s rule. The morphological characteristics of the conidia of the pathogen were observed by optical microscope, and the sequence of the rDNA-ITS and RPB2 of the pathogen was analyzed by online Blast. The BLAST online alignment showed that the ITS sequence of the pathogen was 100% homologous with multiple strains of Alternaria alternata and Alternaria tenuissima, the homology of the RPB2 sequence of the pathogen with the strains of A. alternata and A. tenuissima reached 99.86%. According to the latest references, A. tenuissima (Fr.) Wiltshire was not an independent species but was a synonym of A. alternata (Fr.) Keissler. Combined with the pathological characteristics of pathogenic fungi, pathogenicity determination and phylogenetic tree analysis, the pathogen of guava brown spot disease in Guangdong was identified as A. alternata.     

基于GIS的中国小麦条锈病菌越夏区气候区划

 基于多年的气象数据(1980~2001年),首次从制约小麦条锈病菌越夏的温度因子入手,结合寄主小麦因素,利用地理信息系统(Geographical Information System,GIS),对我国小麦条锈病菌越夏区进行较详细的气候区划。本研究从温度条件上明确了全国适合小麦条锈病菌越夏的范围。研究表明,在我国小麦种植区适合小麦条锈病菌越夏的范围很广。其中甘肃、四川、云南、陕西境内适合越夏的地区是连成一片的,甘肃东部除了西边的几个县外其它地方7、8月份最高一旬均温在20~23℃,条锈病菌越夏困难;西藏、青海境内的小麦种植区几乎都适合小麦条锈病菌越夏;贵州境内适合越夏的地区可能和云南越夏区是一个整体。云南适合越夏的地区甚广,且地形复杂,需要进一步调查研究。     

Genomic and phenotypic characterization of the bacterium causing blight of kiwifruit in New Zealand

Strains of the pathogen causing bacterial blight of kiwifruit in New Zealand, previously identified as Pseudomonas viridiflava, were examined using phenotypic and genotypic methods. Percentage DNA–DNA reassociation values for strains of the pathogen, with the type strains representing P. viridiflava and P. savastanoi, and representative strains within P. syringae , were obtained using the S1 endonuclease method. Strains of the pathogen were most similar to the type strain of P. savastanoi. This similarity was supported by examination of the Δ T _m between representative strains. It is concluded that the pathogen can be considered as a member of the P. savastanoi genomic species. The pathogen from kiwifruit in New Zealand was also differentiated in genomic terms from P. syringae pv. actinidiae . Strains of the kiwifruit pathogen compared using the Biomerieux API Biotype 100 system exhibited consistent determinative tests which distinguished the pathogen from P. viridiflava and P. syringae pv. actinidiae . The origins of the pathogen in New Zealand are discussed.     

番茄茎腐病菌的分子鉴定及致病力检测

本研究采用形态学观察、核糖体DNA转录间隔区(ITS)克隆、系统发育树和致病力检测等方法对河南周口地区番茄茎腐病菌进行分子鉴定和致病力检测,以期为茎腐病的抗病育种及病害防治提供一定的理论依据。形态学观察结果显示,从周口地区番茄上分离的茎腐病病原菌属于镰孢属,ITS序列分析及系统进化树分析进一步确定其为茄镰孢,分离物与茄镰孢福建分离物(JN232141.1)亲缘关系最近,聚在一个进化支上,致病力检测结果表明在测试的植物中该病菌对茄科植物龙葵的致病力最强,该病菌寄主范围广,可侵染茄科、十字花科多种植物。     

短穗鱼尾葵灰斑病菌的鉴定及生物学特性*

［目的］ 明确引起短穗鱼尾葵灰斑病的病原菌及该菌的生物学特性。［方法］ 从短穗鱼尾葵感病组织上分离、纯化病菌,经致病性测定后根据其形态特征进行种类鉴定,并测定其在不同培养条件下的生物学特性。［结果］ 引起短穗鱼尾葵灰斑病的病原菌为小孢拟盘多毛孢菌［Pestalotiopsis microspora (Speg.) Satista &; Peresapud Batista］。该菌在PSA 培养基上长势最好;菌丝生长和孢子萌发的最适温度为25 ℃;完全光照条件最利于菌丝的生长和产孢;在pH5时菌丝生长最好,pH6时孢子萌发率最高,pH2时孢子不萌发;孢子的致死温度为50 ℃。［结论］ 上述结果可以为短穗鱼尾葵灰斑病的防治提供依据。     

百合疫病病原菌的鉴定及培养基的筛选

从具典型症状的新鲜百合疫病植株茎基部病组织中分离到百合疫霉菌,根据其病原菌菌丝的形态、菌落特征,厚垣孢子、游动孢子囊和卵孢子的形态和大小,以及病原菌致病性测定,该病原菌鉴定为烟草疫霉Phytophthora nicotianae van Brede de Haan.供试的16种培养基中,病原菌在胡萝卜琼脂培养基(CaA)和辣椒琼脂培养基(PeA)上生长最好,生长速率分别为1.771和1.770mm/h.在常规培养条件下,病原菌不易产生厚垣孢子、游动孢子囊和卵孢子,在低温、皮氏溶液和土壤浸出液中分别诱导产生出大量厚垣孢子、游动孢子囊和卵孢子.     

利用28S rDNA D1/D2区和ITS rDNA序列鉴定甜瓜白粉病病原菌

为了明确宁夏干旱带压砂甜瓜白粉病病原菌,从病原菌分生孢子中提取DNA,PCR扩增ITSrDNA和28S rDNA D1/D2区段,测序后进行BLAST比对.结果表明,病原菌的ITS rDNA和28SrDNA D1/D2序列与菜豆叉丝单囊壳白粉菌Podosphaera phaseoli、凤仙花又丝单囊壳白粉菌P.bal-saminae、菊科叉丝单囊壳白粉菌P.fwca、苍耳单囊壳白粉菌P.xanthii、瓜类单囊壳白粉菌P.fuligi-nea等叉丝单囊壳属Podosphaera的多个种的ITS rDNA和28S rDNA D1/D2序列之间相似度均大于99%,鉴定甜瓜白粉病病原菌为叉丝单囊壳属Podosphaera.     

枯草芽胞杆菌YB-05对小麦全蚀病菌胞内酶活的影响

小麦全蚀病菌是影响小麦产量和质量的主要致病菌之一,前期研究表明枯草芽胞杆菌YB-05对小麦全蚀病菌的生长具有抑制作用。本试验拟通过研究该菌对小麦全蚀病菌相关酶系的诱导变化情况,解析其对小麦全蚀病菌的抑制作用机理。本试验以小麦全蚀病菌Gaeumannomyces gramini（Sacc.）Arx et Oliver var. tritici（Sacc.）Walker为靶标菌,加入终浓度为MIC₅₀枯草芽胞杆菌YB-05发酵液,通过显微镜观察菌株YB-05发酵液对小麦全蚀病菌菌丝结构和形态的影响,通过酶活力测定检测菌株YB-05发酵液对小麦全蚀病菌胞内苯丙氨酸解氨酶（PAL）、过氧化物酶（POD）、过氧化氢酶（CAT）、多酚氧化酶（PPO）和超氧化物歧化酶（SOD）防御酶活的影响,同时检测菌株YB-05发酵液在离体/活体条件下对小麦全蚀病菌线粒体复合酶Ⅱ/Ⅲ活力的影响。小麦全蚀病菌经菌株YB-05发酵液处理后,显微镜观察到其菌丝变粗、断裂,顶端膨大,分枝增多;处理8 d后,胞内的PAL、POD、CAT、PPO和SOD活性比对照依次高24.52%、72.67%、81.81%、80.36%和112.48%;离体条件处理,线粒体复合酶Ⅱ和Ⅲ的活性与对照组相比差异不显著,而活体条件处理下差异显著,线粒体复合酶Ⅱ和Ⅲ分别比对照组分别降低43.95%和55.87%。菌株YB-05发酵液通过结合小麦全蚀病菌线粒体复合酶Ⅱ和Ⅲ的相关基因,从而影响该基因的表达,抑制小麦全蚀病菌线粒体复合酶Ⅱ和Ⅲ的活力,影响小麦全蚀病菌的呼吸,进而导致抑制小麦全蚀病菌菌丝畸变,从而影响小麦全蚀病菌的正常生长。     

杨树角斑病病原菌分离及其培养特性研究

对杨树角斑病菌进行分离和鉴定,并研究不同培养条件对其培养特性的影响,以获得病原菌的纯培养并筛选出最佳培养条件,为杨树角斑病防治提供理论参考。分别采用组织和单孢分离法分离病原菌,根据子实体形态和病菌rDNA ITS序列对其进行鉴定。观察不同培养基、温度、光照、pH对病原菌生长的影响。结果表明,自然条件下,用杨树角斑病菌的分生孢子分离较病组织分离易成功。根据病菌的形态特征和rDNA ITS序列分析,将病菌鉴定为柳假尾孢[Pseudocercospora salicina(Ell.&Ev.)Deighton]。培养基、温度、光照、pH等因素影响病菌在培养基上的生长。燕麦培养基、pH6～7、25℃、黑暗条件是适合的培养条件。     

Aerial Transmission of Thielaviopsis basicola, a Pathogen of Corn-Salad, by Adult Shore Flies

ABSTRACT Chlamydospores of Thielaviopsis basicola were consistently observed in frass excreted by adults and larvae of shore flies that were collected in the immediate vicinity of naturally infected corn-salad plants obtained from a commercial greenhouse production facility. Approximately 95% of the adult flies and 85% of the larvae were internally infested with the pathogen. Pathogen-free adult shore flies were subsequently shown to acquire the pathogen by ingestion after feeding on naturally infected plants. Viable propagules of the pathogen were excreted by these internally infested adults and were capable of transmitting the pathogen to healthy seedlings, which subsequently became infected.     

蓝莓间座壳芽枯病病原菌鉴定及其生物学特性

<正>蓝莓(Vaccinium corymbosum L.),属于杜鹃花科(Ericaceae)越橘属(Vaccinium)多年生小浆果类果树,果实蓝色,营养丰富,具有良好的保健作用。随着蓝莓的大面积商业化种植,其病害的发生也愈加频繁。2013年7月对沈阳市蓝莓种植园病害调查时,发现一种新病害。该病主要危害基生枝中上部芽眼,受害芽坏死,芽眼周围出现褐色或红褐色椭圆形病斑,凹陷,后期中部呈灰白色,病斑     

黑龙江省番茄白粉病病原鉴定

通过收集东北农业大学日光温室中的番茄白粉菌,并对其进行形态和分子鉴定及分析,明确了该白粉病的病原种类及其分类地位。根据分生孢子的显微形态观察初步确定为新番茄粉孢菌（Oidiumneolycopersici L. Kiss）。进一步根据真菌rDNA-ITS序列检测分析后发现该病原菌与新番茄粉孢菌（O. neolycopersici）的相似性为100%,并对与其相似性较高的序列构建进化树分析发现,本试验研究的白粉菌与其他国家和地区的白粉菌相似性不高,这可能是由于哈尔滨地区白粉菌自身小种进化的原因。     

Elucidation of the infection process of Ustilaginoidea virens (teleomorph: Villosiclava virens) in rice spikelets

This study reports an efficient inoculation protocol that allowed cytological analysis of the infection process of the rice false smut pathogen Ustilaginoidea virens. Examination of serial semithin and ultrathin sections of infected spikelets showed that the primary infection sites for the pathogen were the upper parts of the three stamen filaments located between the ovary and the lodicules. The stigma and lodicules were also occasionally infected to a limited extent. The pathogen infected the filaments intercellularly and extended intercellularly along the filament base. The host cells were degraded gradually. The pathogen did not penetrate host cell walls directly and did not form haustoria. In the balls the ovary remained alive and was never infected. This suggests that the pathogen is a biotrophic parasite that grows intercellularly in vivo.     

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.     

Influence of spatial structure on pathogen colonization and extinction: a test using an experimental metapopulation

The Linum marginale–Melampsora lini plant–pathogen interaction has been studied extensively with regard to its epidemiology and population genetic structure (host resistance and pathogen virulence) in a natural metapopulation. In this study, this system was used in an experimental metapopulation approach to investigate explicitly how the distance (degree of isolation) between local population patches influences disease dynamics within a growing season, as well as the genetic structure of pathogen populations through stochastic colonization and extinction processes. The experimental design centred on four replicate sets of populations, within which patches were spaced at increasingly greater distances apart. Each patch consisted of an identical set of host and pathogen genotypes, with each pathogen genotype having the ability to attack only one of four host-resistance types. Over the 2 years of the experiment, the results showed clear 'boom-and-bust' epidemic patterns, with the strongest determinant of disease dynamics within a growing season being the identity of particular host–pathogen genotypic combinations. However, there were also significant effects of spatial structure, in that more isolated patches tended to exhibit lower levels of disease during epidemic peaks than patches that were close together. Extinction of pathogen genotypes from individual populations was positively related to the severity of disease during preceding epidemic peaks, but negatively related to the level of disease present at the final census prior to overwintering. The probability of recolonization of pathotypes into populations during the second growing season was most strongly related to the distance to the nearest neighbouring source population in which a given pathotype was present. Overall, these results highlight the importance of spatial scale in influencing the numerical and genetical dynamics of pathogen populations.     

甘肃定西地区甘蓝枯萎病病原菌的分离与鉴定

自2009年起,甘肃定西地区出现了甘蓝植株矮化、叶片黄化、枯萎甚至死亡的现象。2015年8月,我们采集了田间病株样本,使用常规组织分离法对病原菌进行了分离和纯化,依据柯赫氏法则进行了病原菌确认,并通过形态学和分子生物学方法对病原菌进行了鉴定。结果表明病原菌的形态学特征与尖孢镰刀菌Fusarium oxysporum一致,其rDNA-ITS、rDNA-IGS以及EF-1α序列与尖孢镰刀菌F.oxysporum相似性达99%,基于病原菌及尖孢镰刀菌各代表专化型EF-1α序列构建的系统发育树将该菌与尖孢镰刀菌黏团专化型F.oxysporum f.sp.conglutinans聚为一类,故引致甘肃定西地区甘蓝枯萎病的病原菌为尖孢镰刀菌黏团专化型F.oxysporum f.sp.conglutinans。     

新疆玉米病害新纪录-玉米普通锈病症状及病原形态特征

报道了2007年发生在新疆奇台县玉米上一种新病害玉米普通锈病症状及病原特征。对该病的症状及病原形态作出了详尽地描述,并与玉米上已知的其他两种锈菌的形态进行了缜密的比较研究与评述。根据病原的形态特征,确定了奇台县玉米的叶锈病病原应为高粱柄锈菌（Puccinia sorghi Schw.）。研究者发现该病原冬孢子柄的长度及其与冬孢子体长的比是判别与其相似的玉米多堆柄锈菌（P. polysora Underw.）的关键而稳定的特征。即冬孢子柄长度大于冬孢子体长1倍以上者鉴定为高粱柄锈菌,相反冬孢子柄长度小于冬孢子体长1倍以上者鉴定为多堆柄锈菌。