Characterisation of a Quantitative Resistance to Vector Transmission of Tomato yellow leaf curl virus in Lycopersicon pimpinellifolium

Two wild genotypes from the same species Lycopersicon pimpinellifolium, WVA106 (susceptible) and INRA-Hirsute (so-called ‘resistant’), were compared with respect to their reaction to Tomato yellow leaf curl virus isolate Réunion (TYLCV-Mld[RE]), using both whitefly-mediated inoculation and graft inoculation. Disease incidence and symptom severity were scored. Presence and quantification of viral DNA were assessed by dot blot hybridisation. Upon insect inoculation, accession INRA-Hirsute showed a moderate resistance against TYLCV that was overcome by a high inoculation pressure obtained by increasing the cumulative number of inoculative whiteflies. Temporal analyses of the disease progress in relation to this criterion exhibited that the protection was quantitative, mainly reducing the TYLCV-Mld[RE] incidence by at maximum 50% at low inoculation pressure. When graft inoculated, the final TYLCV-Mld[RE] disease incidence was 100% in both susceptible and resistant genotypes with severe symptoms, suggesting a reduction of virus transmission by a vector resistance as a possible mechanism. Implications of using such type of resistance in breeding programmes are discussed.     

A Severe Hellenic CMV Tomato Isolate: Symptom Variability in Tobacco, Characterization and Discrimination of Variants

A severe strain of Cucumber mosaic virus (CMV) originating from an infected tomato plant (Gastouni-Olympia, Greece) was isolated in tobacco (Nicotiana tabacum cv. Xanthi nc), after three serial local lesion passages in Chenopodium quinoa and designated CMV-G. CMV-G induces yellow mosaic (YM) symptoms in tobacco. When CMV-G was passed mechanically through C. quinoa, phenotypic variants inducing YM or green mild mosaic (MM) in tobacco were isolated. Aphid transmission, from different hosts, appears to be an effective approach for separating MM variants of CMV-G from YM variants. In particular, aphid transmission from zucchini proved to be very efficient in selecting for MM variants. In contrast, aphids transmitted only YM variants from tomato plants. Molecular characterization of CMV-G and its progeny resulted in their classification in the CMV subgroup IB, free of satellite RNA, being the first discovery of the subgroup IB in Greece. In the Solanaceae family (tobacco, tomato, pepper) YM variants induced more severe symptoms than the MM variants. YM and MM phenotype was stable in tobacco for all seven passages tried using the obtained YM and MM variants. Cross-protection experiments showed that an isolated MM variant was able to protect tobacco plants against a challenge infection by a YM variant.     

Comparison ofPotato Virus Y andPlum Pox Virus transmission by two aphid species in relation to their probing behavior

Two different aphid species,Myzus persicae (Sulzer) andHyalopterus pruni (Geoffroy) (Homoptera: Aphididae), were used to analyze their ability to transmit two different potyviruses,Potato virus Y (PVY) andPlum pox virus (PPV), to pepper (Capsicum annuum) andNicotiana benthamiana plants, respectively. In parallel experiments,M. persicae consistently transmitted both viruses with high efficiency, whereasH. pruni always failed to transmit either virus. This is in contrast to previous reports describingH. pruni as a vector of these potyviruses. Different aphid probing behavior among individual aphids of each species was obtained in electrical penetration graph (EPG) experiments performed on pepper plants. This suggested thatH. pruni did not transmit these potyviruses due to behavioral differences during probing that impeded virus acquisition and/or inoculation. It was found thatM. persicae usually makes its first probe within the first 2 min, whereasH. pruni individuals remained for more than 10 min on the plant before starting to probe. Furthermore,M. persicae individuals displayed their first intracellular puncture during the first minute of probing whereasH. pruni needed ∼ 15 min to penetrate the cell plasmalemma with their stylets. In addition, intracellular stylet punctures occurred very frequently forM. persicae but was a rare event, never exceeding a single one, forH. pruni. The relevance of these findings for the epidemiological spread of potyviruses by different aphid species is discussed. http://www.phytoparasitica.org posting May 14, 2006.     

乳腺分泌物中体细胞的研究进展

不同物种的乳腺分泌物中含有的细胞成分被称为体细胞,其中包括淋巴细胞、白细胞、巨噬细胞和上皮细胞。物种、乳腺感染情况、不同生理阶段和饲养管理条件等因素均会影响乳中的体细胞数量和细胞类型。近年来,乳中体细胞得到了人们的关注和深入研究,显示出广阔的应用前景。人们利用从初乳和常乳中得到的乳腺上皮细胞已经成功进行了乳腺细胞的原代培养和建立了乳腺细胞系,为乳生成、被动免疫转移和乳腺癌的研究提供了良好平台。体细胞中提取的RNA代表了乳腺组织的基因表达,因此为研究乳腺组织的基因表达提供了方便、良好的来源。     

H9N2亚型禽流感病毒传播途径特性的比较及其表面基因序列分析

选择中国大陆最早分离的H9N2亚型禽流感病毒(avian influenza virus,AIV)A/Chicken/Guangdong/SS/94(H9N2)(缩写为SS株)和1998年大流行时期分离的H9N2亚型AIVA/Chicken/Shanghai/F/98(H9N2)(缩写为F株)为研究对象,对其在SPF鸡体内的复制能力和传播途径特性比较后发现,F株在4周龄SPF鸡气管中的复制能力高于SS株,F株可以经气溶胶传播途径传播,SS株不能经气溶胶传播途径传播;利用反转录-聚合酶链反应(RT-PCR)方法获取F株和SS株的HA和NA基因的cDNA,序列分析得知,F株和SS株的HA和NA基因的同源性分别是96.6%和98.1%;HA基因的裂解位点氨基酸序列都是PARSSR↓GL,但有5个氨基酸的差异,即166位N(F)→D(SS)、198位A(F)→V(SS)、217位V(F)→I(SS)、335位G(F)→R(SS)、504位L(F)→S(SS);2株病毒的NA基因在63~65位都存在氨基酸缺失,但在NA基因红细胞吸附位点的氨基酸序列不同,分别是IKKDSRSG(F)和IKEDLRSG(SS)。F株和SS株的传播特性差异是否与其表面基因序列有关,有待进一步研究。     

Partial characterization of phytoplasmas associated with lettuce and wild lettuce phyllodies in Iran

Phytoplasmas associated with lettuce phyllody (LP) and wild lettuce phyllody (WLP) in southern Iran were partially characterized by molecular analyses and host-range studies. Agents of both diseases were transmitted by Neoaliturus fenestratus , a leafhopper colonizing lettuce and wild lettuce, to lettuce, wild lettuce, sowthistle and periwinkle, but not to safflower, sunflower, calendula and sesame. Both phytoplasmas induced bud proliferation, virescence, phyllody and witches' broom in infected plants. Total DNA extracted from infected lettuce and wild lettuce or from vector tissues was subjected to PCR using phytoplasma-specific primer pair P1/P7 or nested PCR using P1/P7 followed by R16F2n/R16R2. PCR product of nested PCR (1·2 kbp) was subjected to restriction fragment length polymorphism (RFLP). RFLP analysis of nested PCR product identified the LP, WLP and N. fenestratus -associated phytoplasmas as members of the pigeon pea witches' broom group, 16SrIX. Phylogenetic analysis of the 16S rRNA gene sequence also clustered LP and WLP phytoplasmas with other known members of the 16SrIX group. While no significant differences could be detected between LP and WLP phytoplasmas, both isolates differed from Lebanese wild lettuce phyllody in molecular properties.     

Detection of lethal yellowing phytoplasma in embryos from coconut palms infected with Cape St Paul wilt disease in Ghana

This study investigated the potential of seed transmission of Cape St. Paul wilt disease (CSPWD) in coconuts. PCR amplification was used to assess the distribution of phytoplasmas in parts of West African Tall (WAT) palms infected with CSPWD. Employing phytoplasma universal primer pair P1/P7 in standard PCR, or followed with a nested PCR using CSPWD–specific primer pair G813f/AwkaSR, phytoplasma infection was detected in the trunks, peduncles, spikelets, male and female flowers of four infected WAT coconut palms. Through nested PCR, phytoplasma was also detected in four of 19 embryo DNA samples extracted individually from fruits harvested from three of the four infected palms and was confirmed as CSPWD by cloning and sequencing. Subsequently, CSPWD phytoplasma was again detected in five of 33 embryos from nine infected palms, and in one of eight fruits from two symptomless palms. Fruits from infected palms recorded higher percentage germinations in two field nurseries (average of 71·0%) compared to fruits from healthy palms (average of 57·6%), and matured fruits that had dropped from infected palms showed the same levels of germination as those harvested directly from the palms. This indicates that infected fruits retain the ability to germinate whether harvested or dropped. No phytoplasmas were detected in any of the resulting seedlings and plantlets obtained through embryo in-vitro culture. Therefore, although phytoplasma DNA can be detected in embryos, there is as yet no evidence that the pathogen is seed transmitted through to the seedling to cause disease in progeny palms.     

影响麦二叉蚜传播玉米矮花叶病毒效率的因素分析

玉米矮花叶病毒（ＭＤＭＶ）在田间主要依靠介质蚜虫非持久性方式传播,通过麦二叉蚜（Ｓｃｈｉｚａｐｈｉｓｇｒａｍｉｎｕｍ）对ＭＤＭＶ传毒效率影响因素的分析,发现接毒蚜获毒前禁食与否及禁食时间的长短与传毒效率呈高度正相关,从蚜量与传毒效率的关系来看,多头蚜虫的传毒效率均比单头蚜高,随着ＭＤＭＶ浓度和传毒蚜量的增加,传毒效率也随之提高,单蚜获毒１０ｍｉｎ后不禁食其传毒效率最高,随着禁食时间的延长,其传毒效     

Shafer气液联动执行机构异常关断事故树分析

输气管道干线截断球阀的气液联动执行机构经常出现误关断的情况,严重影响了管道的安全运行和企业效益.利用事故树定量分析的方法对异常关断事故进行了系统分析.阐述了气液联动执行机构自动关断的原理,利用事故树法详细分析了造成气液联动执行机构异常关断的各种因素,并对各个因素的影响程度进行了定量计算.对可能导致异常关断的29个基本事件进行定量分析后可知：人为失误、ESD误触发、电磁阀掉电、引压管冰堵等因素是造成气液联动执行机构误关断的重要原因.事故树分析结果与管道实际运行情况一致,表明事故树分析方法在实际生产应用中是合理有效的.     

YL2208CW型农用运输车主传动比的模糊优化

作者在建立Ｙ１２２０８ＣＷ型农用运输车动力性与燃油经济性模拟计算方法的基础上，应用模糊数学方法优化农用运输车的主传动器速比，获得了最佳燃油经济性。