Two diseases of dimorphotheca caused by lettuce mosaic potyvirus and tomato spotted wilt tospovirus

In 1997, virus-like symptoms were observed in dimorphotheca plants(Dimorphotheca sinuata) at two different locations in Greece. In a greenhouse near Heraklion (Crete), plants showed chlorotic patches mainly in the older leaves, and a mild stunting; near Katerini (Macedonia), garden plants showed chlorotic rings. Sap inoculation of healthy dimorphotheca plants with extracts from diseased plants from the two regions, reproduced each of the two diseases. Examination by electron microscopy (EM) of samples from diseased plants from the first region revealed filamentous particles, whereas samples from the second region showed quasi-spherical particles. The filamentous particles were decorated in EM with antibodies specific to lettuce mosaic potyvirus (LMV). Samples from the second location reacted with antibodies specific to tomato spotted wilt tospovirus (TSWV) in EL1SA tests. It is concluded that LMV and TSWV are the causal agents of the disease noticed in Heraklion and in Katerini, respectively. http://www.phytoparasitica.org posting May 31, 1999.     

北京辣椒和番茄上番茄斑萎病毒的鉴定

北京大兴区某蔬菜种植基地的辣椒和番茄发现疑似病毒感染,造成较大经济损失.经症状分析和RT-PCR检测,证实其感染番茄斑萎病毒(tomato spotted wilt virus,TSWV).基于TSWV序列特征对该地区TSWV进化及来源进行分析,结果显示其与北京顺义区已经报道TSWV毒株进化关系较近,但较国内其他地区株...     

Assessing the susceptibility of chrysanthemum cultivars to tomato spotted wilt virus

Three methods were compared to assess the susceptibility of vegetatively propagated chrysanthemum to tomato spotted wilt tospovirus (TSWV): mechanical and thrips-mediated inoculation of whole plants, and a leaf-disc assay. As symptom expression was often poor or even absent, TSWV infections and subsequent susceptibility to TSWV were determined by ELISA. All 15 chrysanthemum cultivars tested were susceptible to TSWV, irrespective of their degree of vector resistance (based on feeding-scar damage rates). Thrips-mediated inoculation using different numbers of thrips revealed that 100% infection was obtained when plants were challenged by six thrips per plant, whereas 80 and over 50%, respectively, of the plants became infected when inoculated by a single male or female thrips. However, false negatives were scored even after intensive sampling because of erratic, cultivar-specific and time-dependent virus distribution after inoculation in the plants. Labour-intensive samplings and long incubation periods could be overcome by a readily applicable leaf-disc assay. This assay was as reliable as thrips-mediated inoculation of whole plants, and its use is therefore favoured to assess chrysanthemum cultivars for TSWV susceptibility.     

Transmissibility of four tospoviruses by a thelytokous population ofThrips tabaci from Liguria, Northwestern Italy

Studies were carried out on a population ofThrips tabaci Lindeman (Thysanoptera: Thripi-dae) from Liguria to assess its sex-ratio and its ability to transmit four tospoviruses: tomato spotted wilt (TSWV), impatiens necrotic spot, tomato chlorotic spot and groundnut ringspot. The population was composed of females only (therefore thelytokous). The first instar larvae were allowed to acquire the virus for 48 h on infected leaves of datura, basil or pepper, and then reared on cucumber until emergence, which medially occurred 9.5 days after hatching. Transmission capacity was checked using two inoculation access periods (lAPs) of 48 h each on pepper leaf disks.T. tabaci was able to transmit TSWV isolate P105 with an efficiency of 16.7% and 4.4% in the first and second IAP, respectively, and TSWV isolate BR-01 with an efficiency of 2.0%. The onion thrips did not transmit the three other tospoviruses. During the IAPs, almost all adults fed on the leaf disks, producing evident silvery scars. The presence of tospovirus nucleocapsids in thrips was assayed by Triple Antibody Sandwich (TAS) and cocktail ELISA. Not all adults that had transmitted TSWV were positive in the tests, whereas some non-transmitter individuals proved positive. For each of the other tospoviruses, some thrips were positive in at least one test, although none was able to transmit the virus.     

Biological and molecular characterization of Tomato spotted wilt Virus in Israel

Received April 24, 1997; received in final form June 29, 1997. Symptoms resembling tomato spotted wilt virus (TSWV) infections were documented among ornamental and vegetable crops in commercial greenhouses and open fields in Israel. Plants exhibiting these symptoms were collected from January 1992 to December 1996. Among cultivated plants analyzed for TSWV by enzyme-linked immunosorbent assay (ELISA), 19 species representing five families were found to be infected; natural infection was also recorded in six plant species of weeds. Virus identity was characterized by host range, serology and electron microscopy. Serological reaction with the isolates, found in Israel, using antisera from different sources as well as the sequence analysis of the nucleocapsid gene, demonstrated that the Israeli isolates of TSWV are a member of tospovirus serogroup I, type I (BR-01 strain). No virus transmission was found in seeds collected from virus-infected vegetable and ornamental crops. A non-radioactive molecular probe derived from the cloned nucleocapsid isolate enables specific detection of the virus in crude sap from infected plants. The detection of TSWV in Israel constitutes a severe potential threat to the ornamental and vegetable industry.     

Comparative host reactions and Frankliniella occidentalis transmission of different isolates of tomato spotted wilt tospovirus from Spain

The abilities of different isolates of tomato spotted wilt tospovirus (TSWV) collected from northeastern and eastern Spain to infect 10 host species, and to be acquired and transmitted by the western flower thrips (WFT), Frankliniella occidentalis were compared. Two isolates of TSWV from a single source plant could be separated according to the different type of local lesions they induced in Nicotiana glutinosa. Host ranges of the studied TSWV isolates were very similar, but differences were found in the symptoms induced and in their capacity to infect specific hosts systemically. Lycopersicon esculentumDatura stramonium were evaluated for their potential as virus acquisition host species. The proportion of transmitter adult thrips obtained from WFT larvae fed on L. esculentum was greater than from D. stramonium. No differences were detected between TSWV isolates in their ability to be acquired and transmitted by WFT. No evidence was obtained of alterations in TSWV particles which could affect WFT transmissibility due to the repeated mechanical transfers used to clone the isolates. Our findings do not support the existence of pathological effects of TSWV on WFT.     

Incidence of weed reservoirs and vectors of tomato spotted wilt tospovirus on southern Tasmanian lettuce farms

Thrips species and tomato spotted wilt virus (TSWV) alternate weed hosts were surveyed on two lettuce farms in southern Tasmania during 1994 and 1995. Only one known vector species, Thrips tabaci, was found at either site, comprising on average 36.8% of the total monthly catch. A major peak of thrips activity in the summer corresponded with an increase of disease in autumn harvested lettuce. Two thrips species new for Tasmania were recorded, Pseudanaphothrips achaetus and Tenothrips frici . Infection patterns within the crop indicated that localized weed infestations were the most likely reservoir of virus. ELISA testing showed that TSWV was present in a range of dicotyledonous weed species, although usually infecting only a low percentage of the plants. Arctotheca calendula appeared to be the single most important reservoir host species at one property, whilst this species and Sonchus oleraceus, Malva sylvestris, Brassica rapa ssp. silvestris, Erodium moschatum and Trifolium sp. were probably the most important reservoirs at the other property. Two new natural TSWV host species were recorded, Erodium moschatum and Brassica rapa ssp. silvestris . The property with the highest incidence of TSWV-infected lettuce had a relatively higher proportion of virus-infected weeds but less thrips activity during the infection period.     

北京地区侵染茄子的番茄斑萎病毒分子鉴定与分析

调查发现北京地区一温室栽培茄子Solanum melongena L.出现严重病毒病。利用基于小RNA的高通量测序技术和RT-PCR方法,明确了引起茄子病害的病毒种类为番茄斑萎病毒,将其命名为TSWV-eggplant分离物。进一步克隆了该病毒的基因组全长(S RNA、M RNA、L RNA),并构建其系统发育树。结果表明,该分离物的S RNA与美国分离物亲缘关系较近,M RNA与中国分离物亲缘关系较近,而L RNA与韩国分离物亲缘关系较近。因此,本研究发现的TSWV分离物与国内已发生报道的分离物不同,该分离物是否存在不同分离物之间基因组的重组需要进一步研究。     

The Story of Modern Agrochemicals

Abstract

In Hamoul in the Nile Delta, where barnyard grass was the prevalent weed, two field trials of 12 herbicides were carried out in transplanted rice (cultivar; G12a 170). In the 1972 season granular herbicides were shown to be significantly superior to liquid formulations. In 1973 an improved technique was investigated, broadcasting herbicide/gypsum mixture by hand onto flood water. This type of application was successfully extended to some 7,000 feddans during the 1973 and 1974 seasons with the use of molinate/gypsum mixture. All herbicidal applications seemed significantly superior to hand-weeding once. Among all the tested herbicides, molinate was found to be the most beneficial, since it increased the rice grain yield by 62.5% and 108.0% over one hand-weeding and the control respectively.     

西藏昌都市卡若区蔬菜主要病毒检测及番茄斑萎病毒鉴定

为明确西藏昌都市卡若区高原条件下的蔬菜主要病毒种类, 对温室、大棚和露地栽培的主要蔬菜进行了病毒病调查, 采集典型病毒病症状样品进行ELISA检测, 明确病毒种类; 并利用电子显微镜观察, RT-PCR扩增克隆与测序分析对主要病毒进行鉴定分析。ELISA检测结果表明, 西藏昌都市卡若区温室及大棚栽培的番茄、辣椒和莴苣上的主要病毒有番茄斑萎病毒(tomato spotted wilt virus, TSWV)、马铃薯Y病毒(potato virus Y, PVY)及凤果花叶病毒(pepino mosaic virus, PepMV)。其中TSWV检出率最高, 为45%。进一步对检出TSWV的蔬菜样品进行电子显微镜观察, 发现其中含有典型的正番茄斑萎病毒属Orthotospovirus病毒粒体, 应用TSWV-N基因特异性引物进行RT-PCR扩增克隆和序列分析, 发现西藏昌都市卡若区蔬菜感染的TSWV与云南TSWV分离株亲缘关系最近。本研究结果明确了西藏昌都市卡若区蔬菜的主要病毒种类。综合抗体检测、病毒粒体形态观察与分类相关基因的克隆测序结果, 明确了西藏昌都市卡若区蔬菜感染的主要病毒为TSWV。这也是TSWV在西藏的首次报道, 为了解TSWV的发生分布及其防控提供了依据。     

番茄斑萎病毒的分离鉴定与抗性烟草种质筛选

番茄斑萎病毒(tomato spotted wilt virus, TSWV)是危害云南和四川烟草生产的主要病毒种类之一。本文通过分子生物学检测和苗期汁液摩擦接种,鉴定了云南保山隆阳和四川凉山盐源的烟草分离物毒株、病害表型和主栽品种抗性。结果显示：TSWV保山和凉山分离物在分子进化上与多个云南烟草TSWV分离物同源性较高,序列相似性达99.43%。分离物引起的典型症状为不对称损伤,半边叶上出现点状密集坏死,顶部心叶变灰坏死,半侧茎秆环斑状凹陷坏死、其对应髓部变黑。在供试的24份烟草种质中,烤烟品种‘K326’‘NC89’‘G28’‘云烟85’‘云烟87’‘云烟105’‘云烟116’‘红大’‘中烟100’,抗TMV的N基因型野生烟黏毛烟草Nicotiana glutinosa和‘Samsun NN’,抗PVY的va基因型烟草‘VAM’,均对TSWV表现感病;野生烟花烟草N.alata高抗TSWV,且兼抗烟草花叶病毒(tobacco mosaic virus, TMV),是抗病育种的重要基因资源。     

Genetics of tomato spotted wilt virus resistance coming from Lycopersicon peruvianum

New resistance sources coming from Lycopersicon peruvianum, especially those introgressed in UPV 32 line, are studied. UPV 32 resistance is controlled by a single gene. Resistance and dominance levels of this gene are conditioned by thrips transmission and isolate aggressiveness. A partial overcoming of resistance occurs due to the incomplete penetrance of the gene. Incomplete dominance of resistance also happens, which suggests gene dosage dependence. UPV 32 gene segregates independently of both Sw-5 gene and UPV 1 resistance gene, also coming from Lycopersicon peruvianum. It is proposed to name Sw-6 this new locus from UPV 32. Sw-5 gene and UPV 1 resistance gene show higher resistance than Sw-6. Heterozygotes for UPV 1 resistance gene were more resistant than heterozygotes for Sw-5. The lower dependence of UPV 1 resistance gene on the gene dosage effect makes it very useful for the development of commercial hybrids.     

Characterization of a vector-non-transmissible isolate of Tomato spotted wilt virus

The characteristics of a thrips‐non‐transmissible isolate of Tomato spotted wilt virus (TSWV), designated TSWV‐M, were compared with those of a thrips‐transmissible isolate, designated TSWV‐T. TSWV‐M showed a narrower host range than TSWV‐T. Adult thrips failed to transmit TSWV‐M, although the vector acquired the virus during the larval stages. TSWV‐M was detected by RT‐PCR in adult thrips bodies, but not in thrips heads, suggesting that loss of thrips transmissibility was the result of the absence of virus in adult thrips salivary glands. Whereas N (nucleoprotein), NSs (non‐structural protein) and G_C (the C‐terminal portion of the glycoprotein precursor protein) were present in similar amounts in leaf tissue from TSWV‐M‐ or TSWV‐T‐infected plants, G_N (the N‐terminal portion of the glycoprotein precursor protein) was present at much lower amounts in TSWV‐M‐ than in TSWV‐T‐infected plants. SDS‐PAGE and immunoblotting analysis of TSWV‐M and TSWV‐T virion preparations with G_N‐ and G_C‐specific antibodies revealed similar amounts of the G_N and G_C glycoproteins in TSWV‐T virions, but lower amounts of G_N than G_C in TSWV‐M virions. This resulted in a statistically significant reduction in the G_N/G_C ratio in TSWV‐M virions. In affinoblots, the G_C and G_N glycoproteins of TSWV‐M exhibited weak binding with lectins showing affinity for N‐linked oligosaccharide structures. Sequence analysis of M RNA (medium segment of the TSMV genome) revealed no deletions or frameshift mutations in the G_N/G_C precursor of TSWV‐M. However, five amino acid changes were detected in the G_N/G_C precursor. A single, relatively conservative amino acid substitution (V→I) was observed in the NSm protein. Sequence analysis of S RNA (small portion of the TSMV genome) revealed a large intergenic region with no changes in the N protein and with three amino acid changes in the NSs protein.     

Lipid metabolism in tomato and bean as a sensitive monitor for biocontrol of wilt diseases

The lipids metabolism of tomato and bean plants during biological control of wilt pathogens (Fusarium oxysporum f.sp.lycopersici andF. oxysporum f.sp.phaseoli, respectively) byBacillus subtilis was investigated. The interaction of wilt pathogens with both tomato and bean caused an imbalance and drastic reduction in total lipids, triacylglycerol, sterol and all phospholipd fractions except phosphatidic acid. The application of a formulated biocontrol agent,B. subtilis, eliminated the detrimental effect of both wilt pathogens and consequently prevented catabolism of lipid fractions in both tomato and bean. Moreover, the changes in the lipid fractions as a sensitive monitor for biocontrol of wilt diseases suggest a positive correlation between the application ofB. subtilis and improvement in the host metabolism towards anabolism. http://www.phytoparasitica.org posting Sept. 20, 2006.     

Pest and disease management by intercropping: Suppression of thrips and rust in leek

Abstract

Leek (Allium porrum L.) is an Important field vegetable in most of western and central Europe. Infestations of onion thrips (Thrips tabaci Lindeman) cannot be controlled with the range of insecticides now available in The Netherlands. Leek rust (Puccinia allii Rudolph) is now also difficult to control. Experiments in which no insecticides or fungicides were applied, were carried out to assess the effects on thrips populations and infection by leek rust when leek crops were undersown with subterranean clover (Trifolium subterraneum L.). To evaluate the economic aspects of this approach, both the quality and quantity of the leeks produced in the two systems were compared. Undersowing leeks with clover drastically reduced thrips infestations which was reflected in improved quality of leeks at harvest. Leek rust incidence was also reduced slightly by undersowing with clover and the quality of the leeks at harvest was also better. Although the quality of the leeks was improved when the crop was undersown with clover, the quantity of crop produced was reduced considerably as a result of plant competition.     

Occurrence and diversity of Tomato spotted wilt virus isolates breaking the Tsw resistance gene of Capsicum chinense in Yunnan,southwest China

Widely used resistant peppers (Capsicum spp.) bearing the Tsw locus triggered the rapid emergence of resistance‐breaking (RB) isolates of Tomato spotted wilt virus (TSWV) around the world. However, although TSWV‐induced diseases have rapidly increased in Yunnan, southwest China, in recent years, no information is available about the diversity of TSWV isolates in this region. In this study, the occurrence of natural TSWV RB variants among isolates collected in Yunnan is reported. Initially, a TSWV isolate from asparagus lettuce (TSWV‐LE) was collected in Yunnan in 2012. Surprisingly, this isolate of TSWV induced systemic necrosis on pepper carrying the Tsw resistance gene. Novel TSWV isolates, collected in 2015, included a tomato isolate (TSWV‐YN18) and a tobacco isolate (TSWV‐YN53) that also overcame Tsw‐mediated resistance. TSWV‐YN18 induced systemic ringspots, whereas TSWV‐YN53 caused systemic chlorotic mottling. Variations in the TSWV nonstructural (NSs) protein are the key determinants associated with Tsw resistance‐breaking isolates. It was found that TSWV‐LE NSs retained the hypersensitive response (HR) induction, whereas TSWV‐YN18 and TSWV‐YN53 NSs were unable to induce HR. However, the NSs of all three RB isolates suppressed RNA silencing. Sequence analysis of the NSs revealed that RB isolates of Yunnan have no amino acid mutation sites common to other previously reported RB isolates. However, two amino acids (F74 and K272) on TSWV‐LE NSs make it distinct from TSWV‐YN18 and TSWV‐YN53. The occurrence of different RB isolates and the failure of Tsw‐mediated resistance control pose serious threats to domestic pepper crops in southwest China.     

Development of an assay system using thrips-mediated inoculation to evaluate resistance of Capsicum spp. to Tomato spotted wilt virus

Considerable losses in pepper production by Tomato spotted wilt virus (TSWV) have been reported worldwide. In breeding programs, an assay for resistance that accurately estimates field occurrence of TSWV during pepper production is critical because the virus is vector transmitted. Here, we establish an assay system of TSWV-resistant Capsicum spp. using insect-mediated inoculation within an acrylic chamber in which environmental conditions such as temperature, light intensity, and nutrient supply are controlled. This chamber enables transmission of TSWV from viruliferous plants to plants used in the resistance assay with Frankliniella occidentalis safely, quickly, and precisely.     

Involvement of jasmonic acid signalling in bacterial wilt disease resistance induced by biocontrol agent Pythium oligandrum in tomato

When the biocontrol agent Pythium oligandrum (PO) colonizes the rhizosphere, it suppresses bacterial wilt disease in tomato (Solanum lycopersicum cv. Micro‐Tom) caused by Ralstonia solanacearum, and a homogenate of its mycelia exhibits elicitor activity, inducing an ethylene (ET)‐dependent defence response in Micro‐Tom. Since salicylic acid (SA) and jasmonic acid (JA) play an important role in plant defence responses to pathogens, the involvement of SA‐ and JA‐dependent signal transduction pathways in resistance to R. solanacearum was investigated in tomato roots treated with a mycelial homogenate of PO. Bacterial wilt disease was also suppressed in tomato cv. Moneymaker treated with the PO homogenate. However, the SA‐inducible PR‐1(P6) gene was not up‐regulated in either Micro‐Tom or Moneymaker. SA did not accumulate in homogenate‐treated roots in comparison with distilled water‐treated controls, even 24 h after inoculation. Induced resistance against R. solanacearum was not compromised in SA‐non‐accumulating NahG transgenic plants treated with the PO homogenate. On the other hand, the expression of the JA‐responsive gene for the basic PR‐6 protein was induced in both tomato cultivars treated with the PO homogenate. Furthermore, quantitative disease assays showed that the induced resistance against R. solanacearum was compromized in PO homogenate‐treated jai1‐1 mutant plants defective in JA signalling. These results indicated that the JA‐dependent signalling pathway is required for PO‐induced resistance against R. solanacearum in tomato.     

Phenotypic characterization of Pseudomonas fluorescens PfG32R and its spontaneous gacS mutants and biocontrol activity against bacterial wilt disease of tomato

Pseudomonas fluorescens strain PfG32R actively suppresses the occurrence of bacterial wilt disease of tomato caused by Ralstonia solanacearum. To determine the characteristics affected by spontaneous mutations in the gacS gene, three spontaneous mutants NR1, NR9, and ASW6 were tested for production of several enzymes, antimicrobial activity, and biocontrol activity against bacterial wilt disease of tomato in a greenhouse. Production of biosurfactant and of enzymes such as Tween-80 lipase, gelatin protease, and lecithinase; swarming activity; and antifungal activities against Fusarium oxysporum f. sp. radicis-lycopersici and F. graminearum were inactivated by mutations in the gacS gene, indicating that they are under the regulation of the GacS/GacA two-component regulatory system. Levan production, swimming, antifungal activity against Magnaporthe grisea, and antibacterial activity against R. solanacearum and Erwinia carotovora ssp. carotovora were not controlled by the GacS/GacA system. Biocontrol activities of the three spontaneous mutants varied from strain to strain, indicating that the biocontrol activities of PfG32R are influenced not only by the GacS/GacA system but also by other complex factors, which may not be regulated by the system.