柑桔黄龙病的媒介昆虫及指示植物的试验初报

根据試驗結果,初步認为柑桔黃龙病可借东方桔蚜传病,其指示植物为由力克檸檬、北京香檸檬和墨西哥来檬等1—2月龄的实生幼苗。在这些指示植物和蕉柑幼苗上,用东方桔蚜传病以及用嫁接法传病所引起的症状均相同:在由力克檸檬和蕉柑上表現矮化及梢叶黄化;在北京香檸檬和墨西哥来檬上表現矮化、明脉和“嵌紋”等。同时,在北京香檸檬上,以蚜传发病植株的組織,进行回接的試株和以广州及普宁县病株的組織进行嫁接的試株,有些发生木质部陷点及木质部陷紋的症状。根据这些特点,虽然不能肯定柑桔黄龙病与南美洲柑桔衰退病的病原病毒相同,但它們很可能屬于同一类病毒(却柑桔衰退病毒类)。此病在指示植物上的潛育期最短为27天。在11月气温較低时的潛育期长达二个月以上。5月分在网罩内气温高达42℃,发病試株在一周内消失症状并恢复生长,但試株移到树蔭下(气温降低到25°—30℃左右),一个月内症状又重新出現。     

柑桔衰退病毒分离株分子特征初步研究

柑桔衰退病毒(Citrus tristeza virus,CTV)广泛分布于世界各柑桔产区,迄今已经摧毁了一亿株柑桔,目前仍然严重威胁着以酸橙作砧木的柑桔产区和对茎陷点型CTV敏感的葡萄柚、柚类和某些甜橙的安全。我国广泛分布着CTV的多种强毒株,随着近年来柑桔产业结构调整的深入,茎陷点型CTV对柚类和某些甜橙的危害正变得日益严峻。国外的经验表明,弱毒株交叉保护(MSCP) 是目前防治茎陷点型CTV最有效手段。 CTV属于长线形病毒属(Closterovirus),基因组为19 296个核苷酸组成的正义单链RNA,具有 12个开放读码框(ORF),可以编码17种蛋白质, 其中25 kDa和27 kDa外壳蛋白分别包裹着约     

枸头橙茎陷点病的研究

由柑桔衰退病毒(citrus tristeza virus,CTV)引起的茎陷点病,是世界上许多柑桔生产国家如巴西、澳大利亚、日本和秘鲁等的重要柑桔病害,该病主要为害敏感的柑桔品种,与所用砧木无关。枸头橙(Citrus aurantium)是浙江黄岩桔区特有的砧木种,具有许多优良的栽培特点。前人的研究结果表明,它用作甜橙的砧木时,耐苗黄型衰退病。作者研究发现它对茎陷点病非常敏感,被害严重。1986年以来,作者对枸头橙茎陷点病的发生、茎陷点病对枸头橙植株的树势、产量和果型等的影响、病原病毒的鉴定以及致病力的测定等进行了研究,结果简报如下。     

毒源和寄主对褐色桔蚜传播柑桔衰退病毒效率的影响

褐色桔蚜是柑桔衰退病毒(Citrus tristeza virus,CTV)最有效的传播媒介,为了解不同柑桔寄主种类和毒源对褐色桔蚜传播CTV效率的影响,检测在以锦橙、凤凰柚和墨西哥来檬作毒源植株时,褐色桔蚜对10个CTV分离株的单蚜传毒率,以及蚜传前后CTV分离株p25/HinfⅠRFLP组群构成的变化,并对其中5个分离株与2个国外分离株进行了p20和p25基因相应氨基酸序列的比对分析。结果表明:褐色桔蚜传播CTV的能力受柑桔寄主种类的影响较大,以锦橙作毒源植株可以获得最高的传毒率;CTV毒株强弱以及褐色桔蚜虫态(有翅或无翅蚜)对单蚜传毒率影响不明显;褐色桔蚜传播具有p25/HinfⅠRFLP第3组群构成的CTV分离株的能力较强。     

利用病毒弱株系接种防治脐橙茎陷点病

在田间对枳砧森田脐橙利用选出的柑桔衰退病毒(CTV)和脉突病毒(CVEV)弱毒系对CTV强毒系的交叉保护作用进行了测定。结果表明,经CTV M—15A和M—16A预先接种的植株,树势强健,且果大。此外,用和CTV多克隆抗血清无反应的No.145及CVEV NO.1605弱毒系预接种植株生长也很好。     

重庆地区柑桔衰退病毒多态性研究

柑桔衰退病毒(CTV)存在着复杂的株系分化现象.在使用弱毒株交叉保护防治柑桔衰退病时需要对田间病毒株系组成进行分析,并对选用的株系进行单蚜分离纯化.作者运用限制性片段长度多态性和单链构象多态性对田间获得的168个CTV样品和2个蚜传毒株的外壳蛋白基因进行分析,了解重庆市田间CTV组群构成情况,发现田间CTV以多株系混合发生为主,其中主要是CP/HinfⅠRFLP第1、3和6组群,约占总数的90%,并以强毒株混合感染为主.甜橙中CP/HinfⅠRFLP的组群构成最为复杂.单头褐色桔蚜从柚类至甜橙传播CTV的效率低(不足1%),该蚜的取食可改变CTV的株系组成.     

柑桔碎叶病毒病发生与研究现状简介

1935年作者和赵学源等分别在浙江黄岩和四川重庆,于本地早、槾桔和蕉柑、北京柠檬上鉴定到柑桔碎叶病毒。次年,作者等又在黄岩柑桔等10个品种(系)上鉴定到碎叶病毒。我们的研究表明,柑桔碎叶病毒在我     

柑桔裂皮病发生情况鉴定

 柑桔裂皮病(exocortis)是以枳、枳橙和檫檬作砧木的柑桔树的严重病害,它的病原是一种类病毒^[4]。有的毒系引起砧木部树皮纵向开裂或翘裂,植株矮化,树势衰退;有的毒系仅引起植株矮化。此病除了嫁接传播外,亦通过修枝剪等与韧皮部接触传播。病害的鉴定,以利用指示植物为主。敏感的指示植物是Etrog香橼的USDCS 60-13选系和亚利桑那861选系^[1、2]。此外,亚利桑那861-S-1选系更为敏感^[3]。它不仅适用于鉴定一般毒系,亦适用于鉴定弱毒系。防治措施以通过茎尖嫁接脱毒或鉴定选择无病母树繁殖无毒苗木为主,亦要注意防止通过工具等的田间传播。     

摩洛哥脐血橙植株上一种机械传播性病毒的鉴定

 本文采用叶片接种法和枝条接种法对25个柑桔种类体细胞杂种或品种进行了抗脚腐病鉴定,结果表明:体细胞杂种中枳+酸橙、枳+甜橙为高抗类型;酸橙+兰普来檬、枳+印度酸桔;蚝壳刺+哈姆甜橙、酸橙+澳洲指桔为抗性;酸橙+印度酸桔为中抗。建立了叶片接种法的抗病性分级标准。初步分析了柑桔体细胞杂种的抗性规律。     

6种柑橘类植物对柑橘衰退病毒分离株TR-L514变异的影响

 柑橘衰退病毒(Citrus tristeza virus,CTV)存在复杂的株系分化现象,运用弱毒株交叉保护防治柑橘衰退病时需了解不同类型柑橘对CTV构成的影响。作者将CTV分离株TR-L514嫁接接种到6类柑橘植物上获得了18个亚分离株,并对这18个亚分离株和TR-L514进行了指示植物鉴定,p25基因的限制性片段长度多态性(RFLP)和单链构象多态性(SSCP)分析,p23基因的序列比较。结果表明,CTV株系对不同柑橘类植株的适应性存在差异。TR-L514嫁接到不同柑橘类植株其构成会发生变化,在甜橙上可以同时检测出p25//HinfⅠ RFLP第1和6组群,并具有比在其它4类柑橘上更为复杂的SSCP谱型构成,因此甜橙可能更适宜于CTV的增殖。TR-L514及18个亚分离株的p23基因序列差异可能与不同类柑橘植株的适应性有关。     

Characterization of Citrus tristeza virus isolates in northern Iran

The biological and molecular properties of four Citrus tristeza virus (CTV) isolates isolated from infected Satsuma trees imported from Japan, and growing in citrus groves in northern Iran (Mahdasht orchards, Mazandaran Province), were investigated. CTV-infected samples were collected from sweet orange trees and grafted onto Alemow (Citrus macrophylla Wester) seedlings. On indicator plants, these isolates produced various symptoms including vein clearing and stem pitting on Mexican lime, Alemow, and Citrus hystrix, and yellowing and stunting on sour orange and grapefruit seedlings. Citrus samples were also surveyed for CTV using serological tests. The coat protein (CP) gene of these isolates was amplified using specific primers, yielding an amplicon of 672 bp for all isolates. Sequence analysis showed 98%–99% sequence homology of Iranian isolates with the Californian CTV severe stem-pitting isolate SY568 and 97%–98% homology with the Japanese seedling yellows isolate NUagA. The Iranian isolates were compared by restriction fragment length polymorphism (RFLP) analysis of the CP amplicon for further classification.     

Investigation of biological properties, double-stranded RNA patterns and antigen concentration in citrus species infected with citrus tristeza virus

Biological properties and dsRNA patterns of one Cyprus and three Turkish isolates of citrus tristeza virus (CTV) were investigated. In addition, CTV antigen concentration and effect of tissue sampling time from naturally infected Shamouti sweet orange trees grown in the field of Icel Province, Turkey, were also determined. The Cyprus isolate showed vein clearing symptoms on grapefruit, ‘Madam Vinous’ and Mexican lime and stem pitting symptoms on Mexican lime. The three Turkish isolates showed only vein clearing symptoms on Mexican lime. All four isolates showed a full-length major double-stranded RNA (dsRNA) band of 13.3 × 10⁶ Da mol. wt in extracts from infected Madam Vinous sweet orange trees, and major or minor dsRNA bands with 2.0. 0.8 and 0.5 × 10⁶ mol.wt. All seven different citrus varieties inoculated with the Igdir (D) strain contained full-length dsRNA. The additional two dsRNA of 0.8 and 0.5 × 10⁶ mol.wt were also detected as clearly as full-length dsRNA in these hosts, but were weaker inCitrus exelsa and ‘Interdonat’ lemon. Madam Vinous, rough lemon and Mexican lime were the best hosts for dsRNA analysis. ELISA values were highest in April (OD_405nm =0.476), decreased steadily until August, and then increased gradually through December. ELISA values were lowest in July and August (OD_405nm =0.157 and 0.141, respectively). dsRNA recovery from a field tree infected with isolate Igdir D was good in March, April and May and poor in January and February. No dsRNA band was detected in August or September. http://www.phytoparasitica.org posting July 9, 2002.     

Separation and interference of strains from a citrus tristeza virus isolate evidenced by biological activity and double-stranded RNA (dsRNA) analysis

Separation of strains of citrus tristeza virus (CTV), differentiated by their double-stranded RNA (dsRNA) profiles, was obtained by graft-inoculating citron plants from a Mexican lime that had been recently aphid- or graft-inoculated with a mild CTV isolate (T-385). Up to 24 sub-isolates with differing dsRNA profiles were obtained from the aphid-inoculated lime. Some of these sub-isolates induced stronger symptoms in several citrus species than the original T-385 isolate. One sub-isolate, T-385-33, was mild in Mexican lime, but induced stem pitting on sweet orange. Inoculation of this isolate on Mexican lime, sour orange and Eureka lemon induced mild or no symptoms when inoculum was taken from citron, but very severe symptoms when the inoculum was from sweet orange. Mexican lime and sweet orange plants co-inoculated with T-385-33 from sweet orange in combination with the other 23 sub-isolates showed mild symptoms. The results obtained suggest that there is natural cross-protection among sub-isolates in the original T-385 isolate.     

Molecular characterization of Citrus yellow mosaic badnavirus (CMBV) isolates revealed the presence of two distinct strains infecting citrus in India

Citrus yellow mosaic badnavirus (CMBV) is a non-enveloped, bacilliform DNA virus and the etiologic agent of yellow mosaic disease of citrus in India. The disease was initially reported from the southern parts of India and has now spread to other parts of the country. It is a serious disease of sweet orange (Citrus sinensis) in southern India, where it causes significant yield losses. During a recent survey of citrus groves in the Nagpur region, central India, characteristic mosaic symptoms were observed in mandarin orange (Citrus reticulata) and sweet orange. Virus transmission studies, electron microscopy, PCR amplification and sequencing of cloned PCR products from samples showing mosaic symptoms confirmed the presence of a badnavirus. The CMBV–Nagpur isolate could be transmitted to the Rangpur lime (C. limonia) and acid lime (Citrus aurantifolia) by graft inoculation. Sequence analysis of a segment of ORF-III region and intergenic region (IR) of the viral genome revealed that CMBV–Nagpur isolate formed a distinct clade along with some previously reported isolates that are known to infect acid lime and Rangpur lime. CMBV isolates that infect citrus species other than the acid lime and Rangpur lime formed a second clade. Based on the transmission studies and phylogenetic analyses, it was concluded that at least two strains of CMBV exist in India currently.     

Detection and characterization of <Emphasis Type="Italic">Citrus tristeza virus</Emphasis> stem pitting isolates in Jamaica

An island wide survey for Citrus tristeza virus (CTV) in citrus orchards across Jamaica (13 regions) was conducted over 2 years. Trees (1, 885) showing virus-like symptoms as well as asymptomatic trees were randomly sampled for testing by ELISA and 55 samples from the 6 major citrus growing regions were graft inoculated on indicator plants. Most samples (74%) reacted to polyclonal antibodies against CTV in ELISA, while 20% were positive in tests using monoclonal antibodies specific to severe CTV strains. Samples collected from the 6 major citrus growing regions produced vein clearing and stem pitting symptoms on Mexican lime indicator plants (87%). In addition, stem pitting symptoms were induced on Duncan grapefruit, sweet orange, sour orange or sweet orange grafted on sour orange. Nucleotide sequencing of the coat protein gene sequences isolated from these samples indicated high identities (88 to 95.5%) among the Jamaican isolates and previously reported stem pitting strains from Central and North America and Eurasia (88 to 100%). The results suggest a shared ancestry with isolates from other geographical locations, rather than geographical speciation, and presumably separate CTV introductions into Jamaica.     

Biological characterization of citrus tristeza virus isolates by in vitro tissue cultures

Stem segments from Mexican lime, sweet orange, grapefruit, Citrus excelsa and alemow, infected with five citrus tristeza virus (CTV) isolates, were cultured in vitro . Regeneration of roots and shoots were modified as a result of infection. The effect of CTV on the morphogenesis of stem segments cultured in vitro depended on the CTV isolate and the plant host, and showed a correlation with the in vivo effects observed in biological indexing. Evaluation of the morphogenic response of stem segments of Mexican lime and grapefruit can be used as an additional tool for the biological characterization of CTV isolates. The symptoms on sweet orange plants obtained from regenerated shoots indicated that CTV is unevenly distributed in the host plant cells and that the regeneration process may be utilized as a tool to separate strains from complex field isolates.     

Fruit spot of sweet lime (<Emphasis Type="Italic">Citrus limetta</Emphasis>) caused by <Emphasis Type="Italic">Septoria</Emphasis> sp. in Peru

In 2002, a severe fruit spot of sweet lime (Citrus limetta) was observed in Piura and Lambayeque provinces in northern Peru. Affected fruits showed large oval and sunken lesions, often surrounded by chlorotic haloes. Septoria sp. was isolated from affected fruits. Sweet lime isolates showed larger pycnidia and pycnidiospores than those of Septoria spp. previously described on citrus. In addition, phylogenetic analysis of the ITS sequences clearly separated the sweet lime isolates from S. citri and S. citricola. Isolates were pathogenic to detached sweet lime fruits and the fungus was isolated from lesions on inoculated fruits.     

Photosynthetic and antioxidant responses of Mexican lime (Citrus aurantifolia) plants to Citrus tristeza virus infection

The effect of Citrus tristeza virus (CTV) infection on photosynthetic activity and antioxidant metabolism was analysed in plants of the highly susceptible citrus genotype Mexican lime (Citrus aurantifolia). Two virus isolates differing in their virulence (the severe T318 and the mild T385) were used in the experiments. CTV infection caused a reduction in photosynthetic capacity in infected plants. This limitation was mainly due to a reduction in the carboxylative efficiency whereas the limitation of CO₂ diffusion through the stoma had lower impact. The virus did not damage the antennae and did not reduce the efficiency of light harvesting complexes. Oxidative damage occurred in infected plants, as evidenced by the increase in malondialdehyde levels. Indeed, CTV infection caused an increase in ascorbate peroxidase activity in new shoots developed in infected plants during the 2 years of the experiment. Data suggest that the H₂O₂ removal machinery was not damaged as a result of stress but the defence mechanism was overwhelmed with time due to the continuing pressure of biotic stress.