Partial Purification of Thai Isolate of Citrus Huanglongbing (Greening) Bacterium and Antiserum Production for Serological Diagnosis

We aimed to improve the purification of citrus Huanglongbing (greening) bacterium (HB), Candidatus Liberobacter asiaticum and to produce an antiserum against HB. Periwinkle plants Catharantus roseum L. graft-inoculated with HB were used to produce an antiserum. All young leaves of new shoots incubated at 20–25°C and 25–30°C, a few mature leaves incubated at 20–25°C, and all mature leaves incubated first at 25–30°C and later transferred to 20–25°C developed yellowing symptoms and were then used to prepare immunogen. The HB was partially purified from these leaves by an improved method that included a macerating enzyme treatment of the midribs of infected leaves and homogenization of infected phloem sieve tissues. An antiserum raised against partially purified HB reacted clearly at a dilution of 1/16 with HB-infected citrus extract prepared at a concentration of 40 times, but did not react with healthy or tristeza virus-infected citrus extract in microprecipitin tests. Received 23 August 2002/ Accepted in revised form 4 December 2002     

Detection by PCR of Candidatus Liberibacter asiaticus, the bacterium causing citrus huanglongbing in vector psyllids: application to the study of vector–pathogen relationships

Citrus huanglongbing (HLB), previously called greening, is a serious citrus disease in Asia, eastern and southern Africa. It is caused by Candidatus Liberibacter asiaticus (Las), a phloem-limited, nonculturable bacterium transmitted by the Asian citrus psyllid ( Diaphorina citri ) in Asia. A PCR-based assay was developed for monitoring Las in vector psyllids using a rapid DNA extraction from psyllid bodies and PCR amplification. The entire procedure for Las detection in psyllids can be completed within 5 h. Using this method, Las can be accurately detected in psyllid adults as well as nymphs in different instar stages. The assay is sensitive enough for Las detection in single-psyllid extract from adult, fifth, fourth and third instars. In a transovarial transmission experiment, Las was not detected in eggs or in offspring produced by Las-carrying psyllid females. In a retention test, the Las-carrying psyllids remained Las-positive for 12 weeks after they were moved to common jasmine orange, a Las-immune plant. From these experimental results it was concluded that Las persists in the Asian citrus psyllid vector, but is not transovarially transmitted by the vector. These data help in understanding epidemiological characteristics of Las and psyllids in citrus HLB.     

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柑橘木虱(Diaphorina citri)主要危害柑橘等芸香科植物,传播黄龙病菌,给柑橘生产带来极大危害.从柑橘木虱的生物学及生态学特性、防治,柑橘木虱内生菌多样性、其对黄龙病菌的传播机制等方面进行综述,提出木虱寄主选择机理、专性传菌机制和抗性品种筛选是今后防治柑橘木虱的研究重点.     

龙葵上柑橘木虱存活观察与黄龙病检测

柑橘木虱是毁灭性病害黄龙病的媒介,其寄主范围比较严格,仅为芸香科内的一些植物。我们发现在自然状态下,柑橘木虱成虫可在柑橘园中常见茄科杂草-龙葵上停留。对比试验显示,木虱成虫在龙葵上的存活期最长可达45天,而在藿香蓟、含水海绵和无水海绵上分别为27、9天和2天;通过实时荧光PCR检测发现部分龙葵叶片中含有黄龙病病原菌。这些非寄主植物可能有助于柑橘木虱躲避不良环境或长距离迁移扩散,成为柑橘木虱和黄龙病的潜在库源。     

江西信丰柑橘木虱的药效测定

柑橘木虱（Diaphorina citri K瑄wayama）是柑橘黄龙病的媒介昆虫,目前,其防治以化防为主。为了监测化学农药的防治效果,选用9种柑橘生产上常用的药剂对江西赣州市信丰县的柑橘木虱田间种群进行药效测定,并用华南农业大学昆虫生态研究室用九里香饲养的种群作为敏感对照。测定虫态为成虫。结果表明,对信丰种群,处理24h后敌敌畏效果最好,死亡率达95.5%;其次为毒死蜱,死亡率为84.7%。48h和72h后,除敌敌畏、毒死蜱外,啶虫脒、丁硫克百威、噻虫嗪的防效也显著高于其它处理。另外,吡虫啉SL的防效随时间推移逐渐提高。而甲维盐与清水对照相比一直无显著差异,阿维菌素和高效氯氰菊酯的防效也很低。对敏感种群,24h后效果最好的也是敌敌畏和毒死蜱;48h后除了甲维盐和阿维菌素以外,其余7种药剂的防效均达87%以上,各处理之间无显著差异;72h后,这7种药剂的防效均接近100%。两个种群相比,信丰种群用高效氯氰菊酯、吡虫啉SL、吡虫啉SC、毒死蜱、噻虫嗪、啶虫脒处理24h后校正死亡率显著低于敏感种群,说明信丰种群对这些农药的敏感性都有不同程度的下降。48h和72h后,前4种处理的防效还显著低于敏感种群;另外,72h后阿维菌素和甲维盐处理的信丰种群防效也显著低于敏感种群。信丰种群对高效氯氰菊酯的敏感性下降最为显著,与敏感种群相比死亡率降低了65%~77%,其次为吡虫啉,降低17%~75%,建议该地区暂时停止使用。     

13种常用农药对柑橘木虱田间种群防治效果室内评价

柑橘木虱Diaphorina citri Kuwayama是黄龙病的传播媒介,快速、有效防治这种害虫是综合防控黄龙病的关键。目前,其防治措施主要依赖化学农药。为了了解化学农药对柑橘木虱的田间防治效果,本文以广东省博罗县柑橘木虱田间种群为测试对象,以华南农业大学昆虫生态研究室饲养的种群为敏感对照,室内测定了13种常用药剂推荐浓度对柑橘木虱的防治效果。结果表明,24 h后77.5%敌敌畏EC和5%啶虫脒EC对田间种群的效果最好,柑橘木虱死亡率分别为93.3%和90%,48 h后两种药剂处理的死亡率已达100%;48 h后,350 g/L吡虫啉SC处理的死亡率也达93.3%;72 h后,20%丁硫克百威EC、30%噻虫嗪SC、12%高氯·毒死蜱EC、45%毒死蜱EC、2.5%高效氯氟氰菊酯EW处理的死亡率也达90%以上。两个种群相比,所有药剂在相同时间对敏感种群的防治效果都高于田间种群。其中,用20%甲氰菊酯EC、30%噻虫嗪SC、45%毒死蜱EC、25 g/L联苯菊酯EC、99%矿物油EC等5种药剂处理,24 h后田间种群的校正死亡率显著低于敏感种群;48 h后除上述药剂外,4.5%高效氯氰菊酯ME处理的校正死亡率也显著低于敏感种群。72 h后,4.5%高效氯氰菊酯ME、25 g/L联苯菊酯EC、99%矿物油EC处理的校正死亡率依然显著低于敏感种群。说明田间种群对以上药剂的敏感性有不同程度的下降。此外发现,采用此测定方法22.4%螺虫乙酯SC对田间种群和敏感种群的防治效果均不理想。     

Boron availability and uptake in huanglongbing-affected citrus trees on a Florida entisol

Abstract

Florida sandy soils, particularly, Entisols are low in boron (B) and occasionally have B deficiency for citrus. A study was set-up at Citrus Research and Education Center, Lake Alfred, Florida, on a Candler fine sand to determine the availability and uptake of B in a high-density citrus planting of Huanglongbing (HLB)-affected trees. Boron was applied at 1.12?kg ha^?1 in three splits, at University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) recommended rate (1×), and at 2× the recommended rate using foliar and soil application methods. Soil samples were taken from soil surface to 60?cm depth in 15-cm increments within the irrigated and non-irrigated zones. Soil and leaf samples were analyzed for B using Mehlich III extraction method and acid digestion, respectively. Results showed the leaf B concentration for soil applied rate 1× was significantly higher (P?<?0.001) than that of foliar applied either at single or double rate but both were in the optimum range recommended by UF/IFAS. The sorption study revealed that there was no sorption (K_D < 0.2?L kg^?1) but K_D at 0–15-cm depth was 3× greater than that at 15–60?cm depths. The concentration of B in the leaf tissue remained in the recommended optimum critical range. Sorption coefficients showed negligible B sorption which means most applied B would be prone to leaching under heavy rains or saturated soil conditions on Florida sandy soils thus requiring judicious management for optimizing tree performance and sustaining environmental quality.