Rhizogenic agrobacteria in hydroponic crops: epidemics,diagnostics and control

Rhizogenic Agrobacterium biovar 1, harbouring an Ri‐plasmid (root‐inducing plasmid), is the causative agent of hairy root disease (HRD) in the hydroponic cultivation of tomato, cucumber and aubergine. The disease is characterized by extensive root proliferation leading to strong vegetative growth and, in severe cases, substantial losses in marketable yield. Agrobacterium biovar 1 is a heterogeneous group of agrobacteria and includes at least 10 genomospecies, among which at least four (G1, G3, G8 and G9) have been associated with HRD in hydroponically grown vegetables. This review has synthesized the current knowledge on rhizogenic Agrobacterium biovar 1, including infection process, current taxonomic status, genetic and phenotypic diversity, detection methods and strategies for disease control. With regard to the latter, symptom reduction and prevention of infection through cultivation methods and chemical disinfection (e.g. by the use of chlorine‐based disinfectants and hydrogen peroxide) are discussed and biocontrol strategies are elaborated on. Recent research has led to the identification of a phylogenetically related clade of Paenibacillus strains that have antagonistic activity against rhizogenic Agrobacterium biovar 1 strains, holding great potential for HRD control. Finally, possible directions for future research are proposed.     

广西百色烟区烟草青枯病菌的遗传多样性分析

[目的]分析广西百色烟区烟草青枯病菌的遗传多样性,为了解该烟区青枯病的发生流行规律和该病原菌的致病机制提供参考.[方法]通过致病力测定、生化型鉴定及BOX-PCR对69株来源于广西烟草主产区百色烟区的青枯菌株的遗传多样性进行系统分析.[结果]供试菌株存在明显的致病力分化,强致病力菌株、中等致病力菌株和弱致病力菌株出现频率分别为17.39%、62.32%和20.29%,其中以中等致病力菌群为优势菌群;供试菌株的生化型复杂,其中37株属于生化型III或生化亚型III-1、III-3和III-4,23株属于生化型Ⅰ,1株属于生化型Ⅱ,另有8株属于非标准生化型;BOX-PCR分析结果表明百色烟草青枯病菌存在丰富的遗传多样性,聚类分析结果显示菌株的遗传多态性与菌株的地理来源、致病力、生化型具有一定的相关性,但并无明显的地理种群、生化型种群或致病力一致的种群聚在一起.[结论]广西百色烟区烟草青枯病菌具有丰富的遗传多样性和复杂的生化型,可能是该烟区烟草青枯病为害逐年加重的重要原因之一.     

芝麻细菌性青枯病病原菌及其生化变种鉴定

芝麻细菌性青枯病是我国南方芝麻生产上的重要病害。调查研究表明,芝麻青枯病除前人报道的萎蔫、顶梢常有溃疡裂缝等典型症状外,还有植株畸形、茎秆表皮泡状突起、溃疡裂缝延伸至茎秆中下部、折断茎秆可见菌脓形成的透明细丝等症状。分离获得的病原菌菌株经菌体形态、菌落形态、培养性状、致病性、烟草过敏性反应及16S rRNA基因和16S～23S rRNA基因间区ITS序列测定,证实了芝麻青枯病是由青枯菌Ralstonia solanacearum引起。江西省15个县(市)的22个代表性菌株的生化变种鉴定显示,20株菌属于生化变种Ⅲ,占90.91%,2株属于生化变种Ⅳ,占9.09%。说明生化变种Ⅲ菌群是诱发芝麻青枯病流行的优势种群。     

Genetic diversity of Pseudomonas syringae pv. actinidiae,pathogen of kiwifruit bacterial canker

Bacterial canker disease of kiwifruit currently occurs in at least 15 countries, causing serious damage. The causative agent of the disease is Pseudomonas syringae pv. actinidiae (Psa), which is genetically diverse and is currently classified into five biovars, namely, biovars 1, 2, 3, 5 and 6. In Japan, four biovars except biovar 2 have been found so far. These biovars have been confirmed to have differences in the virulence and composition of pathogenicity-related genes, such as toxin biosynthesis and type III effector genes. Biovars 1 and 6 possess the tox island, a genomic island of approximately 38 kb, which contains phaseolotoxin biosynthesis genes (argK-tox cluster) and is confirmed to have been acquired from other bacteria through horizontal transfers. Also, on the megaplasmid possessed by biovar 6, there exist coronatine biosynthesis genes, and biovar 6 has the ability to produce two phytotoxins, phaseolotoxin and coronatine. In 2014, biovar 3, considered to be of foreign origin, was confirmed for the first time in Japan. Biovar 5, whose virulence is relatively weak, is distributed only in a limited area. In addition to the tox island and various plasmids, a large number of mobile genetic elements are confirmed to be present on the Psa genomes, which might have played a major role in helping Psa to acquire new features. In order to understand how Psa acquired the ability to infect kiwifruit systemically, it is important to make polyphasic comparisons with related pathovars, such as P. syringae pv. theae and pv. actinidifoliorum.     

抗不同生化型青枯菌的生防菌筛选鉴定及其活性分析

为更好地利用生防菌控制青枯病危害,从不同地区的土壤中分离到569株细菌菌株,筛选到3株对5种不同生化型青枯劳尔氏菌Ralstonia solanacearum具有较强拮抗活性的菌株,其中菌株BS2004的拮抗活性最强。以BS2004的菌悬液为对照,分别测定无菌滤液、蛋白酶K及高温热处理后拮抗物质抑菌活性的变化。结果显示,蛋白酶K及高温热处理后,该菌的抑菌活性显著降低,表明其主要抑菌成分为蛋白类物质。在设施栽培条件下用生防菌BS2004菌悬液处理番茄植株,能有效控制番茄青枯病的发生,防治效果达66.75%,同时还发现,重新分离得到的青枯菌菌体数明显受到生防菌的抑制。通过对BS2004的形态、生理生化特征、脂肪酸鉴定、16S rDNA序列等进行分析,该菌株被鉴定为解淀粉芽孢杆菌Bacillus amyloliquefaciens。     

广东省烟草青枯菌的菌系和遗传多样性

从广东省韶关和梅州2个烟草产区采集了来自8个县市的共38个烟草青枯菌菌株,对病菌的生物型、致病型和遗传多样性进行了测定,结果表明广东烟草青枯菌全部为生物型Ⅲ。通过在红花大金元,K326,岩烟97和系3等4个烟草鉴别品种上的致病性反应,将广东烟草青枯菌分为强致病力、中等致病力和弱致病力3种致病型,其中以中等致病力菌株为主,占78.9%;强致病力菌株占13.2%;弱致病力菌株占7.9%。从116个RAPD通用引物中筛选出10条引物,用于对38个烟草青枯菌株DNA的RAPD分析,扩增条带表现出明显的多态性,条带主要聚集在0.3～4.0 kb之间。聚类分析这38个菌株可分为2个组群,即组群A和组群B。组群A中又可以分为7个亚组(A1、A2、A3、A4、A5、A6、A7);组群B也含有4个亚组(B1、B2、B3、B4)。研究结果还表明,广东烟草青枯菌菌株RAPD组群的划分与菌株的寄主来源有一定的相关性,但与地理区域、生物型和致病型没有明显的相关性;生物型不能反映烟草青枯菌菌系的差异。     

Survival and possibilities for extinction ofPseudomonas solanacearum (Smith) Smith in cool climates

Summary The importance of biovar 2 ofPseudomonas solanacearum (syn.Burkholderia solanacearum; syn.Ralstonia solanacearum) in cool temperate climates has been recently emphasised by outbreaks of potato brown rot disease in some European countries. Dissemination of the pathogen in latently infected potato tubers and in contaminated irrigation water, and overwintering in aquatic roots of the weed hostSolanum dulcamara have been implicated. Evidence from the literature suggests that in cool climates the organism is unlikely to persist long term in soil in the absence of a susceptible host. Effective control strategies rely on the enforcement of quarantine legislation at both national and European Community levels. This requires knowledge of the biology of the pathogen in cool environments, methods for accurate monitoring of its survival and distribution at and around disease outbreak sites and application of effective measures for pathogen exclusion, containment and eventual eradication. This paper reviews current knowledge on the above.     

An Efficient Microtiter System to Determine Agrobacterium Biovar

A microtiter system for biovar characterization of Agrobacterium strains which simplifies the analysis of a large number of isolates is described. This method is based on incubation of bacterial strains in microplate wells previously amended with media specifically used by the different Agrobacterium biovars. More than 150 purified Agrobacterium strains isolated from the most common host plants were analysed by the microtiter system. It proved to be an excellent tool using less reagents, time and space for incubation in comparison with the traditional method.     

The presence of crown gall of grape incited byagrobacterium tumefaciens biovar 3 in Israel

Crown gall was previously reported on grape in Israel but the pathogen was not isolated and characterized. The three recognized biovars ofAgrobacterium tumefaciens can be tumorigenic on grape, but biovar 3 is the most important world wide. A single occurrence of tumors in a vineyard yielded bacteria which incited galls on grape,Nicotiana glauca and tomato, but not on bryophyllum. The bacteria were confirmed asA. tumefaciens because they contained DNA which hybridized with T-DNA from a Ti plasmid. Biochemical and physiological tests, octopine production and utilization, and agrocin 84 insensitivity conformed with those of bv. 3. Subsequent occurrences of the grape disease have not been found, but the presence ofA. tumefaciens bv. 3 in Israel is a potential threat to nurseries and vineyards.     

Evaluation of a PCR assay for identification and differentiation of Campylobacter fetus subspecies

Objective To evaluate a polymerase chain reaction assay for identification of Campylobacter fetus and differentiation of the defined subspecies.
Design Characterisation of bacterial strains by traditional phenotyping, polymerase chain reaction, a probabilistic identification scheme and macrorestriction profiling using pulsed field gel electrophoresis.
Procedure The results of identification of 99 bacterial strains as determined by conventional phenotyping or by poly-merase chain reaction were compared. Two of these were type strains of C fetus subsp fetus and C fetus subsp venerealis ; the remaining strains were field isolates putatively identified as C fetus . In cases where the subspecies identity was disputed, isolates were identified by means of a probabilistic identification scheme and by macrorestriction profiling.
Results The agreement between strain identities initially suggested by traditional phenotypic methods and the PCR assay was found to be 80.8%. The polymerase chain reaction proved to be a reliable technique for the species and subspecies identification of C fetus ; equivocal results were obtained in only two instances. Initial misidentifications by conventional phenotyping methods were attributed to methodological differences used in various laboratories.
Conclusion Our results indicate that misidentification of C fetus i n routine diagnostic laboratories may be relatively common. The PCR assay evaluated gave rapid and reproducible results and is thus a valuable adjunctive method for the identification of C fetus and subsequent subspecies differentiation.