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猕猴桃细菌性溃疡病研究进展

花匠小妙招
2024-11-26 16:51

0 引言

猕猴桃果实风味独特,营养丰富,富含维生素C,享有“水果之王”的美称。自20世纪被人工驯化以来,猕猴桃在世界范围内的栽培面积不断扩大,日益成为人们日常消费的水果种类。相比于其他果树,猕猴桃病虫害较少,生产中农药施用量也较低,但猕猴桃细菌性溃疡病却严重危害着猕猴桃的生产。1984年首次在日本静冈县被发现,猕猴桃溃疡病目前已在世界各大猕猴桃产区蔓延,如葡萄牙[1]、西班牙[2]、法国[3]、新西兰[4]、土耳其[5]、希腊[6]等国。作为猕猴桃第一生产大国,猕猴桃溃疡病也已蔓延至中国陕西、四川和贵州等猕猴桃主要栽培省份。鉴于其对世界猕猴桃产业的重大危害,笔者对猕猴桃细菌性溃疡病的发现、病原菌的分类、传播途径、危害、防治方法和致病机理等方面的发现和研究成果进行了综述,期望为国内猕猴桃溃疡病的研究提供更加详尽的理论基础。

1 猕猴桃溃疡病的症状、危害和传播途径

猕猴桃溃疡病病菌一般在冬季和早春开始侵染猕猴桃植株,侵染部位一般是成年植株的主干和主蔓,发病初期侵染部位产生乳白色分泌物,后期为锈红色。病菌侵染导致的茎蔓溃疡会阻碍植株养分运输,导致树势减弱。病菌侵染叶片时会产生黑色斑点并伴有黄色晕圈[7,8]。猕猴桃溃疡病具有隐蔽性、爆发性和毁灭性,并且具有极强的传染性。目前猕猴桃溃疡病已蔓延至中国及世界主要猕猴桃产区,果园一旦感染溃疡病,轻则导致减产,重则毁园。新西兰在发生溃疡病的2010—2012年,染病的果园从3个迅速增加到1232个,占新西兰全部果园的37%[9],导致新西兰主要出口品种‘Hort16A’大幅减产。由于该品种抗溃疡病能力极弱,目前已逐渐被新的抗病性更强的品种替代。猕猴桃溃疡病病菌致病能力极强,目前所栽培的全部猕猴桃品种中尚未发现对其具有完全抗性的品种。虽然研究发现不同品种的猕猴桃对溃疡病菌的抗性不同[10],但不幸的是一些品质极佳商品性非常好的品种抗溃疡病能力却很弱,如新西兰的‘Hort16A’,中国广泛栽培的红心猕猴桃‘红阳’也深受其害。

猕猴桃溃疡病能够在短期之内传播至世界各大猕猴桃产区的原因在于其极强的传染性。出入果园的各种农事工具、人员、车辆等是携带病菌的重要载体,尤其是直接与植株接触的修枝剪。秋冬和早春从患病植株的溃疡处流出的分泌物借助风力可以将病菌传播至附近的植株或果园[11,12]。最近的研究发现昆虫也可能成为溃疡病菌的载体[13]。溃疡病菌的远距离传播主要通过气流到达云层,再借助雨雪回到地面。猕猴桃为雌雄异株植物,生产中需要配植授粉树,近年来也有果农使用商业生产的猕猴桃花粉,但有研究表明溃疡病菌可寄生在猕猴桃花粉中[14,15],因此花粉也可能成为溃疡病的传染源。关于猕猴桃果实是否会传播溃疡病目前尚无定论,不同的研究人员给出了相反的结论[16,17],但建议果园避免引入采收自严重感染溃疡病果园的果实。

2 致病菌Pseudomonas syringae pv. actinidiae的特征、分类和起源

猕猴桃细菌性溃疡病是由一种名为丁香假单胞菌猕猴桃致病变种Pseudomonas syringae pv. actinidiae(Psa)的细菌引起的。自1984年在日本发现该病以来,科研人员已陆续在世界不同的猕猴桃果园收集到该病菌,这些来自不同地区的病菌在分布范围、致病能力、抗药性和基因组构成等方面具有不同的特点。在1984年日本发现Psa的同一年,国内湖南省也出现了猕猴桃溃疡病爆发的果园,并导致了严重损失[18],遗憾的是当时未及时保存病菌以便后续研究。1988年韩国也发现Psa[19]。此时的Psa仅在美味猕猴桃‘海沃德’(Actinidiae deliciosa ‘Hayward’)中发现,并且都可导致严重的病害。1992年同样在意大利的‘海沃德’中发现Psa[20],但不同的是这一类群的Psa虽然在意大利分布广泛,但在被发现后的约20年时间里并未造成严重的猕猴桃病害。2008年一种致病能力极强的Psa在意大利被发现,并迅速传播至欧洲附近国家、中国、新西兰等国[3-4,21],并导致世界各国猕猴桃产业的严重损失。这一类群的病菌不但感染美味猕猴桃品种,对中华猕猴桃A. chinensis的黄肉和红肉品种同样具有很强的致病能力。2010年,在新西兰的几个果园又发现了新的Psa类型,值得庆幸的是这一株系致病性并不强,仅会导致猕猴桃植株的叶斑病[22]。

近年来,随着收集到的Psa株系的增多和测序技术的迅速发展,科研人员开始通过对不同Psa株系基因组的比较分析,来预测筛选Psa基因组中可能的致病基因,并对这些Psa的系统进化和起源进行分析[23]。通过基因组比对,可将目前已发现的Psa株系分为4种类型。第一类包括1984年在日本发现的Psa和1992年意大利的Psa,虽然两者在2个国家对猕猴桃的致病能力有很大差异,但两者基因组几乎是相同的,推测意大利的Psa是由日本传播而来,但由于意大利的地理气候环境以及当地果农的栽培技术不同于日本而使其在意大利的致病能力明显减弱。第二类为1988发现于韩国的Psa,这一Psa类型的基因组与第一类的显著差异在于其含有一个存在于质粒上的可能产生冠菌素的基因,并缺失菜豆菌毒素基因簇[24],同时还包括大量的SNPs和数百的其他基因[23]。经过几年的药物锻炼,目前第一类和第二类的Psa已产生了具有抗铜和抗链霉素能力的基因[25,26,27,28]。第三类为2008年发现于意大利并已传播至世界各地的Psa类型,这一类Psa缺少编码冠菌素和菜豆菌毒素的基因[14,22,29-31]。经过快速的传播,这一类型的Psa在世界很多地区已取代了其他的类型[1-3,22]。第四类为发现于新西兰的弱致病性Psa,这一类型在致病能力和致病因子构成上都与前3组存在明显不同[22]。以上4个Psa类型,第三类是目前传播范围最广对世界猕猴桃产业危害最为严重的一类,分析其与其他3组以及来源于中国的Psa在进化上的关系,结果表明它起源于中国然后传播至世界其他国家[32,33]。

3 Psa的致病机理

病菌的致病机理主要依赖于其操纵植物代谢以吸取营养进行生长繁殖的能力和抑制植物免疫以避免被植物识别和清除的能力。Psa属于丁香假单胞菌,这一包括多个变种的细菌种类可以导致多种病害,其寄主包括大部分的农作物和观赏植物。丁香假单胞菌的变种虽然众多,但其关键的致病因子主要存在于一套被称为III型分泌系统(type III secretion system,T3SS)的效应蛋白分泌系统。T3SS通过分泌效应蛋白来抑制植物的先天免疫应答反应(PAMP-triggered immunity,PTI)和效应因子诱导的免疫应答反应(Effector-triggered immunity,ETI)[34]。不同的丁香假单胞菌变种具有不同的寄主,其具体的致病机理也存在一定的特异性,目前关于Psa的致病机理尤其是致病基因的发掘方面取得了一定的进展。

鉴于不同Psa类型的致病性存在明显差异,Mccann等[23]对不同Psa类型的基因组中的T3SS分泌的效应因子编码基因进行了比较,在4类Psa的基因组中共发现了51个效应因子编码基因,而4类Psa都具有的基因仅有17个,这可能部分解释了这4类Psa在致病性上的差异。Psa在通过T3SS系统发挥其致病作用的同时还利用一些植物毒素来促进其致病效应,如第一类的Psa可以通过产生菜豆毒素使猕猴桃在溃疡病发生时出现环形的病斑[35]。第二类Psa可以产生冠菌素,这一植物毒素通过抑制植物免疫信号分子水杨酸的合成而起到调控气孔重新开始和促进病菌繁殖的作用[36]。相比之下,致病性最强的第三类Psa反而未发现相关的植物毒素。Andolfi等[37]对Psa中发挥致病作用的物质的性质进行了分析,结果表明,采用基本培养基培养的Psa获得的滤液可以引起烟草和猕猴桃明显的类似超敏反应的现象,一些属于胞外多糖的亲水性物质可以对猕猴桃产生很高的毒性。

4 猕猴桃抗病性研究

对植物的抗病机理国内外已进行了多年的探索,并取得了一定的成果。植物生长的环境中存在着大量对其生长具有威胁的生物和非生物胁迫,针对细菌、真菌、病毒等致病因子,植物经过长时间的进化过程已形成了一套完整的免疫防御系统。植物的第一道免疫系统可以识别病原菌表面被称为病原相关分子模型(PAMPs/MAMPs)的特异物质,从而引发植物先天免疫应答(PTI)。植物的第二道免疫系统依赖于对病菌III型分泌系统(T3SS)分泌到细胞质中的效应因子的特异识别,被称为效应因子诱导的免疫应答(ETI)。PTI和ETI一起又可以诱导植物产生超敏反应(Hyper sensitive response,HR),超敏反应在很大程度上决定了包括Psa在内的丁香假单胞杆菌的宿主特异性[38]。

虽然Psa可以感染目前栽培的所有猕猴桃品种,但不同的猕猴桃品种对Psa的抗病性还是有差异的,研究人员对不同抗病能力的猕猴桃品种在生理水平和分子水平进行了分析。李淼等[39]的研究表明,发病后,猕猴桃枝条、叶片中可溶性糖降低,木质素含量升高,抗病品种‘金魁’可溶性糖和木质素含量都高于感病品种‘金丰’。采用RAPD技术分析不同猕猴桃品种与溃疡病抗性的关系发现,抗病品系都有一条1458 bp的DNA片段,而感病品系均无该片段[40]。易盼盼等[41]的抗性鉴定结果表明,猕猴桃溃疡病抗/感病分离比符合由1对主效基因控制的1:1分离比例。通过对SSR引物的筛选,获得了与抗溃疡病基因连锁的SSR分子标记UDK97-28116。采用蛋白组学的方法对感染Psa的猕猴桃中的蛋白质进行分析,发现发生差异表达的蛋白质不仅包括基础防御蛋白和发病相关蛋白,还包括氧化应激蛋白、热激蛋白和运输和植物信号蛋白等[42]。挥发性有机物在植物病害的信号传导和抗病反应的诱导具有重要作用,Cellini等[43]用从感染Psa的猕猴桃组织中提取的挥发性有机物处理健康植株后发现,这些挥发性有机物对猕猴桃植株的生长产生了影响,并诱导了植物的保护反应,但再经Psa处理后,猕猴桃的抗病反应被Psa抑制而失去作用。Fraser等[44]基于猕猴桃属EST文库数据对猕猴桃基因组中的抗病基因进行了预测和定位,为猕猴桃抗病基因的鉴定提供了基础。Wang等[45]对猕猴桃抗病品种‘金魁’响应Psa的基因表达进行了分析,结果表明,Psa感染诱导了猕猴桃免疫系统PTI、ETI和HR中多个抗病基因表达水平的改变,说明‘金魁’猕猴桃的第一道免疫防线可以有效识别Psa,并诱导下游防线的抗病基因抵抗Psa分泌到细胞内的致病因子。

5 防治方法研究

目前对猕猴桃溃疡病的防治主要集中在选择抗性品种、栽培管理防护和药剂防治3个方向。经过多年的田间观测和实验鉴定,目前对常见猕猴桃品种的抗溃疡病能力已有了基本认识,因此生产中应尽量选择抗病性强的品种栽培,如经过2010年溃疡病的爆发后,新西兰已逐步淘汰极易感病的猕猴桃品种‘Hort16A’,重点推广抗病性较强的‘G3’和‘G9’。然而有些抗病性强的品种果实品质和商品性不高,如‘海沃德’、‘秦美’等,而抗病性很弱的‘红阳’因较高的市场价值在国内的栽培面积依然较大。栽培管理措施及水平直接影响溃疡病的发生程度,管理精细的果园一般发病较轻。合理施肥,控制春季萌芽的早晚、伤流的多少和生长势的强弱能够降低病害发生程度[46]。氮肥施用过量会刺激Psa的生长[47],而增施磷、硼肥可明显降低猕猴桃溃疡病发病率[48]。相比于化肥,有机全营养配方施肥,通过补充猕猴桃果园土壤中的养分,有利于全面改善猕猴桃品质,降低猕猴桃溃疡病发病率[49]。Psa的传播途径极其广泛,对生产中的农事操作应进行严密管控,应对进入果园的人员、车辆和农用工具进行消毒,严格防止病原的引入和传播[50]。目前生产上采用化学农药防治溃疡病的措施比较普遍,防治方法也比较简单。不同猕猴桃种植地区对不同杀菌剂的防治效果进行了大量研究评价,筛选出了一些效果较好的药物。如秦虎强等[51]对17种杀菌剂进行筛选,发现氢氧化铜、硫酸链霉素、中生菌素、叶枯唑及噻霉酮等制剂的防治效果较为理想。Song等[52]发现从植物香精油中提取的肉桂醛和草蒿脑对溃疡病菌具有显著的抑菌效果,有望应用于猕猴桃溃疡病的防治。Yu等[53]对从猕猴桃果园土壤分离得到的噬菌体的研究发现了几种对溃疡病菌具有稳定抑制效果的噬菌体,有望成为猕猴桃溃疡病预防的新方法。杀菌剂可在一定程度上抑制病菌的发展,但对病情已完全爆发的果园效果往往不理想。药剂处理一般只能在预防和发病初期发挥作用,但病情严重的植株只能移除销毁。新西兰研究认为,溃疡病菌在实验室极易被杀死,但杀死病菌而不伤害猕猴桃植株却较为困难,当病菌感染达到维管系统时,药剂处理效果变得不明显。一般的杀菌剂均可以杀死表面的溃疡病菌,但是残余的病菌很快就通过分裂产生新的病菌,在很短时间内又达到了处理前状态。经多年化学农药的施用,溃疡病菌已出现抗药性,例如对链霉素的抗性[54]。国内各猕猴桃栽培区域的气候条件、栽培品种和生产技术不同,在溃疡病的防治上应因地制宜地采取综合的防治措施。栽培上提供充足的营养,增施有机肥,增强树势,提高抗病能力;对进入果园的工具和常用的修剪工具进行消毒,减少病原的传入;选择合适的药剂,抑制Psa的发展。溃疡病虽然不能被完全清除,但对具有一定抗性的品种,通过合理的防治措施可在一定程度上抑制病情发展,降低病害导致的损失。

6 展望

自新西兰从中国引种猕猴桃并进行商业栽培至今仅有百余年的历史,猕猴桃细菌性溃疡病自1984年在日本被发现至今也仅34年的历史,世界各国对猕猴桃溃疡病的发现历史和致病菌Psa都有详细记载和保存,因此由猕猴桃和Psa构成的互作系统可作为研究微生物与植物互作的模式系统。经过多年的积累,目前对猕猴桃溃疡病的研究已经取得了一定的成果,如溃疡病的发病规律、致病菌Psa的基因组分析和分类、Psa的致病机理研究、溃疡病的防治方法研究以及不同猕猴桃品种的抗病性研究等,然而还有许多关键问题需要更加深入的研究,如对Psa的致病机理较少且不深入,尤其是对其中关键的特异的致病基因的鉴定,这是今后开发新的预防溃疡病方法的关键。国内猕猴桃种质资源丰富,充分利用这些宝贵的资源进行新品种培育和抗病基因开发将具有重要的作用。面对生产中尚无对Psa完全免疫的猕猴桃品种和完全有效的防治方法的现实情况,控制猕猴桃和Psa的生长环境使其有利于前者而不利于后者是目前防治猕猴桃溃疡病的唯一策略。因此生长中应采取综合措施,一方面采取严格的措施控制Psa的传入和传播,另一方面通过增施有机肥等措施提高树势增强植物抗病能力,同时通过定期喷施具有一定防治效果的试剂抑制Psa的生长。

=2" class="main_content_center_left_zhengwen_bao_erji_title main_content_center_left_one_title" style="font-size: 16px;">{{custom_sec.title}}{{custom_sec.content}}[1]Balestra G M

Renzi M

Mazzaglia A

. First report of bacterial canker of Actinidia deliciosa caused by Pseudomonas syringae pv. actinidiae in Portugal[J]. New Disease Reports, 2010,22(11):2510-2513.

We propose a new reflective liquid-crystal diffraction grating design attained by combining the use of a polymer wall to reduce the detrimental effect of the fringing electric field in a high-resolution grating and a quarter-wave plate to make the device polarization independent. This design could offer significant performance advantages in a projection display system. Results of calculations are compared with experimental data.

López M M

Peñalver J

, et al. First report of bacterial canker of kiwifruit caused by Pseudomonas syringae pv. actinidiae in Spain[J]. Plant Disease, 2011,95(12):1583-1583.

Bacterial canker of kiwifruit caused by Pseudomonas syringae pv. actinidiae was first described in Japan and Korea and is currently an emerging disease that causes major losses in China, Italy, New Zealand, France, Portugal, and Chile. Gold kiwifruit (Actinidia chinensis), especially cvs. Jin Tao and Hort 16A, seem to be more susceptible than green kiwifruit (Actinidia deliciosa) cvs. Hayward and Summer. The bacterium affects male and female woody vines equally, with young vines being more susceptible. The most characteristic symptoms that appear in early spring are reddish orange or white exudates associated with cankers and wounds in branches and/or trunk, as well as brown leaf spots. Buds and fruits were also affected (1). In Spain, 1,132 ha of kiwifruit orchards yielded 25,285 t of fruit in 2009 (2). Most Spanish kiwifruit is cultivated in Galicia (northwest Spain), where the main cultivar is Hayward. In 2010, the first plantation of cv. Jin Tao and one plantation of cv. Summer were established in this area close to Hayward woody vine. In early spring 2011, 80% of the vines in one orchard had twigs with reddish exudates and branches and trunks as well as leaves with angular spots surrounded by yellow haloes. Isolations from both Actinidia spp. were conducted on nutrient agar with sucrose. One hundred and twelve isolates were obtained and seventy-seven were aerobic, gram negative and nonfluorescent on King's B medium. Biochemical tests performed were levan, oxidase, potato rot, arginine didhydrolase, hypersensitivity in tobacco, and utilization of 49 carbohydrates by the API 50 CH system (BioMérieux, Marcy l'Etoile, France). Three PCR protocols were used: two with pathovar-specific primers (PSAF1/PSAR2 and PSAF3/PSAR4) and one with nonspecific primers (PsITSF1/PsITSR2) (3). The results of all biochemical and molecular tests were in agreement with those expected for P. syringae pv. actinidiae. The 16S-23S region of strain EFA 37 isolated from A. deliciosa cv. Summer was sequenced (GenBank Accession No. JF815537) and had 100% sequence identity with P. syringae pv. actinidiae (GenBank Accession Nos. AY342165 and D86357). Pathogenicity tests were performed on 15 plants of A. deliciosa cv. Hayward (five plants per isolate) with the Spanish representative strain EFA 37 and compared with two reference strains isolated from both Actinidia species in Italy and five plants of an untreated control. Three buds per healthy vine were wounded with a sterile needle, inoculated with 30 to 50 μl of each bacterial suspension (108 CFU/ml), sealed, and then covered with plastic. Five leaves per healthy vine were also pierced with a sterile needle and then atomized with the same suspension. Symptoms began to appear after 5 days on inoculated vines, but not on untreated control vines. The bacterium, P. syringae pv. actinidiae, was reisolated from symptomatic plants. The kiwifruit orchard with affected plants was eradicated (25 ha). To our knowledge, this is the first report of P. syringae pv. actinidiae in Spain. References: (1) EPPO Alert List. Online publication. Retrieved from http://www.eppo.org/QUARATINE/Alert_List , June, 2011. (2) Ministerio de Medio Ambiente y Medio Rural y Marino (MARM). Anuario de Estadística, Online Publication. Retrieved from http://www.marm.es/estadistica/pags/anuario/2010 , June 2011. (3) J. Rees-George et al. Plant Pathol. 59:453, 2010.

Poliakoff F

Audusseau C

, et al. First report of Pseudomonas syringae pv. actinidiae, the causal agent of bacterial canker of kiwifruit in France[J]. Plant Disease, 2011,95:1311-1312.

Taylor R K

Romberg M K

, et al. First report of Pseudomonas syringae pv. actinidiae causing kiwifruit bacterial canker in New Zealand[J]. Australasian Plant Disease Notes, 2011,6(1):67-71.

Leaves from gold kiwifruit plants, Actinidia chinensis, with dark brown angular spots and flowers that were brown and wilted, first yielded non-fluorescent bacterial colonies following isolation. These bacterial colonies were identified by diagnostic polymerase chain reaction (PCR) as Pseudomonas syringae pv. actinidiae. These samples were obtained from the Te Puke region of New Zealand. All isolates were Gram negative and were levan positive, oxidase negative, potato soft rot negative, arginine dehydrolase negative and tobacco hypersensitivity positive (LOPAT 1a). Sequences of the gyrB and the rpoD genes of these isolates were 100% homologous to sequences of P.s. pv. actinidiae deposited in GenBank including the type strain. Koch’s postulates were proven by pathogenicity tests on kiwifruit seedlings.

Karakaya A

. First report of bacterial canker of kiwifruit caused by Pseudomonas syringae pv. actinidiae in Turkey[J]. Plant Disease, 2012,96(3):452-452.

A new disease was observed during the spring and autumn of 2009 and 2010 on kiwifruit plants (Actinidia deliciosa cv. Hayward) in Rize Province of Turkey. Disease incidence was estimated as 3% in approximately 10 ha. Symptoms were characterized by dark brown spots surrounded by yellow halos on leaves and cankers with reddish exudate production on twigs and stems. Eight representative bacterial strains were isolated from leaf spots and tissues under the bark on King's B medium (KB) and identified as Pseudomonas syringae pv. actinidiae on the basis of biochemical, physiological (1,2), and PCR tests (3). Bacteria were gram negative, rod shaped, and nonfluorescent on KB; positive for levan production, sucrose and inositol utilization, and tobacco (Nicotiana tabacum cv. White Burley) hypersensitivity; and negative for growth at 37°C, oxidase, potato soft rot, arginine dihydrolase, urease, arbutin, erythritol, lactic acid, aesculin hydrolysis, gelatin liquefaction, and syringomycin production. Identity of the eight isolates was confirmed by PCR using P. syringae pv. actinidiae-specific primers PsaF1/R3 to generate a 280-bp DNA fragment (3). P. syringae pv. actinidiae reference strain NCPPB 3739, and CJW7 from Jae Sung Jung, Department of Biology, Sunchon National University, Korea, were employed in all biochemical, physiological, and molecular tests as positive controls. Pathogenicity was confirmed by artificial inoculation of 2-year-old A. deliciosa cv. Hayward. A bacterial suspension (108 CFU ml-1) was injected into kiwifruit twig tips, stems, and leaves with a hypodermic syringe, and the inoculated plants were placed at 25 to 28°C and 80% relative humidity growth chamber for 3 weeks. First symptoms were observed on leaves within 5 days after inoculation and on twigs after 20 days. No symptoms were observed on control plants that were inoculated with sterile water. Reisolation was made from dark brown lesions surrounded by yellow halos on leaves and cankers on twigs and stem and their identities were confirmed using the techniques previously described. All tests were performed three times and pathogenicity tests employed three plants for each strain. To our knowledge, this is the first report of P. syringae pv. actinidiae causing disease on kiwifruit in Turkey. Kiwifruit production in Turkey has expanded rapidly during the last 10 years ( http://www.tuik.gov.tr ) and phytosanitary measures are needed to prevent further spread of the bacterium to other kiwifruit orchards. References: (1) Y. J. Koh et al. N. Z. J. Crop Hortic. Sci. 38:4, 275, 2010. (2) R. A. Lelliott and D. E. Stead. Methods for the Diagnosis of Bacterial Diseases of Plants. Blackwell Scientific, Sussex, UK, 1988. (3) J. Rees-George et al. Plant Pathol. 59:453, 2010.

Glynos P E

Karafla C D

. First report of bacterial canker of kiwifruit caused by Pseudomonas syringae pv. actinidiae in Greece[J]. Plant Disease, 2015,99(5):723-723.

The new genus Barbatosphaeria is described for a perithecial ascomycete known as Calosphaeria barbirostris occurring on decayed wood of deciduous trees under the periderm. The fungus produces nonstromatic perithecia with hyaline, 1-septate ascospores formed in unitunicate, nonamyloid asci. Anamorphs produced in vitro belong to Sporothrix and Ramichloridium with holoblastic-denticulate conidiogenesis; conidiophores of the two types were formed in succession during the development of the colony. Phylogenetic analyses of nuLSU rDNA sequences indicate that this fungus is distinct from morphologically similar Lentomitella, tentatively placed in the Trichosphaeriales. It groups with freshwater Aquaticola and Cataractispora and terrestrial Cryptadelphia in maximum parsimony analysis; the same grouping but without Cryptadelphia was inferred from Bayesian analysis. Cultivation, morphology and phylogenetic studies of the nuLSU rDNA support the erection of a new genus for C. barbirostris.

Kim G H

Jung J S

, et al. Outbreak of bacterial canker on Hort16A (Actinidia chinensis Planchon) caused by Pseudomonas syringae pv. actinidiae in Korea[J]. New Zealand Journal of Crop & Horticultural Science, 2010,38(4):275-282.

Marcelletti S

Ferrante P

, et al. Pseudomonas syringae pv. actinidiae: a re-emerging, multi-faceted, pandemic pathogen[J]. Molecular Plant Pathology, 2012,13(7):631-640.

Pseudomonas syringae pv. actinidiae is the causal agent of bacterial canker of green-fleshed kiwifruit (Actinidia deliciosa) and yellow-fleshed kiwifruit (A. chinensis). A recent, sudden, re-emerging wave of this disease has occurred, almost contemporaneously, in all of the main areas of kiwifruit production in the world, suggesting that it can be considered as a pandemic disease. Recent in-depth genetic studies performed on P. syringae pv. actinidiae strains have revealed that this pathovar is composed of four genetically different populations which, to different extents, can infect crops of the genus Actinidia worldwide. Genome comparisons of these strains have revealed that this pathovar can gain and lose the phaseolotoxin gene cluster, as well as mobile genetic elements, such as plasmids and putative prophages, and that it can modify the repertoire of the effector gene arrays. In addition, the strains currently causing worldwide severe economic losses display an extensive set of genes related to the ecological fitness of the bacterium in planta, such as copper and antibiotic resistance genes, multiple siderophore genes and genes involved in the degradation of lignin derivatives and other phenolics. This pathogen can therefore easily colonize hosts throughout the year. Taxonomy: Bacteria; Proteobacteria, gamma subdivision; Order Pseudomonadales; Family Pseudomonadaceae; Genus Pseudomonas; Pseudomonas syringae species complex, genomospecies 8; Pathovar actinidiae. Microbiological properties: Gram-negative, aerobic, motile, rod-shaped, polar flagella, oxidase-negative, arginine dihydrolase-negative, DNA 58.558.8 mol.% GC, elicits the hypersensitive response on tobacco leaves. Host range: Primarily studied as the causal agent of bacterial canker of green-fleshed kiwifruit (Actinidia deliciosa), it has also been isolated from yellow-fleshed kiwifruit (A. chinensis). In both species, it causes severe economic losses worldwide. It has also been isolated from wild A. arguta and A. kolomikta. Disease symptoms: In green-fleshed and yellow-fleshed kiwifruits, the symptoms include brownblack leaf spots often surrounded by a chlorotic margin, blossom necrosis, extensive twig die-back, reddening of the lenticels, extensive cankers along the main trunk and leader, and bleeding cankers on the trunk and the leader with a whitish to orange ooze. Epidemiology: Pseudomonas syringae pv. actinidiae can effectively colonize its host plants throughout the year. Bacterial exudates can disperse a large amount of inoculum within and between orchards. In the spring, temperatures ranging from 12 to 18 degrees C, together with humid conditions, can greatly favour the multiplication of the bacterium, allowing it to systemically move from the leaf to the young shoots. During the summer, very high temperatures can reduce the multiplication and dispersal of the bacterium. Some agronomical techniques, as well as frost, wind, rain and hail storms, can contribute to further spreading. Disease control: An integrated approach that takes into consideration precise scheduled spray treatments with effective and environmentally friendly bactericides and equilibrated plant nutrition, coupled with preventive measures aimed at drastically reducing the bacterial inoculum, currently seems to be the possible best solution for coexistence with the disease. The development of resistant cultivars and pollinators, effective biocontrol agents, including bacteriophages, and compounds that induce the systemic activation of plant defence mechanisms is in progress.
Useful websites: Up-to-date information on bacterial canker research progress and on the spread of the disease in New Zealand can be found at: . Daily information on the spread of the disease and on the research being performed worldwide can be found at: .

Yu J

Cornish D A

, et al. Identification, virulence and distribution of two biovars of Pseudomonas syringae pv. actinidiae in New Zealand[J]. Plant Disease, 2013,97:708-719.

Pseudomonas syringae pv. actinidiae, the causal agent of bacterial canker of kiwifruit, was detected for the first time in New Zealand in November 2010. Only in Bay of Plenty, one of the four regions where this pathogen had been detected, did symptoms evolve beyond leaf spots, resulting in cane die-back, wilting of canes, and canker, sometimes leading to death of the vine. Molecular analysis (cts haplotype and BOX-polymerase chain reaction [PCR] electrophoretic pattern) of strains isolated from different regions of New Zealand revealed that two biovars could be distinguished. They have been called biovar 3 and biovar 4 to differentiate them from strains from Japan (biovar 1) or Korea (biovar 2), which have a different cts haplotype or a different BOX-PCR pattern. Biovars 3 and 4 displayed different degrees of virulence, as measured by their ability to cause leaf spots on young, potted kiwifruit plants. Biovar 3, which has also been present in Italy since 2008 and in France, was found in the Bay of Plenty, where cane die-backs were observed. In contrast, no symptoms other than leaf spots have been observed in orchards where strains of biovar 4 have been isolated. We report the distribution and the disease progression of biovars 3 and 4 in New Zealand.

张慧琴, 毛雪琴, 肖金平 , 等. 猕猴桃溃疡病病原菌分子鉴定与抗性材料初选[J]. 核农学报, 2014,28:1181-1187.

为明确我国南方猕猴桃细菌性溃疡病频发区其致病菌的种类与特征，初选出抗性种质材料，以猕猴桃主栽品种红阳、徐香和金丰的溃疡病感病枝条为材料，采用KB 培养基、平板划线和梯度稀释法分离病原菌，利用基于细菌16S-23S rDNA 内转录间隔区序列设计的特异性鉴别引物，对分离得到的6 个代表菌株进行PCR 扩增和测序，获得了大小约为280bp 的特异性片段，其测序结果与登录号为D86357和AY342165的Pseudomonas syringae pv. Actinidia的序列完全一致。采用离体叶片注射接种、离体枝条针刺接种和活体枝杆针刺接种3 种方法鉴定了18 份种质材料的抗性。分析结果表明，红阳等中华猕猴桃最感，布鲁诺实生优株13-3、13-4等最抗，美味猕猴桃海沃德居中。本试验所分离的菌株均为丁香假单胞杆菌猕猴桃致病变种（Pseudomonas syringae pv. Actinidia），筛选出2 份高抗溃疡病的种质材料。为进一步开展猕猴档细菌性溃疡病防治研究奠定基础。

Ichikawa T

Takikawa Y

, et al. Occurrence of bacterial canker of kiwifruit in Japan: description of symptoms, isolation of the pathogen and screening of bactericides[J]. Annals of the Phytopathological Society of Japan, 1989,55(4):427-436.

Ichikawa T

. Epidemiology of bacterial canker of kiwifruit. 3. The seasonal changes of bacterial population in lesions and of its exudation from lesions[J]. Japanese Journal of Phytopathology, 1993,59:469-476.

Mauri S

Buriani G

, et al. Role of Metcalfa pruinosaas a vector for Pseudomonas syringae pv. actinidiae[J]. Plant Pathology Journal, 2017,33(6):554-560.

After 20 years of steady increase, kiwifruit industry faced a severe arrest due to the pandemic spread of the bacterial canker, caused by Pseudomonas syringae pv. actinidiae (Psa). The bacterium penetrates the host plant primarily via natural openings or wounds, and its spread is mainly mediated by atmospheric events and cultural activities. Since the role of sucking insects as vectors of bacterial pathogens is widely documented, we investigated the ability of Metcalfa pruinosa Say (1830), one of the most common kiwifruit pests, to transmit Psa to healthy plants in laboratory conditions. Psa could be isolated both from insects feeding over experimentally inoculated plants, and from insects captured in Psa-infected orchards. Furthermore, insects were able to transmit Psa from experimentally inoculated plants to healthy ones. In conclusion, the control of M. pruinosa is recommended in the framework of protection strategies against Psa.

Talocci S

L'Aurora A

, et al. Detection of Pseudomonas syringae pv. actinidiae, causal agent of bacterial canker of kiwifruit, from symptomless fruits and twigs, and from pollen[J]. Phytopathologia Mediterranea, 2011,50(3):462-472.

Pseudomonas syringae pv. actinidiae (Psa), the causal agent of bacterial canker of kiwifruit, was monitored in symptomless fruits, twigs and pollen of the host using bacterial isolation and DNA-extraction followed by two PCR-assays (direct-PCRs). A procedure for Psa detection from symptomless twigs was established. Out of 16 symptomless twigs samples, Psa was detected in 12 samples by isolation and 13 samples by direct-PCR. Thirteen pollen samples were treated using two different procedures; Psa was detected in eight samples by isolation and ten samples by direct-PCR. By washing 108 samples of fruits, Psa was detected by isolation in only two samples, collected from severely affected orchards. However, one of these samples contained wilted fruits, whereas for the other, only one colony was isolate. From 60 bulk-samples of fruits, endophytic Psa was detected in six samples by isolation and ten samples by direct-PCRs. A Psa-positive bulk-sample of fruits was analyzed separately as individual fruits; there was a faint signal in five or seven fruits out of 50 depending on the PCR assay used. Isolation was negative for these samples. Presence of the pathogen on bulk-fruit samples could be due to low amounts of inoculum distributed over many fruits: as a consequence, there is a negligible risk of introducing the pathogen into countries free of bacterial canker by symptomless fruits. This integrated approach (isolation plus PCR) is proposed as a tool for the analysis of symptomless kiwifruit material for the presence of Psa.

Giovanardi D

. Dissemination of Pseudomonas syringae pv. actinidiae through pollen and its epiphytic life on leaves and fruits[J]. Phytopathol Medit, 2011,50:501-505.

Galeone

Ardizzi

, et al. Pseudomonas syringae pv. actinidiae detection in kiwifruit plant tissue; and bleeding sap[J]. Annals of Applied Biology, 2013,162(1):60-70.

The rapid spreading of the disease during last few years highlighted the need of a quick, sensitive and reliable method for Pseudomonas syringae pv. actinidiae (Psa) detection, to find possible inoculum sources and limit the pathogen spreading. A PCR method, using new primers designed on the gene encoding a putative outer membrane protein P1, was developed to detect Psa in symptomatic and asymptomatic tissue; a nested-PCR was also applied. Bleeding sap samples, collected in early spring from orchards with symptomatic and asymptomatic trees, were used both for PCR assays and for pathogen isolation and identification. The PCR and nested PCR methods were able to detect Psa presence at very low concentration from plant and pollen extracts; RFLP analyses with BclI on PCR and nested PCR amplicons confirmed the assay specificity, while the digestion with BfmI and AluI allowed to discriminate Psa strains isolated before 2008 from those isolated after 2008. Furthermore, the PCR and nested PCR on crude bleeding sap samples detected the presence of the pathogen in 3 and 5 of the 15 assayed samples, respectively. Direct isolation from the same samples and bacterial identification confirmed the results of molecular analysis.

L'Aurora A

Loreti S

. Gene sequence analysis for the molecular detection of Pseudomonas syringae pv. actinidiae: developing diagnostic protocols[J]. Journal of Plant Pathology, 2011,93(2):425-435.

Bacterial canker of kiwifruit caused by Pseudomonas syringae pv. actinidiae (Psa) is seriously damaging Actinidia deliciosa and A. chinensis in central Italy. Since this severe outbreak of the disease may reflect on the trade of kiwifruit pollen and fruits, standardized protocols are needed for the extraction of the bacterium from different matrices and for its detection and identification. Current PCR detection of Psa is aspecific, as the amplified product has the same size as that of P syringae pv. theae. To improve the specificity of molecular detection of Psa, a gene-sequence analysis was done to identify new specific DNA markers. This enabled us to develop a duplex-PCR that distinguishes Psa from P. syringae pv. theae and from other genetically related P. syringae pathovars. This method was also successfully applied to detect Psa directly in infected kiwifruit matrices such as leaves, wood, flowers and in experimentally contaminated pollen and fruits. We propose two protocols for Psa extraction and detection from pollen and fruits. These protocols can be used for epidemiological studies, to establish whether symptomless fruits or pollen can harbour Psa, and can help diagnostic laboratories in the analysis of these type of materials.

Zhu X

Wang Y

. Preliminary studies on kiwifruit diseases in Hunan province[J]. Sichuan Fruit Science and Technology, 1990,18:28-29.

. Outbreak and spread of bacterial canker in kiwifruit. Korean[J]. Journal of Plant Pathology, 1994,10:68-72.

Intercontinental spread of emerging plant diseases is one of the most serious threats to world agriculture. One emerging disease is bacterial canker of kiwi fruit (Actinidia deliciosa and A. chinensis) caused by Pseudomonas syringae pv. actinidiae (PSA). The disease first occurred in China and Japan in the 1980s and in Korea and Italy in the 1990s. A more severe form of the disease broke out in Italy in 2008 and in additional countries in 2010 and 2011 threatening the viability of the global kiwi fruit industry. To start investigating the source and routes of international transmission of PSA, genomes of strains from China (the country of origin of the genus Actinidia), Japan, Korea, Italy and Portugal have been sequenced. Strains from China, Italy, and Portugal have been found to belong to the same clonal lineage with only 6 single nucleotide polymorphisms (SNPs) in 3,453,192 bp and one genomic island distinguishing the Chinese strains from the European strains. Not more than two SNPs distinguish each of the Italian and Portuguese strains from each other. The Japanese and Korean strains belong to a separate genetic lineage as previously reported. Analysis of additional European isolates and of New Zealand isolates exploiting genome-derived markers showed that these strains belong to the same lineage as the Italian and Chinese strains. Interestingly, the analyzed New Zealand strains are identical to European strains at the tested SNP loci but test positive for the genomic island present in the sequenced Chinese strains and negative for the genomic island present in the European strains. Results are interpreted in regard to the possible direction of movement of the pathogen between countries and suggest a possible Chinese origin of the European and New Zealand outbreaks.

. Occurrence of Pseudomonas syringae pv. actinidiae on kiwifruit in Italy[J]. Plant Pathology, 1994,43:1035-1038.

Taylor R K

Weir B S

, et al. Phylogenetic relationships among global populations of Pseudomonas syringae pv. actinidiae[J]. Phytopathology, 2012,102(11):1034-1044.

Pseudomonas syringae pv. actinidiae. the causal agent of canker in kiwifruit (Actinidia spp.) vines, was first detected in Japan in 1984, followed by detections in Korea and Italy in the early 1990s. Isolates causing more severe disease symptoms have recently been detected in several countries with a wide global distribution, including Italy, New Zealand, and China. In order to characterize P syringae pv. actinidiae populations globally, a representative set of 40 isolates from New Zealand, Italy, Japan, South Korea, Australia, and Chile were selected for extensive genetic analysis. Multi locus sequence analysis (MLSA) of housekeeping, type III effector and phytotoxin genes was used to elucidate the phylogenetic relationships between P syringae pv. actinidiae isolates worldwide. Four additional isolates, including one from China, for which shotgun sequence of the whole genome was available, were included in phylogenetic analyses. It is shown that at least four P syringae pv. actinidiae MLSA groups are present globally, and that marker sets with differing evolutionary trajectories (conserved housekeeping and rapidly evolving effector genes) readily differentiate all four groups. The MLSA group designated here as Psa3 is the strain causing secondary symptoms such as formation of cankers, production of exudates, and cane and shoot dieback on some kiwifruit orchards in Italy and New Zealand. It is shown that isolates from Chile also belong to this MLSA group. MLSA group Psa4, detected in isolates collected in New Zealand and Australia, has not been previously described. P. syringae pv. actinidiae has an extensive global distribution yet the isolates causing widespread losses to the kiwifruit industry can all be traced to a single MLSA group, Psa3.

Taylor R

Alexander B

. Second report on characterization of Pseudomonas syringae pv. actinidiae (Psa) isolates in New Zealand[R]. Ministry of Agriculture and Forestry, 2011.

Eha R

Bertels F

. Genomic analysis of the kiwifruit pathogen Pseudomonas syringae pv. actinidiae provides insight into the origins of an emergent plant disease[J]. PLOS Pathogens, 2013,9(7):e1003503.

The origins of crop diseases are linked to domestication of plants. Most crops were domesticated centuries--even millennia--ago, thus limiting opportunity to understand the concomitant emergence of disease. Kiwifruit (Actinidia spp.) is an exception: domestication began in the 1930s with outbreaks of canker disease caused by P. syringae pv. actinidiae (Psa) first recorded in the 1980s. Based on SNP analyses of two circularized and 34 draft genomes, we show that Psa is comprised of distinct clades exhibiting negligible within-clade diversity, consistent with disease arising by independent samplings from a source population. Three clades correspond to their geographical source of isolation; a fourth, encompassing the Psa-V lineage responsible for the 2008 outbreak, is now globally distributed. Psa has an overall clonal population structure, however, genomes carry a marked signature of within-pathovar recombination. SNP analysis of Psa-V reveals hundreds of polymorphisms; however, most reside within PPHGI-1-like conjugative elements whose evolution is unlinked to the core genome. Removal of SNPs due to recombination yields an uninformative (star-like) phylogeny consistent with diversification of Psa-V from a single clone within the last ten years. Growth assays provide evidence of cultivar specificity, with rapid systemic movement of Psa-V in Actinidia chinensis. Genomic comparisons show a dynamic genome with evidence of positive selection on type III effectors and other candidate virulence genes. Each clade has highly varied complements of accessory genes encoding effectors and toxins with evidence of gain and loss via multiple genetic routes. Genes with orthologs in vascular pathogens were found exclusively within Psa-V. Our analyses capture a pathogen in the early stages of emergence from a predicted source population associated with wild Actinidia species. In addition to candidate genes as targets for resistance breeding programs, our findings highlight the importance of the source population as a reservoir of new disease.

. Identification and characterization of coronatine-producing Pseudomonas syringae pv. actinidiae[J]. Journal of Microbiology & Biotechnologygy, 2003,68(11):6423-6430.

Hikota T

Nakajima M

, et al. Occurrence and properties of copper-resistance in plant pathogenic bacteria[J]. Japanese Journal of Phytopathology, 2009,60(2):147-153.

Nam H Y

Koh Y J

, et al. Molecular bases of high-level streptomycin resistance in Pseudomonas marginalis and Pseudomonas syringae pv. actinidiae[J]. Journal of Microbiology, 2003,41(1):16-21.

Goto M

Hibi T

. Similarity between copper resistance genes from Pseudomonas syringae pv. actinidiae and P. syringae pv. tomato[J]. Journal of General Plant Pahtology, 2002,68:68-74.

Yamashita S

Takikawa Y

, et al. Similarity of streptomycin resistance gene(s) in Pseudomonas syringae pv. actinidiae with strA and strB of plasmid RSF1010[J]. Annals of the Phytopathological Society of Japan, 2009,61(5):489-492.

Scortichini M

. Molecular and phenotypic features of Pseudomonas syringae pv. actinidiae isolated during recent epidemics of bacterial canker on yellow kiwifruit (Actinidia chinensis) in central Italy[J]. Plant Pathology, 2010,59(5):954-962.

Scortichini M

. Molecular and phenotypic variability of Pseudomonas avellanae, P. syringae pv. actinidiae and P. syringae pv. theae: the genomospecies 8 sensu Gardan et al.(1999)[J]. Journal of Plant Pathology, 2011,93:659-666.

Genomospecie 8, sensu Gardan et al. (1999), includes Pseudomonas avellanae, P syringae pv. theae and s. pv. actinidiae. To further characterize this genomospecies, 14 P avellanae, three P s. pv. theae and 18 P. s. pv. actinidiae strains were analysed by multilocus sequence typing (MLST) using gapA, gltA, gyrB and rpoD gene fragments. These strains were also checked for the presence/absence of 38 effector protein genes based on the corresponding sequences of P syringae. pv. tomato DC3000 and P syringae pv. phaseolicola 1448A. Nutritional tests and a comparison of the 16S rDNA gene sequences deposited at NCBI database were also done to detect possible differences. MLST analysis, based on 25 kb sequences, revealed that P s. pv. theae and P. s. pv. actinidiae are more closely-related to one another than to P avellanae. This technique clearly revealed that the P s. pv. actinidiae strains causing the current severe epidemics in Italy are different from those of past outbreaks in Japan and central Italy. Nine effector protein genes were displayed by all strains of genomospecies 8. However, each pathogen of this genomospecies displays some distinctive effector protein genes. HopA1 and hopH1 are unique to R s. pv. actinidiae strains of the recent epidemics of bacterial canker on Actinidia chinensis and A. deliciosa in Italy. A triplet, in position 461-463 of the 16S rDNA gene, is different in P s. pv. actinidiae, namely GAT, and in P. avellanae and P s. pv. theae, namely ATC. Contrarily to P s. pv. theae and P s. pv. actinidiae, P avellanae did not utilize sorbitol.

Scortichini M

. Clonal outbreaks of bacterial canker caused by Pseudomonas syringae pv. actinidiae on Actinidia chinensis and A. deliciosa in Italy[J]. Journal of Plant Pathology, 2011,93(2):479-483.

A total of 28 representative Pseudomonas syringae pv. actinidiae strains isolated from all Italian regions (Emilia-Romagna, Latium, Piedmont, Veneto) where outbreaks of bacterial canker of kiwifruit (Actinidia deliciosa) and yellow kiwifruit (A. chinensis) were observed in 2008-2010, were assessed using repetitive-sequence PCR (rep-PCR) with ERIC and BOX primer sets and multilocus sequence typing (MLST) using gapA, gltA, gyrB and rpoD genes. The 2.3 kb sequences obtained from MLST were analyzed by means of mathematical-statistical tests to infer the gene polymorphism and the genetic structure of the strains. Both primer sets used in rep-PCR indicated an overall identity among all 28 Ps. pv. actinidiae strains irrespective of the host plant and cultivar from where they were isolated, as well as of the region or year of isolation. In addition, MLST revealed a low gene polymorphism. A clonal structure and neutral selection were inferred for the P.s. pv. actinidiae strains currently causing severe epidemics on A. chinensis and A. deliciosa in Italy. This indicates that they originated, most probably, from a single or very few introductions of latently infected kiwifruit propagative material, even though the possibility cannot be ruled out that cells of the pathogen already present in Italy may have mutated.

Studholme D J

Taratufolo M C

, et al. Pseudomonas syringae pv. actinidiae (PSA) isolates from recent bacterial canker of kiwifruit outbreaks belong to the same genetic lineage[J]. Plos One, 2012,7(5):e36518.

Stockwell P A

Black M A

, et al. Pseudomonas syringae pv. actinidiae from recent outbreaks of kiwifruit bacterial canker belong to different clones that originated in China[J]. Plos One, 2013,8(2):e57464.

A recently emerged plant disease, bacterial canker of kiwifruit (Actinidia deliciosa and A. chinensis), is caused by Pseudomonas syringae pv. actinidiae (PSA). The disease was first reported in China and Japan in the 1980s. A severe outbreak of PSA began in Italy in 2008 and has spread to other European countries. PSA was found in both New Zealand and Chile in 2010. To study the evolution of the pathogen and analyse the transmission of PSA between countries, genomes of strains from China and Japan (where the genus Actinidia is endemic), Italy, New Zealand and Chile were sequenced. The genomes of PSA strains are very similar. However, all strains from New Zealand share several single nucleotide polymorphisms (SNPs) that distinguish them from all other PSA strains. Similarly, all the PSA strains from the 2008 Italian outbreak form a distinct clonal group and those from Chile form a third group. In addition to the rare SNPs present in the core genomes, there is abundant genetic diversity in a genomic island that is part of the accessory genome. The island from several Chinese strains is almost identical to the island present in the New Zealand strains. The island from a different Chinese strain is identical to the island present in the strains from the recent Italian outbreak. The Chilean strains of PSA carry a third variant of this island. These genomic islands are integrative conjugative elements (ICEs). Sequencing of these ICEs provides evidence of three recent horizontal transmissions of ICE from other strains of Pseudomonas syringae to PSA. The analyses of the core genome SNPs and the ICEs, combined with disease history, all support the hypothesis of an independent Chinese origin for both the Italian and the New Zealand outbreaks and suggest the Chilean strains also originate from China.

Cunnac S

Collmer A

. Pseudomonas syringae type III effector repertoires: last words in endless arguments[J]. Trends in Microbiology, 2012,20(4):199-208.

Many plant pathogens subvert host immunity by injecting compositionally diverse but functionally similar repertoires of cytoplasmic effector proteins. The bacterial pathogen Pseudomonas syringae is a model for exploring the functional structure of such repertoires. The pangenome of P. syringae encodes 57 families of effectors injected by the type Ill secretion system. Distribution of effector genes among phylogenetically diverse strains reveals a small set of core effectors targeting antimicrobial vesicle trafficking and a much larger set of variable effectors targeting kinase-based recognition processes. Complete disassembly of the 28-effector repertoire of a model strain and reassembly of a minimal functional repertoire reveals the importance of simultaneously attacking both processes. These observations, coupled with growing knowledge of effector targets in plants, support a model for coevolving molecular dialogs between effector repertoires and plant immune systems that emphasizes mutually-driven expansion of the components governing recognition.

Imamura M

Yoneyama K

. Role of phaseolotoxin production by Pseudomonas syringae pv. actinidiae in the formation of halo lesions of kiwifruit canker disease[J]. Physiological & Molecular Plant Pathology, 2002,60(4):207-214.

Spivey N W

Zeng W

, et al. Coronatine promotes Pseudomonas syringae virulence in plants by activating a signaling cascade that inhibits salicylic acid accumulation[J]. Cell Host & Microbe, 2012,11(6):587-596.

Phytopathogens can manipulate plant hormone signaling to access nutrients and counteract defense responses. Pseudomonas syringae produces coronatine, a toxin that mimics the plant hormone jasmonic acid isoleucine and promotes opening of stomata for bacterial entry, bacterial growth in the apoplast, systemic susceptibility, and disease symptoms. We examined the mechanisms underlying coronatine-mediated virulence and show that coronatine activates three homologous NAC transcription factor (TF) genes, ANAC019, ANAC055, and ANAC072, through direct activity of the TF, MYC2. Genetic characterization of NAC TF mutants demonstrates that these TFs mediate coronatine-induced stomatal reopening and bacterial propagation in both local and systemic tissues by inhibiting the accumulation of the key plant immune signal salicylic acid (SA). These NAC TFs exert this inhibitory effect by repressing ICS1 and activating BSMT1, genes involved in SA biosynthesis and metabolism, respectively. Thus, a signaling cascade by which coronatine confers its multiple virulence activities has been elucidated.

Ferrante P

Petriccione M

, et al. Production of phytotoxic metabolites by Pseudomonas syringae pv. actinidiae, the causal agent of bacterial canker of kiwifruit[J]. Journal of Plant Pathology, 2014,96(1):169-175.

Pseudomonas syringae pv. actinidiae, the causal agent of bacterial canker of Actinidia chinensis and A. deliciosa, is currently causing severe economic losses worldwide. A study was conducted to verify if a highly virulent Psa strain, isolated during the current outbreaks of bacterial canker of kiwifruit in Italy, produces phytotoxic metabolites in vitro. Culture filtrate, obtained from 14-day-old cells grown in Pseudomonas minimal medium, induced an evident hypersensitivity-like reaction to both tobacco and kiwifruit leaves. From culture filtrates, extracts were obtained using different solvents and pH values. The extracts and their corresponding aqueous phases, were further tested for phytotoxicity. Basic, hydrophilic, low-molecular weight and hydrophilic, high-molecular weight compounds belonging to exopolysaccharides were isolated and analyzed. These compunds proved highly phytotoxic to kiwifruit, tobacco leaves and lemon fruits. Gas-chromatography-mass-spectrometry analysis carried out on crude exopolysaccharides showed glucose as the main monosaccharide constituent. These results suggest that phytotoxic metabolites, other than the antimetabolite phaseolotoxin, could be involved in the virulence of the pathogen to kiwifruit species.

Zhou J M

. Plant immunity triggered by microbial molecular signatures[J]. Molecular Plant, 2010,03(5):783-793.

李淼, 檀根甲, 李瑶 , 等. 猕猴桃品种中糖分及木质素含量与抗溃疡病的关系[J]. 植物保护学报, 2005,32(2):138-142.

以安徽省猕猴桃主栽品种金魁、早鲜、魁蜜和金丰为研究对象,于展叶孕蕾期分别取发病的枝条、叶片,以未发病的健株相应组织为对照,采用生理生化的方法,分析枝条、叶片中木质素和可溶性糖的含量变化以及与抗溃疡病的关系。结果表明:抗病品种金魁健株枝条、叶片中可溶性糖及木质素含量显著高于感病品种金丰。自然发病后,抗感病品种枝条、叶片中可溶性糖含量都降低,感病品种降低更多,金魁叶片可溶性糖含量下降4.20%,金丰叶片可溶性糖含量下降55.35%;木质素含量都升高,且抗病品种金魁叶片中的木质素含量比感病品种金丰高得多,其变化率分别为7.17%、3.01%,枝条中的木质素含量变化率分别为110.39%、68.98%,其差异达到显著水平。相关分析表明,枝条中木质素、可溶性糖含量与品种发病率也呈负相关,r分别为-0.9583和-0.9282;叶片中木质素、可溶性糖含量与品种发病率呈负相关,r分别为-0.8099和-0.8266。从而说明枝条、叶片中可溶性糖及木质素含量与品种抗性呈正相关。抗感品种淀粉含量无明显规律性变化,与品种抗性关系不大。

李淼, 檀根甲, 李瑶 , 等. 不同猕猴桃品种RAPD分析及其与抗溃疡病的关系[J]. 植物保护, 2009,35:41-46.

易盼盼, 樊红科, 雷玉山 , 等. 猕猴桃抗溃疡病基因连锁SSR分子标记初步研究[J]. 西北农林科技大学学报:自然科学版, 2015,43:91-98.

Di C I

Arena S

, et al. Proteomic changes in Actinidia chinensis shoot during systemic infection with a pandemic Pseudomonas syringae pv. actinidiae strain[J]. Journal of Proteomics, 2013,78(1):461-476.

A pandemic, very aggressive population of Pseudomonas syringae pv. actinidiae is currently causing severe economic losses to kiwifruit crops worldwide. Upon leaf attack, this Gram-negative bacterium systemically reaches the plant shoot in a week period. In this study, combined 2-DE and nanoLC-ESI-LIT-MS/MS procedures were used to describe major proteomic changes in Actinidia chinensis shoot following bacterial inoculation in host leaf. A total of 117 differentially represented protein spots were identified in infected and control shoots. Protein species associated with plant defence, including type-members of the plant basal defence, pathogenesis, oxidative stress and heat shock, or with transport and signalling events, were the most represented category of induced components. Proteins involved in carbohydrate metabolism and photosynthesis were also augmented upon infection. In parallel, a bacterial outer membrane polypeptide component was identified in shoot tissues, whose homologues were already linked to bacterial virulence in other eukaryotes. Semiquantitative RT-PCR analysis confirmed expression data for all selected plant gene products. All these data suggest a general reprogramming of shoot metabolism following pathogen systemic infection, highlighting organ-specific differences within the context of a general similarity with respect to other pathosystems. In addition to present preliminary information on the molecular mechanisms regulating this specific plant-microbe interaction, our results will foster future proteomic studies aimed at characterizing the very early events of host colonization, thus promoting the development of novel bioassays for pathogen detection in kiwifruit material.

Biondi E

Buriani G

, et al. Characterization of volatile organic compounds emitted by kiwifruit plants infected with Pseudomonas syringae pv. actinidiae, and their effects on host defences[J]. Trees, 2016,30(3):795-806.

Datson P M

Tsang G K

, et al. Characterisation, evolutionary trends and mapping of putative resistance and defence genes in Actinidia (kiwifruit)[J]. Tree Genetics & Genomes, 2015,11(2):21.

Wang G

Jia Z H

, et al. Transcriptome analysis of kiwifruit in response to Pseudomonas syringae pv. actinidiae infection[J]. International Journal of Molecular Sciences, 2018,19(2):373.

田呈明, 张星耀 . 基于栽培管理措施的猕猴桃细菌性溃疡病防治技术[J]. 西北林学院学报, 2000,15:72-76.

Nari L

Vittone G

, et al. La batteriosi del kiwi in Piemonte: diagnosi e prevenzione[J]. Protezione Colture, 2011,4(2):58-61.

王新义, 李平 . 土壤高磷中硼可有效防治猕猴桃溃疡病[J]. 西北园艺:果树专刊, 2011(1):45.

孟莉 . 有机全营养配方施肥对猕猴桃品质和溃疡病发病率的影响[D]. 杨陵:西北农林科技大学, 2013.

吴延军 . 新西兰猕猴桃细菌性溃疡病发生现状及分析[J]. 世界农业, 2012(4):61-65.

秦虎强, 赵志博, 高小宁 , 等. 猕猴桃细菌性溃疡病菌对17种杀菌剂的敏感性及不同药剂田间防效[J]. 西北农业学报, 2015,24:145-151.

Choi M S

Choi G W

, et al. Antibacterial activity of cinnamaldehyde and estragole extracted from plant essential oils against Pseudomonas syringae pv. actinidiae causing bacterial canker disease in kiwifruit[J]. Plant Pathology Journal, 2016,32(4):363-370.

Pseudomonas syringae pv. actinidiae (Psa) causes bacterial canker disease in kiwifruit. Antibacterial activity of plant essential oils (PEOs) originating from 49 plant species were tested against Psa by a vapor diffusion and a liquid culture assays. The five PEOs from Pimenta racemosa, P. dioica, Melaleuca linariifolia, M. cajuputii, and Cinnamomum cassia efficiently inhibited Psa growth by either assays. Among their major components, estragole, eugenol, and methyl eugenol showed significant antibacterial activity by only the liquid culture assay, while cinnamaldehyde exhibited antibacterial activity by both assays. The minimum inhibitory concentrations (MICs) of estragole and cinnamaldehyde by the liquid culture assay were 1,250 and 2,500 ppm, respectively. The MIC of cinnamaldehyde by the vapor diffusion assay was 5,000 ppm. Based on the formation of clear zones or the decrease of optical density caused by these compounds, they might kill the bacterial cells and this feature might be useful for managing the bacterial canker disease in kiwifruit.

Lim J A

Song Y R

, et al. Isolation and characterization of bacteriophages against Pseudomonas syringae pv. actinidiae causing bacterial canker disease in kiwifruit[J]. Journal of Microbiology & Biotechnology, 2015,26(2):385.

Pseudomonas syringae pv. actinidiae causes bacterial canker disease in kiwifruit. Owing to the prohibition of agricultural antibiotic use in major kiwifruit-cultivating countries, alternative methods need to be developed to manage this disease. Bacteriophages are viruses that specifically infect target bacteria and have recently been reconsidered as potential biological control agents for bacterial pathogens owing to their specificity in terms of host range. In this study, we isolated bacteriophages against P. syringae pv. actinidiae from soils collected from kiwifruit orchards in Korea and selected seven bacteriophages for further characterization based on restriction enzyme digestion patterns of genomic DNA. Among the studied bacteriophages, two belong to the Myoviridae family and three belong to the Podoviridae family, based on morphology observed by transmission electron microscopy. The host range of the selected bacteriophages was confirmed using 18 strains of P. syringae pv. actinidiae, including the Psa2 and Psa3 groups, and some were also effective against other P. syringae pathovars. Lytic activity of the selected bacteriophages was sustained in vitro until 80 h, and their activity remained stable up to 50°C, at pH 11, and under UV-B light. These results indicate that the isolated bacteriophages are specific to P. syringae species and are resistant to various environmental factors, implying their potential use in control of bacterial canker disease in kiwifruits.

. Comparative analysis of Korean and Japanese strains of Pseudomonas syringae pv. actinidiae causing bacterial canker of kiwifruit[J]. Plant Pathol J, 2005,21(2).

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