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1.
Acidovorax citrulli is a seed-transmitted gram-negative bacterium that can cause substantial economic yield loss in watermelon and melon production worldwide. Four small-molecule libraries containing 4,952 compounds were selected for high-throughput screening against A. citrulli wild-type strain Xu3-14 by evaluation of growth inhibition. One hundred and twenty-seven molecules (2.5% hit rate) were identified as bactericidal or bacteriostatic against A. citrulli at 100 μM. Secondary screens indicated that 27 candidate compounds were more effective against A. citrulli Group II strains than Group I strains (classified using repetitive element PCR). Several compounds were inhibitory to other pathogenic bacteria, including Clavibacter michiganensis subsp. michiganensis and Xanthomonas campestris pv. campestris, but did not affect the growth of plant beneficial bacteria Pseudomonas fluorescens and Bacillus subtilis. More than half of the compounds did not inhibit germination of Arabidopsis or watermelon seeds. The effect of small molecules on A. citrulli seed-to-seedling transmission was evaluated by applying each compound to inoculated watermelon seeds and assessing seedling infection. Nine compounds were chosen for further investigation based on their reduction of percentage seedling infection and compiling scores on their specificity, sensitivity, and phytotoxicity obtained in the secondary screens. The five best compounds were selected (thiamphenicol, nadifloxacin, pipemidic acid, ciclopirox, and zinc pyrithione) for greenhouse tests and were found to effectively reduce the seed-to-seedling transmission of A. citrulli in both artificially and naturally infested seeds. These top five compounds provide a basis for future development of an A. citrulli-specific bactericide.  相似文献   

2.
Genetic diversity analysis of Acidovorax citrulli in China   总被引：1，自引：0，他引：1  
Acidovorax citrulli has become quite common in China. A collection of 118 strains of A. citrulli was made from throughout China and other countries to determine their genetic relatedness. Strains were identified as A. citrulli by pathogenicity, phenotypic characterization, and PCR. Genetic diversity was determined using pulsed field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). PFGE electrophoresis resulted in nine genotypes, which could be typed into two groups based on host; group 1 included strains mainly from melon and group 2 included strains mainly from watermelon. MLST analysis resulted in 73 sequence types (ST) among the 118 A. citrulli strains. All A. citrulli strains were typed into three groups: group 1 with 82 strains (including type strain Fc247), group 2 with 35 strains and group 3 a singleton (Fc380). Similar to PFGE results, group 1 included strains mainly from melon and group 2 included strains mainly from watermelon. The difference was the 10 watermelon strains (pslbtw1-3, 5–11) from Beijing grouped with melon strains of group 1 based on MLST, suggesting that these 10 watermelon strains had a close relationship with melon. Our study indicated that there was genetic differentiation among A. citrulli strains between watermelon and melon. Also, our study was the first attempt to compare PFGE and MLST on analyzing genetic diversity of A. citrulli strains and proved MLST could better distinguish A. citrulli strains.  相似文献   

3.
The gram-negative bacterium Acidovorax citrulli causes bacterial fruit blotch (BFB) disease of cucurbits, which represents a serious threat to melon and watermelon production worldwide. To date, there are no efficient means to manage the disease, and reliable resistance sources for cucurbit germplasm are lacking. Mineral nutrition markedly affects plant diseases. Recently, we reported that disease severity on melon foliage and A. citrulli growth in the leaf tissue were significantly influenced by the form of nitrogen supply. In the present study, we investigated the influence of potassium nutrition on BFB severity and A. citrulli establishment in the foliage of melon plants. Fertilization with relatively low concentrations of potassium increased these variables compared with higher potassium concentrations. Since establishment of A. citrulli during the growing season is assumed to increase the incidence of fruit infection, the fact that mineral nutrition influences BFB incidence in the plant foliage is of particular importance.  相似文献   

4.
Bacterial fruit blotch of cucurbits is a destructive disease caused by Acidovorax avenae subsp. citrulli, which is a typical seedborne pathogen. In seed health testing for this disease, we have detected many strains of Acidovorax with some differences from A. avenae subsp. citrulli. Their 16S rRNA sequences were divided into six types. The most common sequence was completely consistent with that of A. avenae subsp. avenae originally isolated from rice. The other sequences were over 99% similar but not identical to those of A. avenae subsp. avenae and A. avenae subsp. citrulli. Some commercialized antibodies against A. avenae subsp. citrulli reacted with several of these strains. Some of these strains incited yellow spots or brownish water-soaked lesions mainly on young true leaves of cucumber and squash after spray inoculation. Histological observations showed that these strains entered the leaf tissues of cucurbit plants through stomata and multiplied in the intercellular spaces of parenchymatous tissues as well as in the vascular tissues. The amount of bacterial multiplication and spread in the tissues differed among the strains, presumably reflecting their ability to induce symptoms. These isolated strains are therefore different from A. avenae subsp. citrulli, and their potential threat to the cultivation of cucurbits is lower than that of A. avenae subsp. citrulli.  相似文献   

5.
This study explored the pathways of ingress of Acidovorax citrulli, the causal agent of bacterial fruit blotch of cucurbits, into watermelon seeds. Up until 7 days post‐inoculation (DPI), a significantly higher percentage of watermelon seeds was infected with A. citrulli when the bacteria were applied (c. 1 × 106 colony‐forming units) to stigmas versus ovary pericarps of female flowers. Immunofluorescence microscopy showed that, with stigma inoculation, A. citrulli colonized style and ovary tissues by 1 DPI, and the bacteria co‐localized with pollen germ tubes in these tissues. With ovary pericarp inoculation, A. citrulli cells penetrated the epicarp and mesocarp tissues by 1 DPI but did not reach endocarp until 4 DPI. Finally, manual pollination followed by stigma inoculation led to >53% A. citrulli‐infected seed lots, while A. citrulli was not detected in seeds/ovules generated by stigma inoculation without pollination (chemically induced parthenocarpy). These results show that stigma inoculation results in faster colonization of watermelon ovules by A. citrulli than pericarp inoculation, even though there is no difference in the levels of infection in mature seeds. The data also indicate that pollen germ tubes play an important role in A. citrulli ingress into watermelon seeds via stigmas.  相似文献   

6.
An Acidovorax citrulli–cucumber pathosystem was established through which A. citrulli mutants with altered pathogenicity, generated by transposon mutagenesis, were identified on cucumber cotyledons. The A. citrulli group I strain FC440 was shown to grow faster in cucumber leaf tissues than a group II strain and was used for Tn5 transposon mutagenesis. A total of 2100 Tn5 insertional mutants were generated, and analysis of the mutant library showed that the transposon insertions were single, independent and stable. A conserved non‐flagellar type III secretion system (NF‐T3SS) ATPase gene hrcN was identified and confirmed to be essential for pathogenicity and functionality of NF‐T3SS in A. citrulli. Comparative sequence analysis of the HrcN protein and its homologues in other representative bacterial plant pathogens revealed that the NF‐T3SS of A. citrulli is close to that of Ralstonia solanacearum and Xanthomonas campestris, but distant from that of Pseudomonas syringae and Erwinia amylovora. The generated Tn5 insertional mutant collection is valuable for identification of genes required for A. citrulli pathogenesis, and the established A. citrulli–cucumber pathosystem will facilitate an improved understanding of A. citrulli biology and pathology.  相似文献   

7.
In Iran, during 2013–16, 16 Gram‐positive corynebacteria‐like strains were recovered from the epiphytic parts of solanaceous vegetables including eggplant, pepper and tomato. The strains were recovered accidentally as a result of monitoring for other bacterial pathogens in solanaceous fields. The strains were phenotypically different from Clavibacter michiganensis strains. Although none of the strains were pathogenic on their host of isolation or on any other solanaceous plants, 12 out of 16 strains were pathogenic on common bean, cowpea, mung bean and soybean. Colonization by strains was observed on maize, zucchini, faba bean, honeydew melon, rapeseed, sugar beet and sunflower plants under greenhouse conditions. In PCR tests, the primer pair CffFOR2/CffREV4, specific for Curtobacterium flaccumfaciens pv. flaccumfaciens, enabled the amplification of the appropriately sized fragment in 12 out of 16 strains, and all 12 strains were pathogenic on dry beans. Phylogenetic analysis, using the gyrB and recA genes, showed all 16 bacterial strains clustered within several pathovars of C. flaccumfaciens. A nonpathogenic yellow‐pigmented strain (Xeu15) was clustered with the type strains of C. flaccumfaciens pv. betae and C. flaccumfaciens pv. oortii. Bacteriocin profiling assays revealed no significant differences among the pathogenic and nonpathogenic strains. Host range and population dynamics of four representative strains on 17 plant species showed population build‐up of the strains only on common bean, cowpea, wheat and red nightshade plants. The results provide important insights into the possible role of nonhost plants as reservoirs of plant pathogenic bacteria, which has important implications in plant disease epidemiology and management.  相似文献   

8.
Long‐term survival of Acidovorax citrulli in citron melon (Citrullus lanatus var. citroides) seeds was investigated. Citron melon seed lots infected with A. citrulli were generated in the field by inoculating either the pistils (stigma) or pericarps (ovary wall) of the female blossoms. Seventeen A. citrulli isolates from 14 different haplotypes belonging to two different groups (group I and II) were used for inoculation. After confirming that 100% of seed lots were infected, they were stored at 4°C and 50% RH for 7 years. After storage, the viability of A. citrulli cells from individual lots was determined by plating macerated seeds on semiselective medium as well as growing seeds for 14 days and scoring for bacterial fruit blotch symptoms. The type of A. citrulli isolate (group I or group II) used did not significantly influence bacterial survival. However, A. citrulli survival was significantly greater in seed lots generated via pistil inoculation (52·9 and 29·4%) than via pericarp inoculation (23·5 and 17·6%). Repetitive extragenic palindrome (rep)‐PCR on A. citrulli isolated from citron melon seed lots after storage displayed similar fingerprinting patterns to those of the reference strains originally used for blossom inoculation, indicating that cross‐contamination did not occur. The results indicate that A. citrulli may survive/overwinter in citron melon seeds for at least 7 years and bacterial survival in seed was influenced more by method of blossom inoculation than by the type of bacterial isolate.  相似文献   

9.
为评价非致病性尖孢镰刀菌FJAT-9290对不同植物的致病性和定殖能力,利用该菌株所含的无毒基因SIX1特异性检测引物P12-R1/P12-F2跟踪其在不同植物中的侵入与定殖情况,并研究其对番茄植株生长特性的影响及对番茄枯萎病的防治效果。结果显示,接种120 d内,菌株FJAT-9290对所供试的11种植物均未造成危害,但在侵入时间与定殖方面存在差异。该菌株最易侵入番茄植株,接种第5天即可在茎基部检测到;其次为甜椒、甜瓜、西瓜和香蕉等植株,接种10 d时可在茎基部检测到;但在韭菜、香葱和马唐草上均未检测到。该菌株在番茄与茄子植株的定殖时间最长,达90 d;其次为甜椒、香蕉和粉蕉,至少60 d;在甜瓜、西瓜和黄瓜上为40~50 d。该菌株能促进番茄植株生长,显著提高其株高和叶片数量,对番茄枯萎病的盆栽与田间防治效果分别达76.70%和69.56%。表明菌株FJAT-9290具有良好的定殖能力且对番茄枯萎病具有较好的防治效果。  相似文献   

10.
Bacterial fruit blotch (BFB) of cucurbits, caused by Acidovorax avenae subsp. citrulli, is a serious threat to the watermelon and melon industries. To date, there are no commercial cultivars of cucurbit crops resistant to the disease. Here we assessed the level of tolerance to bacterial fruit blotch of various commercial cultivars as well as breeding and wild lines of melon, using seed-transmission assays and seedling-inoculation experiments. Selected cultivars were also tested in a greenhouse experiment with mature plants. All tested cultivars/lines were found to be susceptible to the pathogen, and most of them showed different responses (relative tolerance vs. susceptibility) in the different assays; however, some consistent trends were found: cv. ADIR339 was relatively tolerant in all tested assays, and cv. 6407 and wild lines BLB-B and EAD-B were relatively tolerant in seed-transmission assays. We also provide evidence supporting a strong correlation between the level of susceptibility of a cultivar/line and the ability of the pathogen to adhere to or penetrate the seed. To the best of our knowledge, this is the first attempt to assess melon cultivars/lines for bacterial fruit blotch response.  相似文献   

11.
In the Philippines, bacterial wilt caused by Ralstonia solanacearum is one of the most important diseases affecting vegetables and banana. In this study, 89 strains of R. solanacearum isolated from various hosts were screened for their biovar, phylotype, pathogenicity, and genetic diversity. Foreign strains were included for comparison with these Philippine strains. Results of the biochemical and multiplex-PCR tests divided the Philippine strains into five biovars (1, 2, 3, 4, and N2) and three phylotypes (I, II, and IV). Three potato strains belonged to biovar N2/phylotype IV. Pathogenicity tests divided the strains into five pathogenicity types based on their virulence in tomato, potato, eggplant, sweet pepper, and tobacco. Strains classified as biovar N2 were weakly pathogenic to potato (pathogenicity type III) and almost all strains isolated from banana were not pathogenic to the test plants except potato (pathogenicity type V). The results of AFLP analysis divided the strains into four clusters. Cluster 1 was composed of strains isolated from solanaceous crops, ginger (Zingiber officinale), and Morus sp. from the Philippines and other Asian countries. Cluster 2 grouped the potato strains (biovar N2) from the Philippines and Japan and blood disease bacterium strains from Indonesia. Cluster 3 contained the local and foreign strains isolated from potato (biovar 2) and banana (biovar 1). Cluster 4 consisted only of the tomato strain from the USA.  相似文献   

12.
以分离自西瓜上的Aac5菌株为例,通过同源重组的方法,构建了hrc N基因插入缺失突变体,通过PCR方法和Southern blot验证突变菌株,对突变体进行致病性、致敏性、生长曲线和运动性测定。为明确hrc N基因与其他基因的关系,通过实时荧光定量PCR法定量检测了hrp A、hrc V、hrc U、Lux I、LuxR 5个基因的表达量。结果显示:与野生型相比,突变体致病力和致敏性明显减弱,致病时间延迟,群体感应信号减弱,生长能力明显下降,运动性减弱,互补菌株只能恢复部分功能;5个基因在突变体中的表达量均上调,hrc N基因与这5个基因之间均为负调控关系。说明hrc N基因在果斑病菌致病能力上发挥重要作用。  相似文献   

13.
从河北省张家口地区种植的烟草上采集的感病弯管列当植株,从中分离得到20株镰刀菌,采用孢子悬浮液浸根和灌根法对小麦、玉米、棉花、向日葵、番茄、烟草、辣椒、茄子、西瓜、甜瓜等作物和蔬菜进行了安全性检测,筛选出对主栽作物和蔬菜安全且具有促生作用的4个菌株。其中菌株Br-2对烟草、辣椒、西瓜有显著促生作用,且对弯管列当的防治效果最好：施用菌株Br-2后烟草、辣椒、西瓜增高分别为123.53%、62.16%、28.95%;其发酵上清液对弯管列当种子萌芽抑制率为71.79%;小区试验中对弯管列当的寄生率防效为50%,寄生度防效为79.38%;田间试验中对弯管列当的寄生率防效为58.27%,寄生度防效为75.70%。形态学和分子生物学鉴定结果表明菌株Br-2为尖孢镰刀菌。  相似文献   

14.
Zoospores of 12 isolatesO. bornovanus from geographically diverse sites and representing the three host specific cucurbit strains were tested as vectors for seven viruses using watermelon bait plants and the in vitro acquisition method. All isolates of the cucumber, melon, and squash strains transmitted melon necrotic spot carmovirus (MNSV) and cucumber necrosis tombusvirus (CNV) but none transmitted petunia asteroid mosaic tombusvirus (PAMV) or tobacco necrosis necrovirus (TNV). The isolates varied as vectors of three other carmoviruses: cucumber leaf spot virus (CLSV); cucumber soil borne virus (CSBV); and squash necrosis virus (SqNV). All cucumber isolates transmitted CLSV and SqNV but not CSBV. Some of the melon isolates transmitted CLSV and SqNV but none transmitted CSBV. Two squash isolates transmitted CSBV and SqNV but not CLSV. Two isolates ofO. brassicae transmitted only TNV and a third did not transmit any of the viruses. The species of bait plant sometimes affected transmission. The most efficient vector strains ofO. bornovanus, as determined by reducing zoospores and virus in the inoculum, were the cucumber strain for CLSV; the cucumber strain for CNV if cucumber was the bait plant or melon strain if watermelon was the bait plant; and the squash strain for SqNV. The plurivorous strain ofO. brassicae was the most efficient vector of TNV.Olpidium bornovanus is the first vector reported for CSBV and is confirmed as a vector of SqNV. It is proposed that all carmoviruses may have fungal vectors.Ligniera sp. did not transmit any of the viruses in one attempt.Abbreviations CLSV cucumber leaf spot virus - CNV cucumber necrosis virus - CSBV cucumber soil borne virus - MNSV melon necrotic spot virus - PAMV petunia asteroid mosaic virus - SqNV squash necrosis virus - TNV tobacco necrosis virus - TBSV tomato bushy stunt virus  相似文献   

15.
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16.
为筛选高抗瓜类细菌性果斑病的西瓜资源,以24份西瓜品种资源为试材,采用苗期喷雾接种法分别接种分离自甜瓜上的瓜类嗜酸菌Acidovorax citrulli菌株pslb96和ZZ-1,鉴定各品种资源对瓜类细菌性果斑病的苗期抗性。结果表明,24份西瓜品种资源中未发现有对2株菌株表现免疫的材料,有7份资源对菌株pslb96表现高抗,12份资源对菌株ZZ-1表现高抗;9份资源对菌株pslb96表现中感或感病,7份资源对菌株ZZ-1表现中感和感病;对2株菌株均表现高抗的品种资源有野生型种质资源A9及商品种华欣、申蜜968、申选958和申抗988,占总品种资源的20.83%。部分品种资源A4、A13和申蜜7号对菌株pslb96和ZZ-1的抗性表现出明显的差异,表明相同寄主来源的2株不同菌株致病力存在差异。  相似文献   

17.
In 2013 and 2014, an extensive survey of bacterial wilt in Myanmar was performed, and 70 strains of Ralstonia solanacearum (Rs) were collected from wilting plants of tomato, potato, chili and eggplant. Myanmar Rs strains were characterized by traditional and molecular methods. Polymerase chain reaction (PCR) test using Rs-specific primer set amplified one specific band (281-bp) from template DNA of all strains. Pathogenicity tests on the four solanaceous plants differentiated the strains into six pathogenic groups. Biovar determination tests showed that biovar 3 strains predominated (63%) among all Rs strains. Biovar 4 strains (7%) were obtained from both tomato and chili strains, whereas biovar 2 (30%) strains were isolated only from potato. Multiplex-PCR analysis indicated that tomato, eggplant and chili strains belonged to phylotype I, whereas potato strains comprised phylotype I and phylotype II. Strains in phylotype I, which was suggested to have originated from Asia, were the most prevalent in all surveyed areas. Phylogenetic analysis based on the endoglucanase (egl) gene sequences revealed that Myanmar strains partitioned into two major clusters that corresponded to phylotype I and II. Strains in phylotype I were further divided into seven subclusters, each corresponding to a distinct sequevar (15, 17, 46, 47, 48, unknown 1 or unknown 2). All strains in phylotype II belonged to sequevar 1. This is the first comprehensive report of the presence of diverse Rs strains in Myanmar.  相似文献   

18.
Cucurbits are often cultivated in rotation with Solanaceae in double-cropping systems. Most cucurbits have been described as susceptible to root-knot nematodes (RKN) but little is known on their relative levels of susceptibility. Because RKN species differ in rates of root invasion and reproductive traits, isolates of M. arenaria, M. incognita and M. javanica were compared on five cucurbit hosts in experiments run in a climate growth chamber. They included zucchini squash cv Amalthee, cucumber cv Dasher II, melon cv Pistolero, pumpkin cv Totanera and watermelon cv Sugar Baby. All cucurbits were susceptible to the three RKN isolates although M. javanica showed higher invasion rates, faster development and higher egg production than M. arenaria on the selected cucurbits. Apparent differences among cucurbits were primarily due to root invasion rates and formation of egg masses. Both Cucumis species (cucumber and melon) were better hosts for nematode invasion and reproduction than zucchini squash, followed by watermelon. Large invasion rates followed by small reproduction traits were linked to M. incognita on zucchini squash. Reduced invasion rates and egg mass formation along with delayed early development were shown on watermelon.  相似文献   

19.
为有效防控瓠瓜果斑病,自浙江省象山县田间采集具有典型果斑病症状的瓠瓜样本,对其进行病原菌分离、形态观察、致病性测定及分子生物学鉴定,并利用特异性引物PL1/PL2 PCR扩增和基质辅助激光解吸电离飞行时间质谱（matrix assisted laser desorption ionization time-of-flight massspectrometry,MALDI-TOF-MS）技术对其病原菌进行亚群鉴定。结果表明：瓠瓜果斑病田间典型症状是发病叶片和果实上病斑由水渍状小斑点逐渐发展为伴有黄色晕圈的褐色不规则病斑,果实腐烂、有臭味。通过菌体形态和培养特性观察、PCR鉴定、16S rDNA序列分析和7个看家基因的系统发育分析将其病原菌鉴定为西瓜噬酸菌Acidovorax citrulli。从瓠瓜上分离的菌株均属于西瓜噬酸菌亚群I,从西瓜上分离的菌株均属于西瓜噬酸菌亚群II。  相似文献   

20.
Plant beneficial bacteria (PBB) have shown potential for disease control and are particularly important in the management of bacterial diseases, which are poorly controlled by conventional methods. In melon, bacterial fruit blotch caused by Acidovorax citrulli is a seedborne disease that is particularly destructive under certain conditions. PBB strains were screened for their ability to protect seeds and leaves from bacterial fruit blotch, and their antibiosis activity and plant colonization were studied. When Bacillus sp. RAB9 was applied to infected seeds, it reduced the area under the disease progress curve (AUDPC) by 47% and increased the incubation period (the time between inoculation and the first visible symptoms) by 35%. Three of the selected strains (JM339, MEN2 and PEP91) displayed antibiosis against A. citrulli. The RAB9Rif-Nal mutant colonized seeds epiphytically and roots and stems endophytically. Paenibacillus lentimorbus MEN2 sprayed on melon seedlings protected leaves, and when challenged with A. citrulli, it reduced the AUDPC (by 88%), disease index (by 81%) and incidence (by 77%). Given that the production of both melon seedlings and commercially grown greenhouse melons is increasing, biocontrol strategies may well be integrated into bacterial blotch management programs.  相似文献   

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