A chemi-thermal treatment for control of seedborne bacterial pathogens of tomato

A 6-year study led to the development of a tomato seed treatment that controlledPseudomonas syringae pv.tomato (PT),Pseudomonas corrugata (PC),Xanthomonas campestris pv.vesicatoria (XV), andClavibacter michiganense subsp.michiganense (CM). Tomato seeds were immersed, at a ratio of 1:4 (w/v) seeds: chemical, in a solution containing cupric acetate, acetic acid, pentachloronitrobenzene, 5-ethoxy-3(trichloromethyl)-l,2,4-thiadiazole, and Triton x-100, for 1 h at 45±0.1 °C. The treatment was carried out in a thermostat-controlled bath circulator. The pathogens PT, XV and CM were almost eradicated after immersion of seeds for 30 min at 25 °C, whereas PC was controlled only after 1 h of treatment at 45 °C. The effectiveness of the treatment was related to the formation of a Cu²⁺ organic complex in the solution. The treatment did not affect seed germination or seedling vigor. Most of the tomato seeds produced or imported by Israel are now successfully treated by this method.     

Determination of seedborne fungi and detection of aflatoxins in sudanese fenugreek seeds

Following incubation of fenugreek(Trigonella foenum- graecum L.) seeds on potato dextrose agar and moist filter papers at 28±2°C, 59 species and 11 varieties belonging to 21 genera of fungi were determined as seedborne in fenugreek crops. Among these isolates, 45 species and 9 varieties are new records for this crop; and two species are new to the mycoflora of Sudan:Aspergillus stellifer andEmericella variecolor. The genusAspergillus (15 species and 8 varieties) is the most prevalent, followed byDrechslera (3 species),Rhizopus (3 species),Alternaria andFusarium (6 species each),Emericella (4 species and 2 varieties)Cladosporium andPenicillium (4 species each),Chaetomium (3 species) andCurvularia (3 species and one variety). The remaining 11 genera displayed low level of infection. Of the common pathogens of fenugreek plants,Fusarium oxysporum (2.13%) was recovered from the seeds of this crop. Thin layer Chromatographic analysis of chloroform extracts of 13 seed samples showed that two samples were naturally contaminated with aflatoxins B₁, B₂, G₁ and G₂ (7.5–35.2 μg/kg). http://www.phytoparasitica.org posting Nov. 4, 2001.     

Control of seedborne pathogens and diseases of soybean seeds and seedlings

The control of pathogens, including two bacteria, nine fungi and a virus that cause diseases of soybean seeds and seedlings is discussed. Control methods include general management practices, biocontrol agents, fungicides applied to seeds and foliage, and thermotherapy. Guidelines for the use of seed treatment and foliar fungicides are given. The fungicides commonly used are listed and the interaction between certain fungicides and Bradyrhizobium inoculant is discussed.     

Complementary bacterial enrichment techniques for the detection ofPseudomonas syringae pv.tomato andXanthomonas campestris pv.vesicatoria in infested tomato and pepper seeds

A scheme for routine seed testing forXanthomonas campestris pv.vesicatoria andPseudomonas syringae pv.tomato in pepper and tomato seeds was developed. The scheme is based on different bacterial enrichment techniques. As few as 1000 and 10–100 colony forming units per gram of seeds were detected using a liquid enrichment technique or leaf enrichment technique, respectively. Relatively large amounts of saprophytes on the seed surfaces did not interfere with the detection of the pathogens.     

Impact of bacterial spot outbreaks on the phytosanitary quality of tomato and pepper seeds

The impact of disease outbreaks on the phytosanitary quality of seeds was investigated for two pathosystems: tomato–Xanthomonas vesicatoria and pepper–Xanthomonas euvesicatoria. This study, which was performed in Italy and Serbia, aimed to evaluate the season‐to‐season transmission of phytopathogenic regulated bacteria associated with phytosanitary risks posed by seeds produced in areas where bacterial infections are possible. For each pathosystem, field plots were experimentally inoculated to simulate an initial infection rate of 1%, 5% and 15%. The area under the disease progress curve (AUDPC) was calculated for each field plot, the seeds produced were analysed to determine the contamination level and rate, and the plant‐to‐seed transmission was evaluated by a seedling grow‐out (SGO) assay. To investigate transmission under field conditions, a second‐year experiment was performed, wherein seeds collected from the first year were used to establish new field plots. During the first growing season, AUDPC values were positively correlated with the percentages of initial infection for each pathosystem. Seed contamination levels in pepper ranged from 34 to 100 CFU g^?1, and the contamination rate ranged from 1.50% up to 3.17% for X. euvesicatoria, whereas processing and fresh market tomato seeds produced both in Italy and Serbia were not infected by X. vesicatoria. During SGO assays and the second cropping year, no symptoms were observed in either tomato or pepper plants. Therefore, the calculated pepper seed contamination rate for X. euvesicatoria appeared to be less than the threshold necessary to initiate a disease outbreak. Finally, all seeds obtained during the second cropping year were uninfected.     

Comparison of extraction procedures and determination of the detection threshold for Clavibacter michiganensis ssp. michiganensis in tomato seeds

Several seed extraction procedures, used for detection of Clavibacter michiganensis ssp. michiganensis ( Cmm ) in naturally infected and artificially infested tomato seed lots were evaluated. Extraction methods that included grinding the seeds were significantly better at detecting the pathogen in three different seed lots than methods that used only soaking. The detection threshold of Cmm in relation to seed sample size was determined by adding naturally infected seeds into samples of three different sizes. Cmm was detected by agar plating assay, on three media (CNS, mSCM, D₂ANX), and by direct PCR from seeds and Bio-PCR (bacteria cultured on agar media prior to PCR). In samples of 10 000 seeds containing one infected seed, Cmm could be detected only by Bio-PCR and in only one replicate out of five. In samples containing five or 10 infected seeds per 10 000 seeds, three of five and five of five replicates, respectively, were detected by the three detection methods. In samples of 5000 seeds, one infected seed could be detected in all five replicates only after adding a concentration step. A high correlation ( R ² = 0·9448) between artificially infested seeds and the disease incidence was found. Seed lots infested with less than 58 colony-forming units (CFU) per g did not cause disease under glasshouse conditions, whereas lots with about 1000 CFU g⁻¹ caused disease in 78 plants out of 2000.     

番茄细菌性叶斑病菌RPA检测技术研究

青枯菌为应对逆境胁迫,可进入活的但非可培养状态(viable but non-eulturable,VBNC).本文利用叠氮溴化丙锭(PMA)与PCR技术相结合,建立了一种快速有效区分青枯菌死活细胞的分子检测方法.基于hrcS基因序列,设计了一对青枯菌种特异性检测引物hrcSf/hrcSr;利用PMA对青枯菌Po82菌株的细胞悬浮液样品进行预处理,随后进行常规PCR扩增.结果表明,当样品中PMA质量浓度为3 μg/mL、曝光时间大于5 min时,PMA可有效抑制死亡菌体细胞中的DNA扩增;且对可培养和VBNC状态细胞中的DNA扩增没有影响;本试验建立的PMA-PCR方法能有效对包括VBNC状态在内的青枯菌活菌进行检测,避免了假阳性与假阴性结果的产生.     

Evaluation of seedborne bacterial pathogens on common bean cultivars grown in central Anatolia region,Turkey

Bacterial diseases of bean cause economically important losses worldwide. The most important method for managing bacterial diseases on bean is the use of pathogen-free seed. In this study, 198 different dry bean seed samples of six different cultivars including Dermason, Cali, Sira, Battal, Bombay and Seker, were collected from 12 provinces of Central Anatolia Region of Turkey. All were tested to investigate the seedlots as primary inoculum sources of the major bacterial diseases. The data revealed that 22,72 %, 13,63 %, 11,11 %, 1,51 % and 0.5 % of seed samples tested were contaminated with five seedborne bacterial pathogens, Pseudomonas savastanoi pv. phaseolicola (Psp), Pseudomonas syringae pv. syringae (Pss), Xanthomonas axonopodis pv. phaseoli (Xap), X. axonopodis pv. phaseoli var. fuscans (Xapf) and Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff), respectively. All bacterial strains isolated were identified based on morphological, physiological, biochemical, molecular and pathogenicity tests. The results showed that Psp and Pss were found together on cv. Cali; Psp and Xap on cv. Dermason and cv. Sira; and Pss and Xap on cv. Seker, cv. Dermason, and cv. Cali. Therefore, the results in the present study suggested that evaluation and selection of pathogen-free seeds are very important for preventing the spread of pathogens and effective management of seed borne bacterial diseases prevalent in bean growing regions; in addition to implementation of integrated crop production strategies such as crop rotation, sanitation, seed treatment, tolerant/resistant cultivar selection and proper bactericide application.     

Management of bakanae and bacterial seedling blight diseases in nurseries by irradiating rice seeds with atmospheric plasma

The control of seedborne rice seedling diseases in the seed beds is important to avoid epidemics in rice nurseries and paddies, which may result in severe yield loss. Recently, irradiation with plasma containing electrons, creating positive or negative ions and neutral species, has been shown to have an antimicrobial effect, probably via generation of reactive oxygen species. This study examines whether two seedborne rice seedling diseases, bakanae disease caused by the fungal pathogen Fusarium fujikuroi, and bacterial seedling blight caused by Burkholderia plantarii, are suppressed by irradiation of infected rice seeds with atmospheric plasma. Seed germination and seedling growth were not inhibited in plasma‐treated healthy seeds. When F. fujikuroi‐infected rice seeds were irradiated with plasma after being immersed in sterile distilled water, bakanae disease severity index and the percentage of plants with symptoms were reduced to 18.1% and 7.8% of non‐irradiated control, respectively, depending on the duration of plasma irradiation. The bacterial seedling blight disease index was also reduced by plasma irradiation in vacuum‐inoculated seeds to 38.6% of the non‐irradiated control, and in infected seeds harvested from spray‐inoculated heads of rice plants to 40.1% of the control. Therefore, plasma irradiation seems to be effective in controlling two independent seedborne rice seedling diseases.     

Cytokinin induces bacterial pathogen resistance in tomato

Phytohormones are involved in the regulation of plant responses to biotic stress. How a limited number of hormones differentially regulate defence responses and influence the outcome of plant–biotic interactions is not fully understood. In recent years, cytokinin (CK) was shown to induce plant resistance against several pathogens. In the present study, we investigated the effect of CK in inducing tomato resistance against the hemibiotrophic pathogenic bacteria Xanthomonas campestris pv. vesicatoria (Xcv) and Pseudomonas syringae pv. tomato (Pst). We demonstrate that CK enhances tomato resistance to Xcv and Pst through a process that relies on salicylic acid and ethylene signalling. CK did not directly affect the growth or biofilm formation ability of these pathogens in vitro. Overall, our work provides insight into the underlying mechanisms of CK-induced immune responses against bacterial pathogens in tomato.     

Bacterial diseases of tomato in southern Spain: application of a detached tissue assay to evaluate bacterial pathogenicity

Tomatoes are one of the most important crops in southern Spain, especially during the cold season. As a preliminary step in the design of an integrated disease management programme for tomato, a study on the occurrence of bacterial diseases in tomato houses of Almería (ES) was carried out during the 1993/1997 growing seasons. Sixty-four bacterial strains were isolated from tomato plants showing symptoms of bacterial diseases and 41 of them (64%) were characterized as pathogenic. The bacterial tomato pathogens most frequently isolated were Erwinia carotovora subsp. carotovora, Pseudomonas corrugata, Pseudomonas syringae pv. tomato and Xanthomonas vesicatoria. The pathogenicity of the bacterial isolates on tomato was tested by the conventional seedling assay and by an in vitro assay using detached tissues developed in our laboratory. Close correspondence between the two assays was observed. An in vitro detached tissue assay is proposed for determining the pathogenicity of bacterial isolates on tomato.     

番茄青枯病生物防治研究进展

番茄青枯病是番茄生产上最严重的病害之一,化学防治效果不佳,且对环境不友好。本文概述了国内外应用无致病力青枯菌菌株、拮抗细菌和生物技术等方法对番茄青枯病进行生物防治的研究进展,并对生物防治存在的相关问题及应用前景进行了讨论。     

水稻种子携带稻瘟病菌LAMP检测方法的建立与应用

稻瘟病菌Magnaporthe oryzae可通过种子带菌实现远距离传播,导致病害发生并造成严重经济损失。建立灵敏高效且便于操作的水稻种子携带稻瘟病菌的检测方法,是确保种子健康和控制病害发生的先决条件。本研究选取稻瘟病菌的3-磷酸甘油酰基转移酶基因MoSPC3设计合成3对特异性引物,并对反应体系进行优化,建立了环介导等温扩增(loop-mediated isothermal amplification, LAMP)方法。该方法可特异性地检测稻瘟病菌,对稻瘟病菌DNA样品的检测灵敏度可达到0.24拷贝/μL,远高于普通PCR的检测灵敏度。将该方法用于从中国和马来西亚不同水稻种植区收集的92份水稻种子样品携带稻瘟病菌的检测,结果显示,LAMP方法共检测到89份阳性样品,而普通PCR仅显示有2份样品为阳性。综上,本研究建立了一种适用于水稻种子携带稻瘟病菌的LAMP检测方法,具有简便快捷、灵敏度高等特点,丰富了稻瘟病菌的检测体系,可用于大批量水稻种子样品的健康检测。     

Hormetic UV-C seed treatments for the control of tomato diseases

Hormesis is a dose response phenomenon in which low, non-damaging doses of a stressor bring about a positive response in the organism undergoing treatment. Evidence is provided here that hormetic UV-C treatments of tomato seed can control disease caused by Botrytis cinerea, Fusarium oxysporum f. sp. lycopersici (FOL) and f. sp. radicis-lycopersici (FORL) on tomato (Solanum lycopersicum). Treating seeds with a 4 kJ m⁻² dose of UV-C significantly reduced both the disease incidence and progression of B. cinerea, with approximately 10% reductions in both on cv. Shirley. Disease severity assays for FOL and FORL on cv. Moneymaker showed dose-dependent responses: UV-C treatments of 4 and 6 kJ m⁻² significantly reduced the disease severity scores of FOL, whilst only the 6 kJ m⁻² showed significant reductions for FORL. To determine the effects of treatment on germination and seedling growth, UV-C doses of 4, 8 and 12 kJ m⁻² were performed on cv. Shirley. No negative impacts on germination or seedling growth were observed for any of the treatments. However, the 8 kJ m⁻² treatment showed significant biostimulation, with increases in seedling, root and hypocotyl dry weight of 11.4%, 23.1% and 12.0%, respectively, when compared to the control. Furthermore, significant increases in the root-mass fraction (10.6%) and root:shoot ratio (13.1%) along with a decrease in shoot-mass fraction (2.0%) indicates that the 8 kJ m⁻² treatment stimulated root growth to the greatest extent. There was no effect on hypocotyl and primary root length or the number of lateral roots, indicating no adverse effects to basic root architecture or seedling growth.     

番茄细菌性溃疡病苗期接种新方法的研究

 在剪叶、浸根和针刺等细菌病害传统接种方法基础上设计了打顶接种新方法;以番茄细菌性溃疡病菌中国菌株和美国菌株借助打顶法接种佳粉10、合作908和华南红宝石3个国内主栽番茄品种2~3片真叶期幼苗,在昼夜最低、最高温度15~18℃、32~35℃和相对湿度为30%~60%的温室条件下,打顶法接种番茄幼苗后溃疡病发病率为87.5%~100.0%,病情指数随接种菌悬液浓度提高而增大,达到23.96~82.29,3个供试品种之间表现稳定一致;剪叶、浸根和针刺接种方法的发病率普遍在40%以下,病情指数在20以下,3个供试品种之间未表现明显差异;进一步研究显示,使用选择性培养基mSCM能够从打顶法接种后的发病植株上获得培养性状与原接种体一致的分离物,专化性免疫凝聚试剂盒检测到特定的测试线,PCR扩增到614bp的特异性条带,证实该分离物为番茄细菌性溃疡病菌,发病植株为接种体侵染所致。该研究结果表明,打顶接种方法比剪叶法、针刺法和浸根法更适合用于番茄溃疡病菌的致病性测定和评价不同番茄品种苗期的抗病性,具有应用价值。     

常温大气压等离子体对番茄种带细菌的灭菌效果

为了明确常温大气压等离子体(atmospheric pressure room-temperature plasma,APRTP)在番茄种子消毒中的应用效果,以‘中杂302’种子为材料,采用平板培养计数和16S rRNA拷贝数分析法,测定了APRTP处理对种子表面和内部细菌的灭菌效果。结果表明,APRTP处理对种带细菌的灭菌效果显著,在5～30 min处理时间内,灭菌率随处理时间延长逐渐升高,处理25 min对种子表面和内部细菌的灭菌率达99%以上;番茄种子接种细菌性溃疡病致病菌—密执安棒杆菌密执安亚种(Cmm)后,采用APRTP处理25 min可有效杀灭99.84%的种带Cmm菌;种子活力检测表明,APRTP处理可提高番茄种子活力,加快种子萌发速率,APRTP处理过的种子播种后,对幼苗早期生长不会造成伤害。综上,APRTP处理可显著杀灭番茄种带细菌,提高种子活力、促进种子萌发,是一种安全、高效的番茄种子处理方法。     

进境番茄种子中番茄花叶病毒的检测与鉴定

利用双抗夹心 酶联免疫吸附试验(DAS-ELISA)和反转录 聚合酶链式反应（RT-PCR）方法对来自韩国的番茄种子进行种传病毒检测。结果表明,在该批番茄种子中检测到番茄花叶病毒（ToMV）和烟草花叶病毒（TMV）。PCR产物测序结果表明,ToMV特异引物（ToA/ToB）与TMV特异引物（TA/TB）扩增的片段均为ToMV的外壳蛋白（CP）基因及3′非编码区（3′ UTR）,该片段与其他ToMV分离物的核苷酸序列相似性为98.2%~99.9%。本研究利用重新设计合成TMV和ToMV特异引物对该批种子进行RT PCR检测,仅ToMV特异性引物（ToMf1/ToMr1）扩增到670 bp的预期片段,TMV特异引物（TMf1/TMr1）则未出现特异性扩增,表明重新设计的引物可准确区分ToMV和TMV。以上结果证实该批番茄种子仅携带ToMV。     

A Simplified method for determining the resistance of tomato seedlings toFusarium andVerticillium wilts

A simple test for determining the resistance of tomato lines toFusarium andVerticillium wilt diseases was developed. Roots of tomato seedlings at their first true leaf stage were dipped in a heavy suspension of the pathogen for 24 h. The seedlings were then transferred to small beakers containing various concentrations of Hoagland solution. The first and most severe disease symptoms appeared on susceptible cultivars grown in 25% Hoagland nutrient solution. Final results of resistance tests were obtained 10, 8 and 16 days after inoculation withFusarium race 1, race 2, andVerticillium, respectively. The test appears to be simple, results are obtained rapidly, and greenhouse space can be saved.     

抗放线菌St-145对番茄青枯病的防治效果

室内测定结果表明,先接种放线菌St-145菌株2d后再接种茄青枯雷尔氏菌的植株对番茄青枯病的防治效果为73.83%;先接种病原菌2d后再接种St-145菌株对该病的防效为30.86%.St-145菌株对番茄青枯病的大田防治效果为16.39%.