Overwintering of Erwinia carotovora subsp. carotovora in Diseased Tissues in Soil and Its Role as Inoculum for Soft Rot of Chinese Cabbage (Brassica campestris, Pekinensis Group)

To examine whether the pathogenic bacterium, Erwinia carotovora subsp. carotovora, causal agent of soft rot of Chinese cabbage (Brassica campestris L., pekinensis group), can overwinter in plant debris and soil and serve as inoculum the following year, we monitored field populations of rifampicin-resistant, phage-sensitive strains of the bacterium. Chinese cabbage (cv. Matsushima Kohai W1116) were planted in field soil in pots that were sunk into the field on Aug. 2, 1996 and eventually reduced to one plant per pot. Outer petioles of the plants were inoculated with mixture of 13 bacterial strains of E. carotovora subsp. carotovora on Sept.5, 1996. After the soft rot spread throughout the plant, the diseased plant was buried in the potted soil. New seeds were sown in the pots on April 30, 1997, and the disease was observed in June and July. The bacterial strains were re-isolated from the potted soil, diseased tissue and rhizosphere soil by the dilution plating method on modified Drigalski's medium containing 100 ppm rifampicin and by the enrichment technique. In addition to rifampicin resistance, phage sensitivities of some of the re-isolated strains were identical to those of the strains buried in the soil with the diseased plant in the previous year. From these results, some of the 13 strains overwintered in the soil and infested plant tissue and acted as primary inoculum the following year. The frequency of re-isolation varied among the strains, perhaps because of competition among the strains, differences in epidemiological behavior and stabilizing selection among the strains, and the presence of different ecotypes of the organism. Received 21 July 2000/ Accepted in revised form 19 September 2000     

Characterisation of Erwinia carotovora subspecies and detection of Erwinia carotovora subsp. atroseptica in potato plants, soil and water extracts with PCR-based methods

A PCR-RFLP test based on a pectate-lyase encoding gene permits the detection of several Erwinia carotovora subspecies, but requires complete DNA extraction. This paper reports on the suitability of a simplified PCR-RFLP protocol to characterise E. carotovora strains and on the performance of PCR, using the same primers, to detect the atroseptica subspecies in substrates of epidemiological significance. A collection of 140 strains from various hosts and geographical origins was characterised for biochemical traits and PCR-RFLPs. PCR performed on boiled bacterial suspensions yielded an amplification product of 434 bp in 109 of the 140 strains. None of the E. carotovora subsp. betavasculorum strains was amplified, even after complete DNA extraction. RFLPs of the PCR product yielded 24 groups, 3 of which were new. Twenty one groups were specific to one subspecies. Several strains biochemically similar to E. carotovora subsp. atroseptica, but growing at 37 °C, showed PCR-RFLP profiles characteristic of E. carotovora subsp. carotovora. Phenetic and cladistic analyses gave three main domains, not strictly related to hosts or geographical origins. The atroseptica (RFLP groups 1 and 2) and wasabiae (group 21) subspecies constituted one of the domains, despite clustering distantly from one another. Host specialisation and molecular homogeneity suggest a clonal structure within these subspecies. Conversely, E. carotovora subsp. odorifera, despite its limited host range and geographical distribution, and E. carotovora subsp. carotovora showed great molecular diversity, spreading respectively across five and 19 RFLP groups. These two subspecies shared RFLP groups 4, 5 and 6. The tree nodes in the phenograms showed a low robustness when bootstrapping the data matrix. PCR coupled with a 48h enrichment step in a polypectate-rich medium improved detection thresholds of E. carotovora subsp. atroseptica (1.5.10²- 1.5.10³ bacteria/ml in leaves, stems, and tuber peel extracts to 4.10⁷ bacteria/ml in wash water) relative to either immunomagnetic separation coupled with PCR or DAS-ELISA (2.10⁵ in plant samples to 2.10⁷ bacteria/ml in wash water).     

Phenotypic and genetic characterization of Erwinia carotovora from mulberry (Morus spp.)

Phenotypic and genetic characteristics of nine bacterial strains isolated from mulberry ( Morus spp.), which were originally described as Erwinia carotovora ssp. carotovora (Ecc), were investigated. Based on the results of biochemical tests, these bacterial strains were divided into two different types, type 1 and type 2. Two strains of type 1 were similar to Ecc, whereas seven strains of type 2 were distinct from Ecc. A polyphasic study that included serological assay, specific PCR assay for E. carotovora ssp. atroseptica (Eca), PCR-RFLP of a pectate lyase ( pel ) gene and RAPD-PCR was performed on the type 2 strains, and the data were compared with those of related E. carotovora subspecies. The results of serological and specific PCR assays for Eca showed that the type 2 strains were distinct from Eca. In RFLP analysis of the pel gene using Sau 3AI, the type 2 strains showed a unique RFLP pattern. On the basis of RAPD analysis, similarity of RAPD patterns within the type 2 strains was very high. A unique RAPD fragment was isolated from the type 2 strains and used as a probe for Southern hybridization. This probe hybridized only with PCR products from the type 2 strains. Based on phenotypic, serological and genetic characteristics, the type 2 strains isolated from mulberry may belong to a distinct E. carotovora subspecies other than Eca or Ecc.     

Biocontrol of Phytophthora Root Rot of Angelica Trees by Enterobacter cloacae and Serratia ficaria Strains

Bacterial strains isolated from the rhizosphere of angelica trees were evaluated for their antagonistic activity against Phytophthora cactorum, a causal agent of Phytophthora root rot. Of these, three bacterial strains, designated as T-1-8, T-1-14 and T-1-23, strongly inhibited mycelial growth of P. cactorum ARE-862 in a dual-culture plate assay. Biocontrol activity of these strains was then examined by dipping root of young seedlings of angelica trees into a bacterial suspension. The incidence of Phytophthora root rot was markedly suppressed for at least 79 days in pot tests when treated seedlings were planted in naturally infested soil. The suppression was maintained through June of the next year. In addition, these strains significantly reduced the development of Phytophthora root rot up to 47 days in naturally infested field and up to 63 days (the last day of testing) in an artificially (moderately) infested field. Based on their main bacteriological properties, strain T-1-14 was identified as Enterobacter cloacae and T-1-8 and T-1-23 were identified as Serratia ficaria. Received 5 July 1999/ Accepted in revised form 25 October 1999     

Trichoderma Biocontrol of Colletotrichum acutatum and Botrytis cinerea and Survival in Strawberry

Trichoderma isolates are known for their ability to control plant pathogens. It has been shown that various isolates of Trichoderma, including T. harzianum isolate T-39 from the commercial biological control product TRICHODEX, were effective in controlling anthracnose (Colletotrichum acutatum) and grey mould (Botrytis cinerea) in strawberry, under controlled and greenhouse conditions. Three selected Trichoderma strains, namely T-39, T-161 and T-166, were evaluated in large-scale experiments using different timing application and dosage rates for reduction of strawberry anthracnose and grey mould. All possible combinations of single, double or triple mixtures of Trichoderma strains, applied at 0.4% and 0.8% concentrations, and at 7 or 10 day intervals, resulted in reduction of anthracnose severity; the higher concentration (0.8%) was superior in control whether used with single isolates or as a result of combined application of two isolates, each at 0.4%. Only a few treatments resulted in significant control of grey mould. Isolates T-39 applied at 0.4% at 2 day intervals, T-166 at 0.4%, or T-161 combined with T-39 at 0.4% were as effective as the chemical fungicide fenhexamide. The survival dynamics of populations of the Trichoderma isolates (T-39, T-105, T-161 and T-166) applied separately was determined by dilution plating and isolates in the mixtures calculated according to the polymerase chain reaction (PCR) using repeat motif primers. The biocontrol isolates were identified to the respective species T. harzianum (T-39), T. hamatum (T-105), T. atroviride (T-161) and T. longibrachiatum (T-166), according to internal transcribed spacer sequence analysis.     

胡萝卜软腐欧氏杆菌胡萝卜亚种游动性突变体的筛选

 用转座子Tn5对胡萝卜软腐欧氏杆菌胡萝卜亚种(Erwinia carotovora subsp.carotovora,Ecc)进行诱变,获得9个游动性改变了的突变体。M432游动性变大;M143、M451和M574游动性完全丧失;M43、M49、M330、M725和M726游动性较野生型变小。这9个突变体在大白菜叶柄上的致病力均减弱。游动性变小或丧失的突变体鞭毛数目减少或未发现有鞭毛。     

彩色马蹄莲欧文氏菌PCR检测

采用聚合酶链式反应(PCR)技术检测彩色马蹄莲欧文氏菌纯培养和彩色马蹄莲样品,并用分离培养技术加以验证。结果表明,PCR能特异地检测出所有10个彩色马蹄莲欧文氏菌菌株,并证实了昆明地区侵染彩色马蹄莲的细菌为胡萝卜软腐欧文氏菌(Erwiniacarotovora subsp.carotovora)。PCR与分离培养技术检测结果基本一致,但总体上PCR检测阳性率稍高于分离培养检测的发病率。接种马铃薯、大白菜24h后接种点处均出现明显软腐症状。该项技术具有更高的灵敏度,适用于彩色马蹄莲种苗的检测和病害流行学研究。     

天山野果林塞威士苹果和短距凤仙花叶斑病病原真菌的鉴定

为了解新疆天山野果林中塞威士苹果Malus sieversii与其林下伴生植物短距凤仙花Impatiens brachycentra两种植物叶斑病病原菌的多样性及同源性,采用组织分离法获得病原菌,基于rDNA-ITS序列构建系统发育树,并进行ITS序列BLAST同源性比对,对病原菌进行鉴定分类,并依据科赫氏法则测定致病性。结果显示,从新疆新源县天山野果林中的塞威士苹果及短距凤仙花病叶上共分离得到18株菌落形态各异的病原菌,分属于2属4种,绝大多数属于半知菌亚门。其中,链格孢属Alternaria sp.为塞威士苹果和短距凤仙花叶斑病病原真菌中的优势菌群。致病性测定结果显示,其中11株病原真菌对塞威士苹果具有致病性,7株病原真菌对短距凤仙花具有致病性;塞威士苹果所有的病原真菌对短距凤仙花均有致病性,而且短距凤仙花所有的病原真菌对塞威士苹果也有致病性。推测2种植物叶斑病可能由相同来源的病原真菌引发,短距凤仙花染病加剧了塞威士苹果叶斑病暴发,可能是野果林退化的重要原因。     

A potato wilt disease in South Africa caused by Erwinia carotovora subspecies carotovora and E. chrysanthemi

In South Africa during the 1988 season, a wilt disease appeared in seed-potato crops. The disease was initially characterized by a one-sided wilt of the upper leaves, and in its advanced stage was indistinguishable from verticillium, fusarium and pseudomonas wilts. A basal stem rot was occasionally associated with wilted plants when wet, humid conditions prevailed. Erwinia carotovora ssp. carotovora and E. chrysanthemi were isolated from wilted plants, but E. carotovora ssp. carotovora was the predominant pathogen. Stem inoculations in the glasshouse showed that both pathogens were capable of causing wilt symptoms. An indication was found that E. chrysanthemi was more virulent at a higher temperature range (28-32°C) and E. carotovora ssp. carotovora at a lower temperature range (20-25°C). It was found that the potting compost, irrigation water and some parent tubers used for the propagation of plantlets at the Foundation Seed Scheme, Eastern Transvaal, were contaminated with E. carotovora ssp. carotovora.     

宁夏葡萄霜霉病菌致病型鉴定及葡萄品种抗性评价

为合理利用葡萄抗性品种以及田间病害综合治理,采用离体叶盘接种法分别对2018年和2019年自宁夏回族自治区银川市、石嘴山市和吴忠市采集的43株葡萄霜霉病菌Plasmopara viticola菌株进行致病型鉴定及聚类分析,并对17个主栽葡萄品种进行抗性评价及聚类分析。结果表明：2018、2019年供试菌株致病力和供试葡萄品种抗性之间均存在显著差异,菌株平均病情指数与发病率呈显著正相关,皮尔逊相关系数r和回归系数R²分别介于0.45~0.96和0.20~0.92之间;2018、2019年供试菌株的强致病力菌株和弱致病力菌株分别为CS-YL和VI-BYDD、RG-JSJG和CS-YM;2018年和2019年供试菌株致病型被划分为强、中、弱3种类群,2年所占比例分别为10.00%、15.00%、75.00%和34.78%、39.13%、26.09%;供试17个葡萄品种的抗性类型可被划分为感病、抗病、高抗3种类群,2年所占比例均为17.65%、29.41%和52.94%。不同葡萄品种对不同菌株的抗性类型多样化。表明宁夏回族自治区葡萄霜霉病菌菌株致病力分化明显,不同菌株的致病型与其地域来源无关,不同葡萄品种的抗感程度不同。     

Prediction of Heteranthera reniformis competition with flooded rice using day–degrees

In field studies carried out in 1992 and 1993, several durations of growth of Heteranthera reniformis Ruitz et Pavon were established in flooded rice (Oryza sativa L.) to evaluate weed influence on crop yield using day-degree predictive models for weed growth. H. reniformis was allowed to emerge at 7-day intervals from rice emergence until 49 days later. Weeds that emerged with the rice accumulated 403 day-degrees during the first 49 days. Weeds allowed to utilize 308 day-degrees had a dry weight reduction of 20% compared with plants that emerged with the rice. With the loss of all 403 day-degrees dry weight was reduced by about 95%. Maximum leaf area index (LAI) was 2.8, reached at 308 day-degrees. Weed density ranged from 48 to 5 plants m^-2 when all 403 day-degrees were accumulated or lost by the plant respectively. When the weed lost only 95 day-degrees out of the possible 403 (1 week's delay in emergence) rice yield was 34% and 39% lower in 1992 and 1993 respectively. When the weed was allowed to accumulate ail 403 day-degrees yield reduction reached 62% in 1992 and 68% in 1993, very similar to the control plot, which were maintained weedy throughout (64% and 70.5%). After an accumulation of 403 day-degrees the weed reduced the number of rice panicles by 45% in 1992 and 38% in 1993.     

Evaluation of pathogenicity and aggressiveness of <Emphasis Type="Italic">F. langsethiae</Emphasis> on oat and wheat seedlings relative to known seedling blight pathogens

Fusarium and Microdochium species are causal agents of seedling blight of small-grain cereal crops where they may contribute to a significant reduction in crop establishment and final yield. Two experiments were carried out to investigate the potential pathogenicity and aggressiveness of F. langsethiae, a recently identified fungus linked with the contamination of cereals with high levels of the trichothecene mycotoxins, HT-2 and T-2. An artificial seed inoculation method involving conidial suspensions was used and the experiments conducted in a growth cabinet set at either 5 or 15°C with a 12 h photoperiod. Known seedling blight pathogens of the genus Fusarium and Microdochium were used for comparison. At 15oC, F. culmorum, M. nivale and M. majus caused seedling blight of oats and wheat with F. culmorum, on average being the most aggressive than the latter two. At 5oC, only F. culmorum and M. nivale caused seedling blight of oats and wheat. Under the experimental conditions employed, F. langsethiae and F. poae failed to produce seedling blight disease indicating that these two species are not pathogenic to oat and wheat cultivars, Gerald and Claire respectively, at the seedling stage of development. They are therefore unlikely to affect crop establishment and other yield components such as tiller number, grain yield per head as well as grain weight if there is no subsequent foot-rot and/or head blight where infected seeds are sown.     

Enzymatic Maceration of Witloof Chicory by the Soft Rot Bacteria Erwinia carotovora Subsp. carotovora: The Effect of Nitrogen and Calcium Treatments of the Plant on Pectic Enzyme Production and Disease Development

Disease incidence of bacterial soft rot caused by Erwinia carotovora subsp. carotovora and activities of bacterial pectolytic enzymes were studied in witloof chicory. Disease incidence after forcing of the chicory heads was enhanced by the nitrogen treatment and reduced by the calcium treatment of the chicory plants prior to forcing. Significant differences in susceptibility to bacterial soft rot were found for the tested chicory cultivars. Disease severity after 96h ranged from 6% in Clause R2 to 100% in Bea and Tabor. Chicory cultivars Rumba and Salsa showed a final average severity of 65–70%. Activity of the pectolytic enzymes, polygalacturonase and pectate lyase increased in artificially inoculated chicory heads of cultivar Rumba and was not affected by calcium and nitrogen treatments of the plants. Polygalacturonase showed highest activity 48h after inoculation while pectate lyase activity increased throughout 72h of incubation. Maceration of the chicory tissue and bacterial growth increased continuously until 96h after inoculation, when more than 60% of the chicory heads was macerated by pectolytic enzymes of the bacteria. Enzyme activity of Erwinia carotovora subsp. carotovora grown on chicory cell wall extracts was influenced by nitrogen and calcium treatments of the chicory plants. The activity of polygalacturonase reached its highest level at 48h after incubation and pectate lyase activity peaked at 24h followed by a continuous decrease until 72h after inoculation.     

Pathogenicity and aggressiveness in populations of <Emphasis Type="Italic">Pseudomonas syringae</Emphasis> from Belgian fruit orchards

The pathogenicity of 99 Belgian Pseudomonas syringae strains representative of the genetic diversity encountered in Belgian fruit orchards was evaluated by using 17 pathogenicity tests conducted on pear, cherry, plum, lilac, sugar beet and wheat. The P. syringae pv. morsprunorum strains were pathogenic to stone fruit species but the race 1 strains possessing the cfl gene involved in coronatine production were pathogenic in more tests than those lacking the gene. Also, sweet cherry twigs were a better material to detect pathogenic strains of race 1 and sour cherry twigs of race 2, which accorded with race 2 presence in sour cherry orchards in Belgium. Three groups were defined in the pv. syringae based on pathogenicity. One group pathogenic in 71.1% of the tests and to lilac included toxic lipodesipeptide-producing (TLP+) strains. The second group pathogenic in 26.8% of the tests and non-pathogenic to lilac included TLP+ strains. The thirth group pathogenic in 9.1% of the tests and almost specifically pathogenic to pear included TLP− strains. The three groups were genetically heterogeneous. Although strain-host relationships were noted within the pv. syringae, aptata and atrofaciens when considering the strain origins, such relationships were not found in the pathogenicity tests, suggesting that pathogenicity tests could probably not reproduce all the aspects of the host-pathogen interactions. None of the pathogenicity tests was able to provide all the information provided by the complete study. A test on pear buds indicated that strains different from the pv. syringae were pathogenic to pear.     

Methods for assessing the susceptibility of potato tubers of different cultivars to rotting by Erwinia carotovora subspecies atroseptica and carotovora

The susceptibility of tubers of different potato cultivars to soft rot by Erwinia carotovora subspp. uroseptica and carotovora was assessed in 3 years by two methods. In one method, whole tubers inoculated at wounds with either bacterium were incubated under anaerobic conditions for 5 or o days at 15°C. In the other method, wounds made in tuber slices were allowed to heal or not, before inoculation with different concentrations of each bacterium and were then incubated under aerobic conditions for 3 days at 15°C. Most cultivars gave consistent reactions in repeated experiments using the same method, but there was some seasonal variation. A few cultivars were consistently susceptible (Klondyke and Manna) or resistant (Drayton) in both methods but others gave completely contrasting results (Record). In both methods and with all cultivars more rotting was caused by subsp. atroseptica than by subsp. carotovora because of the temperature of Incubation.     

Non‐pathogenic rhizosphere bacteria belonging to the genera Rhizorhapis and Sphingobium provide specific control of lettuce corky root disease caused by species of the same bacterial genera

Lettuce corky root (CR) is caused by bacteria in the genera Rhizorhapis, Sphingobium, Sphingopyxis and Rhizorhabdus of the family Sphingomonadaceae. Members of this family are common rhizosphere bacteria, some pathogenic to lettuce. Sixty‐eight non‐pathogenic isolates of bacteria obtained from lettuce roots were tested for control of CR caused by Rhizorhapis suberifaciens CA1^T and FL1, and Sphingobium mellinum WI4^T. In two initial screenings, 10 isolates significantly reduced CR induced by one or more pathogenic strains on lettuce seedlings in vermiculite, while seven non‐pathogenic isolates provided significant CR control in natural or sterilized field soil. Rhizorhapis suberifaciens FL11 was effective at controlling all pathogenic strains, but most effective against R. suberifaciens CA1^T. The other selected isolates controlled only pathogenic strains belonging to their own genus. In a greenhouse experiment, a soil drench with selected biocontrol agents (R. suberifaciens FL11, Sphingomonas sp. NY3 and S. mellinum CA16) controlled CR better than seed treatments or application of alginate pellets. In microplots infested with R. suberifaciens CA1^T, seed treatment with R. suberifaciens FL11 provided complete control and a soil drench with FL11 significantly reduced the disease. Pathogenicity tests with FL11 on 23 plant species in 10 families resulted in slight yellowing on roots of lettuce and close relatives; similar yellowing appeared on some roots of non‐inoculated lettuce plants. This research showed that biocontrol agents can be genus‐specific. Only one isolate, FL11, provided more general control of various pathogenic strains causing CR even in field soil in pots and microplots.     

土壤拮抗放线菌的分离及其抗菌活性筛选

以常见植物病原真菌和细菌为指示菌,从分离的422株放线菌中筛选出28株可代谢抗细菌活性物质的菌株,其中N331、N393菌株发酵液对供试12种真菌有显著的抑制作用。离体条件下,N331、N393菌株发酵液对供试真菌菌丝生长的抑制中浓度(EC50)均小于15 mL/L;对玉米弯孢病菌、棉花枯萎病菌、小麦根腐病菌、黄瓜霜霉病菌孢子萌发的EC₅₀亦小于15 mL/L。盆栽试验结果表明,N331、N393菌株发酵原液对黄瓜霜霉病的保护效果分别为97.4%和85.6%,治疗效果分别为83.3%和59.3%。     

Biofilm formation and motility of Xanthomonas strains with different citrus host range

Xanthomonas citri subsp. citri (Xcc) strain A is the causal agent of citrus bacterial canker (CBC) on most Citrus spp. and close relatives. Two restricted host range strains of CBC, A^w and A*, from Florida and southwest Asia, respectively, infect Mexican lime. Several studies have linked biofilm formation by Xcc to bacterial colonization prior to and after plant ingress, but none have evaluated connections between biofilm formation and the behaviour of different strains of Xcc on citrus hosts and non‐hosts. In this study biofilm formation and swimming motility were evaluated for citrus pathogenic xanthomonads including wide and restricted host range strains of Xcc, X. alfalfae subsp. citrumelonis (Xac) (the causal agent of citrus bacterial spot) and X. campestris pv. campestris (Xc). Differential biofilm formation was observed in vitro and in planta among the Xanthomonas strains assayed. Minimal medium XVM2 increased biofilm formation, especially for those strains with a host range restricted to Mexican lime. In planta, strains produced more biofilm on leaves or fruits of their host than on non‐hosts. Scanning electron microscopy of biofilms on leaf and fruit surfaces revealed differences in structure of bacterial aggregates with respect to the strain's host range. In addition, swimming motility varied widely depending on the host range of the strain. It was concluded that biofilm formation in vitro and in planta for strains of Xcc and Xac was related to their host range, as these processes affect colonization at the early stages of the infection process.     

Relationship between aggressiveness of <Emphasis Type="Italic">Stagonospora </Emphasis>sp. isolates on field and hedge bindweeds,and <Emphasis Type="Italic">in vitro</Emphasis> production of fungal metabolites cercosporin,elsinochrome A and leptosphaerodione

Stagonospora convolvuli LA39, an effective biocontrol agent of Convolvulus arvensis (field bindweed) and Calystegia sepium (hedge bindweed) produces phytotoxic metabolites leptosphaerodione and elsinochrome A. Stagonospora isolate 214Caa produces the toxin cercosporin. If toxic metabolite production is not linked to the pathogenic ability of the fungus on bindweeds, selection of aggressive strains with limited or no production of the metabolites would reduce any perceived risk of using strains of the fungus as a mycoherbicide. Therefore, 30 isolates of Stagonospora sp. including LA39 and 214Caa were characterised for aggressiveness on both bindweeds, and production of the three metabolites. Nine isolates were more aggressive than LA39 on both bindweeds. Classification of isolates based on metabolite type agreed largely with previous similar characterisation based on polymerase chain reaction-restriction fragment length polymorphism of internal transcribed spacer of ribosomal DNA. Cercosporin producers produced neither leptosphaerodione nor elsinochrome A and together with isolates that produce none of the three metabolites, were less pathogenic on bindweeds. Conversely, there was a positive correlation between elsinochrome A and leptosphaerodione production, and each was positively correlated with aggressiveness of isolates on both bindweeds. Generally, any isolate where elsinochrome A was not detected was not aggressive on any of the two bindweeds. This probably implies that selecting elsinochrome A-negative, but aggressive Stagonospora strain(s) may be difficult. However, aggressive isolates may not produce elsinochrome A in planta at levels that could constitute any risk in the environment. In a preliminary attempt to determine the levels of elsinochrome A and leptosphaerodione produced in diseased bindweeds, none of the toxins was detected in Stagonospora infected bindweed leaves. Detailed investigation focusing on the detection and quantification of in planta production of elsinochrome A by Stagonospora isolates, and determination of the fate of elsinochrome A in the environment, and its relationship with leptosphaerodione may be essential. Similarly, development of molecular tools to monitor the mycoherbicide following field application is vital.     

采用16S rDNA鉴定甜瓜细菌性叶斑病菌

从甘肃河西、新疆阿勒泰甜瓜上分离获得的2株致病细菌,通过16S rDNA序列测定以及序列同源性比较,结合病原菌落培养性状、菌体形态观察和革兰氏染色反应等,初步确定当地甜瓜细菌性叶斑病菌为丁香假单胞杆菌[Pseudomonas syringae pv.lachrymans (Smith et Bryan) Young et al.]