广东省马铃薯块茎软腐病病原菌鉴定

为明确广东省惠州市马铃薯块茎软腐病的病原菌,采用常规病组织分离法获得4株菌株,通过生理生化特征和分子生物学特性对其进行鉴定,并测定了该病原菌对20个马铃薯品种的致病力。结果显示,该病原菌为革兰氏阳性菌,在LB平板上菌落有透明和不透明2种形态;除葡萄糖发酵阳性、对链霉素和青霉素具有抗性等特征不同外,BP-hd-1、BP-hd-2、BP-hd-3和BP-hd-4菌株与短小芽胞杆菌Bacillus pumilus菌株的其它生理生化特征均相同。系统进化分析结果表明,4株菌株的16S rDNA序列分别与短小芽胞杆菌AI-Khrj18(KY123871)、ML270(KC692158)、NCTC10337(LT906438)和ARD21(KX023236)的相似性为100.0%;4株菌株的gyrB基因序列均与短小芽胞杆菌AUEC29菌株(HM585095)的gyrB基因相似性最高,为99.7%～99.8%。生理生化特征及分子生物学鉴定结果表明,引起广东省马铃薯块茎软腐病的病原菌为短小芽胞杆菌。致病力测定结果显示,接种菌株BP-1后20个马铃薯品种的发病率均为100.0%,表明该病原菌对马铃薯有强致病力。     

蔬菜细菌性软腐病防治药剂活体组织筛选技术

为探索快速、高效的蔬菜细菌性软腐病防治药剂的筛选技术,采用多因素分析法对茎段材料、接种方式、菌液浓度等因素进行筛选,建立芹菜茎段筛选技术,并采用所建立的筛选法评价28种枯草芽胞杆菌Bacillus subtilis可湿性粉剂对细菌性软腐病菌的杀菌活性。结果表明,建立的芹菜茎段筛选法可较好地评价细菌性软腐病防治药剂的药效,即芹菜茎段一端在细菌性软腐菌液中浸泡20 min后自然风干,再于待测药剂中浸泡处理1 h,在温度26~30℃、相对湿度70%~85%条件下保湿培养36 h后调查发病指数。采用该方法可快速从23种新型枯草芽胞杆菌可湿性粉剂中筛选出对细菌性软腐病具有较高防效的IVF001、IVF002、IVF004、IVF015、IVF018、IVF021、IVF035、IVF041制剂,防效分别为81.70%、94.77%、83.01%、92.16%、84.31%、96.08%、80.39%和89.55%。芹菜茎段筛选法及室内盆栽法对5种已登记的枯草芽胞杆菌可湿性粉剂的筛选结果显著相关,相关系数为0.878。表明芹菜茎段筛选法可以有效代替盆栽筛选法,并对杀菌剂的药效进行评价,是一种实用性强的蔬菜细菌性软腐病防治药剂筛选方法。     

Development of Stem-base Pathogens on Different Cultivars of Winter Wheat Determined by Quantitative PCR

The progress of development of stem-base pathogens in crops of second winter wheat was plotted in nine experiments in three years. The amount of each pathogen present was determined by quantitative PCR. Where Tapesia yallundae was present in quantifiable amounts, it usually developed earlier than the other eyespot pathogen, T. acuformis. Both species were usually present in greater amounts on cultivars which are more susceptible to eyespot. The sharp eyespot pathogen, Rhizoctonia cerealis, developed more erratically than either of the Tapesia spp. and there were no consistent effects on different cultivars. Fusarium spp., the cause of brown foot rot, were rarely present in quantifiable amounts, but Microdochium nivale was usually present as one or both of the varieties nivale and majus. Late-season (after anthesis) decreases in M. nivale suggest that any brown foot rot symptoms attributable to this fungus would have fully developed earlier. Cultivar differences in amounts of M. nivale were most clear in stems during internode extension and when relatively large amounts of DNA were present. Such differences approximately reflected eyespot susceptibility, cv. Soissons containing most and cv. Lynx containing least DNA. The results emphasise the difficulty in relating diagnoses, by quantitative PCR or other means, at early growth stages when decisions to apply fungicides against stem-base disease are made, to later disease severity.     

陕西省小麦茎基腐病病原菌鉴定及其致病力分析

为明确陕西省小麦茎基腐病病原菌的组成及其致病力,于2019年小麦灌浆期在陕西省宝鸡市、咸阳市、西安市和渭南市共63个采样点采集具有茎基腐病典型症状的病株,对其进行组织分离,结合培养性状和形态学特征,以及利用ITS和EF-1α序列分析鉴定分离菌株所属类群,并对不同病原菌进行致病力分析。结果表明：共分离到224株菌株,基于形态学特征和分子生物学鉴定结果,其中201株菌株鉴定为假禾谷镰刀菌Fusarium pseudograminearum,3株菌株鉴定为禾谷镰刀菌F. graminearum,14株菌株鉴定为三线镰刀菌F. tricinctum,6株菌株鉴定为层出镰刀菌F. proliferatum,其中假禾谷镰刀菌占总分离菌株的89.73%,是陕西省小麦茎基腐病的优势病原菌。不同种的镰刀菌对小麦植株均有一定的致病性,但假禾谷镰刀菌的致病力最强,而且分离自不同地区或者同一地区的假禾谷镰刀菌株间的致病力也存在一定分化。     

Quorum sensing as a target for developing control strategies for the plant pathogen <Emphasis Type="Italic">Pectobacterium</Emphasis>

Quorum sensing is a regulatory mechanism that connects gene expression to cell density in bacteria. Amongst proteobacteria, numerous functions are regulated in this way, including pathogenicity in the Enterobacteriaceae genus Pectobacterium. In Pectobacterium, the signalling molecules involved in this regulatory process belong to the N-acyl-homoserine lactone class. Over the last 6 years, various studies have shown that these signal molecules could be degraded by other bacteria or by plant and animal cells, opening the path to innovative biocontrol strategies. This review explores the various determinants of pathogenicity in Pectobacterium and describes approaches that have been developed to quench the quorum-sensing-dependent pathogenicity in Pectobacterium. These approaches range from signal degradation by physicochemical constraints to the identification of signal-sensing inhibitors and from the identification of enzymes degrading acyl-homoserine lactones to the construction of transgenic plants tolerant to Pectobacterium.     

猕猴桃软腐病病原菌的分离鉴定及其防治药剂筛选

为明确引起猕猴桃软腐病病原菌的种类并筛选有效防治药剂,2015年10月于安徽省金寨县猕猴桃基地采集具有典型软腐病症状的40个果实病样,对分离所得病原菌进行致病性测定、形态学和分子生物学鉴定,同时测定了10种常用药剂对病原菌的抑菌效果。结果显示,结合分离物的形态学特征及rDNA-ITS、β-tubulin和EF-1α基因序列分析结果,确定10株经致病性验证的菌株均为葡萄座腔菌Botryosphaeria dothidea。药剂筛选结果显示,多菌灵对该病原菌菌丝生长抑制效果最好,抑制率高达91.97%,其次是95%三唑醇1 600倍液,抑制率为81.72%,其余药剂对菌丝生长的抑制率均低于80.00%;多粘芽胞杆菌对该病原菌孢子萌发抑制效果最好,未见该病菌孢子萌发,70%代森锰锌可湿性粉剂1 000倍液、12.5%烯唑醇可湿性粉剂3 000倍夜、10%混合脂肪酸水剂100倍液、95%三唑醇原药1 600倍液和1.8%辛菌胺醋酸盐水剂180倍液对病原菌孢子萌发的抑制率均大于81.00%。表明多菌灵和多粘芽胞杆菌是防治葡萄座腔菌菌丝生长和孢子萌发的最佳药剂。     

In Planta - Complementation of Clavibacter Michiganensis Subsp. sepedonicus Strains Deficient in Cellulase Production or HR Induction Restores Virulence

Clavibacter michiganensis subsp. sepedonicus, a Gram positive bacterium that causes bacterial ring rot of potato, was studied in eggplant, an alternate host, using strains that differed in phenotype. Two factors affecting virulence, the ability to induce a hypersensitive response (HR) and cellulase production, were studied. A plasmid-free isolate of C. michiganensis subsp. sepedonicus that causes HR on tobacco but is unable to produce cellulase multiplied efficiently in planta, but caused only weak symptoms. In contrast, a strain that is unable to induce HR on tobacco but produces cellulase was impaired in the ability to multiply in the host and caused no symptoms. When the two non-virulent strains were coinoculated into eggplants, typical disease symptoms developed. This enhancement was not due to formation of a new phenotype or significant increases in population density of either of the strains. Our results suggest that both cellulase production and the ability to induce HR are required for a successful infection process and disease induction by C. michiganensis subsp. sepedonicus. Our results additionally suggest that the ability to induce HR on non-host plants is required for multiplication in the host plant, whereas cellulase expression is necessary for induction of disease symptoms.     

Bacterial leaf and peduncle soft rot caused byPectobacterium carotovorum on tulips in Konya, Turkey

The etiology of a new soft rot disease of tulips, causing leaf spots, leaf blight, neck and bulb rot in Konya, Turkey, was investigated. This disease occurred in tulip fields grown for seed bulbs of various varieties in 2002. Bacteria were isolated from the lesions on leaf, bud neck and bulbs and the causal bacterium was identified asPectobacterium carotovorum on the basis of biochemical and physiological tests. Cells were Gram-negative, rod-shaped, fermentative, potato-rot positive. Colonies were capable of growth at 37°C. On nutrient agar the colonies were creamy-white. The isolates were non-fluorescent on King’s B medium, positive for acetoin production, gelatin liquefaction, acid-production-from-lactose, and catalase; and negative for gas from glucose, reducing substances from sucrose, and phosphatase activity. Additionally, tests for egg yolk (lecithin), sensitivity to erythromycin, and pigmentation on yeast dextrose carbonate agar were negative; growth on 5% sodium chloride was positive. All the bacterial isolates obtained from the leaf, bud neck and bulbs produced the original symptoms following inoculation to the susceptible tulip variety ‘Gander’. The rate of damage caused by this bacterium was evaluated on several tulip varieties under field and storage conditions. Gander was the most susceptible variety in the field whereas ‘Salmon Parrot’ exhibited the highest rate of bulb rot in storage. Disease severity was lower in 2003 than 2002. http://www.phytoparasitica.org posting May 14, 2006.     

白头翁菌核病发生危害调查及其病原菌生物学特性

为明确辽宁省白头翁菌核病发生危害情况及其病原菌生物学特性,于2011—2013年对该省3个白头翁种植基地进行菌核病调查,并采用平板培养法和离体接种法对白头翁菌核病菌Sclerotinia nivalis Saito进行生物学特性研究和致病性测定。结果表明,白头翁菌核病在各种植基地发生程度不一,抚顺市白头翁发病较重,2013年一般地块病株率为0~37.1%,重者达60.4%,本溪市和沈阳市发病相对较轻,病株率分别为1.3%~10.0%和0~3.0%;随着白头翁栽培年限的增加,菌核病危害逐渐加重,1~4年生白头翁的病株率分别为0、12.3%、37.1%和60.4%;坡地沿山体横垄栽植较纵垄栽植发病重。白头翁菌核病菌在PDA培养基上生长最好,菌丝生长速度和菌核形成数分别为10.4 mm/d和101.0个/皿;菌丝生长和菌核形成的最适温度分别为20℃和15℃,最适pH均为6;连续光照和连续黑暗利于菌丝生长,光照条件下菌核形成最多;碳、氮源对菌丝生长和菌核形成的影响较大,菌丝生长最适碳源为果糖、葡萄糖和蔗糖,以尿素作氮源抑制该菌生长。伤口有利于该病的发生发展,刺伤接种较未刺伤接种发病早,接种3 d后开始发病,6 d后即达高峰期。     

青海省青稞根腐病调查及病原菌鉴定

为明确青海省青稞根腐病发生情况及其病原菌,于2016年6—9月对青海省海北藏族自治州海晏县、刚察县,海东市互助土族自治县苗期及成株期青稞上根腐病发生情况进行调查,采集19份根腐病样品,采用常规组织分离法对样品进行分离,并对分离菌株进行致病性测定,通过形态学特征及分子生物学方法对其进行鉴定。结果显示,青海省青稞根腐病分布广泛,发病率较高,为10%～20%;发病植株长势弱、发黄,茎基部缢缩腐烂,穗白粒瘪,茎秆发褐或黑红;19份样品中共分离纯化得到93株病原菌菌株,其中73株为燕麦镰孢Fusarium avenaceum,9株为木贼镰孢F. equiseti,11株为锐顶镰孢F. acuminatum;木贼镰孢的绝对病情指数最强,为79.43,燕麦镰孢次之,为50.90,锐顶镰孢最弱,为23.70,各病原种间及种内致病性差异显著。根据分离率及各病原菌致病性综合确定燕麦镰孢为青海省青稞根腐病的优势病原菌。     

A Survey of Trunk Disease Pathogens within Rootstocks of Grapevines in Spain

Grapevine trunk disease pathogens, and specifically Petri disease pathogens, can be spread by planting infected plants. Due to the increasing incidence of Petri disease and other young grapevine declines reported lately in Spain, a sampling of plants used before for new vineyards were carried out in 2002 and 2004. A total number of 208 plants (grafted and non grafted) were collected, of which 94 plants (45.2%) were infected with at least one of the following pathogens: Phaeomoniella chlamydospora, and species of Phaeoacremonium, Botryosphaeria, Cylindrocarpon, and Phomopsis. Species of the genera Phaeoacremonium and Botryosphaeria isolated in 2004 were identified using morphological and molecular characters. Species of Phaeoacremonium identified were P. aleophilum and P. parasiticum; and those of Botryosphaeria were B. obtusa, B. dothidea and B. parva. This is the first report of P. parasiticum and B. parva occurring on grapevines in Spain. Distribution of pathogens within the plants was studied in 2004. Phaeomoniella chlamydospora was not detected in the graft union of any plant; however, species of Botryosphaeria and Phomopsis were detected along the plant, but mainly in the graft union; Phaeoacremonium aleophilum was detected along the grafted plants, but not in rooted rootstocks. The results suggest that infected plants used for new plantings in Spain are an important source of primary inoculum of the pathogens associated with grapevine trunk diseases in the field.     

Durability of natural and transgenic resistances in rice to <Emphasis Type="Italic">Rice yellow mottle virus</Emphasis>

A monogenic recessive resistance to Rice yellow mottle virus (RYMV) found in the Oryza sativa indica cultivar Gigante and in a few Oryza glaberrima cultivars provided a higher level of resistance than either a polygenic partial resistance found in some japonica cultivars which delayed symptom expression or transgenic resistances which were partial and temporary. This high resistance was overcome by several isolates, but the percentage of such virulent isolates in the fields was low. There was no relationship between the virulence of an isolate towards the high resistance and its aggressiveness in other cultivars. Isolates with either of the two components of pathogenicity – virulence and aggressiveness – were found in each strain and in all regions of Africa, in both wild and cultivated grass species. There was no loss of fitness of resistance-breaking (RB) isolates as they were not counter-selected, impaired or outperformed after serial passages in susceptible cultivars, even in mixture with avirulent quasi-isogenic wild type isolates. Resistance breaking was highly dependent on the amount of virus inoculated and on the mode of transmission. Implications of these results for the durability of the resistances to RYMV and for the development of integrated disease management strategies are discussed.     

海南省芒果可可球二孢对多菌灵的敏感性及菌株适合度研究

针对中国海南地区芒果蒂腐病致病菌可可球二孢对多菌灵的抗性水平及菌株的适合度进行了研究。采用区分剂量法,测定了2016年从海南省芒果园采集、分离的90株可可球二孢对多菌灵的敏感性,并对抗性及敏感菌株在菌丝生长、致病力、渗透压及相对渗率等方面进行了比较。结果表明:海南地区芒果可可球二孢对多菌灵的抗性频率为65.56%,且以高抗菌株为主（8个中抗菌株,51个高抗菌株）;该病菌对芒果危害甚大,其中具强致病力的菌株达65株,占72.22%。高抗菌株的菌丝生长优于敏感菌株,存在极显著差异（P0.01）;抗性菌株的致病力与敏感菌株无显著差异;敏感菌株的相对渗率高于抗性菌株,表明敏感菌株细胞膜的透性较高,胞内电解质渗出较多。研究表明,海南地区芒果可可球二孢对多菌灵的抗性水平较高,且抗性菌株适合度高于敏感菌株,易形成优势群体。     

Characterization of <Emphasis Type="Italic">Dickeya</Emphasis> strains isolated from potato and river water samples in Finland

Plant pathogenic enterobacteria in the genera Pectobacterium and Dickeya (formerly classified as Erwinia) were isolated from diseased potato stems and tubers. The isolated bacteria were identified as P. atrosepticum, P. carotovorum and pathogens in the genus Dickeya with PCR tests. Furthermore, Dickeya strains were isolated from river water samples throughout the country. Phylogenetic analysis with 16S-23S rDNA intergenic spacer sequences suggested that the Dickeya strains could be divided into three groups, two of which were isolated from potato samples. Phylogenetic analysis with 16S rDNA sequences and growth at 39°C suggested that one of the groups corresponds to D. dianthicola, a quarantine pathogen in greenhouse cultivation of ornamentals, while two of the groups did not clearly resemble any of the previously characterised Dickeya species. Field trials with the strains indicated that D. dianthicola-like strains isolated from river samples caused the highest incidence of rotting and necrosis of potato stems, but some of the Dickeya strains isolated from potato samples also caused symptoms. The results showed that although P. atrosepticum is still the major cause of blackleg in Finland, virulent Dickeya strains were commonly present in potato stocks and rivers. This is the first report suggesting that Dickeya, originally known as a pathogen in tropical and warm climates, may cause diseases in potato in northern Europe.     

2019—2020年河南省小麦茎基腐病病原菌鉴定及致病力测定

为监测小麦茎基腐病病原菌的变化,2019—2020年自河南省安阳、濮阳和鹤壁等17个市129个采样点采集小麦茎基腐病病株样品并分离病原菌,对所有分离物进行形态学鉴定,利用特异性引物、ITS和EF-1α基因序列进行分子生物学鉴定,并于室内对优势病原菌菌株进行致病力测定。结果表明,共分离得到892株镰孢菌Fusarium分离物,所得分离物中假禾谷镰孢F. pseudograminearum共851株,所占比例为95.41%,为优势种;禾谷镰孢F. graminearum共16株,所占比例为1.79%。除信阳市外,其他16个市优势病原菌均为假禾谷镰孢。不同假禾谷镰孢菌株存在明显的致病力分化,但多数为强致病力菌株。     

魔芋软腐病病原菌TaqMan荧光探针PCR技术的建立及应用

为实现对田间土壤软腐病病原菌的定量检测,基于魔芋软腐病优势病原菌胡萝卜软腐果胶杆菌胡萝卜亚种Pectobacterium carotovorum subsp. carotovorum的FyuA基因序列,设计特异性引物PCC1/PCC2/PCC3,建立TaqMan荧光探针实时荧光定量PCR技术,并对魔芋根系土壤中软腐病病原菌进行动态监测。结果显示:基于FyuA基因序列设计的引物特异性好,仅能特异性检出胡萝卜软腐果胶杆菌胡萝卜亚种;当模拟带菌土壤中病原菌浓度低至1.88 CFU/g时也能检出,灵敏度高;发病魔芋根际土壤中软腐病病原菌检出率为100.00%,病原菌DNA浓度最高达到了7.52×10~7ng/μL,健康魔芋根际土壤中也存在病原菌,检出率为40.00%;不同种植模式中,林下魔芋土壤中软腐病病原菌数量较少;连作时间与病原菌数量、病情指数存在正相关关系,连作时间越长,病原菌积累越多,魔芋病情指数也越高,魔芋连作4年土壤中病原菌DNA浓度最高达到4.03×10~4ng/μL;对魔芋土壤软腐病病原菌进行全年监测,病原菌数量随着月份增长逐渐上升,在8—10月达到峰值543.20 ng/μL后下降,病原菌数量与魔芋病情指数变化规律一致,但田间魔芋软腐病的发生相对滞后。表明建立的TaqMan荧光探针实时荧光定量PCR技术可用于田间魔芋软腐病的监测。     

Testing variability in pathogenicity ofPhytophthora cactorum, P. citrophthora andP. syringae to apple, pear, peach, cherry and plum rootstocks

The relative virulence ofPhytophthora cactorum andP. syringae originating from almond trees, and ofP. citrophthora originating from citrus, to apple, pear, peach, cherry and plum rootstocks, was studiedin vivo andin vitro. Results of the different experiments were in good agreement. All testedPhytophthora isolates showed little virulence to pear rootstocks-causing only minor crown rot symptoms - and no virulence at all to apple rootstocks. In contrast, they were highly virulent to stone fruit rootstocks, causing crown rot disease. The non-pathogenicity of these isolates to pome rootstocks could be interpreted as strict host specificity.     

Effect of Phenylpyrrole-resistance Mutations on Ecological Fitness of <Emphasis Type="Italic">Botrytis cinerea</Emphasis> and their Genetical Basis in <Emphasis Type="Italic">Ustilago maydis</Emphasis>

Mutants of Botrytis cinerea and Ustilago maydis highly resistant to fludioxonil were isolated at a high frequency, after nitrosoguanidine or UV mutagenesis, respectively, and selection on media containing fludioxonil. Tests on the response of mutant strains to high osmotic pressure resulted in the identification of two fludioxonil-resistant phenotypes (FLD_osm/s and FLD_osm/r), regarding the sensitivity to high osmolarity. Approximately 95% of fludioxonil-resistant mutants were found to be more sensitive to high osmotic pressure than the wild-type parent strains. Genetic analysis of phenylpyrrole-resistance in the phytopathogenic basidiomycete U. maydis, showed that fludioxonil-resistance was coded by three unlinked chromosomal loci (U/fld-1, U/fld-2 and U/fld-3), from which only the U/fld-1 mutation coded an osmotic sensitivity similar to that of the wild-types. Cross-resistance studies with fungicides from other chemical groups showed that the mutations for resistance to phenylpyrroles affect the sensitivity of mutant strains to the aromatic hydrocarbon and dicarboximide fungicides, but not to the benzimidazoles, anilinopyrimidines, phenylpyridinamines, hydroxyanilides or the sterol biosynthesis inhibiting fungicides. A study of fitness parameters in the wild-type and fludioxonil-resistant mutants of B. cinerea, showed that all osmotic sensitive (B/FLD_osm/s) isolates had significant reductions in the characteristics determining saprophytic fitness such as mycelial growth, sporulation, conidial germination and sclerotial production. Contrary to that, with the exception of mycelial growth, the fitness parameters were unaffected or only slightly affected in most of the osmotic resistant (B/FLD_osm/r) isolates. Tests on cucumber seedlings showed that the osmotic-sensitive strains were significantly less pathogenic compared with the wild-type and B/FLD_osm/r strains of B. cinerea. Preventative applications of the commercial products Saphire 50 WP (fludioxonil) and Rovral 50 WP (iprodione) were effective against lesion development on cotyledons by the wild-type and the mutant strains of B. cinerea that were resistant to the anilinopyrimidine cyprodinil (B/CPL-27) and to the hydroxyanilide fenhexamid (B/FNH-21), but ineffective, even at high concentrations, against disease caused by the fludioxonil-resistant isolates (B/FLD) and a mutant strain resistant to the dicarboximide iprodione (B/IPR-1). Experiments on the stability of the fludioxonil-resistant phenotype showed a reduction of resistance, mainly in osmotic-sensitive isolates, when the mutants were grown on inhibitor-free medium. A rapid recovery of the high resistance was observed after mutants were returned to the selection medium. Studies on the competitive ability of mutant isolates against the wild-type parent strain of B. cinerea, by applications of a mixed conidial population, showed that, in vitro, all mutants were less competitive than the wild-type strain. However, the competitive ability of osmotic-resistant mutants was higher than the osmotic-sensitive ones. Furthermore, competition tests, in planta, showed a significant reduction of the frequency of both phenylpyrrole-resistant phenotypes, with a respective increase in the population of the wild-type strain of the pathogen.     

Effect of phytotoxic compounds produced by Clavibacter michiganensis subsp. michiganensis on resistant and susceptible tomato plants

A phytotoxic fraction of high molecular weight was isolated from the culture filtrate ofClavibacter michiganensis subsp.michiganensis, the causal agent of bacterial canker of tomato, and partly purified. This high molecular weight fraction consists of sugars and a minor protein moiety and is therefore probably of similar nature to that of the toxin fromC. michiganensis subsp.michiganensis reported earlier in literature.The high molecular weight fraction was albe to induce wilting, the predominant symptom of the disease, as shown in a bioassay with tomato cuttings. However, this wilting reaction turned out to be non-specific in the bioassay, since (partially) resistant and susceptible genotypes responded similarly. No correlation could be found between the degree of virulence of fiveC. michiganensis subsp.michiganensis strains and the amount of the phytotoxic high molecular weight fraction produced in vitro.As the isolated high molecular weight fraction showed a phytotoxic effect on tomato plants it is worthwhile to test its potential for use as a selective agent in in vitro selection.Samenvatting Een fytotoxische fractie werd geïsoleerd uit cultuurfiltraat vanClavibacter michiganensis subsp.michiganensis, de veroorzaker van de bacterieverwelkingsziekte bij tomaat. Een eerste karakterisering toonde aan dat deze toxische fractie hoog-moleculaire component(en) bevat, bestaande uit polysacchariden en een gering percentage eiwit. Dit is in overeenstemming met toxines vanC. michiganensis subsp.michiganensis die al eerder beschreven zijn.Deze hoogmoleculaire toxische fractie was in staat verwelking te induceren van stengeltoppen van verschillendeLycopersicon esculentum enL. peruvianum genotypen in een bioassay. Gewichtsverandering van de stengeltoppen, uitgedrukt als percentage ten opzichte van het begingewicht, werd gebruikt als parameter voor verwelking. De toxische fractie reageerde niet-specifiek in de bioassay, want er werd geen verschil gevonden in respons van (partieel) resistente en gevoelige genotypen. Er bleek geen correlatie te zijn tussen de mate van virulentie van verschillende isolaten vanC. michiganensis subsp.michiganensis en de hoeveelheid van de toxische fractie geproduceerd in vitro.Het mogelijke gebruik van deze hoogmoleculaire toxische fractie als selectief agens bij in vitro selectie zal nader onderzocht worden.     

模拟干旱胁迫对稻虱缨小蜂的影响

为明确干旱胁迫对稻虱缨小蜂Anagrus nilaparvatae Pang et Wang生态适应性的影响,采用不同浓度的聚乙二醇(polyethylene glycol,PEG)6000模拟干旱生境,研究了干旱胁迫对稻虱缨小蜂生长发育、繁殖的影响,并观察了稻虱缨小蜂对感虫品种TN1和抗虫品种IR36水稻上褐飞虱Nilaparvata lugens Stl卵的选择情况。结果表明,稻虱缨小蜂幼虫的发育历期随PEG6000浓度的升高而延长;成虫寿命则随着PEG6000浓度的升高而缩短,经20%PEG6000处理7 d后雌蜂寿命最短,在TN1和IR36水稻上分别为25.1 h和25.4 h;经20%PEG6000胁迫处理7 d后,在TN1、IR36水稻上稻虱缨小蜂的平均卵寄生量最低,分别为10.9粒和8.1粒。与20%PEG6000处理相比,稻虱缨小蜂对未经干旱胁迫处理水稻上的褐飞虱卵具有明显的选择性。研究表明,模拟干旱胁迫能降低稻虱缨小蜂生态适应性,且降低对褐飞虱卵的寄生力和选择性。