Vegetative-compatibility groups in Verticillium dahliae from Israel

Nitrate-nonutilizing (nit) mutants were used to determine vegetative compatibility among 34 isolates of Verticillium dahliae from cotton, potato, olive, eggplant, chrysanthemum and tomato from 12 sites in Israel. Based on the formation of complementary heterokaryons, 33 isolates were assigned to two vegetative- compatibility groups (VCGs): one VCG contained 15 isolates from cotton, eggplant, chrysanthemum and olive; and the other VCG contained 18 isolates from potato, olive and cotton. The status of an additional isolate from tomato, which was compatible with both VCGs, remained unclear. In a limited pathogenicity test with 10 isolates, two (from tomato and eggplant) were pathogenic on tomato, eggplant and cotton; most isolates from cotton were pathogenic on cotton and eggplant only; and one from cotton was non-pathogenic. Fewer isolates were pathogenic on tomato than on cotton or eggplant. The diversity of vegetative compatibility found in our V. dahliae collection is comparable to that found in studies of American populations.     

茄子黄萎病的发生及病菌生长影响因子

江苏扬州等地棚室栽培条件下,茄子黄萎病一般始见于现蕾期,5月上、中旬进入座果期开始大量发生,5月中下旬至6月上旬达发病高峰;病田土壤2年未栽作物仍能造成茄植株较高发病率.病叶混入土壤引起茄植株发病率最高,而病根混入土壤未见发病.分离自茄子、辣椒和棉花的黄萎病菌菌株在供试的玉米粉、燕麦、理查、马铃薯等培养基上均生长良好,茄子、辣椒黄萎病菌在理查培养基上出现明显的紫红色,棉花黄萎病菌则未出现;三种病菌在pH4～9的培养基上均能生长;棉叶、茄叶、辣椒叶的汁液能刺激茄黄萎病菌分生孢子的萌发,其中以茄叶汁液最明显;病菌经55℃水浴处理20 min,各菌株均未见生长.     

一种新的棉花黄萎病快速接种技术及其在病原菌致病力和寄主抗病性鉴定上的应用

 棉花品种抗黄萎病鉴定一般在田间病圃中进行,其结果受病圃中病原菌分布均匀程度、气象等因素影响极大,往往导致鉴定结果不准确。为了使鉴定方法简单、科学、可靠,我们在温室条件下比较了3种苗期接种棉花黄萎病的方法,即切根蘸孢子法(接种浓度为10⁶分生孢子/mL);菌培养物土壤接种法(0.5%、1%、2%,w/w);微菌核土壤接种法(10³个微菌核/g土)。结果表明,切根蘸孢子法导致棉苗发病均匀、严重、迅速,播种35~45 d后即可得到均匀一致的发病结果。而其它2种接种方法在播种75 d后才得到相对稳定的发病结果。同时,研究还表明接种浓度为10⁴分生孢子/mL所导致的黄萎病显著比10⁵或10⁶的轻。利用切根蘸孢子法在室内鉴定12个棉花品种或品系的抗黄萎病能力,证明该方法是抗黄萎病快速鉴定的有效方法。此外,该鉴定方法还可快速鉴定黄萎病菌不同菌株的致病性,并可应用于作物对其它土传病害的抗病性鉴定上。     

分离土壤棉花黄萎病菌选择性培养基的筛选

 采用土壤检测稀释法、水筛法和不同土样接种量,对5种土壤浸提液改良培养基进行了比较研究。结果表明,土壤水筛法对土壤棉花黄萎病菌的检测效果优于稀释法,其菌落检测数增加4~10倍。培养基每皿0.25 g土样接种量的检测效果高于0.5 g和1g。5种测试培养基中,培养基D对分离土壤棉花黄萎病菌的选择性表现最好,其土壤接种体检测回收率达63.5%~83.3%.培养基D的组份为:土壤浸提液25 ml,KH₂PO₄ 1.5 g,K₂HPO₄ 4 g,尿酸钠0.2 g,半乳糖醛酸钠(果胶)1g,山梨糖1g,Dox盐2 ml,Tergitol NP-101ml,PCNB0.1g,琼脂17g,蒸馏水1000 ml,pH6.4~6.7。每1000ml融化培养基倒皿前加抗菌素液50 ml (含氯霉素0.05 g,链霉素0.05 g,青霉素-G盐0.05 g)。     

Specific Detection of Tomato Pathotype of Verticillium dahliae by PCR Assays

Verticillium dahliae Klebahn is the causal agent of tomato wilt disease. Isolates of V. dahliae can be classified based on pathogenicity to tomato, but the pathotypes are indistinguishable in morphology. We designed PCR primers for specific detection of isolates pathogenic to tomato (tomato pathotype) from the sequences of a pathotype-specific gene, vdt1. With the primer pair Tg5/Tc3, a PCR product (approximately 3.2 kb) specific to tomato pathotype was amplified from the genomic DNA of isolates. Using the primer pair, a tomato pathotype isolate was specifically detected from hypocotyls of inoculated tomato and eggplant. On the other hand, no amplification was observed from non-tomato pathotype isolates of V. dahliae, some other wilt pathogens of tomato and a healthy host plant. Therefore, the primer pair can be useful for pathotype-specific detection of V. dahliae as well as for diagnosis of wilt disease of tomato plant. Received 7 September 2001/ Accepted in revised form 3 December 2001     

Effects of granular nematicides on growth and microbial antagonism to Rhizoctonia solani

Effects of nematicides on growth and microbial antagonism toRhizoctonia solani were investigated as part of a study on the mechanisms involved in the increased incidence of this pathogen in nematicide-treated potato crops.Ethoprophos inhibited mycelial growth ofR. solani on potato dextrose agar (PDA), Czapek Dox agar (CDA) and on water agar (WA). Aldicarb stimulated its growth on PDA up to 14% but not on CDA and WA. Oxamyl inhibited mycelial growth on CDA and WA, but not on PDA.Ethoprophos and aldicarb stimulated development of the mycoparasiteVerticillium biguttatum on cultures ofR. solani. The effect was dependent on the medium on which the host fungus was grown. ForRhizoctonia cultures on PDA, growth of the mycoparasite was highly promoted by aldicarb and to a lesser extent by ethoprophos. WhenR. solani was grown on CDA, the development of the mycoparasite was not affected by aldicarb, slightly stimulated by ethoprophos and slightly inhibited by oxamyl. On water agar, its development on the host mycelium was not affected.In field trials on sandy soil, nematicides encouragedV. biguttatum probably by increased availability of substrate (i.e.Rhizoctonia mycelium) perhaps through reduced activity of the mycophagous fauna.Soil fungistasis was increased by ethoprophos and to a lesser extent by aldicarb at very high doses. At normal field rates, no effects can be expected on fungistasis. So the increased stem and stolon infection of potatoes in nematicide-treated fields was not caused by a direct effect of the nematicides on growth ofR. solani or by suppressing the microbial antagonism.Samenvatting De invloed van granulaire nematiciden op de groei vanRhizoctonia solani en op het microbiële antagonisme tegen deze schimmel werd onderzocht in het kader van een studie over de mechanismen die een rol spelen bij de toename van de aantasting in een met nematiciden behandeld aardappelgewas.Ethoprofos remde de myceliumgroei vanR. solani op aardappeldextrose agar (PDA), Czapek Dox agar (CDA) en op wateragar (WA). Aldicarb stimuleerde op PDA de groei met maximaal 14%. Op CDA en WA werd geen effect van aldicarb waargenomen. Oxamyl veroorzaakte groeiremming op CDA en WA, maar niet op PDA.Ethoprofos en aldicarb stimuleerden de ontwikkeling van de mycoparasietVerticillium biguttatum op cultures vanR. solani. De mate van groeistimulering was afhankelijk van de voedingsbodem waarop de waard,R. solani, werd gekweekt. De groei vanV. biguttatum werd sterk gestimuleerd door aldicarb en in geringere mate door ethoprofos, wanneer de waard gekweekt werd op PDA. Aldicarb had geen effect op de mycoparasiet wanneerR. solani op CDA gekweekt werd, terwijl ethoprofos de groei wel iets stimuleerde en oxamyl een gering remmend effect had. Op WA werd geen effect van de nematiciden op het mycoparasitisme vastgesteld.In veldproeven op zandgrond stimuleerden de nematiciden het voorkomen vanV. biguttatum op de stolonen. Het effect werd waarschijnlijk veroorzaakt door een verhoogde substraat beschikbaarheid (d.w.z. mycelium vanR. solani). De verhoogde beschikbaarheid van dit mycelium kan samenhangen met een door nematiciden gereduceerde activiteit van de fungivore bodemfauna.De bodemfungistase werd verhoogd door ethoprofos en, in geringere mate, door aldicarb bij hogere doseringen. Bij de in de praktijk aanbevolen doseringen kan echter geen effect op de fungistase verwacht worden. De toename in stengel- en stolonaantasting van aardappelen, geteeld in met granulaire nematiciden behandelde percelen, kon niet worden toegeschreven aan een direct effect van de nematiciden op de groei vanR. solani of aan een vermindering van het microbiële antagonisme.     

Quantification of microsclerotia ofVerticillium dahliae in plant material by image analysis

A procedure for the quantification of microsclerotia ofVerticillium dahliae with an image analysis system was compared with counting by eye. Colonised potato plant material was used from plants grown in pathogen-free soil in a greenhouse and from twelve crops (including four potato cultivars) grown outdoors in pots filled with pathogen-free soil under natural conditions. The values obtained from the potato material from the greenhouse were comparable for both methods. Variation in the results mainly resulted from sampling errors. The numbers of microsclerotia in plants grown outdoors were overestimated by image analysis for most crops. The source of the error was related to the presence of plant and soil particles that did not discolour during boiling of the samples in sodium hydroxide. Image analysis was a suitable and reliable method for assessing the number of microsclerotia only in potato haulm samples from plants grown in pathogen-free soil in the greenhouse.Abbreviations cv coefficient of variation - IA image analysis - MS microsclerotia, microsclerotium     

Recent progress in understanding relationships betweenVerticillium species and subspecific groups

Improved understanding of the genetic diversity within fungi in the genusVerticillium has resulted from recent studies based on vegetative compatibility analysis and several techniques of molecular biology. Although the method used to identify vegetative compatibility groups (VCGs) does affect the results, vegetative compatibility appears to be a stable characteristic among isolates. Fairly low VCG diversity has been detected withinV. dahliae andV. albo-atrum using nitrate non-utilizing mutants. VCGs do not appear to be related to pathogenicity to particular host species, with the exception ofV. albo-atrum on alfalfa. However, there is some correlation with virulence on certain hosts and with the ability ofV. dahliae to interact with root-lesion nematodes. Studies based on DNA analysis indicate thatV. dahliae andV. albo-atrum are closely related but separate species. Restriction fragment length polymorphism (RFLP) studies have identified several subspecific groups withinV. dahliae, including two non-host-adapted groups and two that are host-adapted. They also have confirmed that alfalfa strains ofV. albo-atrum are a distinct subgroup that is probably a separate population of clonal origin. Using polymerase chain reaction (PCR), a second non-host-adapted subgroup withinV. albo-atrum was identified that was previously unknown.     

一种新的棉花苗期黄萎病病情指标

 在丛枝菌根菌(AMF)诱导棉花抗/耐黄萎病的研究过程中发现植株叶柄带菌(Verticillium dahliae,VD)量和木质部变色指数的指标与棉株的发病率和病情指数无相关关系。无症健株带苗率达10%以上;从茎基部测定的木质部变色指数不能反映其抗/耐黄萎病的差异。作者提出了"棉株茎木质部非变色高度"的概念,并发现只有当不质部非变色高度≤株高的50%时,叶片才显黄萎症状。与此相应所提出的木质部非变色级与病级、木质部非变色指数与病情指数则具有一定相关关系。木质部非变色指数可作为棉花苗期黄萎病的病情指标。     

山西棉花黄萎病菌致病力分化与其类型和生理的关系

山西省棉花黄萎病菌致病力有明显分化。运城、临汾黄萎病菌属强毒菌系；榆次、汾阳棉黄萎病菌属弱毒菌系，未发现落叶型致病类群。致病力强弱与微菌核和黑色素形成快慢、多少及过氧化氢酶活性有关。