The history of study on plant disease complex involving nematodes is over 100 years. The discovery and verification of these disease complexes is one of the remarkable progresses in plant pathology from the 1950s to the 1970s. Plant etiology has been developed from mono-pathogen etiology to multiple pathogen etiology. This paper reviewed some important cases modes and possible mechanisms of synergism in disease complexes. Looking forward to the 21st century, it is believed that the Chinese plant pathologists will pay more and more close attention to the disease complex problems,and promote deeper study in this field.

Recent advances in the studies of quantitative disease resistance in plants are reviewed in this paper. Eighteen examples of mapping quantitative resistance loci (QRL) in plants with the assistance of DNA molecular markers are enumerated. These studies provided insights into the numbers, types and effects of QRLs and their relations to ecological environment, plant development stage and pathogen races (or pathotypes) etc. QTL mapping opens up broad prospects for marker-assisted selection of complex quantitative disease resistance characters and the positional cloning of quantitative resistance genes.

5606 Samples collected from 16 provinces (including autonomous regions) in China during 1991-1996 identified on 17 differential hosts, namely Trigo Eureka, Fulhard, Lutescens 128, Mentana, Virgilio, Abbondanza, Early premium, Funo,Danish1 Jubilejina2, Fengchan3, Lovrin13, Kangyin655, Shuiyuan11, Zhong4, Lovrin10 and Hybrid46. During 1991-1995, CY29 was the first dominant race and the frequencies was 13.6% -32.2%, but it has the decline tendency; from 1991-1993, CY25 was the second dominant race; and during 1993-1995, the newly named CY31 (6.6% -16.7%) and CY30 (5.7% -7.9%) have the ascend trend and became the second and third dominant races, especially for the CY31 which became the first dominant race in 1996 (13.0%). The other races, for example CY21、22、23、26 and 28, have low frequencies and have a decline tendency too. The occurrence percentage of Hybrid46 pathotypes was 19.6%, 34.8% and 38.2% and that of Shuiyuan 11 pathotypes was 12.2%, 20.9% and 46.6% during 1994-1996. As the frequencies of Hybrid46 and Shuiyuan11 pathotypes increased rapidly, segregation in the two pathotype groups became more obviously. 9 and 12 pathotypes were identified in Hybrid46 and Shuiyuan11 pathotypes separately.

Six varieties (lines) of wheat Jing Shuang 16, Liao 89-1, Liao 89-2, Liao 91-1, Liao 91B18-27-1, and Lumai 12 were tested for black embryo disease by means of specimen examination with microscope and SEM. Their percentage of black end seeds was 76% -457%, (disease index) 32% -135%. Liao 89-1 and Lumai 12 were damaged resulting in weak and serious symptoms. Alternaria from embryo of black end seeds was identified under microscope while other seed borne fungi such as Helminthosporium and Cladosporium were further discovered by SEM

A segregating population of Erysiphe graminis f.sp. tritici was constructed by crossing two isolates. The avirulence/virulence of the individual progenies were evaluated on five differential hosts. The results indicate that the four avirulences which matched the resistance genes Pm4a, Pm4b and the resistance of cvs Baimian 3 and Era, respectively, were controlled by single genes, respectively. The avirulence/virulence segregation did not match the resistance gene Pm3b, however, fit into the mode of single gene segregation. The avirulence genes matching Pm4a, Pm4b and the resistance of cv. Baimian 3 were linked completely but they did not link to the avirulence matching the resistance of cv. Era.

The effects of three types of incompatible interactions between wheat and Puccinia graminis f.sp. tritici on the growth and development of the fungus were studied. Completely incompatible interaction ISr5-Ra/21C₃CKR (Sr5/P5) reduced significantly (p=0.05) the angles between the growth direction of germ tubes of P. graminis f.sp. tritici pathotype 21C₃CKR and long axes of wheat leaves by an average of 6.22°, in comparison with its corresponding compatible interaction ISr5-Sa/21C₃CKR (sr5/p5). Highly incompatible interaction ISr11-Ra/34MKG (Sr11/P11) decreased significantly the rate of appressorium differentiation of P. graminis f.sp.tritici pathotype 34MKG by averages of 21.16% one day and 33.37% two days after inoculation. Three types of incompatible interactions had no effect on location of appressoria on stomas. The spread of P. graminis f.sp. tritici colonies was inhibited signifi cantly (p=0.01) by com pletely, hig hly or moderately incom patible interactions to v arying deg rees. Percentag es of colo nies with necrotic host cells in completely incom patible interaction, highly incom patible interaction and modera tely incom patible interactio n ISr6-Ra/34C 2 MFR (Sr6/P6) were 66.7% -76%, nearly 100% and 52.4% -87.1%, respectiv ely.

The wheat-Elytrigia intermedia addition line Z1 was identified to be highly resistant to strain GPV of BYDV, and this strain exists only in China. The genomes of resistant lines and susceptible lines were analyzed by RAPD using 104 random primers. It was found that primer OPS16 can amplify a specific 1.7 Kb fragment from genome of Z1.
When Z1, Zhong7902, Elytrigia intermedia and Zhong5 were amplified using primer OPS16, this specific 1.7 Kb fragment was also produced in Elytrigia intermedia, Zhong5 and Z1.
When selfbred progenies of resistant and susceptible Z1 individuals were amplified using primer OPS16, this specific 1.7 Kb fragment was amplified in progenies of resistant individuals of Z1, but not in progenies of susceptible individuals.

On basis of the disease grade of wheat scab (DGWS) or disease grain rate of wheat scab estimated after harvest,the author analysed the relationship between DGWS and DON contents of wheat grain.Results showed that the relationship in both cases were very significant.When the disease grade reached more than No.2,the DON content of the wheat grain were more than 1000μ g per kg; When the disease grade was more than No.4, the DON content of wheat grain reached more than 2000μ g per kg.When the DGWS reached less than 25%,the DON content of wheat grain was less than 1200 g per kg;the disease grain rate of wheat scab was 25% -40%,the DON content of wheat grain was 1200-2200μ g per kg, and the disease grain rate reached more than 40%,the DON content of wheat grain was more than 2200μg per kg.

Studied on the directional selection and stabilizing selection from the interaction between rice varieties and blast fungus colony by reinoculated the rice varieties from generation to generation.The possibility were evaluated that the selection action use for forcasting varieties resistance break down.The results can provide scientific basis for the utilization of the resistant varieties and prolonged the utilization period of resistant varieties.The paper were discussed the method of keep relative stabilize of race colony of Pyricularia grisea in natural and continued control the calamity caused by rice blast fungus.

A previous procedure was modified to shorten purification duration and enhance purification efficiency of CMLOX1 and CMLOX2 which are two lipoxygenases induced in rice in response to incompatible infection of blast fungus. Using this modified procedure, the authors obtained 133μ g of CMLOX1 and 208 g of CMLOX2 with electrophoretic homogeneity from 20 grams of the pathogeninfected rice leaves. Furthermore, the proteins were cleaved by LysCspecific proteinase and cyanogen bromide, and partial amino acid sequences of the proteinderived peptides were determined. These involved 30 AA of 3 distinct peptides from CMLOX1 and 87 AA of 7 distinct peptides from CMLOX2. The amino acid sequence information will greatly facilitate the cloning of cDNAs encoding the two lipoxygenases.

Both bacterial cells of Xanthomonas oryzae pv.oryzae (JXOⅢ) and its toxin caused rapid necrosis reaction at infiltrated sites on tobacco leaf.The time needed to initiate the reaction is 0.5 h for toxin and 8 h for JXOⅢ after infiltration.Infiltration with low concentration of JXOⅢ (<10⁷cfu/ml)caused chlorosis at inoculation site 48 h later. While,inoculation with low concentration of toxin (<25mg/ml)gave no macroscopic changes.
Treatment with JXOⅢ and its toxin caused rapid cell death of tobacco leaf at 6 h and 0.5 h after inoculation respectively.Results of tobacco leaf discs' analysis shows that treatment with toxin rapidly increased membrane permeability. The enzyme activity levels of LOX,POX,CAT and SOD were greatly reduced compared with untreated control.While,treatment with JXOⅢ increased the levels of the above enzyme activities.Treatments with eucaryotic metabolic inhibitors,such as,cycloheximide,actinomycin D and lanthanum chloride prevented necrosis reaction on tobacco leaves by JXOⅢ, but not toxin.The results suggest that although JXOⅢ caused cell death by inducing active defense response of plant, its toxin caused cell death by direct to xicity on cell.

The pattern of disease development in the solar greenhouse and results of artificial inoculation indicated that the key initial infection gates of Botrytis cinerea on tomato fruits were the residual petal and stigma, from which the infection extended to fruit stalk and navel, and finally to the other parts. Accordingly, a new method for controlling grey mould of tomato fruits was developed i.e. picking residual petal and stigma in 7-15 d after dipping flowers (10-20 mm diameter in young fruits) by using 2,4-D. Field test showed that the control effect was over 80% and without damage to fruiting.

Abstract A virus isolated from a diseased bean plant in the Beijing suburb was identified as peanut stunt virus, designated PSV Bean isolate (PSV-B) on the basis of host range, transmission characteristics, in vitro properties, virus particle morphology, serology and physical and chemical properties, which was first reported in China. PSV-B infected 21 of 28 species tested in five families. The thermal inactivation point was 60-65. The dilution end point was 10^-4-10^-5 and the longevity in vitro was 6 days. ^{Aphis craccivora} Koch transmitted the virus in a nonpersistent manner. The virus was successfully purified by modified Franck's method for purification of CMV, virus yield was 19.6 mg/100 g infected tissue. Virus particles were spherical with 30 nm in diameter. An antiserum against PSV-B was produced with titers of 1128 in gel diffusion tests. Serologically PSV-B was closely related to PSV-Mi, distantly related to PSV-E. The molecular weight of PSV-B coat protein is about 25 000 D.PSV-B has four kinds of strand RNA.

The information of incidence and disease index of soybean frogeye leaf spot (Cercospora sojina Hara.)were obtained through inoculation experiments conducted in the field from 1992 to 1995.The relationship between disease incidence and severity (I-S)of soybean frogeye leaf spot was analyzed.Results showed that the IS relationship of soybean frogeye leaf spot on leaf could be expressed individually by following linear regression equations.The equation of susceptible variety is SS=-2.8029+0.5252IS±6.4364 (0 ≤ SS ≤ 54.6%,0 ≤ IS ≤ 87.1%,R=0.9139^**,R²=0.8352,S.E.=4.9779,n=86).The equation of resistant variety is SR=-0.3843+0.6334IR±3.7679 (0 ≤ SR ≤ 4.01%,0 ≤ IR ≤ 68.7%,R=0.9700^**,R²=0.9410,S.E.=2.9096,n=66).The IS relationship of soybean frogeye leaf spot was affected by the resistance of soybean varieties to the pathogen.

Two isolates of apple chlorotic leaf spot virus,ACLSVC from apple in China and ACLSVB from almond in Italy,were characterized in biological and biochemical properties.Both isolates could infect Chenopodium quinoa,Ch.amaranticolor and Nicotiana occidentalis when 19 herbaceous plants in 5 families were tested and induced local infected lesions and systemic chlorotic leaf spots.Differences between two isolates were found.ACLSVB caused stronger systemic symptoms with upper leaves to roll or crinkle.Otherwise compared with ACLSVC, ACLSVB could latently infect a winter squash (Cucurbita maxima cv.Buttercup Burgess) and no latent infection was found with ACLSVC.When virus coat proteins (CP) were analysed by 10% SDSPAGE,the CP of ACLSVB migrated faster than CP of ACLSVC and RNA on double strained RNA of those two isolates were revealed.Specific primers were applied to detect ACLSV in herbaceous plants by RTPCR.Products with higher specificity were obtained.

Morbid changes of some Physiochemical substances were found in the roottip tissues of Malus baccata infected with Trichodorus nanjingensis.These changes included the rise of the content of free proline, reduced carbohydrate and hydroproline in cell wall as well as the activity of POD PPOD and PAL. Furthermore, the changing range of all tested substances was different. The increasing range of free proline, reduced carbohydrate and the activity of three kinds of enzymes at early stage was bigger than at later stage but the increasing range of hydroproline was smaller at early stage than at later stage. The decreasing range of total carbohydrate was smaller at early stage than at later stage. The changing tendency of above substances shed light upon the physiopathology of M. baccata infected with T. nanjingensis.

TMV particles were introduced into tobacco mesophyll cells by ultrasonic treatment.The tobacco cells and TMV particles were treated in buffer by ultrasonic treatment with 0.5 W/cm² for 5 min,59.7% cells were infected by TMV.The time course of TMV multiplication was made by ELISA data, the highest level was reached at 48 h postinfection.A large amount of TMV particles were detected by electron microscope.The daughter TMV particles could produce necrotic lesions on leaves of Nicotiana glutinosa.It is shown that TMV particles were introduced into tobacco cells through cell wall.

The tests on effects of heat treatment were conducted on mycelial growth,spore germination and pathogenicity of Colletotrichum musae (Berk.& Curt.)Arx.from banana fruit and C.gloeosporioides Penz.from mango fruit in latent infection.The results showed that mycelial growth and spore germination were suppressed while the pathogenicity were reduced when the pathogens were subjected to 55℃ and 60℃ for 20 mins.C.musae was more susceptible to heat than C.gloeosporioides was.Therefore,the authors suggested that the heating duration and the temperature for postharvest treatment should be set according to the types of fruit and pathogen.

Seven hundred bacterial strains isolated from leaf and sheath of rice plants of Laguna province, Philippines were tested in vitro.Results showed that there were a great number of bacteria that were Gram negative、nonpathogenic and antagonistic to Rhizoctonia solani. Among 195 bacteria strains identified,147 were Gram negative,belonging to 14 genera 39 species, and 48 were Gram positive belonging to 8 genera 13 species. Stenotrophomonas maltophilia, Pseudomonas aeruginosa and Pseudomonas pudita were the predominant species possessed large amount of antagonistic strains. The biological diversities of partial strains of above species were analyzed by rep-PCR. Results showed that DNA bands of different species from same genus crossed each other at sometime; the differences of DNA bands were greater between genus than that between species.

Bacteriocin Echcin is an antagonistic substance with wide spectrum,which is extrac ted from Erwinia chrysanthemi on rice.The effect of Echcin on control of crops fungal and bacterial diseases were studied.The inhibitory activity of Echcin to 14 strains of phytopathogenic bacteria was tested using paper plate method.The sensitivities of 12 species of plant pathogenic fungi to Echcin were examined with agar diluting method.The control effects of Echcin to tomato early blight,to rice bacterial blight in greenhouse,and to wheat sharp eyespot in field were evaluated.Results show that Echcin has strong inhibitory activity to five genera of phytopathogenic bacteria and Phytophthora capsici,Phytophthora boehmeriae and Alternaria solani. Applying Echcin twice led to 75.8% reduction in the tomato early blight.With seed treatment or spraying once,Echcin showed over 60% control effect on the wheat sharp eyespot,which was superior to Jingangmycin.

More than 6 000 transconjugants producing normal extracellular polysaccharide (EPS) were obtained when a wild type Ralstonia (Pseudomonas) solanacearum (PO41) race 3 was induced by Pseudomonas aeruginosa strain PAO1826 (pMO75::Tn5,Km^r) containing a transductant Tn5. Two mutants, PM2644 and PM239 that were defective in 9 kinds of extracellular proteins (EXPs) were selected by screening the transconjugants on SDS PAGE. These two mutants were prototrophic type and could cause hypersensitive reaction on tobacco leaves. However,their virulence decreased greatly in comparison with wild type. Southern blot hybridization showed that both mutants contained only one insertion site in their chromosomes. Marker exchange mutagenesis indicated that like PM2644 and PM239,100 percent of Km resistant transformants were defective in 9 kinds of EXPs.Activity determination of polygalacturo nase and endoglucanase showed that these two enzymes were absent in culture filtrate and bacteria cells of mutants. Two clones (pPSP1 and pPSP2)restored all deficient EXPs and their lost virulence were screened out from genomic library of wild type strain PO41 by gene function complementation test.

Two hundred and two samples of soybean mosaic virus (SMV)collected from seven provinces and one city were identified and classified into seven strains (y₁-y₇) based on disease reaction on eight soybean cultivars. The y₁ and y₂ were the low virulence strains, which only infected susceptible cultivars (1138 2 and Wenfeng 5). The y₃, y₄ and y₅ were the moderately virulence strains, which infect susceptible and moderately resistant cultivars (Qihuang 10,Xudou 1,Youbian 30 and Ludou 4). The y₆ and y₇ were the high virulence strains, which not only infected above six cultivars but also two resistant cultivars (Qihuang 22 and Mijia 1). The low virulence strains, moderately virulence strains and high virulence strains account for 55.9%,28.7% and 15.3% of SMV in Huang Huai area,respectively. Most strains of SMV in Jiangsu, Shandong, Henan, Hebei, Anhui and Beijing were low virulence (43.5% -88.9%). In Shanxi province, moderately virulence strain was predominant (50.0%). The low virulence strains and moderately virulence strains were 50.0% each in Shaanxi province. The rate of high virulence strains was higher in Shandong, Hebei and Henan provinces (22.4% -33.3%). The distribution of SMV strains in Huang Huai area was stable to some extent.

Genetic diversity of 14 pathogenic bacteria isolates of the ‘rice short streak’ and the rice and leersiae bacterial leaf streak were assessed by RAPD with 40 primers.Eleven primers revealed reproducible polymorphism and a total of 158 bands were scored.The frequency of genetic diversity was 89.74%.Results from comparative resarch of cluster analysis base on the RAPD bands of 14 isolates and their pathogenicity on rice suggested that the relationship between LLS2,LLS3,LLS4,RS05,R1008,TAS,and TAX were very close,belonging to the same group (I).Highest similarity was found between TAS and TAX.High genetic diversity was observed among isolates derived from rice bacterial leaf streak,belonging to two different groups (Ⅱ,Ⅲ).Results indicated that isolates LLS2,LLS3,LLS4,R1008,RS05 are closer to the isolates derived from rice (TAS,TAX)than to the others.

The disease-specific protein of rice grassy stunt virus (RGSV) was purified by differential pH precipitation and ultracentrifugation. The ultraviolet absorbed curve of purified specific protein (SP) was typical protein one. The yield of SP was about 28 mg per 100 g of infected leaves. Antiserum was prepared by immunizing rabbit with RGSV-SP, which was further purified by SDS-PAGE. The produced antiserum had a titre of 1:1024 in microprecipitation and 1:256 in double immunodiffusion test. It reacted strongly with purified SP and infec ted plants in double immunodiffusion test and ELISA, but not reacted with purified RGSV ribonucleoprotein and healthy plants. Results from ELISA showed that the reaction between SP-antiserum and RGSV-SP was strong and specific and the concentration of SP varied with rice varieties, plant parts and disease periods of plant.Therefore, it is a simple and rapid procedure using the antibody against RGSV-SP to detect RGSV in plants.

Two expression vectors containing 5' regional deletion and 3' regional deletion of cucumber mosaic virus movement protein (MP) gene were constructed respectively. With IPTG induction, the full length of MP and its two mutants were overexpressed in Escherichia coli BL21 (DE3) pLysS respectively. Using a method to separate the inclusion bodies from the rest of the bacterial proteins by centrifugation, the MP and its C terminal deletion mutant were purified. The purity was about 96.6% estimated by Shimadzu 910 scanning.

AB toxin produced by Alternaria brassicae could increase the membrane permeability in cell of Chinese cabbage. Results showed that there was a positive correlation between the susceptibility to A.brassicae and the change of permeability in cells of different varieties:the higher the conductivity was, the bigger the lesion was on leaf. Results also showed that the changes in activities of SOD and POD in cell were similar. Both of them decreased rapidly within 12 h after treatment and then increased between 12 h to 48 h after treatment. However, there was no significant change in control.Therefore,as A.brassicae,AB toxin can induce the disease on Chinese cabbage.

The recombinant cosmid pCPP430 harboring the hrp gene cluster of Erwinia amylovora was transformed via electroporation into Pantoea agglomerans strain 308R, an epiphyte isolated from tomato. Transformants induced hypersensitive response when infiltrated into leaves of tomato plants. A plasmid of ca 50 kb size was isolated from one of the transfor mant and shown to have same physical map of that of pCPP430. Southern blotting of this plasmid DNA with Dig labeled hrpN DNA as probe revealed the presence of hrpN in the transformant. PAGE of cell envelop associated proteins of the transformant showed an additional band at 44 kd position to that of the recipient CK. Thus, bioassay and molecular evidences all demonstrated the successful construction of a recombinant strain of Pantoea agglomerans that was capable of producing harpin Ea.

The heredity of the resistance of Elytrigia elongata, Haynaldia villosa and Psathyrostachys huashanica and their hybrids with Triticum aestivum to races CY29,CY30 and CY31 of Puccinia striiformis were evaluated. Results indicated that the three wild relatives have valuable disease resistance genes, which can be highly expressed in the background of wheat. Therefore, they are valuable sources of stripe rust resistance in wheat breeding.

Not only pathogen Dothiorella gregaria but also its mycelium extract and culture filtrate could induce the accumulation of hydroxyproline-rich glycoprotein (HRGP) and lignin in cell wall of poplar callus. However, the total amount and the rate of accumulation varied with the resistance of species. The accumulation of HRGP and lignin in resistant species Populus tomentosa Carr. were faster and greater in comparison with those in susceptible species Populus beijingensis Hsu. Further more, the accumulation of the HRGP in cell wall coincided with the accumulation of lignin. These results indicated that the accumulation of HRGP and lignin in cell wall might be relevant to the resistant reaction in cell to poplar canker. Therefore, it was considered as a defence mechanism of host.

Immunoglobulin (IgG) of ToMV antiserum was purified and conjugated with horseradish peroxidase (HRP) by sodium periodate. A DAS-ELISA method for ToMV detection was developed using the conjugant. Some field samples of Solanaceae collected from Zhejiang and Shanxi Provinces were detected by DAS-ELISA and biological tests, results showed that ToMV was a common pathogen of tomato and eggplant. About 50% of detected Solanum melongena samples had ToMV both in Zhejiang and Shanxi provinces.However,there was a significant difference between tomato samples from Zhejiang and Shanxi provinces.In Zhejiang province, only about 10% of samples were infected by ToMV, while the numbers of infected samples were above 60% in Shanxi. No sample was found infected by ToMV in Capsicum annum. This is the first report about the field survey of ToMV in China.

To obtain resistant variants, embryonic calli from pith culture were irradiated with ⁶⁰Co-γ ray. Resistant calli were screened of cultural filtrate containing 60% toxin of Fusarium oxysporum. Plantlet were then regenerated on differentiation medium containing 30% of toxin. Physiological and biochemical assay showed that both proline and chlorophyll contents increased in resistant variants. Meanwhile, the bands of peroxidase isozyme on PAGE increased as well. Inoculation with suspension of conidium demonstrated that 6 regenerated plantlets were resistant to root rot disease.

When aqueous solution of 750-fold Jinggangmycin was added with 0.01%, 0.02% or 0.04% surfactant APSA 80, the surface tension of the solution reduced by 32.87% -53.66%. Contact angle of droplet decreased by 25.26% -51.98%, 36.88% -47.34%, and 22.38% -37.18% on upper surface, lower surface and leaf sheath, respectively. The amount of deposit of chemical increased about 1.6 times. Result of test on potted plants indicated that APSA 80 could improve the rainfastness of Jinggangmycin. Field experiment showed that APSA 80 could increase efficacy of Jinggangmycin and prolong its active duration. Fourteen days after application, efficacy of Jinggangmycin prepared with 0.02% or 0.04% APSA 80 was significantly higher than without surfactant. Twenty-one days after application, efficacy of Jinggangmycin mixed with 0.04% APSA 80 remained 86.58% (1996) and 90.93% (1997), which is much higher than it was used alone.

Results from microscopic and ultrastructural observations show that the causal organism of grapevine white rot in China should be Coniella diplodiella (Speg.)Petrak & Sydow instead of Coniothyrium diplodiella (Speg.)Sacc. The isolated fungus is distinguished from the genus Coniothyrium by its hyphal pad in the pycnidium, smooth conidia, and enteroblastic-phialidic conidiagenous cell.

One hundred twenty one isolates were obtained from samples of peony root rot collected from Heze region in Shandong Province.They were designated as 13 genera (species). Among them, the predominant fungus was identified as Fusarium solani (Mart.) Sacc.based on its colony appearance,growth rate,type of conidiogenous cells,the measurement of macroconidia and its pathogenicity.It is a first record on peony in China.

Strains of Verticillium,including 5 defoliating and 7 nondefoliating strains of V.dahliae and 2 strains of V.albo-atrum, were used as check in the present experiment in which random amplified polymorphic DNA and pathogenicity identification were performed with 34 strains of V.dahliae from cotton in 6 provinces and autonomous regions of North China. The results showed that 94.1% strains, including 26 defoliating and 6 nondefoliating strains, were identical. So the defoliating strains were confirmed to exist in cotton growing areas of Hebei, Henan and Shandong Provinces. The relationship between 22 northern defoliating strains and control defoliating strains from America T₉, V₄₄ was found to be closer than from Jiangsu Province V_B, V₉₉₁. At the same time, two specific RAPD bands were found only from defolia ting strains,named OPB-19₉₆₆ and OPM-20₁₆₉₁. With the primer OPB-19 and OPM-20,RAPD was conductd on 34 strains of _V.dahliae from cotton in North China and the identity between the results from the two specific bands and from the pathogenicity identification were 88.2% and 94.1% respectively. The two testified specific RAPD bands might have some practical value for differentiation.