With the changes of the global climate, cultivation methods and release of new varieties, the maize diseases have changed in recent years in China. In spring maize zone the head smut has been continually severe and the northern corn leaf blight has become severe again. In summer maize zone the southern corn leaf blight has been a problem in some areas and maize dwarf mosaic is slight. Some diseases which used to be unimportant have become main diseases now, e.g. southern corn rust in the south areas of summer maize zone, common corn smut and soil-borne diseases in all of growing areas, bacterial leaf diseases in some fields. On the basis of the result of analysis on resistance of varieties released, which were verified by national and provincial crop committees, it can be predicted that in the north spring maize zone the northern corn leaf blight will he severe because of the low level of resistance in varieties and new virulent race in the pathogen. As release of resistant varieties and use of seed-dressing technique the head smut will be controlled effectively, but in some areas it will be severe continuously. The occurrence of gray leaf spot and curvularia leaf spot will be affected by the weather. In north summer maize zone the southern corn leaf blight will be not severe. Stalk rot and seedling blight will be main problems because most of the varieties possess low level of resistance and new cultivation methods have been developed. Southern corn rust will be severe and heavily.

A 181 bp fragment of NADH dehydrogenase subunit 5 (nad5) gene cloned from mitochondrial DNA of apple was used as internal control in detection of three pear viruses by multiplex RT-PCR assays. The recovered fragments were cloned, sequenced and identified. Sequencing results indicate that the ACLSV on Kuala fragrant pear reveals 116 base difference between 6860 and 7536 bp and sequence identity is 83.75% compared with sequence D14996 (isolates of Japan ACLSV); the ASPV on Kuala fragrant pear shows 72 base difference from 8869 to 9238 bp and sequence identity is 79.5% compared with sequence D21828 (isolates of German pear vein yellows virus); and the ASGV on Kuala fragrant pear has only 21 base difference from nucleotide 6039 to 6311 bp and sequence identities attain 92.3% highly compared with AB004063 in GenBank (isolates of Japan ASGV).

Sweet potato stem nematodes were collected from the sweet potato fields in Hebei, Shandong and Anhui provinces, China and identified as Ditylenchus destructor Thorne, 1945. Female:labial framework well sclerotized,lip region slightly set off from the body, with six lips and four annules,lateral fields are with six incisures and areolation. Median bulb is fusiform and weak thickenings, oesophageal glands usually overlapping the intestine on the dorsal side for half to one body width, some overlapped on the lateral and the ventral side. Tail conoid, slight ventral curvatured and with a narrow rounded terminus. Oocytes arranged in a double row in the anterior part of the ovary;the vulva lips slightly elevated, vulva slit oriented at a straight angle from the body axis, vulva width occupied four annules, the post uterine sac extended about three quarters of the distance to the anus. Male:anterior region similar to female. Cloaca slightly elevated,bursa extended from opposite the anterior end of the spicules to about the three quarters the tail length;spicules curved ventrally arcuate, expanded anteriorly with finger processes; gubernaculum short.

The pathogenicity of 18 strains of Fusarium oxysporum f. sp. cubense (FOC) from banana-growing regions in Guangdong province were identified on the differential hosts. The strain KP021,KP022,GZ981 and JL021 belonged to race 1, and the other strains belonged to race 4. A total of 200 oligonucleotides were used as primers to perform random amplified polymorphic DNA (RAPD) analysis, eight of them could amplify racespecific DAN fragments. Based on the cloning and sequencing of these RAPD marker fragments,the sequence characterized amplified region (SCAR) primers were designed respectively. The PCR amplification of the 18 FOC isolates and 9 new field isolates with SCAR primers showed that 4 SCAR markers could be specifically used to separate race I and/or race 4. These results provide a possible approach to identify the physiological races of FOC by molecular techniques and to monitor the epidemic trend of the 2 races in the fields.

Double-strand RNA (dsRNA) induced sequence-specific post-transcriptional gene silencing was known as RNA interference (RNAi). siRNA, an important intermediate of the RNA-interference pathway, are very effective in antiviral therapy in many organisms including mammals and plants. Oligonucleotides expressed siRNA were designed and synthesized according to the coat protein (CP) gene of Tobacco mosaic virus (TMV) and subcloned to the binary vector pBI121. The interference effects of siRNA targeting CP gene on TMV infection were studied by Agrobacterium-mediated transient expression system. Our results showed that transiently expressed siRNA could specifically interfere with TMV infection. Fourteen days after inoculation with TMV, the upper leaves of Nicotiana tobacum infiltrated with Agrobacterium tumefaciens cultures containing pBI121/siRNA were free of mosaic symptom. Northern blot assays also showed there were no or much less TMV RNA accumulation in these leaves. As for local lesion host, Nicotiana glutinosa, transiently expressed siRNA could reduce the lesion number resulting from TMV infection. In addition, transiently expressed siRNA targeting CP gene of TMV was unable to inhibit Cucumber mosaic virus (CMV), which indicated that the interference effect of siRNA was strictly dependent on the specific nucleotide sequence. Therefore, we supposed that the combination of siRNA technique and Agrobacterium-mediated transient expression system could be used as an antiviral treatment or rapid diagnostic tool in plants.

The influence of temperature on RNA silencing and the level of resistance in transgenic tobacco plants was studied by using Northern blotting and ELISA to detect the virus in T₃ plants that contain untranslatable PVY^N CP gene. The results shown that low emperature could change the RNA silencing that had occurred in transgenic plants and the resistance status. RNA silencing obtained by transgene was inhibited in plants grown at 15℃. The plants lost the characteristic of high resistance and displayed the symptom of susceptibility. RNA silencing obtained by transgene was not inhibited, however, in the transgenic plants that grown at 25℃ or above,i. e. 30℃ and 35℃. The transgenic plants maintained high resistance against PVY^N virus.

Induction and operation of the alternative pathway, the changes of active oxygen species levels and antioxidant enzymes activity during stripe rust infection were studied and discussed in this paper. Experiments showed that the content of H₂O₂ in the disease-susceptible cultivars was higher than that in the disease-resistant ones after 8 d of inoculation. But the change of O₂^-·content was regular. The activities of SOD, CAT and POD increased at the early stage of infection. But after 4 d of inoculation,they presented a trend of decreasing in susceptible wheats and were higher in the disease-susceptible ones than those in the disease-resistant ones. During stripe rust infection, the changes in the capacities and operation of alternative pathway in wheat seedling leaves was similar as the changes of content of H₂O₂. And no significant variance was observed in the aoxl mRNA level in wheat seedling leaves by Northem blotting, except an increase in the fourth day after inoculation. All those results indicate that active oxygen species induce the alternative pathway in some extend,and alternative pathway may participate in the lower active oxygen species and the protection mechanism against pathogen attacking.

A pair of primers and a TaqMan-MGB probe based on the conserved nucleotide sequence of coat protein (CP) gene of several Apple stem grooving virus (ASGV) isolates were designed and synthesized. A novel real-time fluorescent RT-PCR was established to detect ASGV. The covalent attachment of the minor groove binder moiety at the 3'end of the probe raised the melting temperature to a range suitable for real-time analysis, shortened the probe, and solved the problem of detecting virus with high genome variability among isolates, where an identical sequence can not be found without multiple mismatches. The method was ten times more sensitive than normal RT-PCR and suitable for the detection of those viruses with low concentration in fruit trees. The method was rapid, sensitive and completed within a single tube, without post-PCR handling of the amplification products.

Four isolates of Apple stem grooving virus, P-6-1-17, P4-1-69, P-L2 and P-D-21 from pears in China, which displayed different reactions in biological and serological tests, were studied for their molecular characteristics. RT-PCR products of 3'end of the four isolates were cloned and sequenced. The sizes of cloned fragments are 1089 nt from P-6-1-17 and P-L2, and 1069 nt from P-4-1-69 and P-D-21, respectively, which include the 714 nt CP-coding region. The similarities of nucleotide and deduced amino acid sequences of the CP genes among these isolates are 89.8% to 96.4% and 94.9% to 97.9%, respectively. The sequence data obtained in the study were compared with previously reported sequences of ASGV isolates and sequence variant species from different sources. Results suggested that isolates P-6-1-17, P-4-1-69,P-L2 and P-D-21 should be divided into two different subgroups. P-L2 showed different reactions in biological test and its CP gene also has a relatively high variability.

Zucchini yellow mosaic virus Chinese strain (ZYMV-CH) is a major virus that causes severe losses in watermelon. The 109 lines of F₃ derived from the single cross of the resistant wild germplasm P. I. 595203 and the susceptible inbred 98R were identified for their resistance to ZYMV-CH. The genotypes of 109 F₂ individuals were assumed by the segregation of F₃ population resistance. Using bulked segregant analysis (BSA), 640 RAPD primers were screened in resistant and susceptible parents, F₁ and bulks. We found that a 644 bp fragment specifically amplified with RAPD primer AK13 which were present in P. I. 595203 and the resistant gene bulk but absent in 98R and the susceptible gene bulk. It was confirmed that the marker AK13_-644 was linked to the gene resistant to ZYMV-CH in P. 1.595203 by screening 109 F₂ individuals and the linkage distance was 8 cM. The RAPD marker AK13_-644 was confirmed in the introgressed resistant inbreds, and was transformed into SCAR marker SCAK13 -644 successfully. The result showed that this marker could be useful for marker-assisted selection in watermelon breeding for virus resistance.

The gray mould Botrytis cinerea is one of the most important plant pathogenic fungi that cause postharvest disease in grape berries. The pathogen infected latently in flowering period and persistently resided in the fruits during the marketing. The latent infection of grape berries by this pathogen was more dominant than by other postharvest disease pathogens,Alternaria, Fusarium, Cladosporium, Penicillium, Aspergillus and Trichothecium. Conidia and hyphae of B. cinerea survived under low temperature storage (at 4℃) condition and caused serious damage to stored and marketed grape berries. Diseased berries showed the typical symptoms as fruit rot and abscission. This symptomatic feature was characterized in part by the low-temperature tolerance of pectinolytic enzymes secreted by B. cinerea. In this study, we also compared the activity of cell wall degrading enzymes between B. cinerea and other fungi,and found that this fungi utilized pectin much better than others,but not decompose cellulose effectively. The polygalacturonase of this pathogen showed higher activity at 40℃ than those of other pathogens, coincident with the progress of disease symptom in berries at this temperature. On the other hand,there was no significant difference in the enzymatic activity at 25℃ between B. cinerea and other pathogens. Thus, the present work provided some enzymatic evidences for elucidating infection strategy of B. cinerea.

Eighty-one isolates of Bacillus were evaluated for their ability to inhibit the growth of Ralstonia solanacearum in vitro. Four isolates (B2, B5, B7 and B8) showed inhibitory effect on bacterial growth, were identified as Brevibacillus brevis B2, Bacillus subtilis B5, Ba. subtilis B7, and Ba. subtilis B8, respectively, by bacteriological assays, Biolog test and 16S rDNA sequence analysis. Four isolates promoted plant growth and reduced the infection of tomato wilt in sterile and nonsterile soil under greenhouse conditions to a varying degree as compared with non-treated control. Strain B2 showed significantly reduction of the disease infection by 80.0% and 87.4% in sterile and nonsterile soil, respectively.

Fluorescence staining methods of calcofluor, aniline blue, and uranine and the techniques of alcoholic lactophenol trypan blue, coomassie brilliant blue and aniline blue for different phases in life cycle of Pseudoperonospora cubensis were comparaed. The results showed that three kinds of fluorescence techniques can be used to stain sporangia, cystospore, germ tube, appressorium, and sporangiophore of P. cubensis in situ on the leaf surface. But staining with calcofluor was easier to handle, faster, and more reliable than the other two. Trypan blue was appropriate for staining of the intercellular hypha and haustorium.

Root rot of Gerbera jamesonii caused by Phytophthora cryptogea is a serious disease in China, especially in wet condition. Since many pathogens were reported could infect the root of G. jamesonii and the isolation and identification of Phytophthora is really difficult, a rapid and accurate method for specific detection of P. cryptogea is necessary for determination of root rot in diseased G. jamesonii tissue. Based on the alignment of ITS sequences from Oomycetes, two primers were synthesized and a PCR based protocol was designed to detect and diagnostic of the G. jamesonii root rot caused by P. cryptogea specifically. Among 46 isolates representing 23 species of Oomycetes and fungi, a PCR product about 620 bp could only be amplified from P. cryptogea. The detection sensitivity is about 10 pg. The PC primer based PCR assay will provide a accurate and sensitivity tool for detection of P. cryptogea in G. jamesonii root rot.

To assess the threshold and efficiency of immunoStrip and real-time fluorescent PCR for detection of Acidovorax avenae subsp, citrulli in cell suspension from pure culture and in extracts from naturally infested or infected tissues, a comparative study was conducted. The results showed that immunoStrip testing, with threshold 10⁶ cfu/mL, was simple, fast and easy to handle, which adapted for fast detection and diagnosis in field. Compared with classical-PCR (threshold 10⁵ cfu/mL), real-time fluorescent PCR (TaqMan) didn't require agarose gel electrophoresis, ethidium bromide staining, and Southern blotting. Moreover, it had a much higher sensitivity, accounting for 10^3~4 cfu/mL, but required expensive instrument, and was adapted to lab testing and basal research.

The root-knot nematode Meloidogyne enterolobii Yang and Eisenback 1983 is a potentially important crop pathogen in China. To provide means to assist in preventing the spread of M. enterolobii, a single-step PCR diagnostic was developed for the nematode. The diagnostic primers were designed based on an alignment of ribosomal intergenic spacer 2 (IGS2) sequences from M. enterolobii, M. incognita, M. javanica, M. arenaria and M. hapla. The reliability of the diagnostic test has been validated by screening different geographic populations of six closely related Meloidogyne species and natural mixed soil nematode populations. The test is fast and sensitive, it can be used for direct diagnosis of a single nematode and for detection of M. enterolobii in mixed soil nematode populations.

Avirulence genes in pathogens are functional genes that determine if or not the race-specific resistance is expressed in host cultivars. Function lose of the genes results in generation of virulent races in pathogen population. In previous studies, two SCAR markers, SCO12₉₄₆ and SCE12₁₄₀₆ that are linked with the avirulence gene AVR-Pik^m in M. grisea were isolated. In this investigation, the two SCAR markers were mapped on the chromosome I by sequencing the end of the TAC clones and their comparison with the whole genome draft sequence of 70-15. On the basis of this result, four more DNA markers linked with AVR-Pik^m, SSR47T34, SSR50CA24, SSR52TAGG18 and SSR56A28, were identified utilizing the whole genome draft sequence of M. grisea 70-15 and SSR. Further analysis indicated that the four SSR markers lie on the side opposite to the two SCAR markers; the genetic distance between the four SSR markers and AVR-Pik^m is 4.90,7.01, 19.12,21.94 cM, respectively. This mapping will facilitate isolation of AVR-Pik^m by chromosome walking.

One pair of specific primes (REA/FEA) is designed based on the conserved sequence of internal transcribe spacer (ITS) between 16S rDNA and 23S rDNA of E. amylovora,SYBR Green I real-time fluorescent PCR method, which has no post-PCR manipulations and reduces false positive result and contamination risks, is established for detection of this bacteritum. In all tested bacterial strains, only E. amylovora can be detected. Detection limitation of pure culture and artificially inoculated samples were 4 and 24 bacterial cells, sensitivity was 10 times higher than PCR gel electrophoresis detection.

A subtractive libraries in association with appressorium formation expressed genes of M. grisea 24 hours after the conidia inoculated was constructed by suppression subtractive hybridization (SSH). The experiment was carded out with appressorium induced on projection membrane. The ratio of appressorium formation on projection membrane was 96.5% at 1.0×10⁶ conidia.mL^-1. Total RNA was extracted from appressorium and mixture of mycelium and conidia and reverse-transcripted into cDNA. After cut and ligation, suppression subtractive hybridization was performed with appressorium cDNA as tester and the mycelium/conidium cDNA as driver to construct subtractive libraries. Reliability of the libraries was evaluated by approach of comparing RT-PCR products with templates from tester and driver cDNAs. The results indicated that 142 target segments were isolated from the library; seventy one of them were verified to be differential expressed genes by RT-PCR, which suggested that the libraries were reliable and efficient. This study founded the basis of further investigation of genes' expression and function during the course of appressorium formation by constructing subtractive libraries in associated with appressorium formation differential expression genes.

Rhizoctonia cerealis could secrete several extracellular proteases when grown in liquid medium with wheat cell walls as the sole carbon and nitrogen source. A kind of protease was purified after ammonium sulfate precipitation, SP-Sepharose Fast Flow chromatography, Phenyl (high-sub) -Sepharose Fast Flow chromatography and Sephadex G-75 chromatography. It appeared as a single band corresponding to molecular weight (MW) of approximately 40 kD on SDS-PAGE with silver staining. It showed high activities against the trypsin substrate Benz-Phe-Val-Arg-NA, and also the substrates D-Val-Leu-Arg-NA, Benz-Pro-Phe-Arg-NA and D-Val-Phe-Lys-NA. It was strongly inhibited by aprotinin, leupeptin, soybean trypsin inhibitor and partly inhibited by PMSF, indicating that it is quite probably a trypsin-like protease.

The 9 species including 9 strains of T. indica,5 strains of T. walkeri and their similar or related species, Tilletia horrida, Tilletia barclayana, Tilletia setariae, TiUetia sumatii, Tilletia fusca, Tilletia tritici and Tilletia controversa were studied. The primers and TaqMan MGB probes were designed for detection of T. indica and T. walked based on nucleotide differences within the target fragment sequences. The fluorescent monoplex PCR and doubleplex PCR were respectively developed. By the fluorescent doubleplex PCR, T. indica or T. walkeri was specifically detected simultaneously through one PCR reaction with 5 μL reaction volume per tube. These two methods, with the cost being obviously lower, are rather specific, reliable, rapid and suitable for application in routine quarantine.

Clavibacter michiganensis subsp, michiganensis is the most relevant tomato bacterial pathogen. The specific primers sets and TaqMan probe were designed based on the region of ITS to detect Cmm with real-time fluorescent PCR (RTF PCR). The RTF PCR was approximately 100 times more sensitive and more specific than normal PCR. Strong fluorescent signal could be collected during the reaction that the DNA extracted directly from the latent infected seed and seedling were used as template. This method provides a specific, sensitive, rapid detection of Cmm for the seed and the seedling industry.

The role of Calcium signaling in POD activity induced by oxalic acid in Malus hupehensis (Pamp) Rehd. leaves was studied by treating the leaves with Li⁺, EGTA, verapamil (Ver) and chlorpromazine (CPZ). The results showed that these inhibitors could inhibit POD activity induced by oxalate when they were applied at the same time with oxalate or before oxalate treatment. The effect of the inhibitors and oxalate suggested that Ca²⁺, Ca²⁺ -channel, Calmodulin (CaM) and inositol -1,4,5-tfisphosphate (IP₃) might be involved in the signal transduction by which oxalate induced POD activity. In addition, these inhibitors could inhibit POD activity induced by oxalate when they were applied after oxalate treatment. The effect of EGTA and Ver applied after 8 h was greater than that of them applied after 4 h of oxalate treatment on POD activity induced by oxalate. The effect of CPZ and Li⁺ applied after 4 h was similar with that of them applied after 8 h of oxalate treatment on POD activity induced by oxalate.

To characterize molecular and biochemical mechanisms of the hypersensitive reaction (HR) in plants, tobacco plants (Nicotiana tobacum cv. Xanthi n. c.) were treated with the proteinaceous HR elicitor harpin_Xoo from pathogenic bacteria Xanthomonas oryzae pv. oryzae. Tobacco leaves infiltrated with 40μg/mL harpin_Xoo developed lesions reminiscent of the hypersensitive response at the 20th hour after being treated. Using Evans blue and Trypan blue staining, we investigated the kinetics of dead cells in tobacco leaves induced by harpin_Xoo. The results indicated that micro-HR began to occur at the 4th hour after treatment. Since H₂O₂ was suggested to be a signal in cell death,we analyzed the generation of H₂O₂ using DAB staining. H₂O₂ accumulated rapidly and obviously following harpin_Xoo treatment. The results of quantitative RT-PCR showed that the time course of harpin_Xoo induced H₂O₂ accumulation is similar to that of the expression of the gene rboh. Expression of aoxl is a relatively late event, but the expression of sodA is decreased after induction by harpin_Xoo.

This review provides a broad overview of etiology, mechanism of pathogenesis and host resistance and IPM strategies involved in maize stalk rot and ear rot diseases in China. Some different viewpoints in the past are discussed in etiology of stalk rot occurring in China. The relation of both diseases is particularly evaluated based on Fusarium polymorphism analysis at the level of soluble protein, serology, isozymes and DNA, which are also further analyzed in accordance with the knowledge obtained by tracing pathogen infection process within the host root and stem tissue and trapping airborne spores nearby corn plants in the field. The recent researches of both diseases are summarized in physiological and biochemical mechanism of host resistance and resistant genetics, as well as IPM measures centered mainly in the application of biological control agents are summarized.

Reaction components and reaction cycling parameters were optimized for a multiplex RT-PCR protocol to simultaneous detection for three lily viruses with 18S ribosomal RNA used as an internal control. The first strand eDNA was synthesized using reverse transcriptase and primer mixture of three virus-specific reverse primers (0.5 μmol/L each) and 18S rRNA reverse primer (0.5 μmol/L). A series of conditional assays resuited in modification of the standard reaction components. Utilization of a DNA polymerase concentration of 0.100 U/μL, Mg²⁺ of 4.0 mmol/L, and four primer pairs of 0.2 μmol/L each was set for simultaneously amplificating the cDNAs of Lily mottle virus (LMoV), Cucumber mosaic virus (CMV), Lily symptomless virus (LSV) and 18S rRNA with more than 25 cycles. The above multiplex system was able to detect different virus combinations. The feasibility of multiplex RT-PCR was investigated by analyzing 10 leaf tissue samples. Compared to ³²p labeling nucleic acid hybridization, this optimized multiplex RT-PCR system was of higher sensitivity and specificity for detection of the above viruses infecting lily plants.

Fusarium wilt of spinach incited by the pathogenic fungus F. o. f. sp. spinaciae is a very important disease of spinach worldwide. Classical diagnosis of this disease normally requires many days and often gives erroneous results. Differential detection assays employing randomly amplified polymorphic DNA-sequence tagged sites (RAPD-STS) were developed for F. o. f. sp. spinaciae. Unique fragments (GenBank accession number AY337463) from RAPD profiles that differentiated the pathogens and other isolates were cloned and sequenced. Then six pairs of primers were designed and used for two types of polymerase chain reaction (PCR) techniques (a classical PCR and a real-time PCR) to compare the sensitivity. Results demonstrated that only one of the primer sets amplified a clear single fragment specifically for isolates of F. o. f. sp. spinaciae, and worked well in both of the PCR techniques. Classical PCR was able to detect at least 100 pg of pathogen DNA, while the real-time PCR method using SYBR Green Ⅰ on the Smart Cycler was capable of detecting less than 1 pg of pathogen DNA, and was able to rapidly diagnose the disease and quantitatively assay pathogen DNA. This method was optimized for using DNA extracted from the microconidia of the fungus, and may be useful for field disease diagnosis and prognosis.

A polymerase chain reaction (PCR) protocol was developed to specifically detect C. musae, the causal agent of banana anthracnose. Approximately 510 bp fragment of C. musae and the other outgroup fungal genome DNA were amplified by using the universal primers 18SF and 28SR of internal transcribed spacer (ITS) region of eukaryote 18S-28S ribosomal DNA. The species-specific PCR primes ColM1 and ColM2 for C. musae were designed after multiple sequence alignment of C. musae and the other species of Colletotrichum genus. By which a 382 bp single fragment with DNA from the isolates of C. musae was amplified, no product was amplified with DNA from other fungi and DNA of banana tissue. 0.1 pg C. musae genomic DNA was detected by species-specific primers. The PCR protocol provides a rapid and reliable tool for routine detection and identification of C. musae. In addition, it is important that we can inspect whether C. musae infect the banana tissues or not and also significative to take control measures timely.

The low molecular weight RNAs from 11 coleus plants were characterized by Return-PAGE, RT-PCR and Dot-blot hybridization. The results showed that all the 11 coleus plants were infected by Coleus blumei viroid. The amplified products of RT-PCR were cloned into vector pGEM-3Zf (+) and sequenced. 5 sequences variants were registered in GenBank DQ178395,DQ178396,DQ178397,DQ178398 and DQ178399, and compared with reported sequences of CBVd-1 in GenBank showing 85.23%-99.20% identity. No Coleus blumei viroid 1 detected from coleus seeds by RT-PCR and Return-PAGE. This is the first report on the occurrence of CBVd in China.

Based on particular biological characteristics of Cucumber mosaic virus beet isolates CMV-XJ1 and CMV-XJ2, detection was done by RT-PCR. RFLP of RT-PCR products showed that, the resulting fragments digested with Msp Ⅰ of the two isolates were very similar to isolate belonging to subgroup Ⅰ, but distinct difference appeared when they digested with EcoR Ⅰ. Thus CP gene of CMV-XJ1 and CMV-XJ2 were cloned. Sequence analysis revealed both were belonging to CMV subgroup IB, there existed differentiation trend between them.

The accumulation of pathogenesis-related proteins and disease resistance against downy mildew in cucumber plants were analyzed using BTH and oxalic acid. Local and systemic resistance against downy mildew were both rapidly induced in cucumber plants after treatment with 0.5 mmol/L BTH or 10 mmol/L oxalic acid, and duration of the induction could persist for 15 d. BTH or inoculation both systemically induced three proteins of 33, 27 and 22 kD in intercellular fluids, while oxalic acid did not induce the three proteins. BTH or oxalic acid treatment both induced the increase of POD activities, while no new POD isoenzymes were expressed in treated seedlings. The increase of POD activities was related to induced resistance of cucumber to downy mildew.