Mycorrhizal fungi, especially arbuscular mycorrhizal fungi (AMF) and ectomycorrhizal fungi (EC-MF) can antagonize a number of plant soil-borne pathogens, and improve plant disease resistance. It is quite interesting to know whether mycorrhizal fungi (MF) agents may be applied to control soil-borne diseases in fields. The author systematically analyzed the possibility of MF agents to control plant soil-borne diseases, ecophysiology of MF, the production of MF agents, the application methods and the future work in this paper. The potential and the applied range were estimated as well as providing the basis for development of MF bio-control agents.

Antagonistic bacterium strain Bc51 was isolated from citrus leaves in Nanning, China. The strain was identified as Burkholderia cepacia based on its 16S rDNA sequence homology as well as physiological and biochemical characteristics. The suppressive ability of B. cepacia against growth of Xanthomonas axonopodis pv. citri was influenced by the environmental factors, such as temperature, pH and medium. In greenhouse test, 60.3% of lesion development of citrus canker was inhibited by B. cepacia. Less change in suppressive ability of B. cepacia against growth of X. axonopodis pv. citri was observed during 8 continuous transfers on artificial medium. A broad suppressive spectrum of B. cepacia against growth of the other plant pathogens was observed, indicating the potential of B. cepacia for biological control of other plant diseases as well as citrus canker.

The total of 86 isolates of Phytophthora infestans were collected from newly developed winter-growing potatoes in Dehong district of Yunnan province during 2003-2005. The phenotype characteristics in-cluding mating type, virulence spectrum, physiological race structure, and response to metalaxyl were investi-gated systematically. The results showed that 62 isolates tested were all subjected to A1 mating type, and no A2 mating type or self-fertility isolate were found. The virulence detection, monitoring and further analysis of physiological race structure demonstrated that all known R gene of potato could be overcome by corresponding virulence gene both in the artificial inoculation experiments and field monitoring trial of late blight differen-tials. The virulence component of race and its structure in Dehong were complicated as well. Among 66 iso-lates tested, 36 races could be distinguished with different virulence spectrum, and superior race of 1,2,3,4,5,6,7,8,9,10,11 was most common in Dehong with the frequency of 18.18%. Response test to metalaxyl showed that, out of 60 isolates tested, 56.67% were sensitive, 25.00% intermediate resistant, and 18.33% resistant to metalaxyl. The results were preliminary analyzed and discussed.

Restriction fragment length polymorphism (RFLP) and single strain conformation polymorphism (SSCP) assays on coat protein (CP) genes of 4 CTV-isolates and their 31 sub-isolates after single aphid trans-mission were conducted, and CP genes of the 8 sub-isolates were sequenced. CPG/Hinf I RFLP groups and SSCP patterns of all the CTV were discovered, and both demonstrated that single aphid transmission was an effect way to separate CTV isolates. The results of sequencing showed that CP genes of sub-isolates with the characteristic of the same RFLP group had high homomorphism, while these fallen into different groups had lower homomorphism. The relationship among these molecular characteristics of CP genes and biological characters of virus were preliminarily suggested by comparison with identified CTV isolates based upon typical symptoms.

By use of an oligo (dT) 18 as a reverse transcription primer, polyadenylated RNA viruses CTV and CTLV were detected by RT-PCR. CEVd could be also detected in this way. CEVd is a non-polyadenylated RNA viroid, but there is a fragment rich in A in CEVd sequence. On the bases of uniplex RT-PCR, a multi-plex RT-PCR was developed to detect CTV, CEVd and CTLV simultaneously. The results of the multiplex RT-PCR to detect each of the pathogens were consistent with uniplex RT-PCR. The multiplex RT-PCR provides a simple and rapid method for detecting CTV, CEVd and CTLV in citrus plants in a large number at the same time.

An allele-specific PCR-based method was developed to distinguish Fusarium virguliforme, the causal agent of soybean sudden death syndrome (SDS) in North America, from Fusarium phaseoli. Under the rules of allele-specific primer design, one pair of primers, Fsg-α-1/2 were synthesized based on three SNP sites on translation elongation factor 1-α gene, which could distinctively amplify F.virguliforme and produce PCR products of 327 bp. In addition, to distinguish F.virguliforme and F.phaseoli from the other Fusarium spp., one pair of primers, Fu1/2, were designed based on the region of ITS (intergenic transcribed spacer), and produced PCR products of 452 bp. In this test, conventional AS-PCR and duplex PCR were combined to increase the sensitivity and reproducibility, Fu1/2 acting as positive control primer. Thus, AS-PCR approach provided an accurate, convenient and effective method for quick identification of F.virguliforme.

Interaction between rice (Oryza sativa L.) and Magnaporthe grisea is a model system to study the interplays between plants and pathogens. The induced expressions of three key enzyme genes of plant signaling pathway, five pathogenesis-related protein genes, and one defense-related transcription factor control gene were studied in rice leaves by using three rice near-isogenic lines (CO39, C101LAC, C101A51) and two special blast isolates (M209, M210). The results showed that OsLOX, OsAOS and OsPAL were induced by two special isolates in all interactions. Jasmonate-and salicylate-dependent defense signaling pathways were activated at the same time. While OsPR1a, OsPR2, OsPR3-1, OsPR3-2 and OsPR4 were expressed at higher levels in the leaves of incompatible rice plants and also for longer time than that in the leaves of compatible rice plants. OsMyb gene was induced differentially in different interactions between rice and M. grisea. Higher expression of these defense genes in incompatible rice plants might be responsible for resistance against M. grisea.

A suppression subtractive hybridization (SSH) cDNA library was constructed with wheat leaf in-duced by Puccinia striiformis race CY23. The process of library construction was checked and analyzed, results showed that the technique was efficient in the subtractive hybridization. 172 ESTs with good quality were as-sembled to 120 contigs with DNAStar 5.0 software. After function annotation, the most prevalent category was energy and primary metabolism which accounted for 32.5%, genes related with photosynthesis showed the highest frequency;the second category was membrane and transport, resistance and defense genes were in the third one;while genes involved in secondary metabolism, protein synthesis and process and cell structure were less. HR and SAR were supposed to be two main styles involving in resistance reaction through analyzing se-quences with function identified genes. Four interested sequences were selected to testify their expression pro-file at different time after inoculating with P. striiformis race CY23 by reverse transcription PCR (RT-PCR).

Tobacco plants were inoculated with Tobacco mosaic virus (TMV) and expressed systemic symp-toms. A large amount of virus particles and crystals, together with myeloid bodies, multivesicular bodies and secondary vesicles were seen in mesophyll cells and/or sieve tubes of inoculated plants by EM observation. Chloroplasts, mitochondria, endoplasmic reticulum, and other organelles were also found to be distorted, di-sintegrated and collapsed in mesophyll cells of inoculated plants. It was evident that a few virus particles and relative structures (not clear) was produced, and organelles mostly remained unchanging in mesophyll cells of plants treated with chito-oligosaccharides (50 μg/mL), but large starch grains occurred in chloroplasts. Be-sides, much electron-dense material deposited in vacuoles and middle lamella of mesophyll cells of treated plants, that was never seen in uninoculated or untreated plants. It was possible that the electron-dense material was related to induction of resistance to TMV.

The role of hydrogen peroxide (H₂O₂), nitro oxide (NO) and calcium (Ca²⁺) in stomatal clo-sure of tobacco induced by elicitor PB90, a protein elicitor secreted by Phytophthora boehmeriae was investi-gated. Treatment to abaxial surface of young expanded leaves with 1 nmol/L PB90 could induce stomatal clo-sure in wild-type tobacco cv. Bel-W3. Transgenic anti-APX tobacco could produce more H₂O₂ than Bel-W3 after treatment with PB90 and stomatal aperture of anti-APX was smaller than that of wild-type tobacco. Fur-ther experiments revealed that pretreatment with DTT, an antioxidant, DPI, an inhibitor of NADPH oxidase, L-NAME, an inhibitor of nitro oxide synthase, EGTA, a Ca²⁺ specific chelate, KN93, a competitively inhi-bitor of CaMPK Ⅱ, and U73122, an inhibitor of phospholipase C were able to attenuate PB90-triggered stoma-tal closure of wild-type tobacco. It was suggesting that PB90 induced stomatal closure involving H₂O₂ produc-tion via NADPHase, NO generation via nitro oxide synthase and Ca²⁺ signal transduction pathway and the molecules such as H₂O₂, NO and Ca²⁺ functioned as the second signals involved in PB90-induced stomatal closure.

Two inverted repeats cDNA fragments derived from 5' and 3' ends of PVY^N CP gene were cloned respectively, and the corresponding expression vectors pROKⅡ-5' IR and pROKⅡ-3' IR were constructed. Re-combinant binary vectors were then introduced into tobacco (NC89) plants via Agrobacterium tumefaciens-me-diated transformation. 166 and 126 transgenic plants transformed with pROKⅡ-5' IR and pROKⅡ-3' IR were obtained, respectively. Resistance tests indicated that plants transformed with pROKⅡ-3' IR were highly resis-tant to PVY infection, and the proportion of disease resistant transgenic plants was 69%, while plants trans-formed with pROKⅡ-5' IR were susceptible to PVY^N infection. Southern blot results indicated that there were no obvious correlation between the copy numbers of transgene and resistance. Northern blot results revealed an inverse correlation between transgenic transcript accumulation and virus resistance, it demonstrating that the re-sistance was RNA mediated. The results demonstrated that the hpRNA (hairpin RNA) with 50 bp-stem de-rived from the 3' end of the CP gene is sufficient to induce RNA-mediated gene silencing. This information is useful in production of transgenic plants which are resistant to multi-virus infections.

Wheat stripe rust (Puccinia striiformis West. f. sp. tritici Eriks et Henn.) can cause the yield loss of wheat in a large scale in China. It is reported that the key to control is monitoring this disease. A hand-held sensor[ASD FieldSpec HandHeld FR (325-1 075 nm) made by ASD Company, 1990] was used to measure the canopy reflectance of the disease in field via a fire-balloon flight. And the spectral data from near-ground correspondingly was also obtained. As a result, the difference between data obtained from near-ground and fire-balloon were found to be regular and distinctive. The reflectance data from fire-balloon were distinc-tively higher than that from near-ground. Statistic analysis of the reflectance at green band (580 nm) and yellow band (610 nm) was made. Then the regression model between reflectances obtained from near-ground reflectance and fire-balloon at the two of the most distinctive wavelength band. This model, to some extent, could be important to the research of monitoring of wheat stripe rust via higher platform.

In virus-host interaction, there are mechanisms for a host to eliminate virus either actively or pas-sively. Efficiency of light induced sporulation-single conidial spore isolation, spheroplast regeneration, and meristemic culture in eliminating or escaping virus from the hypovirus-infected Cryphonectria parasitica strains EP721, EP713 and Euro7 was evaluated. Single spore isolation was effective in all treatments though with varied efficiency and spheroplast regeneration was also an efficient method to obtain virus-free colonies from in-fected strains. The latter may be particularly useful in obtaining the virus-free culture in case where a virus-in-fected fungus does not produce spores.

The antagonism and control efficiency of four bacterial antagonists, including Bacillus subtilis BS, GF1, and Fluorescent pseudomonads LX1, BCA1, on seven strains of Phytophthora capsici from different origins were studied. Among the four bacterial antagonists tested, BS showed the maximum suppression of mycelial development of P. capsici. The inhibition rates ranged from 33.2% to 59.4%. In biological control assay in vivo, the most effective suppression of pepper Phytophthora blight was achieved when BS was sprayed or BCA1 was drenched on the plants. The control effects were 56.83% and 57.81%, respectively. The mycelial growth was significantly suppressed by crude antibiotic extract of strain BS. The inhibition rate reached 100% when the mycelia were treated with 10-fold dilution of crude extract. Microscopic observation disclosed that hyphal branch of P. capsici increased, the interval between branches shortened remarkably, and the proto-plasm on the apex of branch dissolved after treatment with extract. In addition, the zoospore germination was significantly inhibited by the extract. The colonization of BS in pepper seedlings was studied by a GFP-labeled BS strain. The results showed that BS could colonize in the roots, stems, and leaves of pepper seedlings by seed soaking with the bacteria. The GFP-labeled BS could be detected 60 d after the emergence and the colo-nized population maintained more than 10³ cfu/g.

Effect of essential oil from Asarum heterotropoides Fr. Schmidt var. mandshuricum (Maxim.) Kitag on hypha growth of sixteen plant pathogenic fungi was tested at concentration of 500 μg/mL. The inhibi-tion rates to fourteen plant pathogenic fungi were above 50%, which showed the essential oil had broad-spec-trum antifungal activity. According to the toxicity curve of essential oil to Alternaria humicola, the EC₅₀ to mycelium growth and spores germination were 326.86 μg/mL and 406.24 μg/mL respectively. Furthermore, the effect of essential oil on cell membrane potential of A. humicola was tested by the conductivity method. The results showed the action of essential oil was changing osmosis of cell membrane of fungi.

Rose leaves with virus symptoms (mosaic, ring spot and line pattern) were detected by DAS-ELISA and RT-PCR. The results showed Prunus necrotic ring spot virus (PNRSV) infection in the leaves. CP gene of PNRSV isolated from Yunnan province was cloned and sequenced. Analysis of sequence showed that CP gene of PNRSV-yunnan contained 683 nucleotides encoding 165 aminoacids (EMBL accession num-ber:AY684271). Nucleotide similarity of CP gene was more than 98% between PNRSV-yunnan and group I isolates, and less than 95% between PNRSV-yunnan and group Ⅱ and Ⅲ isolates. According to the results, PNRSV-yunnan was identified as a member of group I.

Endophytic bacteria B20-006, an antagonistic microbe, was applied to coat maize seeds and resul-ted in 67.9% control effect on maize sheath blight caused by Rhizoctonia solani. Moreover, B20-006 was en-sured the ability to penetrate roots, and in turn move along vascular elements of maize plants. For further study of biocontrol mechanism of the antagonistic agent, the changes of major defensive enzymes (PAL, POD, SOD and EST) in specific activity were assayed in plants due to interaction between B20-006 and host maize.

Fifty six endophytic bacteria strains were isolated from the roots of wheat, and one strain named G-32 was screened with antagonism on pathogenic fungi of Gaeumannomyces graminis var. tritici. Preliminary characterization indicated that G-32 was belonged to Bacillus cereus. The inhibitory action to the fungi was as-sayed in lab by using the fermentable extracts of antagonistic endophytic bacteria. The results showed that my-celium of G. graminis var. tritici growed slowly and the biomass reduced 89% compared with the control 6 d after inoculation. The hyphae were deformative which broke into pieces. Colonization was studied with dual-resistant label which suggested that the endophytic bacteria strain could colonize in the root systems of wheat. The control efficacy with G-32 strain against the disease of the wheat take-all in pot tests was better than that of common used chemical fungicide Diniconazole.

The differential genes expression of adult plant resistance gene of TcLr35 was analysed by using cDNA-AFLP technique. The results showed that 33 of 843 amplified bands were differential ones in different growth stages of TcLr35. A polymorphic band amplified by primer pair E-TG/M-CTG was found at different leaf-growing stages from the second to the sixth leaf of TcLr35 and absent in Thatcher and the seedling stage of TcLr35 on TcLr35 without inoculated with Puccinia recondita. Reverse Northern blotting test suggested that band E-TG/M-CTG-192 was a piece of special gene fragment of TcLr35. The band was cloned and sequenced subsequently. The fragment of 192 bp produced by E-TG/M-CTG contained an open reading frame (ORF), but did not show homologous to the published wheat gene sequences.

Plant parasitic nematodes cause heavy yield losses and difficultly to control. Now strategies to manage nematodes are based on crop rotation, nematocides, biological control, use of resistant cultivars etc., but inadequate. With the further investigation of molecular interaction between plant and nematode, and the development of molecular genetic technology, it has been a hot spot in looking for novel ways to prevent nematode by using genetic engineering technology. The paper briefly reviewed new strategies for plant parasitic nematode control mediated by plant resistance genes, foreign proteins, specific expression promoters and RNAi, and their application in plant disease-resistance breeding.

Twenty strains of Fusarium oxysporum isolated from cucumber, melon and watermelon were grouped into vegetative compatibility groups (VCGs) by using nitrate nonutilizing (nit) mutants, and dif-ferent percentages of chlorate resistant mutant and nit mutant obtained from different hosts, positions of the plant and pathogenicity were observed. The results showed that the numbers of chlorate resistant mutants in each inoculation of the strains isolated from different hosts were in the range of 0.89-0.98, which were not significantly different;but it of the strains isolated from root, basal stem and middle stem were 1.27, 0.75 and 0.76, respectively, which were quite different. The percentages of nit1 mutants (75.40%) were evidently higher than those of nitM mutants (13.17%). Significant differences were found among the percentages of nit1 mutants of the strains isolated from different hosts or positions of the plant, whereas slightly differences between pathogenic and nonpathogenic strains. The percentages of nit1 mutant from cucumber, melon and watermelon were 67.73%, 83.71% and 77.50%, or from the root, basal stem and middle stem were 81.82%, 78.48% and 68.64%, respectively. Similar situation was observed for nitM mutants in the strains from different positions of the plant and pathogenicity, but slight difference in the strains from different hosts. The highest percentage of nitM mutants occurred from the basal stem (15.97%) while the lowest from the middle stem (9.87%), and the percentages from the pathogenic and nonpathogenic strain were 14.08% and 9.26%. All isolates were grouped into seven VCGs. Strains from different hosts fell into different VCGs, nonpathogenic strains were uncompatible to pathogenic ones and vegetative compatibility was found in all strains from the different positions of the plant.

Citrus tristeza virus (CTV) exists as a large number of distinct strains differing in biological cha-racters in citrus cultivars. Mild strains cross protection (MSCP) as a strategy aimed at controlling severe variants of the pathogen, require deep understanding the influence of citrus cultivars on composition of CTV iso-lates. 18 subisolates of CTV isolate TR-L514 were obtained by graft from Jin cheng to six citrus cultivars. Bio-logical index was used to detect the pathogenicity on the subisolates and TR-L514. Restriction fragment length polymorphism (RFLP) and single-strand conformation polymorphism (SSCP) assay on p25 gene were conducted, and p23 gene was sequenced. The results indicated that citrus variety might change the composi-tion of CTV isolate, and sweet orange might be more suit to CTV propagation. In sweet orange, TR-L514 was detected to contain p25//Hinf Ⅰ both group 1 and 6, and showed more complex SSCP patterns than that in other 4 citrus cultivars. The sequence diversity of p23 gene might result in the adaptation to CTV in different citrus hosts.

The virus isolate Y322 was obtained from Solanum aculeatissimum showing leaf curl and enation symptoms in Yanshan, Yunnan Province. Complete nucleotide sequence of the DNA-A like molecule of Y322 was determined to be 2 730 nucleotides. Y322 DNA-A was most closely related to isolates of Tomato yellow leaf curl China virus (TYLCCNV) with 88.3%-99.2% nucleotide sequence identities, while less than 79.6% nucleotide sequence identities were found in comparisons with other begomoviruses. Therefore, Y322 was taxonomically considered as an isolate of TYLCCNV. Further studies showed that Y322 was associated with a DNA β molecule. The DNA β of Y322 contained 1 331 nucleotides having the highest nucleotide sequence identity (75.1%-93.1%) with DNA β associated with TYLCCNV, while less than 55.4% nucleo-tide sequence identities were found in comparisons with other DNA β molecules. This is the first report of TYLCCNV in S. aculeatissimum.

10 hermaphroditic isolates including GUY11, KA3, KA9, KA7, 6023, 2539W, 8773R-19, 8773R-27, 8113R-2 and 8113R-10 of Magnaporthe grisea were crossed each other to clarify the cause of difference in fertility analysis conducted by different laboratories. The results showed that 10 isolates were her-maphroditic fertile with clear mating type (either MAT1-1 or MAT1-2) except for strain 2539W, which lost the capability to function as a female. 24 isolates from Fujian rice fields, fertile when mated with 6023/2539W, showed difference in fertility when mated with other 8 hermaphroditic isolates, it might be caused by the difference in compatibility between tested isolates and hermaphrodites. Considering the fertility, compati-bility and host sources, it was suggested that GUY11 and KA3 were the best hermaphroditic isolates in mating type and fertility analysis. Fertility and mating type of 227 isolates from Fujian rice fields were further tested with GUY11 and KA3, the results revealed that 81.1% were fertile with a ratio of 81.0:19.0 for MAT1-2 to MAT1-1. The study is helpful to understand the fungal population genetics and evolution.

Hirsutella minnesotensis is a parasite of second-stage juveniles of soybean cyst nematode, and has great potential in biocontrol. Six natural media were evaluated for growth and sporulation of 4 isolates of H. minnesotensis on agar. Meanwhile 20 carbohydrates, 19 nitrogen compounds and 9 vitamins were tested for growth, sporulation and spore germination of 3 isolates of H. minnesotensis on agar plates and in liquid cultures. In general, YDA was good for growth and MEA was good for sporulation, while TSA was not good for growth and sporulation of H. minnesotensis. Melibiose was the best carbon source for aerial mycelium growth on agar, and glycogen was the best carbon source for the growth in liquid culture and spore germina-tion on agar. Casein and peptone was the best nitrogen source for aerial mycelium growth on agar and growth in liquid culture, respectively. Most of nitrogen compounds supported spore germination of H. minnesotensis except L-Cystine, it could not be utilized by any of the isolates on agar. Vitamins showed no significant effect on the growth, sporulation and spore germination of H. minnesotensis.

Using plasmid pGEMT-PVY-NHC as a template, DNA of TFPI1-161 was obtained by PCR and cloned into plasmid pPIC9K to construct expression plasmid pPIC9K-HC. After being linearized with restri-ction endonuclease Sal I, the recombinant plasmid was transformed into Pichia pastoris by electroporation. The transformants with high level of G418 resistance and slow growth on the MM plates were selected. After the selected transformants were grown in BMGY medium and induced by methanol, the culture supernatant was collected by centrifugation and analyzed by SDS-PAGE. The result showed that the recombinant HC-Pro molecular mass was about 66 kD and amounted to 40% total soluble proteins by gel analysis. Western blot analysis proved that the expression protein could bind to HC-Pro polyclonal antibody specifically.

A typical symptom recovery appears on tobacco (Nicotiana tabacum cv. white Burley) plants in-fected with Cucumber mosaic virus strain M (CMV-M). It is a significant step for finding of symptom reco-very mechanism of virus infection if the variation of virus concentration in tobacco plants infected with CMV-M is demonstrated. A quantitative method for detection of CMV-M was established by purified CMV particles and DAS-ELISA. The results showed that the virus concentration was positively related to severity of symp-toms, with the highest up to 790 μg/g tissue in the first appeared yellow symptom leaves, up to 508 μg/g tis-sue in the upper mosaic symptom leaves;and only 6 μg/g tissue in the recovery symptomless middle leaves, which was about 85 to 135 times less than that in the mosaic or yellow symptom leaves and also much lower than that in the stems and roots. RT-PCR and biological experiment showed that infectious virus did exist in the recovered leaves, but somehow the virus could not reach higher concentration and cause obvious symptom, it indicated that an efficient resistant mechanism existed in symptom recovery leaves.

Disease indexes of four rape varieties infected by 11 Turnip mosaic virus (TuMV) isolates ranged in 26.2-76.0 in the Spring test, while those of 14 rape varieties infected by 5 TuMV isolates in 38.3-55.9 in the Autumn test in 2004. It revealed that the virulence of all tested isolates differed at the high significance and significance levels based on statistic analysis, respectively. 17 TuMV isolates originating from Brassica napus, B. rapa, B. chinesis, Sesamum indicum and Raphanus sativus had the sequence identities of coat pro-tein gene more than 97% with a reference Zhejiang isolate ZJB3. They all belonged to MB group. Another radish isolate WRS1 had identities of 95.4%-98.7% with ZJR1, CH1 and CH2 isolates, belonging to MR group. The nucleotide identities were 88.0%-92.2% among the isolates between the two groups. Phyloge-netic analysis indicated that a radish isolate WRS2 formed a single branch in MB group, possibly WRS2 was the offspring of a recombination between MR and MB groups.

Wheat cultivars Aquileja (AQ), Libellula (LB), Luke (LK), Nugaines (NG) and Xian Nong 4 (XN) were previously reported possessing quantitative, durable resistance to stripe rust disease. The study was conducted to analyze the components of stripe rust resistance in these cultivars and genetic distance among them. Wheat cultivar Ming Xian 169 (MX) was used as susceptible reference. In the experiments conducted at seedling stages in growth room, LB, XN and AQ showed lower density of substomatal vesicle and shorter length of colony of the rust fungus than LK and NG did. AQ and XN showed lower density of haustorium than LK and NG, while higher than LB. Unexpectedly, it was found that the density of substomatal vesicle in LK and NG was higher than that in susceptible reference MX. In the experiments conducted at adult-plant stages in fields, the five quantitative resistance cultivars, AQ, LB, LK, NG and XN, showed lower value of infection type (IT), disease severity (DS), area under the disease progress curve (AUDPC) and lesion length (LL) than the susceptible reference MX. Compared among AQ, LB, LK, NG, and XN, the IT was highest on AQ and lowest on LB, while the DS and AUDPC were highest on NG and lowest on LB. AQ, NG and XN showed longer LL than LK and LB. Lesion density was lower on XN and LB than that on AQ, and still lower than that on NG and LK. From these results it could be concluded that LK and NG were not capable of limi-ting penetration, while could restrict lesion extension at adult-plant stage. LB, XN and AQ were capable of limiting penetration as well as restricting lesion extension. The cluster analyses based on SSR DNA data grouped AQ and LB together, NG and XN were classified into the same group and LK was a separate one. On the basis of these results, transgressive segregation could be expected in the crosses of AQ or LB with any of the remaining three cultivars of quantitative resistance. This was confirmed from the results on the cross AQ/NG previously reported by our laboratory. The information reported here would be valuable to further work on breeding for resistance to stripe rust.

The epidemic of downy mildew in muskmelon was studied for 9 years in Jiashi, Arwat, and Kuqa counties, all located at the margin of Tarim Basin. Three-level spatial structure of long-distance spread of the disease was presented in this paper. An epidemic system in one oasis could be formed around a cucumber greenhouse area from which the primary inoculums was provided. The three-level spatial structure included epidemical region-system (consisted of some growing areas), growing area (consisted of some fields), and field. Jiashi epidemic system was divided into 3 growing areas. Downy mildew appeared first in the muskmelon fields near cucumber greenhouses in the first growing area every spring, and then spread outward further and further to other growing areas. The primary infection (the time when the primary infective points appeared in muskmelon fields) in the second growing area and the third growing area were 20 and 45 d later than that of the first growing area, respectively. The distances from the primary infective point in the second growing area and the third growing area to the infection source in the first growing area were 56.4 and 106.5 km respectively. Therefore, it was conformed that the disease sporangia were disseminated in the air to the second growing area from the first one and then dispersed to the third one in Jiashi.

Endophytic Bacillus subtilis BY-2 was isolated from oilseed rape. After return inoculation treat-ment to oilseed rape, the same endophytic B. subtilis as BY-2 was obtained. In 10 d after inoculation, the number of endophytic bacterium reached up to (2.24-9.02)×10³ cfu/g fresh plant. 25 d later, the number of bacterium was maintained (3.13-8.59)×10³ cfu/g fresh plant. The control effect of BY-2 on Sclerotinia sclerotiorum was investigated. After 2-day-confronting incubation on PDA plates, the inhibition zone reached to 3.1 cm. Meantime, serious mycelium malformation of S. sclerotiorum caused by BY-2 was observed, such as short growth, cytoplasm condensation, cell wall break and protoplasm leak. Even germination of sclerotia was also inhibited, the inhibition rate reached to 60%-70%. The control efficacy of BY-2 against S. sclero-tiorum was 100% on detached leaves in vitro.

The strains of phytohormones-producing bacteria were screened by using High Performance Liquid Chromatography (HPLC). Plant growth-promotion of these strains was determined on wheat seedlings. Strain CX-5-2 was selected and showed the most significant growth-promotion effect on wheat growth. The result showed that wheat seedlings irrigated with bacteria culture broth grew higher than that treated with water. The average height of wheat seedlings was increased about 10.54%. The accumulations of gibberellin and indole-3-acetic acid produced by CX-5-2 were measured with HPLC. Furthermore, CX-5-2 was also antagonistic to many pathogens through dual culture method. Identification of strain CX-5-2 was carried out with 16S rDNA ITS. The result indicated that strain CX-5-2 was belonged to genus Pseudomonas. HPLC was an efficient way to screen the strains of hormone producing bacteria.

The 3' terminal genomic 1 611 nucleotides of Beet mosaic virus Xinjiang isolate (BtMV-XJ) from China was determined (GenBank accession number DQ345522). The sequence started within a single open reading frame which was expected to encode part C-terminus of NIb protein of 201 amino acids, complete cap-sid protein (CP) of 276 amino acids and followed by a 3' untranslated region (UTR) of 168 nucleotides. The comparison of sequence diversity among BtMV-XJ and other three previously reported isolates revealed that it shared 98.3%, 98.1%, 91.4% nucleotide identity, and 99.79%, 99.58%, 97.69% deduced aa sequence identity with the corresponding 3' terminal regions of BtMV-SL, BtMV-UK and BtMV-US, respectively, and that most nucleotide mutations were silent with no effect on aa sequence. In addition, a virus-specific and rapid RT-PCR detection method of BtMV was also developed based on the nucleotide sequence obtained.

The pathogen associated with root-rot disease of aloe, a severe disease of aloe in Yunnan pro-vince, was identified as Fusarium solani (Mart.) Sacc., according to morphology, cultural characters and pathogenicity.

Rhabditis sp. Bn strain was the first time found suppressive on plant parasitic nematodes (PPNs) in the rhizosphere of greenhouse cucumber. The nematode Bn was applied into soil at the rate of 1.0×10¹⁰ Juveniles/hm² 10 days before cucumber plants being planted in October 2004 and then once a month as treat-ment. The same volume of tap water was used as control. The density of PPNs increased sharply in control and reached 1 561 Js/100 mL soil in April, whereas it was less than 400 Js/100 mL soil in treatment, signifi-cantly lower than that of control (P<0.01). The densities of PPNs, Meloidogyne spp. and Tylenchorhynchus spp. were reduced by 70% and 87% respectively by applying Rhabditis sp. Bn strain. The root-knot index of cucumber in treatment was also reduced significantly (P<0.05) in April 2005.

The genetic diversity of 110 strains of Ustilaginoidea virens from Liaoning province and Beijing where the types of rice variety constitution were different, was assessed by AFLP. The results showed that the coefficient of strains from Liaoning and Beijing was 0.92 and 0.55 respectively, and the strains from Beijing were divided into two distinct groups. There was no specific DNA pattern for the isolates from the same rice varieties, and there was no correlation between the clusters based on genetic similarity coefficient and variety origin of isolates.

An isolate of PVS, HZ00P1, was obtained from nature infected Solanum tuberosum from Hang-zhou, Zhejiang province. It was primarily identified by DAS-ELISA and host reaction tests. 3' end partial sequence of the virus isolate was cloned. Nucleic acid sequence of the cp gene and deduced cp amino acid se-quence alignments were compared with 16 other isolates registered in GenBank. The results showed that the 17 PVS isolates were divided into two groups. Among them, two Andean isolates were classified to group Ⅱ, HZ00P1 and the other 14 isolates were assigned to group Ⅰ. Compared with other PVS isolates in group Ⅰ, PVS HZ00P1 had 93.1%-98.1% and 95.9%-99.3% homologies of nucleotide sequence and deduced amino acid sequence respectively, whereas its similarities to the group Ⅱwere 81.4%-81.7% and 93.5%-93.9%. A survey of PVS occurrence in Zhejiang province was achieved by RNA spot hybridization (RSH). Among the 30 samples collected from different areas of the province, 26.7% were found to have the infection of PVS. It is concluded that PVS has become a common virus in Zhejiang province.

The effects of inoculum concentration, leaf stages of host plant, and environmental factors on the infection of Exserohilum monoceras isolate X-27 to barnyardgrass were investigated. The results showed that the lesion was visibly appeared on the leaf when inoculum concentration above 1.00×10⁵ conidia mL-1, 1-2 leaf stage of barnyardgrass was most sensitive for infection of E. monoceras. The data also indicated that dew period was the key factor for E. monoceras infection. Almost 90% of barnyardgrass plants were killed when dew period prolonged to 48 h. Temperature and illumination period did not significantly affect the infec-tion of E. monoceras, 25-28℃ and 12 h dark period after inoculation were enough for infection.

Sixteen testing strains were amplified by polymerase chain reaction using the universal primers of the bacteria 16S rDNA gene, and the nucleotide sequences of their amplified fragment were tested. The homology between these sequences and the 16S rDNA sequence of related bacteria strains in GenBank was analyzed. A phylogenetic tree based on 16S rDNA sequences was constructed and showed that there were three nucleotides difference between the 16S rDNA sequences of No.6-9 strains and the standard strain of A.a.c, the homology was more than 99.8%. They were clustered into the same phylogenetic branch in the tree. The result of PCR showed that only A.a.c strains came into being electrophoresis band. A.a.c was detected from different pathogenic germs, and a rapid and accurate method for detecting was established from molecular biology.

A new bacterial disease from oriental tobacco was first found in Baoshan of Yunnan Province du-ring 2004-2005. The disease was mainly harmful for oriental tobacco leaves. Initial symptoms were black small circular or polygonal specks like water-soaked on the leave. Later these specks expanded and joined together, forming bigger irregular necrotic specks. 28 strains were isolated from diseased leaves of oriental tobacco. The same symptom as that on naturally infected leaves was produced by inoculating the strains on maturity leaves. The pathogen was identified as Pseudomonas syringae pv. tabaci(Wolf et al.)Young et al., according to characters of morphological observation, biochemical and physiological identification, 16S-23S rDNA intergenic spacer sequences analysis and further pathogenicity determination.