This paper briefly introduces the basic concepts of a new field of plant pathology——molecular epidemiology of plant diseases. Molecular biology and biotechnology have been widely used in many areas of epidemiology. In addition to identify the disease-causal pathogens, some molecular approaches have been used to efficiently quantify the initial inoculum causing disease epidemics, demonstrating the advantages over the conventional methods. Population genetics provides useful tools to infer the pathways of pathogen long-distance dispersal and disease spread, and may offer strong evidences of pathogen migration as complement of conventional methods. These bio-techniques have been also used to monitor the spatial and temporal developments of diseases and pathogen populations, to study the pathogen long-term evolution and its effects on disease epidemics, and to reveal the competitions between different pathogen genotypes and the resulting consequences of disease epidemics. Using molecular approaches, screening host resistance will become more efficient. More valuable disease control strategies will become applicable with applications of bio-techniques. Macro-and Micro-approaches will be combined as advantages of methodology, demonstrating a huge potential to promote the research in epidemiology.

Powdery mildew was observed on tomato (Solanum lycopersicum L.) in the greenhouse in Changchun city, and the pathogen was studied with morphological and molecular methods. Based on the characteristics of conidia, conidiospores and conidia germination, the pathogen was identified as Oidium neolycopersici Kiss. Conidia were ellipsoid or cylindrical type, formed singly. Conidiophores were unbranched and hyaline. Foot cell was cylindric, sometimes slightly flexural followed by 1 or 2 cells. The conidia germinated from side and the germ tube terminated in a lobed or a club-shaped appressorium. Appressoria were nipple-shaped or slightly lobed. Chasmothecia were not observed. The rDNA ITS region of the pathogen was amplified by PCR and sequenced. The results showed that the identity was 100% with O. neolycopersici by BLAST the sequences in GenBank, which confirmed that the pathogen of tomato powdery mildew collected in Changchun was O. neolycopersici.

The linkage analysis was conducted on 97 segregating haploid progeny isolates from a cross between 2 isolates, CPW-1 and E17, differed in 8 avirulence genes. The amplified fragment length polymorphism (AFLP) technique was used to construct the genetic linkage map of Blumeria graminis f. sp. tritici. MAPMAKER/EXP (3.0b) and MapDraw V2.1 were used to construct and draw the linkage map. A total of 117 loci were mapped, comprising 112 AFLP markers and 5 avirulunce genes. The markers were distributed over 10 linkage groups covering a total length of 1 425.1 cM. This was the linkage first map that contain 117 loci in B. graminis f. sp. tritici. Some AFLP loci which are clustered tightly with a few avirulence genes was reported for the first time. Construction of the linkage map had laid the foundation for locating and cloning avirulence genes and provided the basis for the genetic research of wheat powdery mildew.

Based on the differences in internal transcribed spacer (ITS) sequences of T. basicola and other tobacco fungal pathogens, a pair of species-specific primers TB-5/TB-3 was designed for T. basicola detection. After screening 10 isolates of T. basicola and other tobacco fungal pathogens, TB-5/TB-3 primers amplified only a single product of about 400 bp from T. basicola. And T. basicola could be specifically dectec-ted by PCR assay with TB-5/TB-3 from tobacco tissues infected naturally and soil samples. The sensitivity of detection was 100 fg genomic DNA per 25 μL PCR reaction volume. The PCR-based methods developed here could simplify both plant disease diagnosis and pathogen monitoring, as well as guiding plant disease management.

Double-stranded RNA (dsRNA) elements and their pathogenicity of 16 strains of Sclerotinia sclerotiorum collected from eggplant grown in Jiamusi of Heilongjiang province, China, were investigated. Transmission of the abnormal hyphal-growth characteristics including slowly-growing and abnormal branchings from 5 hypovirulent strains of S. sclerotiorum to virulent strains of the pathogen were determined on agar medium. The results showed that pathogenicity of these strains of S. sclerotiorum on detached leaves of oilseed rape (Brassica napus) differed greatly. Three pathogenicity types were classified with 7 strains belonging to the strong pathogenicity type (SPT), 7 belonging to the weak pathogenicity type (WPT) and the other 2 belonging to the intermediate pathogenicity type (IPT). dsRNA elements were detected from the mycelia of 10 strains of S. sclerotiorum. Three SPT strains contained 7.4 kb dsRNA, six WPT strains contained both 6.4 kb and 7.4 kb dsRNA and one WPT strain contained only 6.4 kb dsRNA. But no dsRNA was detected in 4 SPT strains and 2 IPT strains of S. sclerotiorum. Therefore, the 6.4 kb dsRNA was more closely related to virulence atte-nuation (hypovirulence) of S. sclerotiorum than the 7.4 kb dsRNA. The results also indicated that the abnormal hyphal-growth characteristics of the five hypovirulent strains of S. sclerotiorum could be transmitted to vi-rulent strains of this fungus in a strain-specific manner. This study further suggests the importance of the 6.4 kb dsRNA in association with hypovirulence of S. sclerotiorum.

Recessive alleles of the barley Mlo locus confer non-race specific broad-spectrum resistance against all the races of powdery mildew fungus, Blumeria graminis f. sp. hordei. To assay the biofunction of Mlo gene in regulation of plant defense response against different pathogens, the cytological events were examined in the interactions between Mlo near-isogenic lines of barley and their leaf blight pathogen, Alternaria tenuissima (Fr.) Wiltsh. The results showed that the Mlo loss-of-function mutants could enhance resistance to leaf blight pathogen in both papilla-associated resistance and hypersensitive response (HR). The effective papilla, which could arrest the pathogen to invade into barley epidermal cells, was 15% in the wild Mlo barley, Ingrid (Mlo);and, in contrast, 49%, 51%, 55% in Ingrid mlo-3, mlo-4, and mlo-5 mutants respectively. The HR of the invaded barley epidermal cells might limit the fungal further extension into adjacent mesophyll cells. The percentage of HR in epidermal cells was 64%-69% in mlo mutant lines but only 26% in wild Ingrid. These suggested that Mlo gene regulate the defense responses by different ways to various pathogens. In addition, it was found that the fungus could also penetrate the barley epidermal cells directly, and its hyphae could also invade and grow in barley mesophyll cells, even in the living ones.

To determine the genetic diversity and physiological races of the rice blast fungus from Hani terrace of Yuanyang county in Yunnan province, simple sequence repeat (SSR) markers were used to estimate the genetic diversity of isolates of Magnaporthe grisea. Sixty-two isolates were studied for physiological races by using the standard differential variety sets developed in Japan for blast resistance in rice. Genetic diversity of rice blast fungus was analyzed with the unweighted pair-groups method using arithmetic averages (UPGMA) method of cluster analysis. Two-hundred isolates were divided into 16 physiological races, 000, 002 and 006 among them were found to be dominant races. The overall genetic diversity of rice blast fungus from Hani terrace of Yuanyang county observed in this study was relatively high (He=0.57±0.27, I=1.17±0.60). All isolates were classified into 9 genetic lineages at 0.20 linkage distance level. It was also noticed that genetic diversity of rice blast fungus also varied with altitude. There were 9 races between 1 600 m and 1 700 m in altitude and highly genetic diversity of rice blast fungus populations was observed at the range of 1 400 to 1 500 m (He=0.57±0.24). The data strongly suggested that there are significant positive correlations between genetic varieties of rice blast fungus and the traditional rice varieties cultivated over decades in Yuanyang Hani terrace.

Histological characteristics of pathogen development, production of reactive oxygen species (ROS) and activities of relative enzymes were analyzed in the incompatible and compatible interactions between wheat and Puccinia striiformis f. sp. tritici. Histological observation revealed that there were distinct differences between the incompatible interaction and compatible interaction, which included inhibition of hyphal growth, formation decrease of haustorial mother cells and haustoria, and hypersensitive cell death in host tissues occured at 18 h after inoculation (hai) in incompatible ones. The results of biochemical measuration showed the rate of O₂^- production and content of H₂O₂ were higher in the incompatible interaction than that in the compatible interaction, and the peaks of O₂^- appeared at 12 hai, H₂O₂ content reached its maxima at 20 hai and 72 hai. However, in the compatible interaction, the rate of O₂^- production were lower or similar to control, and H₂O₂ content were higher than that in control but lower than in incompatible ones. The SOD activities in compatible interaction were usually higher than that in incompatible ones. At 24 hai, the CAT activities in both interactions were all higher than that in control, and CAT activities in compatible interaction were higher than that in incompatible ones at 36 hai and 48 hai, but after 60 hai, CAT activities in compatible interaction were lower than that in compatible ones again. The POD activities increased obviously in both interactions at 24 hai, but more rapidly in compatible ones. The MDA contents were increased significantly at 72 hai in incompatible interaction. The results indicated that there were striking differences about pathogen development, ROS production and relative enzymes activities in the incompatible and compatible interactions, which might have close relationship with resistance expression of wheat against stripe rust fungus.

A wheat line, ICA56, carried a novel single dominant candidate gene conferring high resistance to stripe rust races CYR30, CYR31 and CYR32. By using allelic test, it was found that this novel resistance gene in ICA56 was different from Yr5, Yr10, Yr15 and Yr26 and was designated as YrICA56. Five microsatellite markers were linked to the resistance gene YrICA56 with genetic distance WMC503-16.6 cM, Xgwm296-7.0 cM, Xgwm261-10.4 cM, WMC112-4.5 cM and Xgwm210-14.1 cM based on the F₂ population from Chuanmai28/ICA56. The order of centromere, marker primers and gene was -WMC503-Xgwm261-Xgwm296-YrICA56-WMC112-Xgwm210-centromere-. Based on the results of Mapmaker 3.0 and MapDraw 2.0, the resistance gene YrICA56 was located on 2DS. The stripe rust resistance genes Yr16 and YrKat have been located on 2DS, while Yr16 is an adult resistance gene and YrKat is temperature sensitive. Therefore, it is suggested that YrICA56 might be a new stripe rust resistance gene.

The Triticum aestivum-Haynaldia villosa translocation line V9128-3 was inoculated with seven dominant races of Puccinia striiforms f. sp. tritici prevalent in China, the results of resistance evaluation showed that the translocation line V9128-3 possessed resistance to the current epidemic yellow rust races. V9128-3, susceptible cultivar Mingxian 169 and their progeny of F₁, F₂, BC₁F₁, F₃ were inoculated with race Su-4, one of the F₂ progeny were used for developing molecular markers of stripe rust resistence gene in V9128-3, a portion of BC₁F₁ individuals and F₃ lines were used to validate the the linked markers. The results of inheritance analysis showed that V9128-3 resistance to Su-4 was controlled by one dominant gene. Two markers Xgwm356 and Xwmc658 located on 2AL from 219 SSR primer combinations were found linked to YrHV (temporarily designated). YrHV was 8.5 cM from Xgwm356 and 5.6 cM from Xwmc658, respectively, the two sites linked to YrHV were validated by a portion of BC₁F₁ individuals and F₃ lines. These markers would be used for breeding new wheat cultivars with marker-assisted selection.

Leaf rust resistance gene Lr19 transferred from Thinopyrum elongatum into wheat cultivars has expressed resistance to most pathotypes of Puccinia triticina in China. To identify the molecular marker linked to Lr19, a segregating F₂ population from a cross between the resistance parent TcLr19 and susceptible parent Thatcher were screened. A SCAR marker cosegregating with Lr19 was found and named as Y₁₉SCAR₉₈₂. The result of stability validation test on the 49 international set of near-isogenic lines in Thatcher background suggested that Y₁₉SCAR₉₈₂ was specific and sufficient for Lr19. The detection of the marker in 120 wheat varieties indicated that it could be effectively used for MAS in breeding of the resistance to leaf rust in wheat.

In order to predict the future predominant isolates in the populations of Puccinia striiformis f. sp. tritici in China, parasitic fitness of current prevalent isolates were estimated through testing resistant components. The results showed that the sporulation capacity contributed to most important portion in parasitic fitness, and the next two important characters for rust fungal parasitic fitness were infectivity (represented by number of colonies) and latent period. Germination ability didn't show significant difference among the tested races. The mathematical models had been firstly developed to estimate three principal components of pathogen parasitic fitness:sporulation capacity, infectivity and latent period. According to these models, the relative parasitic fitness of isolates Su11-4, Su11-14 and CY32 was higher than that of other tested races and had already been the predominant races at the present time. Isolate CY31 showed lower parasitic fitness, its occurrence frequency had been decreasing recent years and it was becoming secondary race. Also, for the lower parasitic fitness, the new pathogenic type "T₄" infected the seedling of differential host "Zhong 4" couldn't become the prevalent race in the near future.

YN80 was isolated from Amorphophallus rivieri Durieu showing mosaic and crinkle symptoms in Songming, Yunnan province. Flexuous filamentous particles were found in diseased leave sap and pinwheel inclusion bodies were found in the leave tissue. YN80 had positive reaction to universal antibody of Potyvirus by DAS-ELISA. 3'-terminal sequence of YN80 was cloned and sequenced. cp gene of YN80 consisted of 987 nt, encoded 328 aa (36.1 kDa). Sequence analysis showed that YN80 shared the highest identity (97.0%)with CP amino acid sequence of Dasheen mosaic virus (DsMV). These data indicated that YN80 was an isolate of DsMV. This is the first molecular identification of A. rivieri Durieu isolate of DsMV in China.

Imported cowpea seeds were detected with growing test, ELISA assay and RT-PCR method. The ELISA results showed that cowpea seedlings with symptoms reacted positively with antibody against Southern bean mosaic virus (SBMV). The 979 bp of fragment could be amplified from two positive ELISA samples using primers specific for Southern cowpea mosaic virus (SCPMV), and the sequence determination results proved that the pathogen existing in imported cowpea seeds was SCPMV. The positive ELISA results with SBMV antibody could be further confirmed by RT-PCR amplification with specific primers designed to amplify the coat protein gene and 3' noncoding region of SCPMV and SBMV. The RT-PCR method presented here was suitable for molecular identification of SBMV and SCPMV in entry-exit plant quarantine laboratories.

The NS2 gene of Rice stripe virus (RSV) was amplified by RT-PCR, cloned into pGEM-T vector and sequenced. The NS2 gene was inserted into prokaryotic expression vector pET32a to produce recombinant plasmid pET32a-NS2. The recombinant plasmid was introduced into Escherichia coli strain BL21 (DE3) pLysS. SDS-PAGE and Western blot analysis confirmed that NS2 fusion protein was expressed after induction by IPTG. The recombinant NS2 protein was purified with Ni²⁺-NTA agarose affinity chromatography and the polyclonal antibody against NS2 protein was raised in rabbit. NS2 protein was successfully detected in small brown planthopper (Laodelphax striatellus) at 1:1 600 dilution of the total protein of single planthopper and in infected rice (Oryza sativa) at 1:800 dilution of 10 mg leave by dot immunobinding assay using the polyclonal antibody.

ORFⅡ gene of Banana streak virus GuangDong isolate (BSV-GD) was amplified from a BSV-GD recombinant plasmid by PCR, and the gene was expressed by being cloned into prokaryote expression vector pET-28b (+). The fusion protein was about 16.5 kDa in size and was soluble with SDS-PAGE analysis. The purified protein was obtained by using the histidine labeling kit of N-terminus of protein. The antiserum was obtained by immunizing healthy rabbits with the purified protein. Western blot and ELISA analysis showed that the special antiserum of BSV possessed high titer, which was tested as 1:51 200. The study was a base for further research on BSV including ORFⅡ gene function and virus detection.

The experiments of resistance of different super hybrid rice (SHR) combinations to sheath blight (ShB) (Rhizoctonia solani Kühn) and effect of nitrogen fertilizer (NF) dosage and fertilization methods on ShB occurrence were conducted in Hangzhou during 2005-2006. The results indicated that the resistance level of different SHR combinations to ShB were significantly different. For the same combination, the severity of ShB depends on the seeding and transplanting period. The disease index showed a positive correlation with the nitrogen dosage, but depended on resistance level of combination. The ShB severity of susceptible combination showed high positive correlation with NF dosage. At the flowering stage, there were no effect of nitrogen fertilization method on the occurrence of ShB, but the fertilization method showed significantly effect at dough stage. The occurrence of ShB was significantly affected by the supply rate of nitrogen at different rice growing stage. When the total NF supply was 165 kg per hectare, the occurrence of ShB with high NF rate (80%) at early stage (as basal and tillering fertilizer) and low rate (20%) at late stage (as panicle fertilizer) was more serious than that of low NF rate (60%) in early and high NF rate (40%) as panicle fertilizer. The result was the reverse of conventional viewpoint about that high NF supply at rice late growing stage might lead to severe occurrence of ShB.

Parasitism genes encoding secretory proteins expressed in oesophageal glands of plant parasitic nematodes play critical roles in invasion, establishment of feeding sites and suppression of host defenses. Seve-ral chorismate mutase (CM) genes have been isolated and identified from Meloidogyne incognita and M. javanica oesophageal gland-region cDNA library and from homology-based cDNA cloning of M. arenaria. These chorismate mutases with amino-terminal signal peptides are significantly similar to that of Globodera pallida, Heterodera glycines and bacteria. In-situ mRNA hybridization showed that the transcripts of CM accumulate specifically in the two subventral oesophageal gland cells of Meloidogyne species. RT-PCR analysis confirmed that their transcript abundances were high in the early parasitic juvenile stages, and low or undetec-table in later parasitic stages of the nematode. Southern blot analysis revealed that these CM genes were members of a small multigene family in plant parasitic nematodes. The widespread presence of CMs in specialized se-dentary endoparasitic nematode species suggests that this multifunctional enzyme may be a key factor in modulating plant parasitism.

An isolate of Fusarium sp. was obtained from seed coat of watermelon (cvs. Jingxin No.1 and Xinjingxin No.1) using seed washing test and PDA plate methods. The isolate was identified through morphological observation and molecular detection. Effects on the seed germination were also studied. After observation of morphology, color and growth rate of the colonies, and morphology of macroconidia, microconidia, chlamydospores and conidiophores, it was preliminarily identified as Fusarium oxysporum. DNA of the fungus was amplified by universal primers of fungal rDNA ITS, specific primers of genus Fusarium rDNA ITS and specific primers of F. oxysporum rDNA ITS, respectively. After PCR products were ligated, transformed and confirmed, inserted sequences of the recombinant plasmids were analyzed. The sequencing results were logged in GenBank to BLAST. The results of molecular detection and morphologic observation all showed that the Fusarium isolate should be F. oxysporum. It is the first report of seedborne F. oxysporum isolated from seed coat of watermelon in China. Moreover, the germination energy, percentage germination and germination index of watermelon seeds all decreased significantly after treated with the spore suspension of seedborne F. oxysporum.

ITS1 (internal transcribed spacer 1) regions were amplified from 13 Chinese populations of Ditylenchus destructor and one Dutch population of Ditylenchus dipsaci. ITS1 regions of these populations were digested by five enzymes RsaⅠ, HaeⅢ, MspⅠ, HinfⅠ and AluⅠ. ITS1-RFLP patterns revealed that two patterns existed in 13 Chinese populations of D. destructor with different fragments obtained by four enzymes RsaⅠ, HaeⅢ, HinfⅠ and AluⅠ, and ITS1-RFLP patterns of D. dipsaci and D. destructor were different in fragments obtained by all five enzymes. 13 Chinese populations of D. destructor were divided into two genotypes, i.e. genotype A and B. Genotype A included populations of DeSD1, DeSD2, DeSD3 and DeJS1, and genotype B included populations of DeAH1, DeAH2, DeHB1, DeHB2, DeJS2, DeSX, DeSD4, DeTJ1 and DeTJ2. ITS1 regions were also sequenced and the alignments showed that the pairwise sequence divergences of four populations in genotype A were between 1% and 4%, and that of nine populations of genotype B were 0 and 1%, and the sequence divergences of D. dipsaci and D. destructor were 39% and 48%. Morphometric characters were analysed on four populations of D. destructor and one population of D. dipsai. The results demonstrated that no significant difference in most morphometric characters except c, tail, V and V' among populations of two genotypes A and B of D. destructor. The ITS1-RFLP patterns, ITS1 sequence analysis and morphometric data supported that two genotypes of D. destructor were existed in China.

Effect of ten kinds of sugars on germination of thin-wall conidia of Ustilaginoidea virens (Cooke) Takahashi was determined with agar plate. The sugars were xylose, sorbose, ribose, fructose, mannose, galactose, maltose, glucose, lactose and sucrose. All the sugars exhibited inhibition to the conidia germination in varying degree at 1% concentration, except for sucrose. Inhibition of xylose, fructose, sorbose and ribose was very strong. The viability was not lost in the case that the conidia were treated with xylose or fructose for 6 h. Mixture of several sugars also showed inhibition to the conidia. Two completely different effects were exhibited from the mixture of each sugar and potato juice which was of stimulation to the conidia germination. One was that the inhibition of mannose, glucose, maltose, galactose, lactose and sucrose was covered up by the stimulation of the potato juice. The another was that the stimulation of the potato juice was covered up by the inhibition of xylose, fructose, sorbose and ribose. The results showed that germination of the thin-wall conidia could be controlled by external sugars and certain bioactive substances.

There is increasing evidence that some genes encoding aminotransferase associated with plant carbon and nitrogen metabolism also play critical roles in the induction of plant defense against pathogens. An EST, homologous to the rice alanine aminotransferase gene, was isolated from an incompatible suppression subtractive hybridization (SSH) cDNA library of wheat leaves infected with Puccinia striiformis f. sp. tritici. Using in silicon cloning and RT-PCR, a 1 563 bp cDNA sequence was obtained from wheat and designated TaAlaAT1. Sequence analysis showed that TaAlaAT1 included a complete 1 440 bp ORF and encoded a putative protein composed of 479 amino acids. The deduced amino acid sequence was revealed the presence of the conserved aminotransferase signature and highly homologous to alanine aminotransferase in Oryza sativa, Vitis vinifera, Glycine max, Arabidopsis thaliana and Medicago truncatula. The expression pattern of TaAlaAT1 at transcription level was investigated by semi-quantitative RT-PCR and real-time PCR, respectively, which revealed that TaAlaAT1 transcripts were up-regulated in incompatible interaction of wheat and stripe rust, whereas down-regulated in compatible interaction, and apparently different between incompatible and compatible interaction. It was speculated that TaAlaAT1 was involved in wheat defense response to P. striiformis.

P3 deletion of β-1, 3-glucanase isoenzyme GIII gene promoter was ligated upstream into the gus report gene and P3/gus fusion fragment was then cloned into a binary vector pCAMBIA1300 for Agrobacterium-mediated transformation of rice (Oryza sativa L. cv. Taipei 309). PCR analysis indicated that the fusion gene was presented in 10 T₀ transgenic plants. The integration of the genes in rice genomic DNA was further confirmed by Southern blot. The results showed that 9 plants contain the fusion gene. Histochemical staining and spectrofluorophotometric analysis of transgenic rice leaves showed that the GUS activity was increased after treatment with the fungal elicitor from Magnaporthe griea. Histochemical staining of T₁ rice seeds displayed marked GUS activity after induction with the elicitor, while no GUS activity was detected in untreated T₁ rice seeds.

Plants are often subjected to infections of various pathogens in their whole life. This is so called complex infections. Complex infections of pathogens are challenged for genetic engineering of plant disease resistance. In this study a plant safety expression vector was constructed. The vector harbored twin T-DNAs and the selective marker gene NPTⅡ expression cassette was separated in different T-DNAs from the GUS expre-ssion cassette in which two highly pathogen-specific inducible promoters, EAS4 and hsr203J, were used to drive report gene. Transgenic plants were obtained from the transformation of tobacco by the vector. The GUS activity could not be detected or was very low in the transgenic tobacco plants without induction. Whereas the GUS activity was much higher when the plants were treated with parasiticein or inoculated with spore suspensions of Phytophthora nicotianea[0] and Ralstonia solanacarum. The results showed that the two promoters in transgenic plants were highly pathogen-specific inducible and could be used as a powerful tool for genetic engineering in plant disease resistance.

By using Agrobacterium tumefaciens-mediated transformation, more than 5 000 transformants were obtained from Magnaporthe grisea CY2, an isolate with very weakly pathogenic to rice. Among 30 pathogenic mutants were screened by inoculation with mixed spore suspension of 20-30 transformants onto the near-iso-genic lines (NIL) contained 25 rice blast resistance genes. Mutation had quite different frequency at different pathogenicity-related loci for the pathogen. No any mutants were found from lines with the other resistance genes while as many as 14, 7 and 2 mutants were found from the line F128-1 carrying Pi-ta², the line IRBL-2 carrying Pi-a and the line IRBL-4 carrying Pik-s, respectively. It was indicating that T-DNA might have insert hot spot in the pathogen. The mutants showed different pathogenic types on the NILs with the same blast resistance gene and it implied that the NILs might carry other resistance genes. LTH, a line without any blast resistance genes considered commonly, might have resistance genes depending on the fact that 7 mutants were harvested from it and could not infected with the wild type CY2.

Both the Chenopodium quinoa and Vicia faba were respectively infected with two Broad bean wilt virus 2 (BBWV-2) isolates, PV131 and P158, and their cytopathological changes were observed by transmission electron microscope. In the PV131 isolate infected C. quinoa cells, the membrane proliferated and contained vesicles and electron-dense materials. The extensive proliferation of membrane might act as the viral replication center. Viral particles distributed in the cytoplasm and some of them accumulated into crystals or aggregated into tubules. The diameter of the tubule was about 75 nm and there were nine viral particles on the transverses section. The similar data were got from the other three kinds of infected mesophyll cells but PV131 and P158 virions did not accumulate into crystals in V. faba cells. All the observations indicated that the differences of pathogenicity between PV131 and P158 isolate were determined by their genome but not the host types.

In order to establish a rapid identification technology of resistance to sheath blight (SB) in rice seedling stage,five cultivars with different resistance to SB were adopted in identification of seedling stage in artificial climate incubator or temperature-controlled greenhouse and the results were verified through an experiment at rice adult stage in field.The results showed that about 85% relative humidity was suitable for SB mycelium to develop infection structures and infect rice seedlings.The SB resistance levels among 5 cultivar seedlings differed significantly at 1% levels and could be divided into two groups,relatively susceptible (Lemont,Wuyujing 3) and relatively resistant (YSBR1,Jasmine 85,Teqing).The symptom severe degrees of seedlings at different leaf-age (4-leaf stage or 5-leaf stage) were significantly different and the average disease rating at 4-leaf stage was significantly higher than that of 5-leaf stage.The differences of resistance among different cultivars in greenhouse were less than that in the field,but the resistant-to-susceptible order among the cultivars were consistent with that in the field.Rapid identification technology of rice SB resistance in seedling stage could be used for screening resistance of rice germplasm on a large-scale scope or primary resistance identification.

Wheat stripe rust, caused by Puccinia striiformis f.sp. tritici, is one of the most important wheat diseases in China. The level of the disease epidemics is determined by long-distance transport of the pathogen. The key to predict the pandemic of wheat stripe rust is to predict the pathway of long-distance transports of the pathogen. Since air current is the main driving factor for its dispersal, physical models of atmospheric dyna-mics provide powerful tool to analyse the long-distance transports. In this study, historical cases of long-distance transports of the wheat stripe rust pathogen were analysed using HYSPLIT-4 model. The results indicated that the occurrence of wheat stripe rust epidemics in deposition regions was consistent with air parcel movements from the source regions. Besides dry deposition caused by gravity, spore deposition was affected, to a great extent, by the wet deposition from precipitations. Our results suggested that HYSPLIT-4 model could be used to quantify the long-distance transports of Puccinia striiformis f.sp. tritici, and provided a new approach for seasonal forecast of the regional outbreaks of wheat stripe rust in China. The approach demonstrated in our case should be methodologically and technically useful to study long-distance transports of other airborne pathogens.

According to the principle of plant disease epidemiology, the spatial dynamics of gray leaf spot of maize was studied by artificial inoculation to cause the disease gradient in experimental fields. The spatial dynamic models of gray leaf spot of maize were established by SAS 9.13. The results showed that:1. Exponential Model and GOMPERTZ Model were the optimum One-Dimensional Model in Shenyang region; 2. Gau-ssian Model was the optimum Two-Dimensional Model; 3. Circular Model and Oval Model were the optimum 3-Dimensional Model. According to the spatial dynamic models, the theoretic spread distances of gray leaf spot of maize were in a range of 20 to 50 m.

Sugarcane mosaic disease, caused by Sugarcane mosaic virus (SCMV), Sorghum mosaic virus (SrMV), Maize dwarf mosaic virus (MDMV) or Johnsongrass mosaic virus (JGMV) in Potyvirus, is one of the most important viral diseases of sugarcane. In the study, four primer pairs specific to SCMV, SrMV, MDMV and JGMV, respectively, were designed and used to detect 29 sugarcane leaf mosaic samples collected from 9 locations in Jiangxi province. The representative RT-PCR products were sequenced. The results showed that 22 samples were infected by SCMV, three by SrMV, and four were mix-infected by SCMV and SrMV. MDMV or JGMV were not identified in all samples. The result indicates that SCMV is the major pathogen of sugarcane mosaic disease in Jiangxi province, and SrMV is also a pathogen for the disease.

Total RNA was isolated from phloem of young shoots and retro-transcripted to cDNA by RT-PCR(Reverse Transcriptase-Polymerase Chain Reaction) with specific primer pair of CVd-Ⅲ (citrus viroid-Ⅲ), the results of molecular detection indicated that the CVd-Ⅲ specific bands, about 300 bp, were detected in 27 of the 49 samples collected from different counties in Hunan Province and 1 sample presented by Catania University. All the amplified cDNA fragments were cloned and sequences, sequence analysis compared with the reported CVd-Ⅲ sequences in GenBank showed that:sequences of 21 samples were the same and completely identical with CVd-Ⅲb (AF184147); however, the sequences of the other 6 samples and presented sample were diversified from the reported CVd-Ⅲ sequences in GenBank.

Periwinkle(Catharanthus roseus) yellows is a common disease in Hainan. Periwinkle's leaf tissue with symptoms was assayed for phytoplasma infection by using PCR assay employing phytoplasma universal 16S rRNA gene primers (Rl6mF2/Rl6mR1). A PCR product (about 1.4 kb) was amplified from periwinkle showed yellows. Nucleotide sequencing and phylogenetic tree analysis showed that the amplified 16S rDNA contained 1 432 nucleotides, the most homology was 98.1% with the members of elm yellows group (16S r Ⅴ) and clustered in the same clade, while it was under 96.1% with other phytoplasma groups. Our results suggested that the phytoplasma sample belonged to 16S rⅤgroup and was tentatively named as Hainan periwinkle yellows phytoplasma (PY-Hn). This is the first report of existence of 16S r Ⅴ group phytoplasma in naturally infected periwinkle.

Near the HMW-glutenin gene of wheat (Triticum aestivum), there is a locus (temporarily named TaXa) encoding LRR-receptor-like protein kinase, which is homologous to disease resistance protein Xa21 of rice (Oryza sativa). Through RT-PCR approach, a cDNA clone of ZS2002 was isolated from the orthologous locus of TaXa in Triticum turgidum. ZS2002 was 3 081 bp long and encoding a peptide composed of 1 026 amino acid. The protein included N-terminal conserved sequence, LRR domains, a transmembrane region and a serine/threonine protein kinase domain. ZS2002 was expressed in root, stem, leaf and spike. The transcribing in seedling leaves was significantly enhanced by Blumeria graminis f.sp. tritici. TaXa gene might play a role in powdery mildew resistance reaction in Triticum.

Three hundred and one endophytic bacteria strains were isolated from healthy sugar beet plants in severely diseased plots in Changji County,Xinjiang Province.Three endophytic bacteria strains,1-5,4-1 and 4-3,showed relatively strong antagonistic against Cercospora beticola.Strain 1-5 was identified as Paenibacillus polymyxa,while strains 4-1 and 4-3 were as Bacillus flexus and Stenotrophomonas sp. by their morphological,physiological and biochemical characteristics.The results from several experiment trials showed that the endophytic bacteria could reduce the disease incidence of sugar beet.The control efficiency reached from 67.6% to 80.2%, indicating that biocontrol with endophytic bacteria was an alternative and potential method to control sugar beet fungi disease.

Huping jujube fruit in Shanxi province suffered serious losses from shrink disease during 2005-2008.In this study,the genomic DNAs of fungi and bacteria isolated from decayed jujube fruits were amplified by polymerase chain reaction(PCR) using the universal primers of the fungus ITS rDNA and bacterium 16S rDNA,and the nucleotide sequences of the amplified fragments were tested and then analyzed by using Megablast in GenBank.The main parasitical fungi and bacteria isolated from fruits were identified as Alternaria alternata,Irpex lacteus,Penicillium expansum,Cladosporium tenuissimum,Bacillus subtilis,B.megaterium,B.pumilus,and Paenibacillus polymyxa.After inoculating the jujube fruits with these parasitical mi-croorganisms,only the fungi of A.alternata,P.expansum and C.tenuissimum showed high pathogenicity,and no bacteria were capable of inciting the disease.

Genetic diversity and variability of Xanthomonas oryzae pv.oryzae(Xoo) strains collected from Guangdong were analyzed by using IS-PCR and rep-PCR fingerprinting techniques.Genomic DNA from 114 strains was amplified with two specific primers J3 and ERIC,89 and 40 haplotypes were revealed respectively.Dendrograms were generated from the data by using UPGMA analysis.The strains tested were similar each other at a level of 70%,eleven and eight clusters were gruoped with J3 and ERIC respectively.The predominant groups were both of the cluster 1 for each primer J3 and ERIC involving 89(78.07%) and 52(46.61%) strains,respectively.The genetic diversities of the population of tested strains were 0.891 9(for J3) and 0.827 8(for ERIC),respectively.The results indicated that the genetic diversity of Xoo in Guangdong was various.114 strains were inoculated with six differential cultivars including near-isogenic rice lines carrying single resistance gene,IRBB14(Xa14),IRBB13(xa13),IRBB4(Xa4),IRBB203(Xa3),IRBB5(xa5),and a highly susceptible cultivar Jingang 30.Six races,X-gd1,X-gd2,X-gd3,X-gd4,X-gd5 and X-gd6 were identified.Among them,X-gd4 was predominant in Guangdong province.

Three isolates were isolated from diseased seedling stems of pea imported from Australia in March 2008.Inoculation on pea seedlings with these isolates caused the same symptoms as naturally infected plants,while symptoms did not occur on control plants(inoculated with sterile water).The bacteria sharing the cha-racteristics of the inoculated isolates were recovered from symptomatic plants,hence fulfilling Koch’s postulates.All three isolates were identified as Erwinia persicina by pathogenicity,staining reactions,morphological characteristics,culture patterns,physiological and biochemical reactions,and 16S rDNA gene sequences.

A new disease of tobacco seedlings was observed at different localities in Xichou County of Wenshan Prefecture and Changning County of Baoshan City,Yunnan Province from 2006 to 2007.The symptoms were common in the float beds and transplants with small,white and dark green lesions and brown lesion on stem,sometimes wet symptom was developed.A fluorescent bacterium was isolated from diseased tissues onto KB medium.These isolates were identified as Pseudomonas aeruginosa based on pathogenicity,morphology,physiological and biochemical characteristics.Biolog test analysis and sequence analysis of 16S rDNA showed the similarity to P.aeruginosa was 99%.The disease was first reported from Philippine.This is the first report of the disease from Yunnan,China.

The movement of BYDV-GAV in oat plants was studied by RT-PCR.Healthy oat plants were inoculated with BYDV-GAV by vector Schizaphis graminum on the second leaf.The coat protein gene was amplified with total RNA from the first to sixth leaf and root of inoculated oat plants at different growth stages to test the replication and movement of the virus in the plants.The results showed that the second leaf(inoculated leaf) was identified as positive after inoculation for 5 days.After 7 days,the fourth leaves were infected,it was the new leaf at that stage.After 9 days,some of the third leaves were identified as positive.After 16 days almost all of the leaves were infected.The roots were identified as positive only at 5th,7th and 9th day respectively,and also all of the first leaves were always identified as negative,which might be due to the virus content in the plant was too low to detect.The movement of the virus in oat plant will provide basic information for selecting optimal tissue to study the movement mechanism.

Two types of rDNA-ITS(Type A,900 bp and Type B,1 100 bp) were demonstrated to exist in Ditylenchus destructor populations on sweet potato in China.The D2/D3 regions of 28S rDNA from 22 populations of D.destructor were amplified with universal primer pairs D2A and D3B.All 22 populations yielded one single fragment about 780 bp.Sequence analysis and alignment were conducted by using the software MEGA4 and DNAMAN5.2 and all 22 sequences were submitted at the GenBank.The results showed that sequence differences of D2/D3 region were only in a few sites,and that the similarity was 97.2%.Two types could be distinguished in the phylogenetic tree by using UPGMA method.The evolutionary relationship between two types and the origin of Ditylenchus species were discussed.