Studies on pathological changes of vascular in cotton seedling inoculated with Fusarium oxysporum f.sp. vasinfectum or treated with its crude toxins was carried out on resistant cultivar Zhong 12 and DPL16 variants which were on same genetic background. The results showed that mycelia were present in the vessels and parenchyma in stems after inoculation. Susceptible cultivar DPL16 had highest amount of infected vessels while the resistant cultivar Zaoshu DPL16 had the fewest infected vessels. The tylose and gum in vessels could be seen in all cultivars but their frequency of occurrence was higher on resistant cultivar. The tylose and gum also could be seen in stem or petiole after treated by crude toxins also,the resistant cultivar produced occlusion in vessels more quickly than susceptible ones.

The strains of Papaya ringspot potyvirus (PRSV) such as PRSV126、Ys、Vb、Sm were identified with strain specific primers of PRSV. It was found that the primer PR21/PR22 could distinguish Ys from Vb and Sm, while another pair of primer PR300/PR301 could dif ferentiate Vb from Ys,Sm and PRSV126. The PRSV strains could also be identified by RT PCR restriction fragment length polymorphism(RT-PCR-RFLP) with one restriction enzyme of Hae Ⅱ,Sau3A I and Hinf I. The results indicated that Ys could be identified with single digestion of Sau3A I or of Hae Ⅱ, and PRSV126 with Hinf I. The strains of Vb,Ys and Sm could also be identified respectively by RT-PCR-RFLP single strand conformation polymorphism(RT-PCR-RFLP-SSCP).

Rep PCR was used to analyze the genetic diversity in a population of 40 Xanthomonas strains. These strains included 30 Xanthomonas oryzae pv. oryzicola isolates from different rice regions in China and 10 reference strains of other Xanthomonas spp. Rep PCR was performed using DNA amplification with primers based on short bacterial repetitive elements(ERIC, BOX).The combination of results from Rep PCR with the two primers demonstrated a higher diversity than either one primer; The results indicated that significant genetic diversity exists within the population of X.o. pv. oryzicola in China. All strains of X.o. pv. oryzicola were clustered into 6 groups at a level of 80% similarity. In addition, strains from infected rice plants were recovered with a number of naturally occurring avirulent or weak virulent strains with Rep PCR fingerprints different to those of virulent ones; There was a high degree of correlation between strains groupings generated by Rep PCR and pathogenicity analysis. It suggested that there are different distributions of BOX and ERIC in genomic DNA of several rice leaf streak pathogen. The results suggested that Rep PCR technique may be a useful tool for detecting genetic variation among strains of X.o. pv. oryzicola and identification of strains as well as classification studies.

The NIb coding region of Maize dwarf mosaic virus (MDMV) from Beijing was sequenced. It comprised 1563 nucleotides and encoded a putative protein of 521 amino acids containing the consensus motif GDD. The protease cleavage sites between the NIa/NIb and NIb/coat protein were found to be Q/C and Q/S, respectively. The similarity between the NIb sequence and the Bulgarian isolate was 70.6% at the nucleotide level and 76.6% at the amino acid level. The NIb sequence was most similar to SCMV SC with identities of 81.3% and 92.1% at the nucleotide and amino acid levels, respectively.

The results of inoculating the mixtures of mono-cell clones with different virulence of Xanthomonas oryzae pv. oryzae on the differential varieties showed that the pathogenicity of mixtures was changed in a different degree as the ratio of different mono-cell clones change, reciprocity of different virulence mono-cell clones and reciprocity between mono-cell clones and the hosts.
The result of virulence of strains of Xanthomonas oryzae pv. oryzae isolated from the same rice field revealed a lot of variability in the isolates from different infected plants and different parts of an infected leaf. It is suggested that the different virulent cells existed in a single field even in a single leaf. Therefore the cultures isolated must be a mixture with the variant cells and their pathotypes reflected the virulent composition of a natural population in a rice growing area.
The pathotypes of 36 strains isolated from a single rice field were very similar to the 208 strains isolated from 48 counties, it could be the reference for investigating the variation of a natural population of Xanthomonas oryzae pv. oryzae in the rice growing area.

The influence of Curvularia lunata toxin on defense enzyme (PAL, PO and SOD) activities was studied in different varieties of corn, and the potential function of toxin as the inducer of resistance in corn was also investigated. Results suggested that the activities of PAL and PO were much more easily to be stimulated by toxin in resistant varieties than in susceptible ones, but on the contrary, the lower activity of SOD was found in resistant varieties when treated with toxin compared with that in susceptible ones. Based on the results, it was presumed that the lower activity of SOD would benefit the accumulation of active oxygen (AO) which was considered generally as an inducer of resistance. In addition, the research showed that the toxin at certain concentration could be used as an inducer of host resistance.

Phytophthora infestans from potatoes collected from Yunnan Province during 1998 to 2000 were investigated for their mating type, colony growth pattern, ability to grow on oatmeal agar, linear growth rate and amount of sporangia produced. A total of 157 isolates from 23 locations in 13 counties in Yunnan were all A1 mating type. Representative isolates showed significant variation in growth rate and amount of sporangia produced, which indicate the existence of genetic diversity among the population of P. infestans in Yunnan. Results also show that colony growth pattern and the growth on oatmeal agar did not relate to the mating type of the isolate.

The allelism test and genetic analysis were used to identify a recessive resistance gene to Maize dwarf mosaic virus strain B of the maize inbred Huangzao 4. The gene is located on the long arm of chromosome 6, near the centromere. The linkage distances from Mdm1 to the resistance gene, the resistance gene to the breakpoint of the translocation, T6-9b, are 1.9-4.5 cM and 33.8 cM respectively. We proposed to designate this gene as mdm1 (t) for Maize dwarf mosaic virus resistance.

Cowpea chlorotic mottle virus (CCMV) RNA3 mutant clones were constructed by using PCR point mutagenesis. TP7 mutant clone was constructed by making a Sal I restriction site immediately before the 5' end of the capsid gene, TP8mutantclonewasconstructedby making a BamH I restriction sites immediately before the 5' end of the 3a gene, AG1 mutant clone was constructed by making a Not I restriction site immediately after 3' end of the capsid gene. Cowpea seedlings were inoculated with a mixer of RNA transcripts of the cDNAs of TP7, TP8 or AG1 mutant clones and wild type RNA transcripts of the cDNAs of CCMV RNA1 and RNA2, respectively. After inoculation systemic infection symptoms appeared 6 days on TP7 (TP7 RNA transcript combining with RNA1 and RNA2 transcripts) inoculated plants and 9 days on TP8 (TP8 RNA transcript combining with RNA1 and RNA2 transcripts), AG1 (AG1 RNA transcript combining with RNA1 and RNA2 transcripts) and wild type virus inoculated plants. Symptoms developed earlier and severer on TP7 inoculated plants.
Three kinds of multiple component inoculations were established through sap co inoculation with 20 days inoculated leaves of TP7 and TP8, TP7 and AG1, TP8 and AG1 (refer to TP7 +TP8, TP7+AG1 and TP8+AG1 respectively). Restriction nuclease digestion of RT PCR products, which derived from the cowpea plants after 20 days co inoculation of TP7+TP8, TP7+AG1 indicated that TP7 dominated in their mix infections. TP8 and AG1 have similar competitive abilities and similar levels of populations in the TP8+AG1 mix infections.

The ultrastructural alteration of Chenopodium amaranticolor and Chenopodium quinoa infected with Grapevine fanleaf virus Hangzhou isolate (GFLV H) was studied by transmission electron microscope. Isometric virus particles were found in the cytoplasm of infected parenchyma cells of leaf tissue. The virus particles often lined up in aggregated tubules. In systemically infected C. quinoa virus particles are aligned in tubular structure protruding through the cell wall within plasmodesmata. Membranous proliferation and fibril containing vesicles developed in the cytoplasm, usually adjacent to the nucleus in both host plants. Some multivesicular bodies and myeloid bodies protruding into the vacuole and virus specific vesicles associated with the tonoplast were also observed. The cellular organization, such as chloroplast and mitochondria, were often affected.

The infection process of Melampsora larici-populina Kleb. on leaves of poplars was examined with electron microscopy. The results showed that there were 1-3 germ tubes developed from a germinated urediniospore and the germ tubes always developed several branch tubes further. The germ tubes directly penetrated into the leaf through stomata. Sometime, several tubes penetrated through one stoma at the same time. No penetrate directly through epidermal cell was observed in this study. No well defined appressorium was formed before the penetrated of the pathogen. After invading into stomata the germ tubes developed substomatal vesicles and further formed round inflated bodies usually with one or two infection hypha. In tercellular hypha extended at first between host cell, then penetrated host cell and produced haustoria there. There was no difference in organelle structure between the haustoria and intercellular mycelia. The mature haustoria consisted of a tube like neck and a expanded body. When pathogen hyphae grew in the intercellular space between cells or along the cell wall, the host cell of mesophyll maintained in normal state.

The causal agent responsible for the root rot of tea cutting seedlings, Fusarium solani, could grow at temperature between 10 and 35℃, with the optimal growth at 25℃; the best condition for sporulation was at 27-31.5℃ with RH at 96%; highest spore germination rate was obtained when the temperature was 30℃ and the RH was 100%, or in water when the temperature was 25-27℃ and pH was between 5.6 and 8.1. Treatments of darkness or with fluorescent light or darkness with alternative scattered light did not have significant effects on the mycelium growth or sporulation. The treatment of ultraviolet light could caused significant reduction on mycelium growth. The lethal temperature for the spores was 58℃ for 10 minutes. The pathogen could survive in the debris for more than 18 months at room temperature. When cultured in artificial media, the pathogen could utilize monosaccharides, disaccharides as well as alcohols as carbon sources and L-cystin, ammonium oxalate, urea and DL-α-aminopropionic acid as nitrogen sources.The fungus did not grow or sporulate well when L-lysine was the only nitrogen source.

Eight species, Gliocladium roseum,Arthrobotrys oligospora,A. musiformis,A. guizhouense, A. conoides, A. dactyloides, A.superba, A. vermicola, which parasitize Rhizoctonia solani, were screened and their parasitic activity to Rhizoctonia solani and the effects of media nutrition on parasitic activity of G. roseum and A. guizhouense were tested in vitro. Results indicated all of the eight could parasitize R. solani at different level. G. roseum had the highest parasitic capacity which reduced 58.67 percent of sclerotia formation of R. solani. On the overlapped colony, most of mycilia of R. solani were parasitized by G. roseum. The nutrition of media affected parasitic capacity distinctively. The host's mycilia were heavily parasitized on WA and CMA and less on PDA and CSA. Both high ratio (300:1) and low ratio (1:1, 10:1) of C:N did not favor the parasitism, only specific ratio of C:N(50:1, 100:1) were favorable to the mycoparasitism.

Some Trichoderma strains are promising biocontrol agents (BCAs) of plant disease. It is observed that chitinolytic enzymes of Trichoderma play an important role in mycoparasitism which is considered as one of the mechanisms involved in the antagonism of Trichoderma against plant fungal pathogens.
The induced production, the physical and chemical characteristics of chitinases from Trichoderma strains and their antagonism against plant fungal pathogens are reviewed in the present article, and the potential use of the chitinases and chitinase genes from Trichoderma for biological control is also discussed.

Results from simulation experiments by means of a pandemic model of wheat yellow rust PANCVDE showed that the racial resistance spectrum and the acreage of the tester cultivar as well as the meteorological conditions are usually the leading factors determining the durability of resistance of a cultivar. Besides, considerable effect on durability were showed to be exerted also by other factors of the background system for the tester cultivar, including the acreage of the susceptible cultivar, the acreage of the horizontal resistant cultivar, the racial resistance spectrum of other vertical resistant cultivar, the comprehensive resistant cultivar, as well as the aggressiveness of the new race. Simulation results mostly coincided with commonknowledge and experiences in relevant respect, and some suggestions could be derived, such as the quantification of selection pressure, the protective action of horizontal resistance to the vertical resistance, and the necessity for estimating the aggressiveness of a new race. System simulation approach might be useful for the study on durability of disease resistance of wheat yellow rust as well as other similar diseases.

A survey on diversity of pathogenic bacteria including frequency and transmission of the pathogens from plain, hill and mountain areas of Zhejiang Province was conducted during 1997-2000. More than 3 906 bacterial isolates were recovered from 303 rice seed samples. Two hundreds and one pathogenic bacteria accounting for 5.15% of the total isolates were obtained after colony morphology, bacteriology and pathogenicity test. Together with 23 standard reference strains 299 pathogenic and representative nonpathogenic isolates were confirmed by Biolog. Results showed that the seedborne bacteria belonged to 6 higher virulent and 5 low virulent species. The pathogenic species isolated from the samples of plain area were more than those from mountain area. However, the low virulent species were prevalence in the two areas. Isolation frequency of the higher virulent species from hill was significantly higher than those from other areas. Among 11 seedborne bacteria only Xanthomonas oryzae pv. oryzicola, Pseudomonas fuscovaginae and Acidovorax avenae subsp. avenae were confirmed as seedborne and seed transmission by using both artificial inoculated and naturally infected seeds.

Optimization for the perfect stage production of Magnaporthe grisea in vitro were investigated by using juice of tomato with different maturity, changing pH and adding CaCO₃ in the oatmeal tomato agar medium. Results showed that the number of perithecia and ascospores and the percentage of viable ascospores were markedly increased when juice of mature tomato was used, pH was adjusted to around 5.5 and 0.1% CaCO₃ was added in the medium. Additionally, the optimal time for isolating ascospores is about 7-18 days after perithecia formation. During this period survival percentage of ascospores can reach up to 85.5%.

The root exudates of 7 cotton cultivars with the different resistance to V. dahliae were collected and their effects on pathogen were tested. Results showed that the root exudates of resistant cultivars inhibited spore germination and mycelium growth of V. dahliae, but the root exudates of susceptible ones had an opposite effect to pathogen. The kinds and amount of amino acids in the root exudates of susceptible cultivars are much more than resistant ones. The phenylalanine and proline were found only in the root exudates of susceptible cultivars. The content of carbohydrate in the root exudates of susceptible cultivars is distinctly more than resistant ones.

Transgenic chili pepper that expressing CMV and TMV coat protein genes were inoculated with CMV particles and CMV-RNA, respectively to compare the disease development and the virus content in transgenic plant. Results showed that the transgenic chili pepper exhibited high level of coat protein mediated resistance(CP-MR) to both CMV particles and CMV-RNA. In inoculated and newly developed leaves in CP(+) plants challenged with the CMV particles and CMV-RNA, the development of systemic symptom was remarkably delayed; the rate of plants showing symptoms and the severity of disease were strongly reduced; and the virus multiplication and dispersion were obviously suppressed. These results indicated that viral RNA did not overcome CP-MR in transgenic chili pepper.

Three wheat cultivars with powdery mildew resistance genes Pm2, Pm4b and Pm6 respectively and a susceptible variety were crossed with four new breeding lines, namely CA9550, CA9640, CA9641 and CA9648 to identify the resistance genes they contained. Result indicated that CA9640, CA9641 and CA9648 each contained a resistance gene Pm2, and CA9550 had two resistance genes Pm2 and Pm4b.

The Sumai 3 and Ningmai 6, resistant and susceptible, respectively, to wheat head scab caused by Fusarium graminearum, were inoculated using the single floret inoculation method with B4-1, a F. graminearum strain with high trichothecene production potential. When the spike and peduncle tissues were assayed for trichothecenes after inoculation, deoxynivalenol (DON), 15-acetyldeoxynivalenol (15-ADON) and 3-acetyldeoxynivalenol (3-ADON) were detected, but no nivalenol and fusarenon -X were found. During the period from 4 to 20 days after inoculation, average concentration of DON in symptomatic spikes of Sumai 3 decreased from 29.5 to 15.7 μg/g dry weight (gdw), while that in Ningmai 6 increased from 23.1 to 47.7 μg/gdw. The concentrations of 15-ADON and 3-ADON in symptomatic spikes were higher in Ningmai 6 (8.6-10.0 μg/gdw and 2.6-8.3 μg/gdw, respectively) than those in Sumai 3 (1.5-3.6 μg/gdw and <1.7 μg/gdw, respectively). All three trichothecenes were less than 0.5 μg/gdw in asymptomatic spikes of both Sumai 3 and Ningmai 6. Although no trichothecenes were found in peduncles of Sumai 3, a large amount of DON and 15-ADON (61.7 μg/gdw and 55.3 μg/gdw,respectively) and a small amount of 3-ADON(2.3 μg/gdw) were identified in peduncles of Ningmai 6. This is the first report that trichothecenes are produced in the peduncles of susceptible cultivars.

Two kinds of cytoskeleton depolymerizing reagents, cytochalasin D(CD) and oryzalin, were separately injected into the primary leaves of wheat (Triticum aestivum) (cv. Lovrin 10) seedlings immediately before the leaves were inoculated with an incompatible race 366 of leaf rust (Puccinia recondita f. sp. tritici) to study their effects on the hypersensitive reaction (HR), an important defense response of host cells in the incompatible interaction of wheat leaf rust. The results showed that both the reagents could obviously reduce the number of the necrotic cells. The higher the concentration, the fewer the necrotic cells. These results indicated that the polymerized filamentous state of actin or tubulin is necessary for host plant to express HR, and strongly suggest that microfilaments and microtubules play an important role for wheat to block the infection of leaf rust fungus.

The infection and movement of Maize dwarf mosaic virus strain B (MDMV-B) in corns were studied using resistant inbred (Huangyesi-3), susceptible inbreds (8112 and Mo17) and tolerant inbred (478). Immunological detection of direct tissue blotting (IDDTB) and enzyme linked immunosorbent assay (ELISA) were applied to detect MDMV in inoculated corns and the disease symptoms were investigated. The results show that the resistance of maize to MDMV B is due to prevention of the systemic spread and replication of virus, but not the virus infection.

Tomato fruits (Lycopersicon esculentum Mill., cv Zhongjia-1) inoculated by Botrytis cinerea showed a rapid increase in ethylene production, and the higher activities of ACC synthase and lipoxygenase (LOX) as compared to control fruits during 7 days storage at 25℃. Adding ethylene absorbent can obviously slow down the infection of B.cinerea on inoculated tomatoes, and significantly reduce ACC synthase and LOX activities. These results indicated that the disease progress of fungal infection are positive related to the ethylene production, ACC synthase and LOX activities.

The invasion, multiplication and extension of two motility mutants of Erwinia carotovora subsp. carotovora in Chinese cabbage were investigated. In total, three inoculation methods were used:dish filter paper adsorption, soil drench and needle puncture. Results showed that both kinds of motility mutants could enter in and reproduce slightly in Chinese cabbage within a short period. With the time pass by, the number of bacteria of both mutants declined. Both mutants could extend within a shorter distance than the wild strain Ecc-12.

The DNA of 12 falcate Colletotrichum strains from different vegetable in Guangzhou was amplified with 14 selected Operon primers. RAPD patterns generated from all primers were high similar or identical for 11 of the 12 strains, only pattern of 1 isolate from Zingiber officinale was different clearly. UPGMA analysis showed that 12 strains were divided into two groups. Eleven of the 12 strains clustered into groupⅠ, and the strain from Z.officinale formed groupⅡ. Base on these results, the 11 strains were identified as a distinct species-C. capsici, and the strain on Z. officinale may represent another species. These results didn't support that 3 strains originated from the genus Allius hosts belonged to C.circinans.

Phytoplasma was observed in the phloem sieve elements of cactus (Opuntia dillenii)cluster young tissues by examine ultra thin sections under the electron microscope. Using primers (R16F₂/R₂) for 16S rRNA to detect phytoplasma of cactus witches' broom by polymerase chain reaction, DNA fragment of 1.2 kb were amplified in DNA samples extracted from infected cactus but not in those extracted from healthy plants. The result of comparing homology of nucleotide sequences of amplified 16S rDNA fragment shows that the phytoplasma of cactus witches' broom (CWB) is closely related to peanut witches' broom (PnWB). Therefore, we can estimate that CWB is one of the phytoplasma of 16Sr Ⅱ group.

Triple antibody sandwich ELISA (TAS-ELISA) was established to detect whitefly-transmitted geminiviruses (WTGs) with polyclonal and monoclonal antibodies (MAb) that were raised against WTG. The tests showed that MAb SCR18 could be widely used for detection of WTGs in China. The PCR method was also established to detect WTGs with primers PA and PB, which were designed based on the conserved sequences in intergenic region and coat protein gene on WTGs genomes. Field samples were tested with TAS-ELISA and PCR method.The result showed that WTGs exist on tobacco, tomato and squash in Yunnan Province and the result of TAS-ELISA detection was consistent with PCR result.