Peanut virus diseases are economically important to peanut production. In recent 10 years, great progress has been made in researches on molecular biology of Peanut stunt virus (PSV), Peanut stripe virus (PStV) and Tospoviruses infecting peanut, which made better understanding of the genome, genetic diversity, evolution and determination of species, subgroup and strain of the viruses. Following molecular characterization of two subgroups of PSV, a third subgroup was established from PSV Chinese strains based on serology and sequence analysis of RNA3. It was demonstrated that PStV strains with symptom diversity were evolved independently in China and some Southeast Asian countries based on comparison of sequence homology of coat protein gene. The progress in molecular biology of Tospovirus has increased the viruses from Tomato spotted wilt virus (TSWV) alone to 13 species in past 10 years, among which 5 species infect peanut.

Watermelon mosaic virus 2 (WMV-2) was detected in infected pumpkin plant collected from Heilongjiang (HLJ) Province by electron microscopy and enzyme-linked immunosorbent assay (ELISA). A specific fragment about 850 bp in length covering coat protein (CP) gene region was amplified by reverse transcription polymerase chain reaction (RT-PCR) and immuno capture PCR (IC-PCR). The PCR product was cloned into pGEM-T vector. Sequences analysis showed that CP gene of WMV-2 isolate HLJ had 852 nucleotides in length, encoding 284 amino acids with molecular weights of 31.8 kDa. Comparison showed it shared 92.2%-94.0% nucleotide acid identities and 94.5%-98.1% amino acid identities with the published sequences, respectively. When compared with the two reported Chinese isolates, WMV-2-HLJ CP shared 98.5% or 91.5% nucleotide sequence identity and 98.5% or 95.0% amino acid sequence identity with that of WMV-2 Shanxi isolate or Zhengzhou isolate.

Citrus bacterial canker disease (Xanthomonas axonopodis pv. citri) is now still on the list of quarantine pest of international and Chinese administration. One pair of specific primers (JYF5/JYR5) designed from published sequence based on encoding a conserved hypothetical protein gene in genome of Xac (Nature, 2002) was screened and developed for specifically detecting different pathovars of Xac and citrus leaves and fruit with suspicious symptom of CBCD as well as healthy leaves of citrus spiked with pathogen of Xac. The specification of primer pair is better than the previous ones designed from plasmid DNA or from 16S rDNA sequences of Xac. PCR amplification product of 413 bp target band was generated from target pathogen but not from non-pathogenic xanthomonads of citrus epiphytes and several plant pathogenic bacteria as well as from soaking solution of healthy citrus tissue. Limit of detection was 10 cells or 1.56 pg per micro liter per reaction. Stabilized results were obtained using different type of thermocyclers with corresponding PCR profiles. The accurate and rapid molecular diagnosis technique was applied in the eradication program and for epidemiological purposes in maintenance and protection of non-quarantine area of citrus production was established. It is easy to use and will promote standardization of reaction process based on detection kit of PCR with pre-coated solidly reagents and simplified sample preparation procedure.

The transmission electron microscope and cytochemical technique were employed to examine the alteration of ultrastructure and cell wall components of maize leaf tissue, uninfected and infected by Curvularia lunata (Wakker) Boed. After invading into the maize leaf tissue, the pathogen spread inter-cellularly and then formed intracellular hyphae in the necrotic host cells. As the extension of the hy-phae, a series of cytopathological changes occurred in the host tissue, including plasmolysis, necrosis of protoplasm, degeneration of organelles such as chloroplasts and vacuoles, and collapse of host cells. The cytochemical labeling of main cell wall components in C. lunata-infected leaf tissue showed that the labeling densities for cellulose, xylan, pectin were significantly reduced as compared with that in unino-culated healthy tissue. These results indicate that cell wall-degrading enzymes such as cellulases, xy-lanases, pectinases secreted by C. lunata are closely related to the penetration and extension of pathogen.

The dynamic changes of malondialdehyde (MDA) content and superoxide dismutase (SOD), peroxidase (POD) and polyphenol oxidase (PPO) activities induced by Colletotrichum capsici f. nicotianae toxin on tobacco were studied. The activities of SOD,POD and PPO in both resistant cultivar (Burley21) and susceptible cultivar(NC82)increased in the early stage after treatment,and decreased in the late period. However,the resistant cultivar Burley21 showed a higher level of SOD, POD and PPO activities and a lower changing rate of MDA content than those in the susceptible cultivar NC82. Moreover, the activities of three tested enzymes in Burley21 also declined more slowly in the late time after inoculation. It demonstrated that Burley21 possessed stronger protective potential and was more resistant to membrane lipid peroxidation.

The effects of Potato virus Y (PVY) infection on chloroplast ultrastructure and photosynthesis were investigated in potato. Electron microscopy showed that PVY infection disrupted the development of chloroplast and cell structure, resulted in the decreased size and irregular shape of chloroplast and starch particles. As the disease progressed, chlorophyll content, electron transfer rate and net pho-tosynthetic rate significantly decreased. The maximal photochemical efficiency, however, was not influenced by viral infection. It seems likely that the disrupted chloroplast together with the inactivation of enzymes in Calvin cycle are responsible for the suppressed photosynthesis by PVY.

Sugarcane mosaic virus (SCMV) is an important seed-borne virus in maize. This paper is report on the detection of SCMV in maize seed (inbred Mo17) by ELISA, electron microscopy, biological assay and tissue culture technology. The SCMV particles or inclusions were found in testa, aleuronic layer of endosperm and embryo tissue, but not in starch layer of endosperm. The virus particles in aleuronic layer and embryo have been shown to invade the growing maize seedling.

A proteinaceous elicitor which could induce hypersensitive response (HR) reaction on tobacco was purified by (NH₄)₂SO₄ precipitation, ultra speed centrifugation, preparative IEF and ion exchange techniques from cells of strain M51, an hrp-mutant of the wild type RS105 (Xanthomonas oryzae pv. oryzicola, Xooc). The molecular weight of this protein was 25.5 kDa determined by 15% SDS-PAGE. It possessed many similarities with HarpinEa(from Erwinia arnylovora) and Harpin_Xoo(from Xanthomonas oryzae pv. oryzae, Xoo) in physical and biological properties. This protein was heat-stable and sensitive to protease K. It also could elicit a typical HR reaction on tobacco leaves, which was dispelled by eu-karyotic metabolic inhibitors:actinomycin D, cycloheximide and LaCl₃. We also found that the protein had the ability to induce disease-resistance to TMV when sprayed on tobacco. Thus, the protein is designated as HLP_Xooc(Harpin-like protein).

When ginger plant was infected by M. incognita, the root was damaged first, and the height, fresh weight of above-ground part, fresh weight of root and rhizome weight were decreased significant, yield was decreased 47.96%. Results also indicated that content of GA, IAA and ZR in ginger leaves infected by M. incognita all were decreased significantly, while that of ABA was decreased in early growth stage and was increased in later growth stage. The ratio of GA and ABA was decrease dramatically, growth of ginger was influenced seriously, more yellow leaves and early plant decrepit. Content of GA, IAA, ZR and ABA in rhizome were changed like that in ginger leaves, but content of ZR and IAA were increased dramatically in September, this was related to the development of giant cell after root-knot ne-matode infected rhizome and set up infected base because giant cell could cause rhizome split. At later growth stage, M. incognita increased GA/ABA and content of GA, so promoted transportation of nutrients to root part and led to the compensation growth of roots; but decrease of IAA and ZR were unfavorable for M. incognita setting up infected site, so too much root knot couldn't be developed in roots.

The relationship between the pathogenicity of a new toxin extract from Alternaria alternata (Fr.) Keissler infecting crofton weed (Eupatorium adenophorum Spreng) that is one of the most troublesome invasive weeds and its inhibition on photosynthesis was studied. The results showed that the toxin extract greatly inhibited oxygen evolution rate and appearance quanta efficiency declined evidently before any distinct change in leaf appearance was observed. The main action site of toxin in chloroplast was on thylakoid membrane. It inhibited electron transfer reaction of two photosystems. The toxin did not affect prominently photosynthetic pigment content and RuBP carboxylase level and activity.

The near-isogenic lines (NILs) of rice with CO39 genetic background and three major physiological races (ZC₁₃, ZE₁ and ZB₅) of rice blast fungus, Magnaporthe grisea, occurring in Guangdong Province were used to establish the cohort life and reproductivity tables on twelve race×line combinations showing compatible and incompatible reactions. Survival and reproduction of the pathogen, as well as their effects on disease development were studied for the compatible combinations. The function of resistant genes against pathogen infection was also studied for the incompatible combinations. The result indicated that in compatible and incompatible combinations, each step from pathogen vegetative growth to reproduction may more or less involve susceptibility/resistance expressions of the host. In CO39 NILs, no difference in spore germination and hyphae growth rate among the tested spores of the same races was found. However, those among spores between the races were significantly different. The critical time points of expression of compatible or incompatible reaction were at the beginning of colonization and reproduction of the pathogen. Lower colonization rate and slower lesion formation related to expression of more resistance of the host. Among those in reproductivity table relating to population dynamics, four parameters, average sporulation per lesion per generation (F'), net reproduction rate (R₀)> maximum relative growth rate (r_max) and index of population trend (I). were more applicable to reflect the relationship between the reproductive status of M. grisea and expression of susceptibility/resistance of the host.

The induced resistance to C. cucumerinum in etiolated cucumber seedlings was elicited by crude pectinases extract (PE) from the solid-state fermentation with P. oxalicum BZ-2002. Etiolated cucumber seedlings of 4 susceptible cultivars inoculated with C. cucumerinum at 48 h after spraying treatment with PE exhibited different degrees of increased resistance to the disease. Cucumber seedlings of cv. Zhongnong No. 5 expressed the highest resistance with inducing efficiency of 62.51%. Different concentrations ranging from 20 to 300 U/mL of crude PE were tested for their effect on induced resistance to cucumber scab. The results indicated that the plants treated with PE at the concentration of 20 U/mL resulted in a little higher disease index than control plants, induced resistance of the plants was enhanced at the PE concentrations between 40 U/mL and 200 U/mL. Spraying cucumber seedlings with PE 12-72 h before inoculation provided significant control of the disease compared with control and the reduction rates of disease index were 29.64%-60.02%. No protection was observed in seedlings treated with PE 0-6 h before inoculation or 0-48 h after inoculation. With the increase of inoculum, the efficiency of induced resistance caused by PE was reduced. No inhibitory activity was observed on conidial germination and germ-tube growth of C. cucumerinum at various concentrations of PE (20-200 U/mL). On the contrary, they had stimulative effect on conidial germination and germ-tube growth.

The coat protein genes of Tobacco mosaic virus, Cucumber mosaic virus and Potato virus Y were amplified from the extracted RNA of infected tobacco leaves by RT-PCR, using the specific primers designed according to the nucleotide sequences of the coat protein gene of the three viruses. These three fragments were cloned into pGEM-T easy vectors respectively, and then the nucleotide sequences were determined, their lengths were 442,776 and 808 bases respectively. Using these clones, digoxigenin-labelled cDNA probes were synthesized by PCR, and applied in dot-blot hybridization to detect TMV, CMV and PVY. The sensitivity for detection of the total RNA of infected tobacco leaves by TMV, CMV and PVY was 1:1 000, 1:10 000, 1:320 respectively; while that using simple extraction of infected leaves was 1:100, 1:100 and 1:10 respectively. The result showed that the three probes were stable, sensitive and specific.

Bacterial strains 2P24 and CPF-10 are two biocontrol agents isolated from wheat rhizosphere in Shandong Province. These two strains were classified into the genus of Pseudomonas by analyzing the 16S rDNA sequence. Further detection of physiological and biochemical characteristics revealed that both strains belonged to P. fluorescents The strain 2P24 fell into biovar I and CPF-10 fell into biovar V. Both 2P24 and CPF-10 produced several antifungal compounds, such as antibiotic 2, 4-di-acetylphloroglucinol (2,4-DAPG), hydrogen cyanide (HCN), siderophore (s) and extracellular pro-teinase, and showed inhibitory to Rastonia solanacearum, Fusarium oxysporum and Rhizoctonia solani in the dual-culture test in plates. In greenhouse, strain 2P24 and CPF-10 showed 63.0% and 62.4% efficiency to control tomato bacterial wilt, respectively.

Statistics of codon usage in the genomes of bacterial phytopathogen Xanthomonas campestris pv. campestris and X. axonopodis pv. citri were calculated based on the published genomic data. Codon usages in these bacteria were dominated by codons containing high-GC content, with the average GC content at synonymously variable third position of codons (GC3s) being 0.806±0.077 (Xcc)and 0.791±0.075(Xac), respectively. Calculation of effective number of codon usage (Nc) and codon adaptation index (CAI) revealed that highly expressed genes exhibited higher frequencies of GC content and tend to use biased number of codons, while for lowly expressed genes, the opposite tendencies was true. Correspondence analyses based on absolute numbers of codon usage (N) were according to the above results. Comparative analysis revealed little difference between genes from leading and lagging DNA strands, so that gene location was not a contributive factor. Our findings suggest that for Xanthomonas genomes, highly GC content, gene expression level, and gene family and origination are fundamental factors to shape the pattern of biased codon usage.

In April 2002, a serious Anthurium disease broke out in a commercial plantation in Xishuang-banna, Yunnan Province, P. R. China. The early symptom appeared as irregular water-soaked spots on the margin or in the middle of leaves. Eventually, brown to blighted areas were often observed together with striking yellow zones along leaf margins. Yellow, mucoid colonies were consistently isolated from infected tissues. The strains reproduced the typical symptom after spraying or rubbing on both Anthurium and Dieffenbachia leaves. The colonies re-isolated from inoculated leaves were as same as those from infected tissues. The pathogen was preliminarily identified as genus Xanthomonas, based on bacterial morphological, cultural, physiological and biochemical properties. The pathogen was further identified as Xanthomonas axonopodis pv. dieffenbachiae (McCulloch and Pirone) Dye by carbon source utilization and pathogenicity tests.

Six typical Phytophthora strains which cause soybean root rot in Longhai, Fujian were chosen for identification. The morphological characteristics, pathogenicity, host range and the sequence of ribo-somal DNA-ITS were studied. Based on its abundant, rounded hyphal swellings in chains, right-angle and shrinking in branch, non-papillate, ovoid sporangium, internal proliferation of sporangiophore, zoospores formed within sporangium, homothallism, rounded oogonia and paragynous antheridium as well as its narrow host range, the symptom of Soybean Phytophthora blight after inoculation, the pathogen was identified as Phytophthora sojae. The sequence of ribosomal DNA-ITS of Fujian isolates was closest relative to that of P. sojae published in GenBank with 99.8% identity. The results indicated that these strains were P. sojae. This is the first report that P. sojae exits in Fujian, China.

Schisandra is Chinese traditional medicinal materials. The rust caused by Aecidium schisan-drae is an important disease of S. sphenanthera in LaBa River nature protective area. The percentage of diseased plant and the diseased leaf reach 91% and 36% respectively when the disease occurs seriously. The disease caused leaf spot, leaf cast and weakened the development of the tree. A hyperparasite (Tuberculina sp.) of A. schisandrae was first time reported. The natural hyperparasitic percentage averaged 35.5% in LaBa River nature protective area. The hyperparasites attack aecium of A. schisandrae and hinder the release of aeciospores. This paper reported the symptom of the rust and the morphological characteristics of the rust pathogen. The hyperparacitism and the morphological characteristics of the Tuberculina sp. were also reported.

Reactions to water stress were studied on the stripe rust-tolerant wheat cultivars and the typical susceptible cultivars after infection of the pathogen Puccinia striiformis West. The results showed that these stripe rust-tolerant cultivars exhibited tolerance to water stress as well. These cultivars expressed the compatible reaction to pathogen infection under normal water supply conditions, whereas turned to the incompatible reaction to pathogen infection under water stress conditions. Water transpiration in these diseased leaves slightly increased at early stage of infection. However, after then the water transpiration rate, water diffusive resistance, relative water content, and water potential of these diseased leaves gradually turned to the same levels as those of healthy leaves. Additionally, lower osmotic potential and higher turgor potential than those of healthy leaves were also observed in these cultivars, indicating the characteristics of water balance in leaves. In contrast, on the stripe rust susceptible cultivars, the water transpiration rate increased sharply, leaf diffusive resistance, relative water content, water potential, osmotic potential and turgor potential decreased remarkably in diseased leaves under water stress conditions after infection of the pathogen, indication the characteristics of losing of water balance.

A water soluble elicitor (GP66) was isolated and purified from hyphal cell wall of the strain 97-151a of Magnaporthe grisea race ZC₁₃ through centrifugation, ultra-filtration and chromatography. SDS-PAGE showed that the elicitor GP66 had only one band of 66 kDa. Sephadex G-100 gel filtration showed that molecular weight of the elicitor was 64 kDa. Anthrone-colorimetric assay and Coomassie blue G-250 staining showed that the carbohydrate and protein contents were in a ratio of 3.84. Bioassay detection indicated that GP66 could increase the levels of the activity of POD and PAL in rice leaves. Digestion with trypsin and boiling at 100℃ for 10 min did not abolish the elicitor activity, but complete loss of activity was observed after periodate treatment. The results suggest that the carbohydrate moiety contains the active site of the elicitor, and the protein moiety may not be necessary for elicitor activity.

It has been demonstrated that RNA-mediated resistance to virus infection in plants is associated with RNA silencing, in which dsRNA in the transgenic plants may play an important role in triggering the silencing process. In this research, we designed cDNA constructs using direct repeat (DR) and inverted repeat (IR) of the coat protein gene segments of Potato virus Y (PVY),or introduced these constructs into tobacco plants via Agrobacterium tumefaciens-mediated transformation system. Resistant assays of the transgenic plants showed that highly resistant plants to PVY infection were obtained in both DR-and IR-transgenic plants. However, higher proportion of resistant plants was obtained from the IR-transgenic plants than that from DR-transgenic plants. Further analysis demonstrated that the resistance was RNA-mediated. These results indicate that using IR constructs of viral gene segments as transgenes may be a feasible strategy to produce virus-resistant plants by genetic engineering.

The complete nucleotide (nts) sequences of RNA1 of two isolates of Rice stripe virus (RSV), isolated from Chuxiong (CX), Yunnan Province, and Hongze (HZ), Jiangsu Province, were determined. RNAl of both CX and HZ isolates were 8970 nts. Comparison of the nucleotide and amino acid sequences of seven ORFs among these three isolates demonstrated that the closer phylogenetic relationship between HZ and T isolates than that between CX and T isolates. Comparison of the L proteins of Tenuiviruses RSV and Rice grassy stunt virus (RGSV) with those of Bunyaviruses indicated that Tenuiviruses were most closely related to the genus Phlebovirus. The alignment data showed that Tenuiviruses L protein shared with Bunyaviruses the three conserved regions corresponding to the so-called polymerase module. These comparisons also showed the existence of an additional fourth conserved region in the L protein of Tenuiviruses that contains at least two active sites, indicating that this region has an important role in the function of this protein. Further analysis showed that the two active sites were necessary for primer mRNA synthesis with cell-derived capped primers in influenza virus. The result indicated that Tenuiviruses could also have the cell-derived capped primer mechanisms.

Relationships between regulations in the generation rates of active oxygen species (AOS), activities of defensive enzymes, levels of membrane lipid peroxidation and resistance of the cultivars during the interactions of cowpea (Vigna sesquipdalis Wight) and rust pathogen (Urornyces vignae Barcl) were analyzed. The results showed that superoxide dismutase (SOD) activity increased in immune and susceptible cultivars, and the peaks appeared at 12 hours after inoculation (a. i.), but decreased at first and increased at 12 hours a. i. in resistant ones, the peaks appeared at 24 hours (in highly resistant one) and 48 hours a. i. (in moderately resistant one). At 24 hours a. i., SOD activity in immune and resistant cultivars were higher than that in susceptible ones. Within 12 hours a. i., the catalase (CAT) activities decreased in all immune and resistant cultivars, but increased in susceptible ones and the first increase peak appeared at 12 hours a. i. The results also showed that superoxide anion (O₂^·) generated in all cultivars infected with rust pathogen, and net change of O₂^· generation rates in immune and resistant cultivars were lower than that in susceptible ones at most determination stages. A negative relationship between net change in malondialdehyde (MDA) content and resistance was found, being basically in conformity with the tendency of change of O₂^· generation rate. These results indicated that metabolism of AOS played an important role in the interactions of cowpea and rust pathogen.

The conidia germination and appressoria formation of Colletotrichum gloeosporioides, the pathogen of persimmon anthracnose, was tested on concave glass slides in different environment. As the concentration of glucose went up, rates of conidia germinating increased but the percentage of appressoria formation decreased, and the length of germ tubes augmented and the diameter of appressoria was steady; with time prolonging, the percentage of conidia germinating and appressoria formation all climbed. The conidia could germinate and form appressoria over wide pH range from 2.0 to 9.0; the optimal pH for conidia germination and appressoria formation was between pH 5.0 and pH 6.0. The pathogenicity test under different pH condition illuminated that the disease occurred on twigs at 23℃ within pH 4.0-8.0, also appeared at 17℃ and pH 6.0 without spore masses on lesions of twigs surface, however, was absent at 17℃ and pH 5.0 as well as at 15℃ and pH 5.0 to pH 6.0. The optimal temperature for the mycelium growth was about 25℃, and higher temperature inhibited its growth. The scanning electron microscopy examination showed that the length of germ tube, growing longitudinally along the ridge and transversely cross the ridges and grooves, varied greatly, and the appressoria formation occurred at the bottom of groove or near.

Five bacterial strains with complementary biocontrol activities were selected and mixed as one biocontrol agent AR99 for the control of Capsicum bacterial wilt. In the greenhouse test,the biocontrol efficiencies of the mixture and individual bacterium suspension R1, A9, J3, R9 and A6 strains were 91.1%, 88.9%, 80.5%, 80.5%, 66.7% and 57.0%, respectively, with that of the mixture AR99 being the highest. Field plot tests for the biocontrol of Capsicum bacterial wilt were done by composting method and root-drenching method in Huaian, Jiangsu in 2000 and 2001. The average disease control effieciencies of AR99 were 94.0% and 77.0%, with the average yield increasing efficiencies of 367.0% and 57.8%, respectively, by the composting method and root-drenching method 70 days after treatment.

Bacillus subtilis strain G3, a chitinase-produing biocontrol agent, showed a strong activity to inhibit the growth of pathogenic fungi Botrytis cinerea and Cladosporium fulvum. The antifungal substances were prepared from the solid culture filtrate. They were iturin and surfactin extracted from acid precipitate and the chitinase obtained in crude proteins by ammonium sulfate precipitation. Iturin showed a relatively weak activity to inhibit spore germination of C. fulvum, but a strong activity to break the germ-tube and new hyphae. Surfactin and chitinase were inhibitory to spore germination and suppressive to germ-tube elongation. In the antibiosis detection with B. cinerea on plate,iturin inhibited mycelial growth and caused the vesicle structures in the tips of hyphae,then the cell wall broken and the protoplasm leaked out. Chitinase also inhibited mycelial growth and caused the hyphae abnormal. Surfactin showed no antifungal activity to B. cinerea.

Endophytic Bacillus sp. strain TB2 isolated from stem of tobacco was an efficient biological control agent to control Pepper Phytophthora blight. Seed coating and root drenching with TB2 cultures gave 70.0% and 88.1% control efficacies respectively, on capsicum seedlings 20 d after inoculation of the pathogen P. capsici, while spraying on fruits gave 65.2% control efficacy to the fruit Phytophthora blight 14 d after inoculating the pathogen. The research on biological control mechanisms showed that the strain TB2 could inhibit the mycelial growth and reduce the sporangia and zoospores production of P. capsici. The treatment with strain TB2 considerably increased the SOD and POD activities in the capsicum fruits. Inoculation with P. capsici on fruit also significantly increased the MDA content and SOD, POD and CAT activities. However, the MDA content and SOD, POD and CAT activity of the capsicum fruits co-inoculated with the strain TB2 and P. capsici at the same time did not remarkably change comparing with fruits inoculating with sterile water.

The effect of soil temperature,moisture,pH value and organic matter on survival of microscle-rotia of V. dahliae of cotton was estimated. Results showed that soil temperature at 40, 30 and 0℃ had significant effect on survival of microsclerotia while temperature at 10 and 20℃ had less effect on survival,particularly 10℃ had least effect. The higher soil moisture, the higher effect on survival of microsclerotia. Once soil moisture below 15%, it had less effect on survival, especially 5% gave least effect. It demonstrated that microsclerotia had strong resistance to stress of soil dryness. The pH value below 5.5 or over 7.5 had higher effect on survival of microsclerotia while pH 6.5-7.5 had less effect. The higher content of organic matter in soil, the lower viability of microsclerotia and it gave the less effect on survival at lower content of organic matter. Results also indicated that by improving and controlling soil habitat factors for survival of V. dahliae, it was possible to effectively minimize the numbers of microsclerotia survived in soil and to prevent disease occurrence and development.

Transcriptional regulation of defense gene expression is a crucial part of the plant defense responses. Transcription factors play important roles in the transcriptional regulation of gene expression. Here, we review the structure features and functional characterization of the ERF transcription factors, and based on our current research, discuss the regulatory roles of transcription factors in plant defense responses.

Oxalic acid (OA) is a phytotoxin produced by pathogenic fungi including Sclerotinia sclerotiorum. Effect of oxalic acid on spore germination and mycelial growth of C. minitans, the mycoparasite of S. sclerotiorum, was studied in media. The results indicated that OA could not stimulate the spore germination of C. minitans. On unbuffered and buffered media (water agar), the lowest OA concentration for inhibition of C. minitans germination was 150 and 700 μg/mL, respectively. On potato dextrose agar (PDA) amended with OA at 100-2 000 μg/mL, C. minitans could grow,and OA at 300-500 μg/mL in PDA could significantly stimulate the mycelial growth of C. minitans. On an unbuffered synthetic medium amended with OA ranging from 100 to 2 000 μg/mL as the carbon source, C. minitans could grow. The optimum OA concentration was 500 μg/mL and the maximum OA concentration was 2 500 μg/mL. On the buffered media, C. minitans grew at the OA concentration ranging from 100 to 4 000 μg/mL with the optimum OA concentration between 1 500 and 2 500 μg/mL. On opaque media containing calcium oxalate, a clear zone under each colony of C. minitans in each plate was observed. These results suggest that C. minitans could tolerate OA both for its spore germination and for its mycelial growth and C. minitans may degrade oxalic acid.

To develop a rapid and sensitive method for the detection and identification of Meloidogyne incognita,M. javanica and M. arenaria, four and three random amplified polymorphic DNA (RAPD) fragments specific for M. incognita andM. javanica, respectively, were identified. Based on the sequences of these RAPD markers, various sequence characterized amplified region (SCAR) primers were designed and tested for their amplification specificity and efficiency against populations of M. incognita,M. javanica, M. arenaria, M. hapla and M. enterolobii. This resulted in three pairs of SCAR primers that were used in combination to reliably and sensitively identify M. incognita,M. javanica and M. arenaria. The SCAR markers can be readily amplified from one third of a single second-stage juvenile, male or female, thus demonstrating that the SCAR-based PCR assays have practical value for routine identification of M. incognita,M. javanica and M. arenaria in soil and root samples.

G. roseum 67-1, a strain with high pathogenicity to sclerotia of S. sclerotiorum, was isolated from pea rhizosphere soil collected from Ledong, Hainan Province. One hundred percent of sclerotia were parasitized 7 d after they were inoculated with G. roseum 67-1 on PDA plates. Spores of this isolate succeeded in parasitizing sclerotia within 24 h after inoculation. The inhibition band was observed during the dual culture on PDA plates. Microscopic observation of sectioned sclerotia showed that sclerotial tissue collapsed by the parasitism of G. roseum 67-1. Change of protein composition was found in the infected sclerotial tissue. Our results show that this isolate, with ability to grow under wide temperature range and to produce mass spores, is of great potential to control soybean stem rot caused by S. sclerotiorum.

Rod-shaped virus particles about 300 nm×18 nm were isolated from Syringa oblate expressing systemic mosaic in leaves. The double-stranded RNA pattern revealed one single band of about 6.4 kbp. The virus contained coat protein of approximately 17.6 kDa. According to these results, the virus isolate was identified as a member of Tobamovirus. A pair of primers were designed based on Tobamovirus RNA RdRp gene, and a fragment of about 1 000 bp(GenBank AY566703)was amplified by RT-PCR. The PCR product was cloned and sequenced. The sequence shared 99.90% homology with TMV-B strain (GenBank Accession No. AJ011933.1). Another pair of primers was designed based on TMV RNA CP gene. A fragment of about 800 bp(GenBank AY566702)was amplified. The recombinant plasmid was obtained and sequenced. The sequence shared 99% homology with TMV-B strain (GenBank Accession No. AJ011933.1). CP gene sequence and amino acids shared 99.37%, 100% homology with TMV-B strain respectively. On the basis of above results, the virus isolated from S. oblate in Beijing is Tobacco mosaic virus (TMV).