This paper deals with the ultraviolet absorption, fluorescence and Raman spectra of rice bunchy stunt virus(RBSV)..On the spectra, there were significantly different results among RBSV, rice dwarf virus (RDV) and rice ragged stunt virus (RRSV)by comparative study. It is not only possible to detect virus concentration, relative ratio of its protein and nucleic acid so as to identify a virus but also helpful to elucidate the structure and its function of a virus and to reveal the mystery of life itself.

The experiment results showed that the elimination of satsuma dwarf virus (SDV) is difficult by shoot-tip grafting (STG) or by heat treatment alone.But SDV could be completely excluded by heat treatment at 40℃/day and 30℃/night(each for 12 hours)for 7~43 days combined with STG. Seventy-two plants obtained after heat treatment combined with STG were all free of SDV. It is suggested that the beat treatment for 7 days combined with STG should be the best method for the elimination of SDV.

A recombinant cosmid (pNAX3103) containing hrp gene region from Xanthomonas campestris pv. oryzae race 3 (JXO Ⅲ) was transferred to different raceS. Their virulent gene mutants by triparent mating, and pNAX3103 could be introduced into different races but not to their mutants. The fuction analysis revealed that hrp gene region in pNAX3103 had no obvious effect on the growth, the production and excretion of protease, pectase and cellulase in different races of pathogen, and it could enhance the virulence of race 1 (JXO I) and change the compatibility of race 5(JXO V) on rice cultivar IR26. When the mutants were tested pNAX3103 could npt be introduced into mutants XcoM5102, XcoM5103 of race 5 (JXO V) and complemented mutant XcoM1107 of race 1(JXO I) not to restore the phenotypes of the pathogenicity and amylase activity as wildtype strain (JXO I). The DNA homology of 10 strains of different races Xco and 4 of phytopathogenic bacteria were analyzed by pNAX3103 as a probe. Homologous hybridization bands were found in all tested strains of Xco, and also in X. c. pv. campestris, X. c. pv. oryzacola, X. c. pv. citri, and Erwinia carotovora var. carotovora, but not in the strain of E. chrysanthemi.

The mechanisms of population resistance of wheat variety mixture to Puccinia stri-iformis, P. recondita and Erysiphe graminisa had been studied by field experiments. The two components of variety mixture were Jinfeng 1 (susceptible cv.) and Jimai 24 (resistant cv.). The results showed that the population resistance might be partitioned into three parts:the influence of the reduced density of the susceptible plants, the barrier effect of the resistant plants, and the induced resistance due to the non-virulent pathogen bio-types. From the on-set to the end of the epidemic, the lower density of susceptible plants accounted for most of the reduction in disease development in mixtures. As the epidemic progressed, the barrier effect and induced resistance increased in importance. The relative importance of each mechanism varied according to different diseases.

The nucleal condition of uredinial stage of wheat stripe rust was studied with electron and flouresence microscopy. It was found that urediniospore usually contained two nuclei, while the germ tube from urediospore possessed two,three or four nuclei and germ tube with two nuclei was dominant. The multinuclea) condition in intercellular hyphae and Haustoria mother Cell was very common although intercellular hyphae and Haustoria mother cell with two nuclei could be observed. The observation from serial sections showed that there were two,three,four,five or six nuclei in Haustoria,in which four nuclei was dominant. All types of cell in uredinia were found to be binuclei. The results here obviously indicated that the nucleal condition of wheat stripe rust was complicated and different from that of other rust.

Biotype 3 Agrobacterium tumefaciens strain MI3-2 from grapevine in nature is responsible for the formation of tumors on a very narrow host range of plants, particularly vitis(grapevine)cultivars. The previous work demonstrated that the DNA in MI3-2 exhibited little or no homology to a wide host range(WHR, strain A348) virA locus and auxin gene in the TL-DNA of PTiA6. In this report the cosmid clones from WHR vir region and T-DNA were mobilized into the narrow host range (LHR) strain (MI3-2) by tri-parental mating procedure, complementing the corresponding genes in merodiploid of MI3-2 strain, and assayed for their ability to allow tumor formation on Kalanchoe, petunia, sunflower, tomato and tobacco. The results showed that pvck232 containing the WHR TL -DNA, pvck219 and pvck257, both containing WHR virA locus, and when presented in the LHR strain, expanded host range to some of these plants and allowed tumor formation weakly on Kalanchoe leaves. Pvck225 and pvck242, which contained the PTiA6 virB, virG, virC, virD and virE, were unable to expand host range. This indicated that WHR virA locus could play an important role in expanding narrow host range of the MI3-2 strain.

Studies on the inheritance both of severity type(SE) and infection type (IT) in Pingyuan 50, a wheat variety which is believed to be durably resistant to stripe rust. To the 8 races involved in the study, the variety reacts 0-3 ITs and shows less SE in comparison with Mingxian 169, a variety which was used as susceptible control. Analysis of crossing and segregation suggests that the two constituents of disease vary, in genetic nature, with races. To 4 of the 8 races in question, the less SE is conditioned by gene(s) independent of that responsible for low IT. To 3 races, no gene is found, which is relevant to less SE and is independent of gene(s) reponsible for low IT. To another race, low IT may be relevant to dominant gene(s).

The effect of cations on activities of pectinases produced from Pythium aphanidermatum causing cucumber seedling damping -off were first studied systematically on the basis of host-parasite relationship. There were five kinds of cations detected in healthy hypocotyl cell wall, in which the highest contents of Ca²⁺ and Na⁺ were found. It was interested that seedlings increased calcium contents and resistance to degradation of hypocotyl cell wall by pectinases, as seedling age grew. There were obvious influences of various cations on activities of PG produced in vitro or in vivo, and these influences from the cations changed as reaction time lasted. PG had different sensitivity to cations, depending on the PG produced in vitro or in vivo. Moreover, Ca²⁺ was considered to expose double affection on PG activity, i. e. Ca²⁺ at lower concentration tended to stimulate PG activity, at higher concentration to inactivate PG activity. Na⁺ could inhibit PG activity if it accumulated to enough concentration. PGTE was more sensitive to Ca²⁺ than PMTE.

Witches' broom and samll leaf appeared in diseased pepper plants (Capsicum frutescens). The petioles become long and thin, while flowers turned green, Severe infection of pepper showed stalkbanding, infloresence-clustering, flower-withering and scalephyllody. Many trials indicated that the causal agent can be transmitted by Tettigella virid is is and graft, but not by aphides and sap inoculation. All of the vascular bandies were degenerated and orange fluorescence spots obvious were in discaled phloem of leaf midrid, when stained with 0.25% toluidine blue o (TBO) solution observed under fluorescence microscopy. Spherical bodies, 172-311 nm in diameter in sieve tubes of the ultrathinsec-tions from infected pepper were seen in electron microscopy. Oxytetracycline (OTC) treatment made effectively more bright. It is demonstrated that the pepper witches broom was caused by mycoplasmalike organism (MLO) and is regarded as a first of such disease in China.

Reaction of 39 wheat cultures (lines) and 17 near isogenic Lr gene lines interacting with 21 Puccinia recondita f. sp. tritici cultures were compared to detemine the probable genes for seedling resistance in the cultivars. Many of the cultivars (lines) studied can be combined into groups on the basis of sharing the same genes for resistance. The cultivars may have the genes indicated in parathesis as follows:Nuo -77-17-1 (Lrl7), Nuo77 -14-2317 and Kehan No. 9 (Lr14b), Longmai 12 (Lr10), Dongnong 120 (Lr14a),Jian66 (Chuyi)(Lr18), P_mv76-SIS (Lrl7 in addition to Lr1)and Jian60(chuer) (Lr3 in addition to Lr10),some of the cultivars (lines) may have genes in addition to the Lr genes determined.

A new virulent race of head smut (Sporisorium reilianum (Kühn) Langdon & Fullerton) designated as race 3 was characterized by its ability to attack ATx622 and BTx622, a line resistant to race 1 and race 2 in Yingkou area of Liaoning province, where the hybrids developed from ATx622 as a female parent were first released. The differentia] hosts of race 3 are ATx622, BTx622, ATx623 and BTx623.

The stubby root disease of apple caused by Trichodorus pakistanensis Siddiqi, 1962 occurred in Beijing. The disease showed typical symptoms of stubby roots which caused the nonproductivity of more than 7 acres of the old orchard. Apple trees infected by this nema-tode seriously declined or died.

The isolate G-14 was obtained from infected alfalfa plants showing dwarf mosaic symptoms in Xingjiang. It infected 19 of 40 species from 6 of 9 families by sap inoculation. The isolate was transmitted by beetle Hypera variabilis but not by aphids. TIP=55~60℃, DEP=10^-3-10^-4, LIV=21 days. The viral particle was isometric,about 28 nm in diameter. The lattace-like inclusions which arrange in good order were found in leaf tissue of infected alfalfa plants. This isolate reacted with the antiserum of CPMV in agar gel double diffusion test, and has three protein components of different ML. Wt., each with two nucleic acid components.
This isolate G-14 of alfalfa is demonstrated to be CPMV.

Field tests of studying the overwintering and survival of Phytophthora boehmeriae Sawada by means of a vital stain MTT(tetrazolium bromide) were carried out in Hebei Province. The results showed that both sporangia and oospores could survive in the boll residues in the soil. The survival period of sporangia in the soil was about 3——4 months and the percentage of survival was 58.0%. Therefore they must play a major role in the infection cycles to cotton bolls. However, the viability of sporangia were considerably effected by low temperature and no viable sporangia were observed at 0 C in January. The oospores were confirmed to be the overwintering propagules of P. boehmeriae and survived at least 300 days from 1990 to 1991 with 76 days below 0℃ (the lowest one was -2.8℃). The final survival rate was 48.8%. Bioassays and morphological observations of the overwintered oospores on cotton boll residue, and the relationship between the oospores inactivating rate and temperature revealed that the overwintered oospores were the source of the primary infection of cotton boll blight.

Seeds of susceptible cotton variety were shown into the soil containing Dinitroani-lines. After transplanting the cotton seedlings showed markly increase of the resistance a-gainst Fusarium wilt (caused by Fusarium oxysporum f. sp. vasinfectum, FOV). The index of induction effect for disease resistant reached 70%.
Dinitroanilines are nonfungicidal compounds. Experimental results showed that the compounds did not inhibit FOV from growing, but did enhance the conidial germination and hyphal growth in the case of treated cotton seedlings. The rate of infection by FOV was less than that of control, and FOV was confined below the hypocotyl. Protein patters from treated cotton leaves differ from the control. The colour of one of the bands was apparently darker than that in cotrol. It indicates that the quantity of certain protein was increased. Extraction of fungitoxin substances from treated cotton tissue inhibited the pathogenic conidal germination or retarded the growth of the pathogen. The results of I.F. spectra, U.V. fluorescence and TLC stain were all different from those of control.

This paper is a part of research projects on ornamental and floral plants diseases in Southwest China and of the Project Supported by National Natural Science Foundation of China. Seven fungous diseases of 7 species of garden trees and flowers collected from Kunming, Chengdu and other places were listed.

The urediospores of the millet rust fungus in small glass tube and the rusted leaves in paper envelopes were stored in the refrigerator. On 10 months or more the better part of the urediospores can germinate and may infect the millet. As time goes on the germination percentage and the infection instensity of the urediospores have changed on the decrease. The tests of the host range showed that urediospores infect more than one species of Setaria but there was no evidence of any infection on Setaria glauca (L.) Beauv.

The heterocaryosis of wheat stripe rust was studied with biological and cytological methods. Three new isolates had been obtained from the mixtures of different races, reproducing on the same wheat cultivar simultaneously. It was found that the virulence of the new isolates was obviously different from that of original races and the multinucleal rate in the new isolates was much higher than that in original races, which indicated that the new isolates were produced by means of heterocaryosis. The multinucleal rates of the nes isolates were demonstrated to decline with generations, but the virulence of two isolates of them kept stable. The urediospores with three or four nuclei were observed in field samples from south Gansu Province and the multinucleal rate in the urediospores from susceptible wheat cultivars was much higher than that from the resistant cultivars, which showed that the chance for heterocaryosis of wheat stripe rust on susceptible cultivars may be greater than that on the resistant cultivars.

Five species of Pythium were isolated from diseased roots of wheat, barley and wheat-field soils at different locations in Zhejiang Province from November of 1989 to March of 1990. They are:P.d issotocum,P. irregulare,P. polypapillatum, P.spinosum and P.ulti-mum.
In inoculation tests, all five species isolated from wheat and barley roots were pathogenic to their hosts.which caused root rot, root tip browning and necrosis,distor-ture of the first true leaves, suppression of plant growth and various stunting as well as shortening of different parts of plant.

Morphologically normal buds were collected as explants from the root-sprouting seedlings infected by MLOs. After being sterilized with 0.1% HgCl₂ for 10 minutes, the explants were cultured into MS basal medium supplemented with 0~3 mg/1 6 -BA. 30 days later, all in vitro shoots, from the elongation of the original buds or adventitious organogenesis, exhibited typical symptoms of witches' broom. With the treatment of a high concentration of cytokinin (2~3 mg/16-BA), the witches' broom shoots wilted within 30 days. However, the degree of witches' broom decreased when 0.5mm meris-tems were used as explants. After the tissues from the root, shoot, petiole and callus of witches' broom plants in vitro were dyed with DAPI, fluorescence microscopy showed that strong MLO specific fluorescence emitted from the sieve tubes of these tissues. Compared with the morphology of MLOs in the field plants, more MLOs in the in vitro cultures were found with electron microscopy to be at the stage of active reproduction (budding and dumb-bell stage). The intensity of MLOs in the in vitro cultures was kept at a high level, throughout the whole experimental period (one year) with one subculture every month. This study indicates that tissue culture of host plants is a good solution for the preservation and multiplication of pathogen MLOs.

Resistance could be induced to blast disease on rice plants by using seed soaking or leaf spraying method of liquids of Na₂SiO₃, Cycloheximide, KC1, MnSO₄ and extractsd of the root of Purple-flowered peucedanum (Pevcedanum decursivum) and Dahnrian angelica (traditional chineses medicine). With spraying method of inoculation, the indices of resistance effect on susceptible varieties to leaf blast was 43%~93%, while to neck blast by injection inoculation was 29%~78%. It is evident that the inducing effect was higher on susceptible varieties of rice and with avirulent strains of pathogen than those on resistant varieties and with virulent strains of pathogen. The indices of inducing resistance were also higher in the case with virulent strains and leaf spraying inoculation than in that of soaking seed with drug extract.

The pathogenicity of Phytophthora boehmeriae was tested by cross inoculating between the isolates obtained from cotton, common papermulberry (Broussonetia papyrifera) and ramie (Boehmeria nivea), and their host plants. Results showed that parasitical specializa-tion didn't present among the isolates of P. boehmeriae. The results also showed the pathogenic abilities of the isolates were different to their original as well as other host plants, while the pathogenic abilities of the isolates from cotton seedlings were similar to those isolates from cotton bolls. The pathogenicities of the isolates from common paper-mulbrry to cotton increased when they infected cotton seedlings continuously, it suggested that common papermulberry might be a wild host plant of the pathogen of cotton blight.

The authors have isolated and identified a mycoplasmalike organism (MLO) disease on the strawberry plant in Shenyang. The experiment was carried on during 1987~1990. The diseased plants showed stunting and witches' broom symptoms clearly. Collections were made and observed from two cultivars of strawberry, i. e.; Hoko-Wase and Haru-Kaori, Which were planted in the suburbs of Shenyang city.
This disease could be transmitted to the health indicated strawberry plants by small leaf grafting. The indicative strawberry plants for infection such as:EMC, UC-10, and UC-4 etc. were shown stunting, chlorotic and witches' broom symptoms.
According to the ultra -thin sections of the diseased plant observing under the electron microscope, the authors revealed the presence of mycoplasma-like organisms (MLOs) in the sieve tubes of the diseased strawberry plants.
The symptoms could be restrained or lightened by the use of tetracycline treatment, which is also a specific property of MLO disease.

Numerical study of 96 strains of plant pathogenic pseudomonads (includ-, ing 5 strains of nonfluorescent pseudomonads) obtained from 21 kinds of plants were conducted. It showed that all fluorescent strains were separated into 2 groups. Group I grew slowly, gave negative reactions in arginine dihydrolases, and had narrow nutrition spec-trums. Most strains of group I could not use DL-phenylalanine, L-phenylanine, L-hy-droxyproline, L-isoleucine, L-serine, L-citrulline, DL-nor-valine, L-cysteine, tannic acid, rhamnose as sole carbon sources and aspartate as sole carbon and nitrogen (C/N) sources, but strains of group I could use these compounds as sole C or C/N sources. Strains of group I were separated into 10 subgroups which were correspondent with patho-vars or nomenspecies, and correlated with host origines; the distinctions among subgroups were shown in their abilities to use some substrates. Strains of group Ⅱ gave positive reactions in arginine dihydrolases, and had wide nutrition spectrums.

The influence of temperature on mycelial growth of Phoma asparagi Sacc. was studied in vitro. The favorable temperaturre for mycelial growth was observed as 20~30℃ for Phoma asparagi Sacc. in Tianjin with optimum at 25℃. No growth was observed with Phoma asparagi Sacc. at 10℃ and>35℃.20% decoction of stem and leaf of asparagus, or decoction+PDA and PDA media were available and stimulative for spore germination. The amount of pycnidiosporulation of Phoma asparagi Sacc. on 20% decoction of stem and leaf of asparagus or its decoction + PDA media were significantly abundant than that on other 3 different madia reported before. The continuous light induced pycnidium formation. There was remarkable difference under various light treatments. Exposure of pycnidiospores of Phoma asparagi Sacc. to the Diniconazole (8 h/2 ppm) resulted in the ultra-structural changes.

The growth of cotton seedlings were reduced significantly (P<0.05) in pots inoculated with spiral nematode H. pseudorobuslus 100-1000 per 100cm³ soil compared with the non-nematode pots 30 days after sowing in greenhouse.
Symptoms of fusarium wilt of cotton seedling of 86-1 (fusarium resistant) only occurred in treatments inoculated with both fungus (Fusarium oxysporum f. sp. vasinfectum) propagules 7.5×10⁵ per gram soil and nematodes (H. pseudorobustus) 500-1000 per 100 cm³ soil, but never occurred in the treatment with fungus alone. The fusarium wilt index of seedlings were correlated with the initial nematode population levels positively (r=0.97). Field experiment demonstrated that the application of fumigent da-zomet 8~14 grams per M² soil was more effective than that of non -volatile nematicides carbofuran, fenamiphos and ethoprop for control of nematode fusarium wilt disease complex.