A new technique, the Immuno-isolation was established and be used to detect Xanthomonas oryzae pv. oryzae (Xoo) in rice seeds with monoclonal antibody (McAb) 3Al. The result showed that the immuno-isolation provided an effective tool for selective isolation of Xoo from rice seeds sample may containing lot of saprophytic bacteria, also high sensitivity of 50-100 cfu/ml during detecting, The reisolated rate of the target bacteria (pathogenic bacteria) ranged from 45~70%. Among 500 naturally infected seeds from divers 5 locations, 438 grains were positive to carry with Xoo by using the new isolation method. Most colonies obtained from immuno-isolation plate were proved to be Xoo by indirect ELISA and pathogenisity test.

280 isolates were obtained from the rice leaves infected by rice Phyllosticta leaf blight collected from 13 counties of Jiangsu Province, China. According to the results of identification and inoculation, Phyllosticta oryzicola Hara is the main pathogen causing leaf blight of rice. Otherwise,other fungi such as Pestalotia orysae Hara, Alternaria alternata (Fr.) Keissl., Rhynchosporium oryzae Hash, et York., Curvularia pallescens Boed., C. lunata (Walk.) Boed., C. geniculata (Tracy et Earle) Boed., Fusarium spp., Bipolaris spp., Nigrospora oryzae (Berk, et Br.) Fetch, N. sphaerica (Sacc.) Mason, could accidently be obtained by the isolation of the diseased leaves. The conidiogenous cells of Phyllosticta oryzicola were observed to be holoblastic-solitary under the transmission electron microscope.

The presence of double-stranded RNAs were demonstrated in Fusarium oxysporum f. sp. glycines 1193-3 after screening 18 strains (10 formae speciales) of Fusarium oxysporum. The dsRNA genome contains six components with sizes of 3.8kb,3. Okb, 2.4kb, 0.48kb and 0.21kb. This strain has two morphological variations-sectoring and large production of pink conidia.

The epidemy of cotton Verticillium wilt was investigated during 1981~1990 in a heavily diseased field at fixed field plots and planted the susceptible cultivar 86-1 in Xinxiang county, Henan province. The results showed that there is a great difference of disease in different years. Two types of the disease years were divided:the first, light disease year with high temperature and low humidity, the wilt index on 30 July being 15.39, and the second, severe disease year with low temperature and high humidity, the will index being 33.44 on 30 July. It occurred 4 in 10 years of each type. It can be seen that the wilt index of latter is 2.17 times of the first. The key factor influencing the development of the disease was the temperature in July of the year. If the ten-day mean temperature in July of two sucessive ten-days is higher than 27℃, the increasing of wilt index could be slowed and it would be a light disease year. There is a direct relation between the humidity and the wilt index:that is the humidity of July was higher than 80%. a severe disease year would occur under low temperature.

The sensitivity and variability of P. megasperma f. sp. glycinea to metalaxyl were tested in vitro. The results showed that the mycelial growth of 17 strains isolated from China was sensitive to metalaxyl on CA medium. However, the sensitive degrees were different between these strains that the range of Ec50 and Ec95 values were 0.0042~0.0297 ug/ml and 0.7688~6.1682ug/ml. respectively. Meanwhile, the hyphal growth of 3 isolates from U. S. A. was tolerant to metalaxyl in CA medium, in which the range of Ec50 and Ec95 values were 0.3725~0.4818ug/ml and 125.97~280.59ug/ml,respectively. The sensitive degrees of mycelial growth of single spore isolates of B1 and S367 strains to metalaxyl were changeable on CA medium, in which the range of Ec50 values were 0.0058~0.2537 ug/ml and 0.0069~0.1735 ug/ml. The formation of sporangia and oospores of all strains were inhibited by metalaxyl at 1.0 ug/ml on CA medium. The fun-gitoxicity of metalaxyl on P. megasperma f. sp. glycinea was tested in vivo also, the result showed that the systemic protection values of metalaxyl at 1.0 ug/ml was 94% to 100%.

According to the inoculative experiments in green house,the results showed that the latent period of soybean frogeye leaf spot was determined by the effective accumulative temperature for certain cultivars. The dynamic variation of daily rate of lesion appearance can be forecasted by the effective accumulative temperature. The paper showed that the relationship between the accumulative daily rate of lesion appearance and effective accumulative temperature of 3 cultivars might be described Gompertz model. The model of 3 cultivars are:
Hongfeng 3 pp=104.2276exp[-29.9088exp(-0.06625TT)] r=0.9094
Hefeng 25 pp=106.1627exp[-33.6979exp(-0.06329TT)] r=0.9659
Suinong 8 pp=107.2370exp[-24.0048exp(-0.05851TT)] r=0.9439
respectively, in which pp is accumulative rate of symptom appearance,TT is effective accumulative temperature.

Root black spot of citrus was first reported in the world, which was caused by Phaeocytostroma sp.. The symptom and histopathology of the disease and the morphology of the pathogen were described in the paper.

Specimens of Hemicriconemoides mangiferae Siddiqi recently was collected from the fruit orchards in Fujian province. This species was found associated with the rhizospheres of Euphoria Longana Lam., Litchi chinensis Sonn., Mangifera indica L.,Canarium album (Lour.) Raeusch., Eriobotrya japonica (Thunb.) Lindl. and Vitis vinifera L.. Face view of head and vulva of female, lateral field of male and cuticle spines of juveniles were observed by scanning electron microscopy.

In this paper, T. kohonen self-organization of artificial neural network model was applied to establish computer intelligential expert system for assessment of beginning occurrence stage of citrus canker on the basis of the tip sprout stage of sweet orange and the climate in regular period. The data was obtained by systematic survey during 1984~1990. The expert system was used to predict the beginning occurrence stage of citrus canker on spring tip and young fruit in 1991. It showed that the histological coincidence was one hundred percent.

Conidia of Alternaria mali were placed on lower surface of susceptible leaves of apple, and inoculated at 28℃ for 3hr up to 24hr. After 3hr of inoculation,ultrastructural changes of plasma membrane appeared as the earliest event in epidermal and mesophyll cells,plasma membrane was separated from cell wall and invaginated into protoplasm. Then, the vesicles,granular and tubule structures appeared between the cell wall and plasma membrane. In chloroplasts, electron-dense materials deposited, granum loosed and arranged confusedly, chloroplast membrane was broken. After 24hr of inoculation,the leaf surface appeared necrosis,and the ultrastructure of necrotic cells were severely damaged. The cytoplasm concentrated,in which electron density increased,and cellular membranes presented negative images. The granules appeared around outside of cell wall. In chloroplasts of boundary cells between diseased and healthy areas, matrix concentrated and numbers of plastoglobulus accumulated. In the cells 2mm away from the necrotic area,the ultrastructural changes were also observed as follows. Some materials with irregular shape and even density were presented in many mesophyll cells and the electron-dense materials were deposited in the xylem cells.

The Agin-SD60, an agglutinin from chinese cabbage, and lipopolysaccharide (LPS) of Erwinia carotovora subsp. carotovora were tested for their roles in the contact recognition of the plant with the pathogen by 3 methods. In adsorption inhibition tests, the Agin-SD60 from 5 plant species including chinese cabbage, cell wall protein (CWP) and lectin from the host, and LPS and EPS (extracellular saccharide) from 7 species of bacteria, were used as inhibitors of adsorption of the pathogen on root surfaces of the host. The A-gin-SD60 from chinese cabbage and potato showed about 98% adsorption inhibition, and no inhibition was given by Agin-SD60 from other plants and by lectin and CWP of chinese cabbage. Of LPS and EPS from different bacteria, only LPS of Ecc and Eca (E. carotovora subsp. atroseptica) was able to inhibit adsorption at 93.37% and 78.6% respectively. In agglutination tests, the pathogen was agglutinated by Agin-SD60 from Chinese cabbage and potato but other plants. Then the ODD tests were made with combinations of Agin-SD60 from different plants with LPS from different bacteria and EPS from the pathogen. Cross reactions were detected between LPS from Ecc and Agin-SD60 from chinese cabbage, and between Agin-SD60 from chinese cabbage and LPS from Ecc and Eca. These results indicated that Agin-SD60 of chinese cabbage is the cognor and LPS of the pathogen is the cognon, for the recognition between chinese cabbage and soft rot Er-winia.

A filamentous virus isolate, CA, was isolated and identified from chrysanthemum showing mottle symptom in Beijing area. Chenopodium quinoa and Nicotiana tobacum ‘xanthi’ were the best indicator and propagation species. Isolate CA could be transmitted by Myzus persicae in non-persistant manner efficiently. The properties of crude sap were:TIP=50 -60℃, DEP=10^-3-10^-4,LIV=2~3 days. The purified CA preparetion contained flexuous particles 692nm in average and one type of coat protein of Mr 32.3×10³. Pinweel and bundle inclusions were found in the infected leaf cells.
CA antiserum with microprecipitin titer of 1:512 was obtained. The IgG was used for the ELISA test of tissue culture of chrysanthemum.
According to the result of identification isolate CA is considered as a member of Po-tyvirus. The tests of double diffusion, Precipitin, Latex and ISEM demonstrated no sero-logical relationship between CA and PVY.

Purified PLRV, stems and leaves of potato plant, rose-end and heel-end of dormant tuber, sprouts of broken dormant tuber with secondary infection by PLRV and viruliferous Myzus persicae adults were detected by indirect enzyme linked immunosorbent assay (ELISA) on nitrocellulose membranes respectively. The results indicated that the minimum amount of purified PLRV as little as 45.83pg~4.583pg can be detected and PLRV can be detected in stems and leaves of infected potato plant, rose-ends and heel-ends of dormant tuber with secondary infection,sprouts of broken dormant tuber by Dot-ELISA at dilutions of 1/2048,1/512,1/2048-1/8192,1/512-1/2048 and 1/2048-1/8192 respectively.
PLRV in viruliferous Myzus persicae adults can also be detected at least with dilution of 1/2.

The relationship between the diseased panicle rate and the diseased seed rate (P-S re-lationship)of rice kernel smut (Neovossia horrida) on D shuan A-line and Zhengshuan 97 A-line were studied through field investigation. The results showed that the P-S relationship of the disease on the two A-lines might be described with exponential functions,and the P-S relationship models of the two A-lines were established. Analysis of covariance showed that there was a significant difference between the two regression intercepts, and the integrative P-S relationship model was established.

Bacillus subtilis B-903 strain was isolated from apple orchard in Zhengzhou. The antagonistic spectrum and antifungal mechanism of B-903 strain's antibitic substance and the control experiments were reported in this paper. B-903 antibiotic substance was an inhibitor to 12 species of pathogenic fungi supplied for test and the antifungal mechanism was mainly deformation of the spore and cell of hypha and disintegration of the cell wall. The experiments showed that soaking the cotton seeds with B-903 culture filtratd could ef-fecienlly control the disease of cotton seedling and enhance the growth of the seedling. The control effects of this antibiotics for Physalospora piricoia Nose and the leaf spot with spraying B-903 culture filtrate were better than or at least equal to those of chemical fungicide.

Two strains of watermelon mosaic virus, WMV-2(1) and WMV-2(2), were got from The Lab of Plant Virus Disease, Dept. of Plant Protection, Shenyang Agricultural University. The two strains showed different symptomatic responses on plants within host range and indicative plants, and also resulted in different pathophysiological responses of host. When WMV-2(1) and WMV-2(2) were inoculated on an indicative plant, summer squash (Cucurbita pepo), the differences shown between these two strains were their affections on contents of chlorophyll, intensity of photosynthesis, conductivity and peroxi-dase activities in the host tissues. The results indicated that the host pathophysiology of these two strains was also distinctive, WMV -2(1) showed stronger influence than WMV-2(2) on destroying chlorophyll, reducing the photosynthesis activity, increasing the activities of peroxidase, etc.. The authors are of the opinion that these criteria could be used as a preliminary step to differentiate the two strains of watermelon mosaic virus.

Different metal ions had various effect on in vitro growth production of extracellular enzymes and enzyme activities of strain StEcc-12 of potato soft rot (Erwinia carotovora subsp. carotovora). In liquid media containing polygalacturonate, Ca²⁺ increased growth of StEcc-12 and raised its production of extracellular pectic lyase (PL), polygalacturonase (PG) and protease up to 1.4~23.5, 0.3~2.9 and 0.7~6.5 times, respectively. Mn²⁺ had the same effect as Ca²⁺ on bacterial growth and production of 3 extracellular enzymes. Ni²⁺ inhibited significantly the growth of pathogen, but the unit activities of 3 extracellular enzymes in suspension containing Ni²⁺ is 1.7 times higher than check. Addition of above 3 ions alone into a crude extraction inhibited PL activities. Zn²⁺ han no effect on bacterial growth, and higher content of A1³⁺ inhibited, but these 2 ions increased production of extracellular enzymes. As Fe²⁺ and K⁺ increased, bacterial growth and PL activities in extract solution decreased, synthesis of PL and PG reduced, but protease production raised. Mg²⁺ had no significant effect on in vitro growth and extracellular PG. Increased Mg²⁺ promoted PL synthesis and its activities. All 8 ions could agglutate poly-galacturonic sodium, but only Ca²⁺ and Mg²⁺ effectively binding it at a content similar to those in potato tubers (102.2ppm and 179.2ppm, respectively).

Experiments dealt with the effects of base manure amount, sowing time and density in autumn Chinese cabbage field on the occurrence of downy mildew Peronospora parasitica (Pec) Fr., black rot Xanthomonas campestris (Pammel)Dowson and soft rot Erwinia carotovora (Jones) Holl diseases were carried out by adopting the orthogonal rotation combined design. The order of importance of these three factors for eace diseases was determined. and the corresponding regression equations were developed. A series of perliminary numerical bases in optimized management of these significant practices for disease control and high yield targets of cabbage production were derived.

Isozyme patterns of 11 Chinese races and an albino strain from America wheat stripe rust (Puccinia striiformis tritici) were analysed and compared by polyacrylamide gel elec-trophoresis. Significant differences of electropheretic pattern of Esterase, Peroxidase, Catalase, Alikaline phosphatase, Acid phosphatase, Glutamate oxalate transaminase and Polyphenoloxidase were detected among 11 Chinese races. Based on the data of isozyme phenotype, the tested races can be divided into 5 groups, namely, A(CY8), B(CY10), C (CY17), D(CY19, 22, 23, 25, 27, 26), E(CY28, 29), which illustrated the evolution of Chinese races of wheat stripe rust. Isolates of the same race from different regions or single spore lines from the same race showed highly isozyme phenotype homogeneity. Chinese stripe rust possessed specific isozyme patterns compared with isozyme patterns of albino strain from America strain in this study and of data abroad. The results indicated that the isozyme patterns of wheat stripe rust were useful geneur markers which were indepen dent of virulence.

The resistance was tested in offspring M₁, M₂ and M₃ of mutants resistant to Helminthosporium sativum of wheat which was obtained by cell engineering. The experimental results demonstrated that the resistance was retained in the offspring of M₁, M₂ and M₃ of mutants resistant to Helminthosporium sativum. In the meantime, as compared with standard control variety, the peroxidase activity of mutants increased remarkably. Two additional isoperoxidase bands appeared in the disease-resistant mutants.

The analysis scientifically by means of 418 year-times meteorological materials, from 38 stations during 1980-1990 in Jiangsu, showed that the limits of winter wheat scab occurrence depend upon following sensitive indexes:appearing frequency, periods and total hours of ‘The high-humid period of weather’ during sensitive period of wheat scab. Based on that, the areas of wheat scab occurrence in Jiangsu are divided into four climatological zonations, they are:The climatological zonation of winter wheat scab serious occurrence, Zonation of middle level occurrence, Zonation of light level occurrence and Zonation of extremely light level occurrence. Among the four climatological zonations, they are further divided into two climatological subzonations:the climatological area of frequent occurrence and area of occasional occurrence. The results showed the geographic distribution of winter wheat scab in Jiangsu province and it will be scientific foundation of regional long term prediction and integrate management of the disease.

Barley yellow mosaic virus (BaYMV) causes one of the most important diseases of winter barley in parts of Europe and Asia and yield losses can only be prevented by cultivating resistant varieties. However, a resistance-breaking strain of BaYMV (race 2) has. recently been reported which overcomes the effect of original resistant gene. We have cloned and sequenced a 1 kb region from the putative NIa proteinase gene of a BaYMV race 1 and race 2 isolate. The two sequences displayed 97.0% identity at nucleotide level and 97.3% amino acid identity. This minor sequence variation was used to develop a PCR-based system using specific primers to distinguish these isolates.

The results of study indicated that the primary inocula of rice Phyllosticta leaf blight (Phyllosticta oryzicola Hara) were associated with the diseased rice leaves, rice seeds, and field grasses. In diseased-area, the diseased leaves in the field were the main primary inocula. The percentage of diseased seeds was generally 0.5~2.5%, and the infected part was almost only in or on glumes. The grasses such as Echinochloa crusgalli var. mitts, E. crusgalli var. zelayensis, Paspaium distichum, Setaria viridis, Leersia japonica, Leptochloa chinensis, Eleusine indica, Chloris virgata, Imperata cylindrica, Zizama caduciflora, Digitaria sanguinalis, Arundo donas, and Cyperus sp. are also the hosts of P. oryzicola. Furthermore, the experiment showed that the secondary infection of P. oryzicola occurred in the field.

Corn stubbles infected by take-all fungus were collected from 22 cities or counties within 10 provinces (autonomous regions) in northern China in 1988~1992.21 isolates obtained and purified from diseased tissues showed the higher pathogenicity. On the basis of their characters in culture, morphology, physiology, pathogenicity and others, all isolates were divided into two groups:one was M₁, M₂, M₃a, M₃b, M₃e, M₃f,M₃g, M₄a, M₄c, M₄d, M₅a, M₅b,M₆, M₇a, M₇b,M₈a, M₈b, M₉, which belonged to Gaeumannomyces graminis (Sacc.) Arx et Olivier var. maydis Yao, Wantg et Zhu; another was M₃c, M₃d, M₄b, which belonged to a race of Gaeumannomyces graminis (Sacc.) Arx et Olivier var. graminis Trans, on corn. The pathogen varieties differed in cultural characteristics, pathogenicity, number of phialospores and others and showed some phenomena of physiological differentiation.