A spherical virus about 21nm in diameter was isolated from the diseased plants of N.tazetta var.chinesis showing yellow stripe in China. This virus isolate infected 15 species and varieties belonging to 35 families.By mechanical sap inoculation, the virus infection usually resulted in the development of necrotic lessions on the inoculated leaves of Chenopodiaceae, Leguminosae and some members of Amaranthaceae, Aizoaceae and Solanaceae.In the case of most infected plants of Leguminosae, the symptoms of necrotic lessions were usually followed by leaf vein necrosis. However besides the chlorotic stripe on the leaves of narcissus after back inoculation, it rarely produced systemic symptoms on other host plants. In the present studies, Chenopodia quinoa, C. amaranticolor,Glycine max, Uigna sinensis, Gomphrena globosa, Tetragonia expansa and Nicotiana clevelandii were generally used as a set of diagnosis host plants.The last named three species were also used to propagate and maintain the virus. In C.quinoa sap,TIP was 80-85℃,the DEP was at 10^-5-10^-6 and its longevity at 25℃ was 2 months. By electron microscopy, no specific inclusion bodies associated with the virus infection had been found in narcissus leaves.

The results showed that there were four viruses in main strawberry producing regions in China, which were strawberry mottle virus, strawberry mild yellow edge virus,strawberry vein banding virus and strawberry crinkle virus.The percentage of strawberry plants infected by all these viruses attained 80,2%,in which 41.6% by one and 38.6% by two or more viruses.SMoV, SMYEV and SVBV were isometric particles 25-30nm,23nm and 50nm in diameter respectively, and SCrV was bacilliform particle 380×70nm in size.The results confirmed that these viruses could be transmitted by grafting ang dodders, but not by sap. Myzus persicae could transmit SMoV and SMYEV, in nonpersistent and persistent way respectively. The population pear of M. persicae occurred was a great coincidental with the infection by strawberry viruses in the field.

Isolates of ninty-eight bacilli including YIB and YDB were identified according to the key in "The Genus Bacillus". The results indicate that Bacillus cereus is the superior in its yield increasing effect, then B.brevis and B.firmus.Most of YIB applied in field practice were B.cereus isolates, such as 83-10,a-47, etc. In addition, the basic biological properties of several important YIB and YDB were studied.The suitable growth conditions as carbon resources,nitrogen resources, pH value, temperature and amino acid requirment were evaluated.

Fourteen strains of bacteria causing knot disease on Myrica rubra in China were compared with reference strains of Pseudomonas syringae subsp. savastanoi pv.olea from olive, PDDCC4352-75 and PB230, in their bacteriological characteristics. There were only a few differences in 27 biochemical and physiological tests, i.e.strains from Myrica couldn't use betaine, lactose and maltose as sole source of carbon, but the olive strains did. Moreover, in contrast with olive strains,the Myrica strains showed postive reaction in nitrate reduction and negative reaction in starch hydrolysis.The strains from both hosts showed partial homology in serological reaction.G+C mol% of DNA of Myrica strains was 59.90-60.89,which was similar to that of olive strains. In cross inoculation tests on hosts, however, Myrica strains couldn't produce typical knots on olive and oleander stems as the olive strains did, similarly, olive strains couldn't infect Myrica rubra as the Myrica strains did. On basis of above mentioned results the Myrica strains were identified as a new pathovar of Pseudomonas syringae subsp. savastanoi, named Pseudomonas syringae subsp. savastanoi pv. myricae (Chaoei Ogimi et al.) comb.nov.

An improved method was developed for the purification of mycoplasmalike organism associated with maize bushy stunt disease. Diseased corn plants were crushed with a tissue homogennizer using slow and gentle cycle until most of the parenchyma tissue was broken.The retained vascular tissues were then incubated at 35℃ for 1 hr in an enzyme solution containing 0.8% (W/V) cellulose, 0.2% (W/V) pectinase, 0.2% (W/V) hemicellulose, 1 mM CaCl₂ and 0.3 M mannitol. The suffered tissues were macerated with a tissue grinder and the suspension solution was subjected to one cycle of low and high speed centrifugation. The pellets were suspended and centrifugated twice in discontinuous Percoll density gradient.Indirect enzyme-linked immunosorbent assay and electron microscopy confirmed that highly purified and intact MLO could be obtained with this method.

The amount of sporulation of fungus (Cercospora arachidicola Hori) on the peanut stalk medium is more than that on other 3 different media reported before.The amount of mycelial growth on Landers medium, one of the reported medium, is the biggest among all 6 provided media. In the process of cultivation, the fungus grew and sporulated nonsensitively under various light treatments.There was remarkable difference for various temperature treatments. 2% of glucose solution is available for conidia germination. The artificial isolates of the fungus which had been obtained from diseased peanut plants were confirmed with the pathogenicity.

The downy mildew[Plasmopara halstedii (Farl.) Berl. et De Toni] infects sunflower between temperature 5-25℃ and the optimum temperature of the infection is 10-15℃.The seedling of 3-14 days could be infected, but those of 3-day are most susceptible.The systemic symptoms occurred at the constant temperature 15℃, 20℃ and 25℃ as well as the alternating temperature 8℃ and 15℃,13℃ and 20℃,18℃ and 25℃,23℃ and 30℃. The highest rate of the symptoms is at constant temperatura 20℃ and alternating temperature 13℃ and 20℃. There is no sporulation at constant temperature 30℃ and alternating temperature 28℃ and 35℃.

The sympotoms of brown (purple) sheath and sheath rot, were induced by using different inoculation methods with all the isolates obtained from different sources although the frequencies differed with the inoculation methods, rice cultivars and pathogen isolates. It is suggested that brown (purple) sheath disease should not be considered as a new disease but pne kind of symptoms of rice sheath rot disease.

The seedling cuttings of cotton were treated with VD-toxins from 4 isolates of V. dahliae (T-9, SS₄, VD-8, VD-5). The results suggested that the ABA content from the seedling cuttings treated with VD-toxins was significantly greater than that from those of controls, ABA content from the seedling cuttings treated with VD-toxins was significantly greater than that from those of controls, ABA content from the seedling cuttings of T-9-toxin-treated v as remarkably increased because VD-toxin content in the culture fluids from T-9 isolate was higher than that from other isolates.
Stomatal resistance from leaves with VD-toxin-treated seedling cuttings was obviously higher than that from controls. The results of the ion leakage experiments indicated that electrolyte was three to four times increased from the leaves of the seedling treated with the VD-toxin solution than from the leaves of controls.The permeability from VD-toxin treated laef cells of the seeding was obviousy increased controls. The free protoplasts from VD-toxin treated leaf cells of the seedlings was significantly destroied than that from double distilled water.The breaking plasma membranes was 30 to 50% greater from the free protoplasts treated with VD-toxin than that from the free protoplasts of controls.

Virulence of Puccinia graminis f.sp. tritici was studied by testing 40 near-isogenic lines for stem rust resistance. Race HKR(21C3)was the most common virulence combination, making up 33.1% of the 127 isolates from 70 collections. The second most common race was RKR(34C2),which made up 24.4% of the isolates. No virulence was found on wheat lines with genes Sr9e, 11,38, Tmp and Gt.Virulence frequency to Srl3, 22,24,27,29, 30, and 37 was low,all below 10%. Virulence frequency to Sr6, 7b,8a,9a, 9d, 9f, 9g, 10, 12, 14, 15, 16, 18, 20, 23, 28, 34, dp-2 and H was high, all above (or near) 90%. Both the virulence combination and virulence frequency of Puccinia graminis f. sp. tritici are different between China and North America.

Compatible mating strains of Phytophthora drechsleri A1 and A2 produce oospores abundantly in paired cultures on VA medium. Survival of oospores was 82.95% under the soil surface in winters of 1988-1989. The rate of oospore germination was higher under the alternation of day light and night darkness than under entire darkness. Furthermore the soil extract was more suitable for oospore germination than in distilled water.

Fresh urediospores of race 21C3 of wheat stem rust were equally mixed with those of race 34C2 or 116.The mixture was inoculated to the eight wheat cultivars which were selected from different winter-sowing areas. The reproduced rust sori from the mixture were reinoculated to the eight cultivars from generations to generation.
It was found that the race 21C3 had higher survival ability than races 34C2 and 116.This result indicates that the survival ability of pathogen is negatively correlated to its virulence, which explains that the race 21C3 holds the trend to predominance.

Barley yellow mosaic virus (BaYMV) was rapidly detected by protein A immunosorbent electron microscopy in barley plants suspected to be infected with this virus. Wide range of homogenous antiserum dilution (320-20,480) in 0.03 M phosphate buffer pH 7.0 for virus particle trapping and incubation for 30min. at room temperature (25℃) or 3 hrs at refrigerator (4℃) could give satisfactory results. Attachment of virus particles from infected sap diluted 3, 125 times to protein A-antiserumcoated electron microscopy grids provided a test that was at least five times more sensitive than standard immunosorbent electron microscopy technique for BaYMV detection. BaYMV particles mainly distributed in top mosaic leave and no one checked in stems and roots.

A destructive root rot disease of the midicinal herb, Pseudoginseng (Panax pseudo-ginseng Wall. var. notoginseng(Burkill)Hoo & Tseng was found occurring widespreadly and seriously in Shao-guan Prefecture of Guangdong Province. According to the morphology, pathogenecity and mating types tests, the pathogen was identified to be a forma specialis of Fusarium solani (Mart.) Sacc.:Fusarium solani f. sp. radicicola (Wr.) Snyd.& Hans.

Rhizoctonia solani, Fusarium moniliforme, F.oxysporum, F. graminearum, Sclerotium rolfsii and Pytliium aphanidermatum were isolated from diseased plants in heavily infected sorghum fields. Among them, the number of isolates of the former three organisms was far greater than that of the latter.The result of pathogenic detection indicated that R. solani AG5 was the sole pathogen of sorghum seedling disease, while the other five organisms only caused subsidiary infection because of their non-pathogenic nature to cotton seedlings. The best period for isolation from cotton seedlings in field was at 10-15 days after emergence. Most of the surface sterilant used in tests inhibited the isolation of R.solani from diseased tissue. Anomalous conditions of temperature, light and soil moisture easily usually interfered with the results of the etiological study.

By differential centrifugation and Sepharose 4B column chromatography, the virus was qurified from the inoculated leaves of propagation hosts of Chenopodium quinoa, Gompherena globosa and Tetragonia expansa. It was shown that C. puinoa was the most efficient host for the virus propagation and purification.
The purified virus shared a single sedimenting component of 73S (S20.w) in analytical ultracentrifugation. Its coat protein was made up of only one polypeptide with molecular weight of 27.88K±2.99K daltons in SDS-PAGE.The viral nucleic acid was composed of one single strand RNA determined by denatural agarose electrophoresis after RNase A digestion and denaturation. The virus contained 12-15% RNA estimated from UV absorption spectrum of max absorption at 258nm and min absorption at 244nm with A260/A280 of 1.515.
Based on the biological and biochemical properties, this virus was considered to be a previously undescribed one with a cryptogram of R/1:*/12 -15:S/S:S/*. And it was tentatively named as Chinese Narcissus Strip Virus (ChNSV).

The fastidious bacteria were observed in thin sections of centrifugaters of vascular sap extracted from twigs of apple infected with apple scar peel disease (ASPD). They were also observed in thin sections of pedicels and tender fruit stalks of diseased apples. The bacteria were found within pears, the carriers of ASPD, as well. However, they have never been found in samples made from healthy apples. After inocu lation with the bacteria extracted from diseased apples, the apple saplings showed the downturn of leaves, a typical symptom of ASPD at the seedling stage. The symptoms of leaf downward curl and scar skin could be depressed considerably by treatment with penicillin.It is therefore considered that the fastidious bacteria observed seem to be the pathogen of ASPD.

From naturally field-infected barley cultivars with different resistance to BaYMV, the ultrastructural analysis of roots and leaves showed that (1) the BaYMV were found in all materials but the concentration of virus roughly corresponded with the severity of symptoms, (2)the chloroplast structure was destroyed by BaYMV, and the number of destroyed or dysplasia chloroplast in leaf cells with serious symptoms were more than that in leaves without symptoms,(3)the matrix of mitochondria in cells infected by BaYMV decreased and some of them expanded and destructed, (4) in cells infected by BaYMV, the cell plasma membrane and endoplasmic reticulum loosed and destructed, and some of the viruses associated with ER, (5) not only laminated inclusion, one side orientated pinwheel and all side orientated pinwheel inclusions, but also pinwheel with stem inclusions were found in cells infected by BaYMV.Finally, the relation of cytological change with external symptoms were discussed on the basis of results obtained in the present study.

The soft rot bacteria (ECC) were grown in the liquid MS medium containing different carbon sources and compared for the cell wall degration enzymes produced in the culture supernatants. The extracellular pectate lyase and polygalacturonase were not detected but extracellular proteolytic enzyme activity was detected in the supernatants of the same medium. Extracellular proteases produced by StEcc-12 were purified by ammonium sulfate fractionation and diethylaminoethyl cellulose column chromatography (DEAE-52). lsoelectric focusing tests showed that the extracellular protease had two kinds of isoenzymes with isoelectric points of 8.3 and 8.9 respectively.The denatured temperature of the protease is about 50℃.The pH changing did not obviously effect on activity of the protease. Soft-rot was evident when potato tubers were treated by purified proteases.The sections from the tissue treated by purified proteases showed that the cell walls obviously degrated.
Transposon Tn5 originated from E.coli 1830/pJB4J1::Tn5 was inserted into wild type strain (StEcc-12) by conjugation.11 mutants which protease activity was defective were obtained from 2000 transconjugates. These mutants did not liquefy gelatin or hydrolyte casein. The ability of these mutants to macerate potato tissue was obviously lower than the ability of wild type. Isoelectric focusing maps of mutants was apparent different from the maps of wild type strain. The results suggest that protease of Erwinia carotovora subsp. carotovora should be in cooperation with pectinase in the process of soft-rot of potato tuber tissues.