Wheat varieties with different resistance genes were inoculated for the induction of resistance and susceptibility to mildew, with various sequences of non-virulent and virulent isolates of Erysiphe graminis f.sp. tritici. The induced resistance was most pronounced when a non-virulent isolate (inducer) was inoculated prior to a virulent isolate (challenger). Post-inoculation with a non-virulent isolate or simultaneous inoculation of the non-virulent and virulent isolates may also induce the resistance but less pronounced, depending on the inducer densities. Increase of inoculum density of non-virulent isolates (inducer) increased the amount of induced resistance, Once induced, the resistance was active up to 6 days, susceptibility was induced by all inoculation sequences used but the effect was much smaller than that of induced resistance. There exised variety inducer of inducer challenger intercations in the induction of resistance. Acquired virulence of a non-virulent isolate growing on a resistant variety disappeared in the absence of the virulent isolate. No systemic effect of induced resistance was detected.

The chlamydospores of false smut of rice are divided into yellow and black types by their color. The surface of both yellow and black chlamydospores has verrucas which on the black chlamydospores are remarkable higher than those of yellow's. In normal culture conditions, yellow chlamydospores can germinate, but the black ones not. When yellow chlamydospores are preserved at 4℃ and 25℃,their germinative ability can keep 1 year and 80 days respectively. The optimum germination pH value is pH 5~pH 8 and the optimum temperature of germination for yellow chlamydospores is 25℃~30℃. Light can promote chlamydospores production. It can produce a large number of conidia under PD and PS liquid culture. Sclerotia collected in field can germinate and product matured stroma, perithecia and ascospores under sand-culture condition. False smut of rice can produce toxins, the toxins with a certain concentration can inhibited seed germination and embryo-bud growth.

Transmission rate and location of maize dwarf mosaic virus attachment sites (VAS) in the stylets of aphids by immunofluoresence label were observed. The results showed that the rate of transmission of MDMV is different between five aphids, including schizaphis graminum, Rhopalosiphum padi, Rhopalosiphum maidis, Macrosiphum avenae, and Myzus persicae Among them Schizaphis graminum has the highest transmission rate. MDMV VAS is different from different aphids stylet. VAS is quite obvious in S.graminum stylet, locating on the maxillae at about 50 μm from the tip. In addition, experiment shows that the HC-Pro transmiasion of MDMV is in accordance to the procedure of "recognition-adhesion-release".

We discovered that Coniothyrium minitans has the ability to produce antibacterial substance when we studied its ecological properties.In this paper,13 bacteria species (or types) were used to test their senstivities to the antibacterial substance produced by Coniothyrium minitans. The heat-stability and acid-stability of this substance were also examined. To analysis this substance,the movement of this substance on the paper was observed with the use of paper chromatography, and paper electrophoresis. The results showed that the antibacterial substance inhibited the growth of both Gram positive and Gram negative bacteria, especially showed strong activity against Xanthomonas oryzae pv. oryzae, one of the most important rice pathogens. It could tolerate heat (1 h under 121℃) and acid treatment. According to paper chromatographic analysis and paper clectrophoresis analysis,there were two valid components in this antibacterial substance,the one was neutral,and the other was of weak aidity.

Rape seedlings were fed ¹⁴C-oxalate through roots. The organic substances in leaves were extracted by acetic acid-ethanol solution and were fractionated by chemical and chromatographic methods. It's found from autoradiographic profile of seedlings that radioactivity in resistant varieties to Sclerotinia sclerotiorum was mainly confined to major veins of leaves and stems, whereas in susceptible varieties radioactivity was distributed rather uniformly throughout the seedlings. More than 57% of oxalate (OA) absorbed was metabolized into other organic substances. And the higher rate of its metabolism was found in resistant varieties than that in susceptible ones. Radioactivity in soluble OA was about 1.2% of the total in leaves and more than 28% in insoluble OA. In the acetic acid-ethanol fraction, radioactive neutral substances (mainly sugars) accounted for 43.2%~81.1%. OA induced increase of peroxidase activity, and the increase in resistant varieties was more than that in susceptible ones. The activities were positively correlated with resistant levels of varieties. The experiments with leaves extracts and the purified found that OA inhibited activities of polyphenoloxidase and phenylalanine ammonia-lyase, but the OA concentrations required for the inhibition of both enzymes were different.

The soluble mycoprotein and Esterase etc isozyme patterns of 10 physiological races of Cercosporidium sojinum were analyzed and compared with polyacrylamide gel electrophoresis. Significant difference of electropheretic pattern was detected among 10 races. In general, the similar coefficient(sc) among 10 races were about 0.22~0.96,Race 4 was more far related to the other races, An average coefficient of similarity was low. The results indicated that the isozyme pattern of physiological races of Cercosporidium sojinum were useful genetic markers which were independent of virulence.

Inoculation tests on soybean cultivars (or lines) and random amplified polymorphic DNA markers were used to assess pathogenicity and genetic diversity among 35 isolates of Cercosporidium sojinum collected from Northeast region in China. Based on Pathogenicity tests on nine differential soybean cultivars and lines, isolates were differentiated into 6 groups. Of 105 RAPD loci which amplified with 13 random decamer primers, 78.1% were polymorphisms. Genetic distances between each of the isolates were calculated, and cluster analysis were used to generated dendrogram showing relationships between them. The results showed that genetic diversity were existed among isolates from same location as well as different location. The relationship between pathogenicity and RAPD markers were presented in some isolates of C. sojinum.

The results of inoculating 1~7 lower leaves of tobacco pot plants of five cultivars showed:as leaves became mature or senescent from bottom upward to top of tobacco plant,their color was changed from green to yellow,the chlorophyll content was decreased,dissolvable sugar content of leaf sap and reducing sugar of diffused leaf sap were increased,but the disease resistance was decreased correspondingly.If leaf color was used as creterion of resistance,green growing leaf was immune;rather yellowish green leaf was highly resistance,only pin-tip size brown specks were formed which could neither expand nor sporulate;greenish yellow leaf was moderately susceptible,spots about 0.2 cm in diameter could be formed on it,and most of them could no enlarge any more under general climate condition;mature yellow leaf was high.Susceptible,on which typical spots larger than 0.5 cm in diameter were always formed and sporulated profusely.Spore germination rate and disease index after inoculation with medium of 1% glucose were higher than with medium of 1% sucrose.Spore germination rate and disease.
incidence after inoculation with medium of mature tobacco leaf were also higher than medium with yellowish green and green tobacco leaves.The results indicated that maturity of tobacco leaf was highly correlated with the resisatance to brown spot disease.

Rhizopus stolonifer and Fusarium semitectum have different way of infection of melon fruit.The hyphae of R.stolonifer produces high activities of pectin methyl-esterase(PME),pectin methylgala-cturonase(PMG) and ploygalacturonase(PG) when infect melon fruits.These enzymes cause fast deformation of middle lamella of fruit tissue,lead the sap leakage,plasmalysis and the soft rot.Its hyphae can only grow between the intercellular space of the melon fissue. F.semitectum produces high activities of pectin-esterase,pectin and pectic lyases and cellulase,lacking pectin and pectic hydrolases.Its hyphae can directly penetrate the cell wall of melon fruit tissue and cause Fusarium rot after it infects melon fruit.The way of the different rot of the two pathogens are highly depended upon their different secretory cell wall-degrading enzymes.

Routine studies on the pathogenicity determination of the withered carnations,collerted from 12 main production bases of carnation in the southern part of China,showed that Phialophroa cinerescen (Wr.) van Beyma and Fusarium oxysporum Schl.Snyd & Hans.f.sp. dianthi (Prill & Dell)Snyd.& Hans.were the main pathogens.When the commercial cuttings of carnation were planted in the pathogen-free soil,3.4%~8.0% of the plants were diseased,while planted in the infested soil 66.7% of the plants were infecteds. The incidence mainly, happend from the end of May to the mid August and more than 2/3 of them occurred in the monsoon season.

Inoculation tests showed that a Fujian isolate of the banana bunchy top virus could infect various bananas including Musa nana (Xiangjiao), M. paradisiaca (Fenjiao) and M.sapientum (Dajiao),however,it could not infect 24 other plants tested at the same inoculation pressure.These plants were Canna indica,Colocasia esculenta,Achasma zerwbet,Canna edulis,Curcuma domestica,Catharanthus roseus and Cucumis melo etc.,some of which were previously doubted to be hosts of BBTV.Virus from infected Xiangjiao cultivars was the major source of the disease epidemics in Fujian,China,whereas infected plants of Fenjiao and Dajiao could have a long-term effect on the habitation of the disease in a given area.The significance of the present results on the epidemiology and control of the disease was also discussed.

Electrophoresis of-esterase and malate dehydrogenase(MDH) was conducted using Phast System(Pharmacia Biotech.) for the rapid identification of root-knot nematodes on Nicotiana tabacum and Salvia splendeus in Yunnan.Four species were used in the experiment,ie. Meloidogyne arenaria,M.javanica,M.incognita, and M.hapla. The procedure of electrophoresis using PhastSystem is provided here.The experiment demonstrated that PhastSystem is an ideal instrument for rapid identificaion of root-knot nematode species.

Forty-two Agrobacterial isolates from China and 28 representatives of Agrobacterium and Rhizobium were classified by numerical taxonomy and DNA homogenic analysis.Forty-one strains of agrobacteria and two strains of rhizobia fell into three agrobacterial species.Twenty-three agrobacteria isolated from grapes in Innermongolia Autonomous Region and other regions were grouped into A.vitis.Ten strains from cherries and peaches in Shandong and other provinces were grouped into A.rhizogenes.Whereas,eight agrobacteria from 4 plants of 4 regions,two new rhizobia from Glycyrrhiza pallidiflora in Ningxia Hui Autonomous Region were placed into A.tumefaciens.The classification status of one isolate of agrobacterium and one of Rhizobium require further investigation.

Since 1990,we have found four kinds of variegated flowers among flowering plants from Kunming and Yuxi etc.The variegated flowers have been known a peculiar flowers which caused by virus infection.The infected flower is characterized by a brilliant and striking variegated colours and is more beautiful than the flowers free from virial disease.As far back to 16 th century the Dutch Tulip with a white mottle as streakes on petals and was more lovely strange than the ordinary one had discovered.Since then,this special flower doubled its price in market.Many people were attracted to the tulip bussiness and the state flower trade was ever boasted and greatly profitable. People called this period of history as "Tulipo-Mania".Henceforward the plant pathologists demonstrated by inoculation that the variegated flower was cause by the tulip breaking virus (TBV).

499 isolates of Puccinia recondita f.sp. tritici from 12 wheat-growing areas in China were tested in 1992~1996 by using near-isogenic lines (or monogenic lines) of wheat leaf rust resistance as differentials.The results indicated,that:(1)PHT was dominant pathotype with the frequency of 26.6% while others remained less than 7.4%;(2)The frequencies of V2a,V9,V15,V19,V20,V24,V28,V37,V38 and V13+3ka were no more than 30%,followed by V2b,V18,V25,V27+31,V33+34 with the frequencies of 30%~60%,which suggested the corresponding resistance genes be effective resistance genes to wheat leaf rust in China;(3)Isolates from differently ecological regions showed obvious difference in the composition of virulence genes (or pathotypes),distribution of frequency and in their diversity.In this paper a combining system of the fixed differential genes plus supplementary differential genes for wheat leaf rust research in China was proposed,and an idea of the ecological breeding for resistance and reasonable deployment of resistance genes based on the virulence zone of Puccinia recondita f.sp. tritici in the different wheat regions was also discussed.

Polygalacturonase-inhibiting protein (PGIP) purified from wheat (Triticum aestivum L.)yellow seedling was initiated to directly effect four fungi:Fusarium graminearum Schw., Exserohilum turcicum Leonarddsuggs, Pyricularia oryzae CaV.and Sclerotinia sclerotiorium (Lib) de Bary.The endo PGs from four kinds of fungi were inhibited by PGIP and their growth was delayed by PGIP,furthermore PGIP caused the abnormal growth of F.graminearum and E.turcicum.

The toxins produced by strains of Xanthomonas oryzae pv. oryzae Ah28,GX50 and OS14 were extracted with ethylacetate.Seeds and seedlings of Zhenshan97 cms line(A) and its maintainer (B) were treated with toxins.The toxin caused discoloration and cell death of rice leaves which were similar to those of the pathogen.The toxin also induced necrotic hypersensitive reaction of broad bean leaves and wilting of rice seedlings.In addition,the toxin could significantly inhibit the growth of roots and shoots and kill the root cap cells of rice.The toxicity of toxin was possitively correlatede with the concentration and virulence of pathogen.The toxins produced by strains which were specific to Zhenshan 97 A also showed stronger toxicity to male sterile cytoplasm than to normal cytoplasm.

A biotin labelled in situ hybridization technique was used to physically map two RFLP markers UMC84 and UMC30 which were tightly linked to the Htn1 gene in the chromosomes of maize.The results showed that two markers were located on the chromosomes 8,6 and the average detection rate of in situ hybridization was 14.7%.The percent distances of UMC84 and UMC30 from centromere on the chromosome 8 were (38.26±1.97)% and (37.92±3.48)% respectively and on the chromosome 6 were (33.58±3.28)% and (34.96±2.13)% respectively.This indicates that there are no difference between genetic and physical distances of two markers UMC84 and UMC30 and the sites of UMC84 or UMC30 should be the location of Htn1.

A new leaf spot disease of maize,mainly caused by Curvularia lunata (Walk) Boed. and C.inaequalis (Shear) Boed.,is becoming prevalent in north China.The optimum temperature for growth of C.lunata is 28~32℃,and it grows well at 4~12 pH values,maize leaf extract accelerated germination of conidia and growth of germ tube.At dry condition, C.lunata successfully overwintered in diseased leaves and become primary infection sources in fields.The conidia of C.lunata are different in shape,and progenies isolated by using single spore technique are same on pathogenicity. Some isolates of C.lunata,especially isolated from Beijing are high in pathogenicity.Under artificial inoculation condition,120 maize accessions are evaluated for resistance to Curvularia leaf spot,of which,49 accessions were resistant types (HR,R and MR),and Nongda 108,Zhongyu 5,Gaoyou 115,CN95 and CN165 are high resistant.The resistance was high in seedling stage and low in adult plant.

The extreme propagation capability and high adaptability power to the world agro climatic regions of tobacco blue mold sporangia play an important role on the dispersal and development of the disease.Although many contributions on the pathogen taxonomy,biology,pathology have reported, so far only limited works on the pathological charctristics for plant quarantine.Based upon a series of experiments,the authors indicated that:(1)The germinability of the sporangia is closely related with the age of sporulation.For 1~2 days sporangia after visible sporulation,the germination percentage rise to 83% after 4 hr,incubation,while those of 4~6 days after sporulation,its germination percentage down to 36.1% and 29.6%.(2)The lowest temperature for sporangia germination is 2℃.Optimum range for germination is 14~21℃,and 35℃ is the highest.(3)The survivability of sporangia in high temperature depends on the length of exposure of sporangia under high temp. such as under 30℃ for 12 hr.or 35℃ for 8 hr.than transfer to 15~20℃ for further incubation,the effect is mainly inhibition.If it is exposed under 30℃ over 12 hr.or 35℃ over 8 hrs.the sporangia loss its infectivity.(4)TBM infection could be achieved when the relative humidity on a leaf surface reaches sub saturated level for 4 hr.Infection increased positively with lengthening of the described relative humidity duration. (5)Under normal condition,each drop of a sporanguim containing 5~6 spores can cause 33% infection,while containing only a single spore can still causes 12% infection.Evaluation of the above results,it will facilitate the pest risk analysis of Tobacco Blue Mold pathogen.

Cotton seeds (Gossypium hirsutum) of resistant or susceptible cultivar were sown in soil treated with trifluralin at 2 μg/g soil.The 10 day old seedlings were inoculated with Fusarium oxysporum f.sp. vasinfectum (Fov).Catechin accumulation slowly with in the seedling leaves and stems/roots was detected.In the healthy seedlings,catechin accumulated slowly with the seedling growing.After inoculation,catechin levels in the diseased seedlings were significantly higher than those in the healthy ones.When infected,the seedlings of the resistant cv.showed markedly higher rate and levels of catechin accumulation than those of susceptible cv..The trifluralin treated seedlings showed the fastest and the greatest catechin accumulation after inoculation.The results indicated that catechin accumulation was involved in the resistance mechanisms of cotton cultivars and trifluralin induced resistance to Fusarium wilt.Catechin compound was observed to inhibit mycelial growth,sporulation and macroconidia germination of Fov,and to inactivate polygalacturonase (PG) of Fov in vitro.The activity of partial purified PG from Fov was also inhibited by catechin compound and catechin fraction from TLC separation of the 50% ethanol extracts from cotton tissues.The results presented suggested that the involvement of catechin in cotton resistance to Fusarium wilt may be related to its effects on the fungal growth,sporulation,spore germination and the PG activity of the pathogen.

In this study,it was further confirmed that oxalate was able to induce the systemic resistance of cucumber to Colletotrichum orbiculare.The treatment with oxalate reduced necrosis number by 49.7% and necrosis area by 58.6% compared with control.Correspondingly the systemic induction of peroxidase(POD) by oxalate,which may be closely correlated with resistance to pathogen,was investigated in cucumber.The results are as follows:(1)The induction of souble POD activity was increased with the increase in the concentrations (10~40 mmol/L), reaching maximum at 40 mmol/L;(2) During 7 to 13 days after treatment with oxalate,the induced soulble POD activity started declining whereas the ionically cell wall-bound POD activity still remained at the induced level;(3) A new isozyme of POD was identified by native PAGE with thinlayer scanning in oxalate-treated cucumber leaves,in which the Rf is about 0.63;(4) The induction of souble POD could be inhibited by free radical scavengers manitol and ascorbate;(5) Signal transduction from the first true leaf to the second entailed about 5h for the systemic induction of POD after oxalate-treatment.The induction effectiveness was enhanced if the treated leaf remained longer on the plant.