On the basis of previous studies of uni-lateral and circular spread,an elliptical spread model was developed simulating the disease spread caused by prevailing wind of different directions and velocities during a shore period of time.The elliticity was tentatively estimated according to the ratios between the wind velocities of down-wind and up-wind,and that of down-wind and side-wide direction.With disease densities of each compartment of the field around the focus as the vertical axis,an elliptic cone was formed to describe the disease distribution,and the horizontal cross-sections of the cone are the isolines of disease density with an elliptic trajectory.Then the disease density of each compartment could be deducted according to the disease gradient model.When coupled or united with the reported temporal model,a temporal-spatial comprehensive model can be obtained.

It was shown by applying different models(Logistic,Gompertz and Weibull)to data obtained by field disease investigation that the Weibull model describes disease progress of groundnut rust (Puccinia arachidis Speg.)the best,and the Gompertz the next best with residual sum of squares,Q,and the coefficient of determination,R2,as criterion.With equations of disease progress,calculations were made of the expectation values of days for disease to reach the incidences and severities of 0.5,5,10,20,30,40,50,60,70,80 and 90%,and disease increase rates were also calculated at the same points.The results showed that the disease occured earlier in fall crop than in spring crop,but developed faster in spring crop.It was also demonstrated that Weibull and Gompertz models could reflected the practical disease progess nearly equally well,however,the Logistic model over-estimated when the disease incidences and severities were 0.05 or 0.6.All these results,especially those obtained with the Weibull and Gompertz models,can be applied to disease forecasting.
The deceptive highness of the coefficient of determination,R²,in the case of nonlinear equations when linearized is discussed and a suggestion is thus made of using nonlinear residual sum of squares,Q,as a criterion for comparing the descriptions of different equations instead.

Based on biological tests such as the comparative transmission by means of 4 aphid species,the comparative transmission after acquisition and inoculation at different temperature,the comparative trans-mission after acquisition virus through membrane on purified virus preparations by means of 4 aphid species and transmission by adults and nymphs of greenbug and English grain aphids,and ELISA assays.The 13 isolates of WYDV collected from spring wheat field in Nei Menggu Fengzhen county in 1984 could be identified as GAV.The GAV is transmitted very effectively by greenbug and English grain aphid but not by the oat bird-cherry aphid and the corn leaf aphid.The strain is now known to be present in winter and spring wheat area in northern China.

Anti-PMMV,CMV-CA and PSV-Mi IgG were purified from antiserums of Peanut mild mottle virus(PMMV),Cucumber mosaic virus-CA(CMV-CA)and Peanut stunt virus-Mi(PSV-Mi)isolated from peanut.Indirect ELISA test was used to detect the virus from peanut seeds.All of these viruses existed in the seeds singly or sometimes in mixture.
Germinating seeds were detected with cotyledon,plumle and radicle separately for PMMV and CMV.These viruses existed in all these 3 parts and the highest concentration was in the plumule.There was no significant difference in the ratio of amount of viruses of the infected seeds between germinated and dormantsets.
Test procedure was simplified by indirect ELISA in of using the com-mecial conjugated IgG and therefore quick determination of seed-born virus was feasible.

Twenty isolates of Pseudomomonas solanacearum from mulbery collected from 12 counties and areas of Guangdong province were classified,according to the conventional methods based on biochemical reaction,host range,pathogenicity,lysogenicity,colony morphology and serological test,as biotype,race,pathotype,lysotype,colony-type and serotype.No any relationship of them to each other was shown in the present studies.With the results of serolpgical tests,20 isolates from mulbery and 4 others from peanut,tomato,potato and beef wood (Casaurina equistifolia) respectively were divided into 8 serotypes;those from mulbery belong to 4 of them.The relationship between the strain of mulbery and that of peanut,tomato,or beef wood was found to be closer than that of potato.It is thus believed that serotyping is supposed to be the primary basis for the classification of the speies of Ps.solauacearum at the sub-specific level;and the subsequent classification of the other types would be in the order as follows:biotypes,races and pathotypes.

Asparagus lettuce mosaic disease is widespread in all parts of Shandong.The loss of the disease was associated with the age of asparagus lettuce plants.In the fields,when the disease occurred during stages of seedling growing,the loss was the largest.Artificial inoculations showed that the asparagus lettuce plants infected during stages of three-leaf and seven-leaf were no more edible.
Test were made on 62 species of 15 families,among them only 14 specles were infected.The virus can be transmittcd through Rhopalosiphum pseudobrassicae,Aphis gossypii and Macrosiphum euphorbiae.The transmisson throngh Myzus persicae was most efficient,with a mean of 40% plant infected per individual aphid.
The percentage of seed transmission of the plant that develop mosaic in the field was between 1 to 2.The lettuce plant inoculated just before bolting produced fewer virus infected seeds than those inoculated soon after planting,the seeds of the plants that become infected after flowering did not carry the virus.

Studies on root rot caused by Cylindrocarpon destructans (Zinss)Scholten in ginseng revealed that latent infection from this fungus was found in healthy ginseng root.In the 1-5-year-old roots,root rot percentage and latent infection sites increased with the age.The root system of 3-year-old seedling could be all infected,especially the tap root.
In pot trials,deer feces amendment significantly reduced both the root rot percentage and the disease index of ginseng roots to 50% more than those of the chock.Transplanting 3-year ginseng seedling in spring,good results would be obtained in the control of root rot.

The occurrence of latent infection of pathogenic fungi on mango in Hainan Island was proved in the present work.The authors obtained cultures of pathogenic fungi from the fruits without any symptoms and wounds.The pathogenicity of these isolates were demonstrated.These isolates were identified to be Colletotrichum gloeosporioides Penz.,Colletotrichum acutatum,Alternaria spp.,and Diplodia sp..Most of the latent infections occurred in the peel of fruits or at the stem ends,however,the location of the latent infections might vary according to the climatic change.

The root-knot nematode disease is one of the most serious kenaf pest.In 1981-1984,it was investigated in the principal kenaf growing areas of Hunan,Zhejiang,Guangdong and Guangxi provinces.The caused organisms are southern root-knot nematode(MeIoidogyne incognita),Javanese root-knot nematode (M.javanica)and peanut root-knot nematode(M.arenaria).Southern root-knot nematode is the predominant species.In Yuanjiang county of Hunan province,this nematode can reproduce four generations on sandy loam in a year.The best period of using nematicide was discussed in the present paper.

The rice gall dwarf disease in the epidemic districts in Guangdong prevailed chiefly in the fall crop of rice,especially the hybrid varieties due to much smaller quantity of seeds sown in a given area of nursery plot and much smaller population density of plants as compared with ordinary varieties.There were no immune Varieties observed.The disease was not important at all in the spring crop,but the crop infected in spring served as the source of inoculum for the fall crop.A few weeks before the spring crop was harvested,the fall crop had already started,and right after the germination of the seeds infection might take place.The infection rate in the nursery reached its peak right after the harvest of spring crop when the vector insects were forced to migrate from the spring crop.The closer the nursery to the spring crop fields,the higher the infection rate,however,the highest ones were located within a distance of 10-16 meters.Earlier sowing and earlier planting also gave higher infection rate.Rice seedlings were susceptible to the disease only before 8-leaf stage and were susceptible at and before 6-leaf stage;the seedlings infected at 9-leaf stage or older never showed any symptoms.Thus the disease incidence in the field throughout the whole season was practically the same as that in the nursery.
According to the epidemiology of the disease mentioned above,the disease was rather easily and effectively controlled by applying the following 2 measures:(1) The seed-sowing date of the fall crop,especially the hybrid varieties,was properly postponed for 7-8 days to middle of July,and the transplanting date to early August;(2)Insecticide was applied once every 4-5 days at and after needle-leaf stage of the seedlings.In case of postponing seed sowing date,2-3 applications might be sufficient.These measures were found very effective according to the results of the experiment in 2,670 mu^* in 1983 and were then extended to all the diseased districts or counties in Guangdong province in 1984,resulting in a reduction of diseased area from more than 0.5 million mu in 1982 to only 33,600 mu in 1984 and of disease incidence from 20-30% in average to less than 0.5% in the same period of time.A gain of 25 million kg of yields was estimated.

The symptoms of WYMV on wheat plant are yellow mosaic.The inclusion bodies are one to several enveloped in infected surface cell.Virus particles are slighly flexuous filament of size 13×100-600 nm,often with pinwheels and aggregate virus particles in the cytoplasm.The 13 species of Triticum hosts are known.The virus was transmitted through diseased roots and sap in infested soil.The fungus Polymyxa graminis is thougtht to be a vector,its hosts included 28 species of graminaceous plants.WYWV is transmited by infested soil even though the virus was mixed with sterilized soil in the ratio of 1:1,000,the rate of infection is rather high within a depth of 10 cm of the surface soil in the infested field.The methods of prevention of this disease have been practiced by selecting and breeding resistant varieties and integrated with crop rotation,additional manuring as well as late sowing.

This is a report on the studies of the physiologic specialization of stripe rust of wheat in China during 1975-1984.During this period,9245 samples were collected and identified on 23 differential hosts,namely Trigo Eureka,Fulhard,Bima 1,Lutescens 128,Xibei 54.Beijing 8,Funo,Lovrin 13,Quality,Virgilio,Xibei Fenshou,Abbondanza,Fengchan 3,Kangyin 655,Jubilejina 2,Early Premium,Mentana,Danish 1,Taishan 1,Shuiyuah 11,Zhong 4,Lovrin 10 and Gansu 96.In the middle of 1970s,the percentage of occurrence of races CY17 and CY 18 reduced from 43.37% and 20.78% to 7.66% in 1975 and 1.81% in 1977,while the race CY 19 raised from 15.06% in 1975 to 81.05% in 1977.Starting from 1980,the race CY 19 has been further subdivided into 5 races,namely CY 19,CY 23,CY 24,CY 25 and CY 26 according to their pathogencity.Since then the race CY 25 has become the dominant race in China,of which the percentage of occurrence during 1981-1984 was 31.25-44.21%,while that of the less important race CY 23 was 12.68-27.58%.In recent years,a race indentified as CY 28 which is very virulent to the source of resistance of Lovrin 10 and its related cultivars has been discovered.Breeding wheat for resistance to this race is urgently needed.

One isometric virus was first found from commercial seeds of sugar beet (Beta vulgaris) in China.The virus was unable to be transmitted by mechanical inoculation of beet sap and aphid inoculatoin using Myzus persicae,but was seed-transmitted to a large proportion of seedlings.87.5% of plants raised from commercial beet seeds were found to be infected.Infected plants were symptomless.The virus was present at a very low concentration in beets and was detected by electron microscopy of concentrated preparations made from individual plants.
The virus preparation did not react with antisera of cucumber mosaic virus but was serologically related to beet cryptic virus,usually forming a single precipitation line in gel immuno-diffusion tests.Purified preparation showed average particle diameter of 30 nm.After isopycnic centrifugation in CsCl solution,the virus preparation formed a main band of mean density 1.376g/ml and two fainter bands.In ultra thin sections of beets no virus-like particles or no cytological abnormalities were observed.On basis of the above stated properties,it is primarilly concluded that the virus belongs to Beet Cryptic Virus reported by Kassanis(1977).

On the basis of the identification of resistance of corn germplasm to maize head smut(Sphacelotheca reiliana var.zeae) six inbred lines with different degrees of resistance were used in this experiment designed with dialle cross to detect their genetic and combining abilities for resistance.The results showed that the resistance to maize head smut was mainly controlled by additive genes.There was a significant difference in general combining ability to the disease resistance between different corn inbred lines.Therefore,in the breeding of the resistance of maize to the maize head smut attention must be paid both to the screening of the source of resistance and to the test of the combining abilities of resistant sources.

A virus isolate which caused the Maize Dwarf Mosaic symptoms has been isolated from the infected Flaccid pennisetum(Pennisetum flaccidum).The viron is flexuous,375-750×13-14 nm.Pinwheel inclusion bodies were observed in the ultrathin sections of infected leaf.The virus was transmitted by mechanical means,as well as by vectors(Aphis gossypii,Rhopalosiphum padi and R.maidis) non-persistently;TIP 52-58℃,DEP 10^-4,LIV 3 days(room tempersture).Its host range is confined to the grass family with the exception of Johnson grass.All these characteristics showed that it is somewhat related to MDMV-B and the relationship was demomstrated serologically.This isolate was different from SCMV strains,because it infected Paspalum dilataum and Bromus rubens resulting in systemic mosaic symptoms.However,this virus isolate was different from MDMV-B by its conspicuous difference in symptoms on host cultivars such as Sorghums Xinli and No.7 and Atlas.
Therefore the isolate is considered to be a new MDMV strain,named MDMV-G or MDMV-Flaccid pennisetum.Maize,Sorghum and Millet are susceptible to MDMV-B and -G.Both strains can be found in various parts in Shanxi Province.Flaccid pennisetum is the main overwintering host of the G strain.

Tomato big-bud and tomato rosette were first discovered in Hainan island of Guangdong Province in 1982.Both diseases were found to occur in the same tomato plant;their causal agents were subsequently isolated separately by grafting the diseased buds to a number of tomato plants and were further confirmed to be MLO by electron microscopy and by tetracyclin and penicillin treatments.
The tomato big-bud MLO was found to basically have the same morphology,host range and induced similar symptoms on tomato and other hast plants as those reported in Australia,Isreal and the United States of America;but it might probably be a different strain because it did not infect both Callistephus chinensis and Physalis floridana.
The tomato rosette MLO had rather limited host range.It could only infect and cause typical witches-broom symptom on tomato,Solanum nigruum and Vinca rosea,but not Datura stramonium,Capsicum frutescens,Nicotiana tabacum Havana 38,N.glutinosa,Solanum melongena and S.surattens,all of which could be infected by tomato big-bud MLO.Since the tomato witches-broom disease (MLO) reported in Taiwan Province (1978) produced big-bud symptom at the later stage of the disease,it is therefere considered that the two diseases mentioned above are not identical.

The survival ratio of Chinese cabbage buds decreased when the seeds were planted in the sterilized soils inoculated with RL₄,a rifimpicin-resitant strain of Erwinia carotovora pv.carotovora Dye.
The infected seedlings shortened and the leaves became dark-green.The pathogenic bacteria were recovered from the contaminated seedlings and the range of bacterial quantity in different tissues was from 10²-10⁷CFU/g,with a larger number in the young stem than the number in any other organs.The pathogenic bacteria,which invaded the buds and the roots at any time of seedling period,could be detected in the tissue through out the life of the plants.The ratio of contaminated seedlings was from 50% to 100%,and gradually increasing with the age of the plants,resulting in reaching a summit,100%,17 days after sowing.The anaerobic technique and selected medium containing rifim-picin increased the sensitivity and specificity in isolating the latent pathogenic bacteria within Chinese cabbage.

In a survey of virus diseases of faba beans in April 1985,seed-borne broad bean stain virus (BBSV)was detected in autumn sown experimental trails in four provinces,namely Hubei,Jiangsu,Sichuan and Zhejiang.Incidence in different cultivars and seed lines ranged from 0-18%.All seed used in those trails come from The International Center for Agricultural Research in Dry Areas (ICARDA).
Symptoms in leaves of infected plants ranged from a mild to coarse mosaic or mottle,sometimes with leaflet malformation;some leaves appeare normal.The Virus has spherical particles about 28 nm in diameter and was identified by double diffusion serology using an antiserum to a British isolate of the virus.
No weevil vectors (Apion spp.and Sitona spp.)were seen on the faba beans and no evidence of feeding damage or virus spread by weevils was found.Probably all infected plants in those trails (ICARDA's trails) had been infected through the seed.
BBSV was not detected in farm crops which seeds come from Chinese origin or native.

Rainfall was closely related with the hawthorn blossom blight epidemics.During the leaf expanding stage of hawthorn,more rainfall amount and the rain frequencies were the main factor to induce the occurrence of the leaf blight.During the blossom period,considerable precipitation and the rain frequencies induced the incidencc of the fruit blight seriously.
As to the hawthorn blossom blight epidemics,the temperature was,however a minor factor.When the spring temperature was higher,the leaf blight and fruit blight often occurred,earlier,while in contrary,both blights were to delay.

In controlling the powdery mildew of Hami-melon,spraying with a monomolecular film-forming substance has been tested in Xin jiang.Two sprays resulted in a prevention of the disease development about 80%.It was as effective as the usually employed fungicides.
In general by using MMFS the increase of the fruit yield was about 20%,and the increase of the soluble sugar of the Hami-melon was up to two degrees of concentration in this area.

In 1978-1981,the inheritance and combining ability of rice resistance to bacterial blight(Xanthomonas oryzae)has been observed with twelve verities and thirty combinations.The results indicated that 1) the greater value of The inheritance in broad sense of the resistance of F₁ and F₂ population of crosses and the quicker relative genetic advance proved that the resistance of the combitation of crosses can be selcted in the earliest generation.2)The variance of general combining ability was highly significant(i.e.p<0.01)and the ratio of GCA:SCA was also higher.This showed that the variance of additive gene was marked.3)The effect of general combining ability of parents was of definite direction.The square deviations of the resistant parents were of negative value,while those of susceptible parents were of positive value 4) The effect of specific combining ability of parents was of one definite direction.5) The effect of resistant inheritance was stable for IR26 and IR36.

In our previous paper,three viruses Cucumber mosaic virus(CMV),Squash mosaic virus (SqMV) and Watermelon mosaic virus 2(WMV-2) were isolated from the diseased Hami-melons (Cucumis melo var.Hami) in Xinjiang.Recently three other viruses were isolated.Two of these viruses,named Hami-melon necrosis virus (HmNV) and Hami-melon vein necrosis virus (HmVNV),have been identified.The third detected virus remains unidentified.
In 1981-1984 the distribution of the above viruses were investigated in six localities and 20 varieties either by the agar double diffusion test,or the microprecipitate test,or through the use of indicator plants.The results showed that the percentages of mixed infection by WMV-2+CMV,WMV-2+SqMV,CMV+SqMV and WMV-2+SqMV+CMV in the epidemic year 1983 were higher than in 1982.The infection percentages of each virus were also different due to the localities and varieties.

Seventy-one isolates,identified as binucleate Rhizoctonta,were assigned to 7 Ceratobasidium Anastomosis Groups (CAG1-CAG7),pairing with Ogoshi's(1979 and 1983)AGA to AGK tester isolates,CAGl-CAG7 isolates were anastomosed with AGD,AGBa,AGA,AGG,AGB(O),AGK and AGF isolates respectively.Six isolstes were induced to sporulate and identified as Ceratobasidium conrnigerum.The biologic and taxonomic implicatiens of each anastomosis group are discussed.

In the present study,a Fuzzy pattern recognization method was considered to be applicable to plant disease epidemiology.The procedure of its application to plant epidemiological events was described in detail.Two examples showed good results in applying this method.

The development and severity of the soybean mosaic disease were gresatly related to the infection time in the developmental stage of the soybean plants.The primary leaf stage was the most susceptible.However,the resistance increased gradually as the plant developed.Susceptibility exhibited in short incubation period,high incidence and severe symptoms.Resistance increased obviously after flowering and podding stage.Among the various species of aphids found in soybean fields,Aphis glycine,Myzus persicae,Rhopaloslosiphum maidis and Eriosoma sp.transmitted SMV.The earliest appearance of aphids in the field was after early or mid-June.Two infection peaks were in mid-July and August.These were closely correlated with the vector spread of SMV which occurred about 15-20 days later.Infection gradients presented difinitely in six observation plots in contrast with the control plot.Excluding seed transmitted diseased seedlings,no other primary infection source was found.The distance of vector transmission was rather short that most of them occourred within 5-15 M from the infection source.For vector transmission happened very late,only mild symptoms including mottling seeds were resulted and the effect upon the growth was negligible,because the infection was in the time when host plants were in a state of maturing resistance.Seed transmission may be considered to play a critical role on epidemic of SMV under the circumstances in Heilongjiang province.

In 1983 and 1984 experiments with 2 strains,W-2 and S-3,of Xanthomonas campestris pv.oryzae (Ishiyama) Dye to inoculate riceplants p1,p2,F1,P2,and F3 generaton from 8 crosses revealed that in each resistant parent,the number and action mode of resistance gene(s)to W-2 were the same as those to S-3.As for the resistance to W-2or S-3,The cvs Early 36 had 2 dominant resistance genes and VT34-12 complementary dominant resistance genes.Both IR26 and 3624-33 had 3 complementary dominant resistance genes.
In VT34-1,there was 1 gene conferring resistance to both strainsW-2 and S-3,and there were 2 other genes,each conferring resistance to 1 of the 2 strains.In Early 36,its 2 independent resistance genes to strain W-2 were linked to its 2 independent resistance genes to strain S-3,respectively,with a gamete recombination value of 13.3% and a gene recombination value of 6.887%.In IR26 and 3624-33,their 3 independent resistance genes to W-2 were also linked to their 3 independent resistance genes to S-3,however,there was no way to estimate the recombination values either for the gametes or for the genes.Simultaneous selection of resistance to the 2 bacterial strains was considered to be feasible.

Several wheat varieties were selected including high resistant(HR),moderate restant(MR),moderate susceptible(MS) and high susceptible(HS) ones,namely MN7213(HR),Jup73-Atd "s"(MR),SI2-Nb (MS) and Vilela Mar.(HS).They were used as testing materials.The virulence of the fungus,Erysiphe graminis f.sp.tritici,collected from Shenyang,was identified with the virulence formula as 4/1,2,3a,3b,3c,5.
After an inoculation of the fungus to wheat varieties of different resistance and susceptibility in their three leaf stage(12 hours later)each of the varieties appeared to have peaks of enzymatic activities of phenylalanine ammonia lyase(PAL).The PAL activity of the resistant varieties was twice higher than the susceptible ones.The relay time was also longer being lasted 48 hrs.Peaks of enzymatic of susceptible varieties decrease rapidly approached to the normal level after 24 hrs.The accumulation of ferulic acid (preoursor of lignin)in the resistant variety was not only faster (resistant 48 hrs,susceptible 72 hrs after inoculation) but also greater.The amount of lignin were positively corre-lated with disease resistance of the tested wheat varieties:0.327%(HR),0.284%(MR),0.132%(MS) and 0.11% (HS).It is also found thatchlorogenic acid (phenolic phytoalexin,a metabolic of phenylalanine)accumulated rapidly accompanied with the increase of PAL activity.The times and quantities of chlorogenic acid accumulation were different.For the resistant varieties to reach the peak accumulation (3.3μg/ml) needed 48 hrs and for the susceptible ones (1.35μg/ml)96 hrs.
The results showed that there is a close relationship between the enzymatic activity of PAL as well as the chlorogenic acid and lignin and the resisstace of wheat to powdery mildew.

One of the isolates Turnip Mosaic Virus was inoculated on Nicotiana glutinosa.The expression of symptoms was different at various seed-ling ages and culture temperatures.Inoculations made at 3 leaf-stage under temperatures 20℃ and 25℃,all the infected plants showed systemic lesions,while imoculation at 6 leaf-stage under 30℃ and shaded for 24 nours,all the infected plants showed systemic concentric lesions.Inoculation made at 3 or 6 leaf-stage under 35℃ for 25 days,most of the infected plants produced systemic ring spots.The results give the evidence that different expression of symptoms occurred in different conditions.

From 1982-1984,we identified 25 rice-strains in five natural disease plots in different counties,we have found that strain 15(multi N-2)and strain 20 with higher yield are most resistant to rice blast.Strain 1(791-6-3-3),strain 5(3-37-10-2)and strain 14(multi N-1) give higher yields and are moderately resistant.But further experiments are needed for studying their stability.Strain 11 is supposed to have herizontal resitance.Its horizontal resistance needs to be further identified.
In identifying the resistance of rice to the rice blast,the methods of inoculation should be in combination with the natural infection method.We should especially point out that in identifying the resistance of rice plants to the heavy application of nitrogen and use of cold irrigation water are not necessary.

Chinese cabbage seeds germinated on wetted filter paper in the petri dishes.The solution to wet the filter paper included washed and unwashed bacterial suspension,the supernatant,the extract of the medium and physiological saline (0.8%) as a control.After incubation at 25℃ for 26 hrs,the diseased plants reached 8-95% of the total seed-lings treated with various suspensions containing the soft rot bacteria.The height of the diseased seedlings ranged from 17% to 80% of the control.The observations on the surfaces of the diseased young roots by the scanning electron microscpe indicated that a great number of the bacteria attached preferentially to the root-hair region earlier and to the growing and mature regions of the root later.It was evident that the cell walls of the mature regions were degraded by the bacteria and the holes were eventually formed by the perferation of the pathogen on the adjacency of the epidermal cells.The bacteria were found in the vessels and parachyma cells of the diseased seedlings at 16% and 3% of the examed sections respectively.The bacteria in the tissues of the infected seedlings could produce the microfibrils.The pathogenic bacteria in the vessels could destroy the vessel walls to make the vessel elments loose (spiral vessels) and multiporous (pitted vessels).

By purification of viruses and separation of sucrose density gradient we obtain an extracted virus from the sample of Crotalaria sessiliflora mosaic which is collected in the Agronomic Institute of the Japan Northeast University.The virus we found is similiar to CMV in gravity.And,by identifying through electronic microscopy and ultrathin sections of virus tissue,it is also similiar to CMV in shape,size of pellelt and crystal of cytoplasm and sap of vesicle.Therefore,we have an initial idea that the virus is in the same group of CMV.that the divi-Further more,in the experiment of agar immune response,we have observed ding line of settlement of the virus mixes together with that of PSV completely We have still a preliminary determination that the host reaction is in accord with that of PSV.Hence,we believe that the virus pathogen of Crotald-ria sessilifor mosaic is in the same group of PSV.

Pathogenic races of Pyricularia oryzae in Dandong region were tested using two sets of differential varieties,Kiyosawa,s differential varieties and Chinese differential varieties.In this paper,83 monosporous isolates were divided into 34 pathogenic races by kiyosawa,s differential varieties and 80 monosporous isolates into 12 pathogenic races by Chinese differential varieties.Dominant races are Japanese race 307.0 and Chinese nace ZF₁.All known resistance genes identifie up aate,except pi-ta²,are invaded by pathogenic races.Strains which infect Tetep and Zhenglong 13 in Chinese differential varieties exist in Dandong region.
High-yielding and resistant varieties Zhonghua No.8 and Zhonghua No.9,which were developed by Pollen culture,have high resistance to most of pathogenic races,but they are infected by races 577.3 and 577.7.These two races have low distribution frequency in Dandong region.Therefore,the resistance of these two varieties,Zhonghua No.8 and Zhonghua No.9.cannot be broken down in one or two years.

The hyperparasite of larch rust of Triphragmiopsis laricinum was identified as Darluca filum (Biv.) Cast.parasitizing in the teliospore mass of Triphragmiopsis laricinum.
Conidia of Darluca filum germinate at low temperature,range of 2-27℃,with optimum 4-12℃.Different nutrient solution has different influence on germination of conida.High percentage germination produced in 5% glucose solution or distilled water.No germination occured in 2.5% ammonium sulfate,pH also has some influence on germination,Conida germinate very well at pH6,but non above pH9.
Darluca filum has high antagonistic effect on Triphragmiopsis laricinum,Teliospres parasitized by 80% and above can lose germinating ability.These spores may be gradually destroyed,even disappeared.It may be taken as abase for biological prevention research of Triphragmiopsis laricinum.