Five hundred and fifty-three isolates of soybean root rot,collected from 7 counties in Shandong province,were studied and demonstrated that they belong to Fusarium solani,F.oxysporum and F.equiseti during 1987-1988.Among them,F.solani was of the highest frequency and incidence.This isolate was designated as Fusarium solai(Mart.) Sacc.f.sp.glycines Li & Luo.a specialized form of Fusarium solani (Mart.) Sacc.,based on its cultural,morphological and pathogenic characters.

Sectoring in Fusarium graminearum Schw.causing wheat scab cultured onPDA was studied.The frequency of sectors formed on FDA was 4.3-11.4%,with an average of 8.1%.All sectors were observed to be variable after being successively transfered.Comparing with their corresponding parent cultures,sectorial variants were characterized by less or no aerial mycelia,deeper amaranth on the substratum,slower growth of mycelia,less production of conidia and perithecia,and weaker virulence to wheat spikes.

Results from serological detections with antisera of rice tungro spherical and bacilli form viruses(RTSV and RTBV) from IRRI and electron microscopy showed that rice tungro was caused by RTBV with its size about 150-350 X 25 nm and RTSV about 30 nm in diameter as well in Fujian,China,Many starch grains accumulated in the mesophyll and bundle sheath cells of the diseased leaves.Necrosis and deformation of some phloem cells were also observed.Symptom of yellowing caused by RTBV or together with RTSV was more severe than that by RTSV alone and diseased plants by RTBV or together with RTSV died more quickly and easily.The detailed distribution of RTBV in China remains to be determined further.

Carnation vein mottle virus showed a very narrow host rang.It infected only several kinds of test plants of caryollaceae and allied families(Cheno-podiaceae etc.).Chenopodium quinoa and Dianthus babatus,which could be infected by the virus,proved to be the best indicators and propagation species.The preparations of this virus contained flexuous filamentous particlesC 790 x 12 nm.It could be transmitted by Myzus persicae in non-per-sistant manner and the rate of transmission is 58%.In ISEM test,the parti-cles of carnation vein mottle virus could be coated evenly by antiserum kind-ly provided by Dr.A.Hein.The studies of ds-RNA in infected plants,ultra-structure of infected plants and disease management were also undertaken.

A typical mycoplasma-like organism was observed by electron microscope in the sieve tubes of Chinese cherry with destructive yellow symptom found in Xi Chang,Sichuan Province.Most of the premorphic bodies were spherical and dumbell shaped,some beaded chain-like,lotus-root-like,or bullet-like.The body had a peripheral trilamilar unit membrance,but no cell wall,nuc-leus and other memberous structures.In the experiments with antibiotics,tetra-cycline was effective against the disease,but penicillin had no effect.A prim-ary conclusion was reached that the destructive yellow disease of cherry was caused by a mycoplasma-like organism.

This paper deals with the distribution of the citrus root nematode,Tylenchulus semipenetrans Cobb.,in Sichuan Province damadge with reberence to its citrus trees as well as resistance of citrus species and the effects of chemical control.The nematode disease occured widely in citrus growing areas.94.7 per cent of the citrus orchards are suffering from the nematode disease.15.0 per cent of the citrus orchards are seriously injured.The density of larvae in the fibrous root was lower during the summer than in the winter or spring,but the density of female in the fibrous root changes little all the year round.Based on the resistance determination of 7 citrus species,two of which trifoliate orange (Poncirus trifoliate) and the citranges (P.trifoliate×Citrus sinensis),are resistant to the disease.But the trifoliate orange is the most resistant while the other species are susceptive.Accor-ding to the tests of chemical control,Temik,Rugby,Nemacur and Mocap result in effective control of the nematode disease.

It is proved that Blumeria graminis DC.Speer is able to overwinter in the south of the Northeast China.In winter,the fungi survived on the basal leaves and sheaths of the winter wheat seedling with hyphal mats.Its cle-istothecia are able to oversummer when mixed with wheat seeds and kept under dry environment.The local volunteer wheat seedlings and wild hosts of powdery mildews are unimportant in the infection cycle of B.graminis DC.Speer.
The results of the analyses of virulence frequency (Vf) of the fungal populations indicate that the local powdery mildew populations of Gong Zhu Ling (Jilin Province),Shenyang,Haicheng,Dalian (Liaoning Province),Yantai (Shandong Province) belong to the same population,since their Vf indexes are similar.
The analysis of local primary disease development date and the high altitude synoptic chart shows that the primary infection source of the nor-theastern spring wheat region comes from Yantai winter wheat region through remote air transporation.Under the control of a definite climate system,the conidia are carried into the northeasten spring wheat region at a height of 700 mb.

The quantitative studies on the sporangia infection probability and patt-terns of lesion appearance of Tomato Late Blight (Phytophthora infesians(Mont) de Bary) revealed that the temperature range of sporangia infection was 7 to 33℃.Under the same DT(Dew Temperature),IP (Infection Proba-bility) increased with increasing DP (Dew Period),under the same DP,at first,IP increased with increasing DT,then decreased with increasing DT ranging from 7 to 33℃.The minimum DP for sporangia infection was 3hours.The optimal combination of DT and DP for IP was DT 17℃ X DP 24 hr.
Infection probability was a function of DT and DP:
IP=-0.78469-0.17962*DP+0.05693*DT*DP-1.34744E-03*DT²*DP
-4.7973E-04*DT*DP²
The latent period was about 3 days under our experimental conditions in 1987.The daily rate of lesion app earance decreased with time from the first day to the third day.On the first day,the daily rate of lesion appear-ance was maximum,about 60 percent.The Richards model was used todescribe the daily cumulative rate of lesion appearance (CROA):
CROA=(1+5.465E+35*EXP(-0.9272*TT))**(-1.0/47.09)
TT——accumulated degree days
66.265<=TT<=103.18.

The important parts of the grey system theory-the principle and method of the grey relational grade analysis are introduced in this article.And the prevailling system of Botrytis fabae of sheyang County from 1973-1984 were analysed by this method.The results showed that the source of inoculum,the rainy days in the second ten days of April the rainy days from last Nove-mber to next January,and the dewy days in the first twenty days in April were leading factors influencing the prevailling level of Botrytis fabae.The above results were proved to be correct and reliable by the analyses of variation coefficients and variances.And it was consistent with objective reality,which also helped to show the defects of the viewpoint that the source of inoculum is not a leading factor affecting the prevailling level of Botrytis fabae.Therefore,when we forecast the prevailling level of Botrytis fabae,we must first take the above mentioned leading factors into considera-tions.This new mathematical method is simple,more covenient and more effective than any other ones so far applied.
Discussions are also made for certain problems in application of this method.

Eight-five isolates of Erysiphe graminis f.sp.tritici collected from mildewed wheat leaves in Sichuan province during 1987-1989 were inoculated on 11 wheat cultivars and isolines with known powdery mildew resistance monogenes.The virulence gene frequencies of vl,v3b,v3c and v5 appeared very high (more than 90%),followed by v3a,v7 and v8 (88.2-65.9%),the virulence gene frequencies of v2 and v6 were 42.4% and 37.6% respectively,and those of v4a and v4b were low (less than 15%).Virulence gene combinations,such as v2+v6,v2+v4b,v2+v4a,v4b+v6,and v4a+v8 were rare,suggesting that cultivars with corresponding resistance gene combinations will be highly resistant.Most isolates tested seemed to have seven or eight known virulence genes and exhibited broad virulence spectrum.There-fore,breeding for resistance to powdery mildew in wheat in Sichuan province is more difficult than expected.

Apothecia and ascospores of the fungus Sclerotinia sclerotiorum,artificially produced by inducing,were used to test the effect of Tautomycin on them for antibiosis.Owing to that ascospores are the most important primary infection source of rape sclerotinia blight,the antibiotic effect of Tautomycin to ascospores will be of great significance for the disease control.The effect of Tautomycin was demonstrated by tests on mycelia,ascospores,and sclero-tia either in vitro or in vivo.It has been revealed that such a new antibiotic is promising to be used in biological control of rape sclerotinia blight.

Monosomic analysis of resistance to stem rust,race 21C3 and 34C2 was carried out in variety Orofen as differential host of Puccinia graminis var.tritici in China.Difference or identify between the resistant genes carried by Orofen and the Sr genes denominated by international organization has been identified.The results showed that Orofen carried two genes,a gene(Sr5) on chromosome 6D for resistance to races 21C3 and 34C2.Gene Sr5 governs IT O-;1^- to race 21C3.Gene Sr6 controls IT O-;1⁺⁺X-to race 21C3 and IT;1-;1⁺⁺X-to race 34C2.Gene Sr5 is epistatic to gene Sr6 tested by race 21C3.

Soybean downy mildew[Peronospora manschurica (Naum.) Syd.] is a serious disease in China.During 1987-1989,10 samples of soybean downy mildew collected from 9 counties of Sui Hua region were inoculated on 12 differential hosts:Pridesoy,Norchief,Mukden,Richland,Roanoke,Illini,S-100,Palmetto,Dorman,Kabott.Cgden,and Woodsyellow,in a separated greenhouse and fields.The result indicated that there were three new physio-logical races of Peronospora manschurica in the region and were found to be different from the reported 32 races in USA,and were therefore designated as Zhong No.1,Zhong No.2 and Zhong No.3.

Screening in laboratory and testing in pot planting proved that P.oligandrum was antogonistic against R.solani AG-4,P.ultimum,P.spinosum and P.irregulare.Treating tomato seed with oospores of the P.oligandrum resulted in effective reduction of 79.4% and 63.6% seed rot and damping-off induced by P.ultimum and R.solani AG-4.P.oligandrum was principally parasitic on R.solani AG-4 and it's hyphae greatly branched and penetrated the hyphae of R.solani AG-4.However,P.oligandrum was antibiotic to P.ultimum only with releasing substances to dissolve the hyphae of the latter.

Fifteen hybridomas secreting specific monoclonal antibodies (McAb) against the pathogens of rice bacterial leaf stripe (RBLS) were made.The McAb showed the active reaction to the pathogens of RBLS and no cross reaction to the bacterial cultures belonging to different genera res-pectively.28 samples,by the indirect assay of ELISA,were active to the McAb in the detection of 30 samples infected by the man-made innoculation in the detection rate of 93.3%.Out of 46 samples of grains from diseased fields,36 samples were positive and 10 were negative to the McAb.11 McAb-positive and 10 McAb-negative extracting solutions were respective-ly innoculated to the rice seedlings.There were 7 McAb-positive extrac-ting solutions infected the rice plants tested,while McAb-negative extrac-ting solutions showed no symptoms.
The sensitivity of the method was 0.0125mg/ml-0.00125mg/ml (pro-tein concentration).

The recently developed method of dot-immunobinding assay(DIBA) was adopted in this experiment to detect three plant viruses of different mor-phology.The purified TMV was satisfactorily detected by DIBA at 0.184ng/ml,purified PVY at 1.28x10³ ng/ml and purified CMV at 0.056ng/ml,requiring about 5 hours to finish a test.Also the sap of tobacco plants infected with TMV,PVY and CMV respectively were detected by DIBA at dilutions of 1:819,200,1:102,400 and 1:819,200 respectively.Since the background and nonspecific reactions are critical problems in DIBA,the use of HRP-A resulted in no background color and less nonspecific reac-tions than in the case of using HRP-IgG.Therefore it is of the opinion that to select appropriate dilutions of antiserum and healthy leaves are also important.The present experiments showed that DIBA inherited almost all advantages of ELISA,yet more sensitive,economic,rapid and simpler than the latter.The writers prefer to use DIBA rather than ELISA to detect and identify plant viruses.

Phytophthora cyperi is the pathogen of Cyperus malaccensis blight.This disease universally occur in Guangxi.It infects bracteal leaves,stalks and leaves of Cyperus malaccensis brevifolius.Physiological determination givesthe results:the temperature range for sporangia formation is 10-30℃,the optimal temperature is 15-25℃,under the saturated humidity condition.

Five species of Pythium,namely,P.spinosum,P.aphanidermatum,P.dissotocum,P.Kunmingense,and P.ultimum were found among 38 specimens isolated from diseased plant tissues and soils,collected in Yinchuan,Yongning,Guyuan,Penyang,and Qingtongxia cities or counties,Ningxia Hui Autonomous Region.The other specimens were unknown,due to the absence of sexual organs.Soil and in vitro inoculation tests showed that the 5 spe-cies were all pathogenic,causing seed-rot,damping-off,and tissue-rot.A Iist of their pathogenicities to the seedlings of several vegetables was given,in which,P.aphanidermatum was most harmful.

A study of etiology and biology of mosaic disease of soybean occuring widely in Shandong was carried out during 1984-1986.Results of sap inoculation on 14 species from 5 families with the virus isolate obtained from soybean field indicated that it systematically infected soybean only,and indu-cing mosaic symptoms,The thermal inactivation point of the virus was 65-70℃,the dilution end point was 10^-3-10^-4 and longevity in vitro of leaf extract was 3-4 days.The virus was transmitted by Aphis glycine,A.cracci-vora and Myzus persicae with non-persistent manner,and also by seed.Virus particles were flexous rodabout 711-729 x 12-13nm.The virus reacts with antiserum of SMV by SDS-agar gel double diffusion test,immunosorbent electron microscopy and ELISA.On basis of these characteristics,this was identified as Soybean Mosaic Virus(SMV) belonging to the potyvirus virus group.

This paper deals with some species of Xiphinema,colleced by the first author from vineyard soils in provinces of Hunan,Shandong and Hebei,China,during 1987-1989,Xiphinema americanum Cobb,1913 is a new record from grape in this country.X.hunaniense n.sp is characterized by the most anteriorly situated vulva(V=24-27),a posteriorly slopping vagina(at an angle of 8-21° with the transverse section of body),a genital tract only with a posterior genital branch which is divided into two ovary branchs,along mucro(20-22μm) on the median of tail terminal,tail variations bet-ween juveniles and and adults,and males unknown.X.hunaniense n.sp.is most closely related to X.brasilense Lordello,1951,but distinguished from it by higher values of a,and c,smaller value of V,weakly set off lip region,posteriorly slopping vagina,single genital tract with two branched ovaries,and tail variations between adults and juveniles.

The first leaves of wheat cultivars Lovrin 13 and Huixianhong were heavily inoculated with several races of stripe rust.Changes in photosynthe-sis,photorespiration and dark respiration during infection process were mea-sured in inoculated leaves with FOW infrared gas analyser.Net photosynthesis rate declined slightly in the initial stage of infection and rapidly increased by about 50% in the stage of symptom appearing and pustule formation.Respiration remarkably increased in the late stage of infection,following an initial decline.Photorespiration rate in infected leaves rose to 60-70% and dark respiration rate rose to 1.6-1.7 times that of health leaves.The duration and degree of these changes were dependant on the degree of incompatibility between host and stripe rust.
The significance of these results was disscused,