| The genus Phytophthora includes a diverse group of notorious plant pathogens worldwide,which can cause considerable damage to crops,forest trees,ornamentals and herbs,infecting their roots,rhizomes,foliage and fruits,causing root rot,canker,spot and wilting.Since people are increasingly aware of the risks of Phytophthora,the full-scale investigations of Phytophthora existing in forests and natural ecosystems were launched around the world.There was a substantial rise in the species of Phytophthora recognized worldwide,from 58 species in the 1990 s to above 140 described species and informally desiginated taxa in current years.Since 2005,our group has started the investigation of Phytophthora and its diseases in the forest ecosystems across the country,and made it clear about the species and distribution of Phytophthora in Rhododendron-oak forest in Southwest China.Based on the results,this study was carried out.The main results are as follows:1.From 2015 to 2017,baiting was used to investigate and monitor Phytophthora in Wuling Mountain Forest Ecosystem in Hebei Province.A totle of 122 isolates of Phytophthora were obtained from streams and canopy drips,and they were identified as four species based on sequence and morphology,including 39 P.plurivora isolates,one P.chlamydospora isolate,78 P.gonapodyides isolates and three P.lacustris isolates.P.gonapodyides is the most numberous species,while P.plurivora recovered from the canopy drip may be the most destructive species threatening to the local forest ecosystem.2.In this study,reference isolates of Phytophthora species conserved in the laboratry were rechecked by morphology and some unknown isolates were identified.The result of rechecking was consistent with original result,with 100% accuracy.It shows that the methods of isolation,purification and conservation in our laboratory are reliable.3.During the review,it was found that the strains closed to P.polonica based on preliminary sequence analysis of ITS did not conform to the type isolate described in morphology in the literature.It was identified as a new species by polygenic sequence analysis,morphology,physiology and pathogenicity test,and officially named Phytophthora pseudopolonica Wen-wen Li,Wen-xia Huai & Wen-xia Zhao sp.nov.P.pseudopolonica formed hyphal swellings readily and abundantly on culture plugs suspended in sterile water;Abundant thin-walled spherical chlamydospores were generated in sterile water,CARP,and V8S;Sporangia were not observed on any media,and only a few were produced in pea broth and sterile water.Sporangia were nonpapillate and noncaducous,with extended internal proliferation or nested proliferation.P.pseudopolonica is homothallic;rich oogonia of the tested isolates were produced on CA,CARP,and V8 S after 1 week.Antheridia were generally paragynous.P.pseudopolonica was slightly pathogenic to leaves in vitro of Castanopsis fargesii,Castanopsis sclerophylla,and Cyclobalanopsis glauca.4.Furthermore,phylogenetic analysis based on ITS and β-tubulin gene locus was carried out on P.intercalaris,a new record species in China.The results showed that the sequences of ITS and β-tubulin genes of all isolates were more than 99% consistent with that of reference strains,eventhough there was high sequence consistency among isolates of P.intercalaris from different region,but some base sites were different and formed different gene types.5.Sequence related amplified polymorphism(SRAP)was used to analyze the genetic diversity of P.plurivora isolates from different geographical origins.11 pairs of polymorphic primer combinations of 100 pairs of SRAP primers were screened out,and 177 DNA bands were amplified,in which 163 polymorphic bands and 40 specific bands.There were 11-21 polymorphic loci and 0-8 specific loci for each pair of primers,and polymorphic ratio of primers was 81.8%-100%.The genetic parameters(H=0.3303,I=0.4867,PPL=93.94%)indicated that P.plurivora was rich in genetic diversity.NTSYS software was used to cluster the tested strains,and the result showed that P.plurivora from different areas were close in relationship,but there were differences among strains,and the result of SRAP group had no direct correlation with geographical origin. |
