Research Of Pythhim Species In Some Forests And Nurseries Of China

Pythium species is a widely distributed oomycete. Most of them are saprophytes whichcan both live a terrestrial and aquatic life. Some of them are bacterial parasite, and their hostrange is very wide that they can parasitize many plants and animals. Some species of Pythiumare valuable at biocontrol as well as industrial, agriculture and pharmaceutical production. Atpresent, there are over200species have been reported all over the world. In China, the totalnumber is sixty-one, including ten new species.Pythium has been researched mainly in agriculture, and has plenty report on their harm tofarm crops. In contrast, as forestry and nursery garden been more complicated ecosystem, thediversity of Pythium should be even more and widespread, however, it hasn't receive enoughattention yet. From2010.9to2011.10, soil and water samples were collected from differentsites including sixteen flower nurseries in Beijing, natural oak forests in Zhenping County,Shaanxi Province, and alpine azalea-oak forests in Shangri-La County, Yunnan Province. Pyrusspp., Rosa chinensis, Syzygium aromaticum, Quercus aliena, Quercus mongolica, andRhododendron spp. were chosen to be the trial baiting plants. Totally,132Pythium strains wereisolated and identified as eighteen species by morphological characteristics and rDNA-ITSsequencing analysis. Among them8species that were recorded before,8species were recordedfor the first time in China and2species were unknown. The8originally recorded Pythiumspecies were: Pythium heterothallicum Campbell&Hendrix (thirteen strains), Pythiumaphanidematum(Edson)Fitzpatrick (5strains), Pythium ultimum Trow(eighteen strains),Pythium sylvaticum Campbell Hendrix(1strain), Pythium vexans de Bary(forty-twostrains), Pythium perplexum Kouyeas Theohari(5strains), Pythium debaryanum Hesse(1strain), Pythium carolinianum Matthews(1strain)；The8newly recorded species ofPythium were:Pythium sterilum Belbahel&Lefort(1strain), Pythium attrantheridium AllainBoule&Le′vesqu(e4strains), Pythium segnitium Pau(l1strain), Pythium orthogonon Ahrens(1strain), Pythium violae Chesters&Hickman(1strain), Pythium pachycaule Ali-Shtayeh(2 strains), Pythium litorale Nechwatal&Mendgen(twenty-eight strains), Pythium nunn Lifshitz,Stanghellini&Baker(5strains); two undescribed species were：Pythium sp.I(2strains),Pythium sp.II(1strain). Among them, Pythium ultimum was the dominant species in Beijing,isolating frequency was35%; Pythium vexans dominated in Zhenping County, ShaanxiProvince, isolating frequency was74%; Pythium litorale dominated in Shangri-La County,Yunnan Province, isolating frequency was70%. This study described the morphologicalcharacteristics of all the eighteen species, discussed their morphological features and taxonomystatus, and phylogenetic tree was constructed based on rDNA-ITS sequence with the method ofNJ which confirmed the result of morphological identification.This research explicitly identified Pythium strains to the degree of species by combiningtraditional morphological characteristics and molecular biology techniques, which provides animportant classification tools under Pythium genera.