The Investigation And Identification Of The Genus Pythium In Hainan Island

Species of the genus Pythium are distributed worldwide and many, they are supposed from saprophytes to parasites, to mutualists in parasitism development. More than 250 species have been described and 58 species found in China. Pythium can parasitise in a wide variety plants,cause serious damage to various agronomically important crops. Such as pre_and post_emergence damping_off diseases of seedlings, rots of roots, basal stalks or seedings, decays of fruits and vegetables during cultivation, storage, transit or at the market. Nowadays, more than 80 species are important phytopathogens. On the orther hand, some species of Pythium have shown to be capable of parasitic on other fungi , which may be used in biological control, such as Pythium acanthicum Drechsle. Some species of Pythium are also of potential benefit to human beings as they can synthesize biotin, folic acid, pantothenic acid, riboflavin, thiamine, etc.Some can transform sterols,such as cholesterol,ergosterol and sitosterol, and so are of important to medicine manufacturing.Hainan island climate characterized by the tipical tropical marine climate, rain and heat is very adequated, the Plant and microorganisms are various. But except the 11 species of Pythium which described by Yu yong nian, the genus Pythium in Hainan are still not to be investigated and indentificated systematically.In order to make sure the species of Pythium and distribution in Hainan island , abundant for the microorganism resources of Hainan, during 2004～2005, We collected 350 soil samples from different sites of 17 country(or city) and 4 virgin forests of Hainan island, and gained a total of 1341 isolates of the genus Pythium by the method of bait and selected medium isolation. The main result as follow:1. Based on morphological character and the results of rDNA ITS1 sequence analysis, 1301 isolates of Pythium were indentified as 16 speciese and 3 dubiously speciese ,and other 113 isolates didn't produce sexual organ in culture, were classified as Pythium Group F, A, B, D, C, L, G, P, HS, SP,respectively, according to their hypha and sporangium morphology. The 16 species are Pythium acanthophoron Sideris, Pythium carolinianum Drechsler, Pythium graminicola Subramanian, Pythium helicoides Drechsle, Pythium intermedium de Bary, Pythium inflatum Matthews, Pythium middletonii Sparrow, Pythium splendens Braun and Pythium spinosum Sawada ,Pythium acanthicum Drechsle, Pythium aphanidematum(Edson)Fitzpatrick, Pythium catenulatum Matthews, Pythium deliense Meurs, Pythium indigofereae Butler, Pythium myriotylum Drechsler and Pythium vexans de Bary. Off them, the front 9 species are new records in Hainan. The 3 dubiously speciese were Pythium hydnosporum (Mont.) Schr?ter, Pythium oedochilum Drechsler, Pythium sylvaticum Campbell &Hendrix.2. The results of statistic analysis on 1341 isolates of Pythium indicate that Pythium vexans, Pythium deliense, Pythium aphanidematum, and Pythium acanthicum were dominant species in Hainan, and Pythium vexans was the most wide-distribution species.3. The sequencing analysis on rDNA ITS1 of the four isolates showed that isolate Py0623H was Pythium helicoides, Py0600a was Pythium acanthophoron, Py0600c2 was Pythium carolinianum and Py0410s was Pythium splendens. The sequencing analysis results of this four species were indentically with the indentification by the morphological character, it showed that the rDNA ITS1 sequencing was the important tool to assist the taxonomy of Pythium.4. Blast disease of oil palm caused by Pythium splendens, is an import plant quarantine disease in China.We gained a isolate of Pythium splendens Py0410s from the soil of gibbon virgin forest in Bawangling natural reserve of Hainan. The pathogenicity of Py0410s to the oil palm was examined and the result indicated that this isolate can cause the seedling blast of oil palm.