Biological Characteristics And Molecular Identification Of Dominant Mycorrhizal Fungi In Dendrobium Loddigesii (Orchidaceae)

The main study in the paper are to research the biological characteristers of dominant mycorrhizal fungi isolated from Dendrobium loddigesii, molecular and morphological identification.In this paper, we research on the ecological characteristics of dominant mycorrhizal fungi isolated from Dendrobium loddigesii in different temperatures, water stress and pH conditions. Morphological and molecular identifications were used to identify strains of mycorrhizal fungi. The results are as following,All of the strains have no growth in 5℃. When the temperature reaches 10℃, the fungus resumed growth, growth rate is accelerating as the temperature increasing, and the increase was more moderate; when the temperature reaches the optimum temperature (25℃or 28℃), the growth rates of strains bring about maximum; however, when the temperature exceeded the optimum temperature, in addition to F12 and B28, the strains'growth rates would decrease slowly as the temperature increase. Most fungi were able to maintain normal growth in 15-35℃, they conformed a wide range of temperatures, and the growth curves were flat-shaped or wide roof-shaped. Therefore most fungi have a strong adaptive faculty in natural environment.All of the fungi grow well in neutral to alkaline (pH between the 7-9) culture mediums, and the diameters of fungi were not significant. However, the tolerances of acid mediums were more diversity. only F13 can withstand stronger acidic environment(pH 4); F24a, F24b grew at pH 5, F12, F14 and F23 grew in mediums with pH≥6; B28 had week acidoresistance, which could only survive in neutral and alkaline environment. All of mycorrhizal fungi colony diameter reached the minimum value in the pH 4 conditions, no hypha or little hypha has grew. All of mycorrhizal fungi have strong alkali-resistant.F13 and F23 had on the most widely adaptability to PEG, which were able to grow on the culture mediums with high PEG concentration(PEG≤30%), and the growth rate decreased as the PEG concentration increase gradually. and F23 reached the maximum colony diameter when PEG concentration was 20%. B28 had the worst tolerance to PEG. The adaptation range of PEG was narrow, B28 can only withstand PEG concentration less or equal 10%. Except for F12 and B28, the other colony strains could keep growing when PEG concentration below 25%, and the growth rate increased when the PEG concentration decreased gradually. PEG modeling-water stress simulation experiment showed that low level of PEG was less effect to 7 species of endophytic fungi of Dendrobium loddigesii, but high level of PEG affected fungi significantly, that when the PEG concentration reached 30%(-1.53 MPa), most mycorrhizal fungi were restricted completely. So presumably, when the soil moisture falls below a certain value, the growth of endophytic fungi to be completely curbed.In the experiments, we used different with different medium culture mediums, such as PDA(Potato Dextrose Agar), OMA(Oatmeal Agar), WA(Water Agar),high and low temperature alternating training, UV/scattering alternative culture methods to induce fungal sporulation, but only one fungus produces spores. As in the laboratory, it is difficult to induce asexual spores or fruiting bodies, so difficult for orchid mycorrhizal fungi can be used as classification based on morphological and anatomical features.Protocols in Molecular Biology was taken in the experiment. rDNA internal transcribed spacer analysis(rDNA ITS)was used to study diversity of fungi isolated from Dendrobium loddigesii. The results showed as following,The fungi we identified, belonged to Ascomycotina (6 species), Basidiomycotina (2 species) and mitosporic fungi (1 species).4 colony strains had been Identified to species, Tulasnella calospora(F12), Epulorhiza(B28), Acremonium alternatum(F13), Lecythophora and T. calospora (anamorph:Epulorhiza repens)(F25).Analysis of fungi diversity and specificity indicated that, Geographical factor affected diversity and specificity of mycorrhizal fungi isolated from Dendrobium loddigesii, which is a key factor to the further study of Orchidaceae; Environmental complexity directly effects the diversity of Orchidaceae mycorrhizal fungi, Orchidaceae survived in complex habitats had more mycorrhizal fungi diversity; Orchidaceae has strong specificity to mycorrhizal fungi, however the certain fungi don't have the same specificity to orchids; Tulasnella is a common fungus in both Terrestial and Epiphytic orchids.