The Interaction And Effect Of Three Arbuscular Mycorrhizal Fungi On Growth Of Astragalus Sinicus L. Under Salt Stress

Mycorrhiza is the important symbiosis formed by mycorrhizal fungi and plant roots.The identification of different arbuscular mycorrhizal(AM) fungi in the ecology system is usually based on our understanding of the morphological features of the asexually produced spores,but detection of different species in an AM fungi community inside the roots is almost impossible by this method.Molecular techniques open the possibility of identifying glomalean fungi in the same root fragment.In this study,the eukaryotic-specific primer pair LR1 and NDL22 was used to amplifying partial sequence of 25S rDNA from the spores DNA of Glomus claroideum and Scutellospora castanea.The sequences of products were aligned with a bulk of homologous sequences blasted from NCBI,and the primers Gc2 and Sc2 were designed based on the specific sites found in the sequences.The specificity of two primers were verified very well by nested-PCR,and they can be used as molecular probes.AM fungi present in all types of soils in nature,including the saline soils.However, different AMF species may differ in their ability to minimize stress effects and in promotion for the growth of plants.Three AM fungi(Glomus mosseae,Glomus claroideum and Glomus intraradices) were compared for their ability of root colonization and the behavior in the root of Astragalus sinicus L.under salt stressed soil conditions. Plants were harvested 7 weeks after sowing.At harvest,the dry weight of shoots and roots were measured,the intensity of root fragment colonization was recorded by Trypan blue staining and was expressed as M%,the activity of succinate dehydrogenase which is considered as an indicator of viability of mycorrhiza was measured by histochemical staining at different salt levels and was expressed as SDH%,so did the activity of alkaline phosphatase which was proposed as a physiological marker for analyzing the efficiency of mycorrhiza and expressed as ALP%.It was revealed that the tolerance of plants to salinity was improved by inoculating with AM fungi,the colonization of AM fungi was declining in general with addition of NaCl.However,the extent of declining was different. For G.mosseae and G.claroideum treatments,the percentage of root mass with enzyme-active hyphae was decreased following the increase of NaCl addition.However, the enzyme activity of intercellular hyphae produced by G.intraradices and the mixed inoculum in plant roots was less affected by salt stress.The taxon-discriminating primers B15,Gc2 and gil combined with either LR1 or NDL22 were used to detect G.mosseae,G. claroideum and G.intraradices respectively in mix-inoculated root system.Fifteen mix-colonized root fragments stained by Trypan blue were randomly sampled from all salt levels and amplified by three pairs of taxon-discriminating primers at the second PCR reaction respectively.The results suggested that the community was dominated by G. intraradices at all salt levels.The frequency of the three fungi presented in the mixed-inoculated root fragments obtained by nested-PCR(M'%) was compared with the extent of colonization obtained by TB staining when inoculated alone(M%).It was found that G.mosseae or G.claroideum was detected more frequent when inoculated in the presence of other fungi compared with inoculated alone in saline soil,especially at high salinity level.It was speculated that there was a synergistic interaction between these AM fungi under salt stress.