Diversity Of Endophytes Associated With Leymus Chinensis And Its Effects On Host Physio-ecological Characteristics In The Mid-Eastern Inner Mongolia Steppe

Endophytes are symbiotic with grasses (Poaceae) ubiquitously existing all over the world, and they could confer to their hosts competitive advantages. However, most present studies are focused on two commercially cultivated grasses, tall fescue (Festuca anmdinacea) and perennial ryegrass (Lolium perenne), while studies on the native grasses are few and show different, even contrary, results. At present, the most widely studied endophytes that are symbiotic with cool-seasonal grasses in the subfamily Pooideae are Epichloe species and their anamorphic relatives in genus Neotyphodium-collectively called epichloe endophytes. Neotyphodium species were widely regarded as being mutualistic with their hosts, as their reproduction completely relies on the hosts. While, Epichloe species may partly or completely depress their hosts flowering and seed setting by producing stroma ("choke disease"), during the sexual reproduction process, the relationships between Epichloe species and their hosts, greatly depend on the rate of stroma production on hosts flowering stems. However, some studies showed that the rate of stroma production of Epichloe species could be affected by the environmental conditions, especially moisture and nutrients. Besides, studies on cultivated grasses showed that Neotyphodium species could confer to their hosts biotic stress resistance, for example, pathogen resistance. In order to find out the relationships between Epichloe species and their native grass hosts when the symbionts are under different moisture and nutrients conditions, and the effects of Epichloe species on their native grass hosts, during the stage outside the sexual reproduction process, in this study, first, the distribution and diversity of the endophytes associated with Leymus chinensis in the mid-eastern Inner Mongolia steppe were investigated, by morphological classification and phylogenetic analyses. Then, a pot experiment lasting two years was carried out to find out the effects of endophytes on the growth, physical, and reproductive characteristics of L. chinensis, under different moisture and nutrient conditions, especially under high moisture and nutrient condition. Next, the effects of the endophytes on the pathogenic defense of L. chinensis were studied. Finally, the methods of building endophyte-infected (El) and endophyte-free (EF) experimental systems were sought. Several main conclusions were drawn as follows:(1) The overall average of endophyte infected rate of L. chinensis was low, while in this study, L. chinensis infected by the endophytes was at a relative high rate of27.6%to63.3%in the Abaga Banner, while in others, at0to9.1%. The endophytes associated with L. chinensis were composed by three morphotypes, and the morphotype Ⅰ (MTI) was dominant which was identified as Epichloe bromicola depending on the morphological characteristics and phylogenetic analyses, making up72.4%to91.2%.(2) The improvement effect of endophytes on the growth of L. chinensis was affected by moisture condition with a time lag but scarcely by nutrient condition, and causing the shape and structure of host leaves changed might be the way of endophytes to influence the growth of L. chinensis.(3) In this study, the reproduction styles of different endophyte-L. chinensis symbionts were distinct, and the moisture and the nutrient condition could affect the rate of stroma production of endophytes associated with L. chinensis, and further affect the relationship of endophyte and L. chinensis.(4) The endophytes associated with L. chinensis could improve the pathogenic defense of the hosts, and different strains with distinct inhibition and antifungal abilities made a contribution to the improvement. These indicated that the endophytes associated with L. chinensis could be proposed as a latent biocontrol agent.(5) Using the fungicide-propiconazole to soak the seeds with a short period of time or to spread once on the leaves of seedling and adult, at a low concentration, could kill the endophytes.This study furthered our understanding of the symbiosis of Epichloe species and L. chinensis, and supplied some experimental basis and theoretical direction for the development, utilization and conversation of these beneficial microorganism.