Biological And Physiological Characteristics Of Elymus Dahuricus/Neotyphodium Endophyte Symbiont

Elymus dahuricus, as an important forage grass in northern China rangeland, plays important role in grassland livestock production and environmental protection. It is well known that grass endophyte enhances the biotic and anbiotic stresses tolerance of the host plants, and in the same time it produces secondary compounds in the plants which are toxic to the livestock intaked the host grass. However, there is no information available on the endophyte in E. dahuricus in the world literature. A series of experiments were conducted to investigate the distribution of endophyte in the E. dahuricus populations in China and its taxonomy and biology. Endophyte infected (E+) and endophyte free (E-) populations with the similar genetic background were established to study their growth and physiological triats. The results were summarised as the follows:1. Endophyte infection rates were ranged 0 - 100% among the 26 wild E. dahuricus populations grown at provinces (Autonomous Regions) of Inner Mongolia,Hebek Shanxi,Beijing,Shanxi,Gansu,Qinghai,Xinjiang and Sichuan. Endophyte was isolated from seed, leaf blade, leaf sheath and stem. The fungus was identified as a species of Neotyphodium according to its morphological characteristics. However, morphological diversity was existed among the isolates. The endophyte varied in its ability to grow on media containing different carbon and nitrogen nutrients, and to produce biomass on media with various osmotic stress.2. The results of the field trials conducted for two years indicated that compared with the E- plants the E+ plants from two wild populations i.e. Wulingshan and Qinyuan populations had higher herbage dry matter yields, more tillers per plant and more reproductive tillers per plant. However no such results were found from E+and E- plants of Wutaishan population. Daily dynamics of phytosynthesis rate of the E+ and E- plants from the above three populations showed similar pattern as the plant growth.3. Endophytes infection significantly improved the activity of some protection enzyme of E+ plants of Wulingshan and Qinyuan populations compared with E-plants. These protection enzyme are superoxide dismutase (SOD), perxidase (POD), catalase (CAT) and ascorbic acid oxydase (APX); reduced the content of hydrogencontent (H₂O₂) significantly (P<0.05). Meanwhile, protection enzyme activity have seasonal variation and reached the max in October and go down bottom in June.4. The contents of soluble sugar, starch and nitrogen in E+ plants are significantly higher than those of in Wulingshan and Qinyuan populations, but no such effects were found in Wutaishan population. Regardless the endophyte infections, the contents of soluble sugar and starch of all E. dahuricus population were increase as plant growth from the spring and reached the top at the end of the season. The stem base accumulated more sugar and starch than leaf.5. Peramine were found in the sheath of E+ plants of Wlingshan and Qinyuan populations by HPLC test. No peramine was detected in Wutaishan population. Peramine contents in the sheath showed seasonal variation which has the highest content at the end of growing season.6. E+ plants showed advantage in growth over the E- plants under drought conditions which indicated by the higher plants, more tillers per plant and higer herbage dry matter yield than the E- plants. The E+ plants also showed the higer activity of of superoxide dismutase (SOD), perxidase (POD), catalase (CAT) and ascorbic acid oxydase (APX), the higher contents of chlorophyll and the proline, and the higher relative water content in the leaf and the lower content of H₂O₂ . However, no such advantage were observed from E+ plants.7. Baiwangshan population with 100% endophyte infection showed higher seed vigor and ability to germination than other seed lots when the osmotic stress reduced to -1.5Mpa, and the seedling of SOD and the POD enzyme activity is also higher than other low infected population.