Effects Of Endophyte Infection On The Resistance Of Achnatherum Sibiricum To Herbivore Insects Under Simulated Herbivory And Clipping Treatment

Grass-endophyte interaction has received much attention recently. It is well documented that endophytes are able to enhance the resistance of agronomical grasses to herbivory. For native grasses, however, the related reports are limited and the conclusions are variable.In this study, endophyte-infected Achnatherum sibiricum, a native grass, was adopted as plant material. Methyl jasmonate (MJ), applied to simulate herbivory, and clipping treatment were used to study contributions of the endophyte to Locusta migratoria resistance of the host grass. The results were as follows:Endophyte infection could significantly enhance resistance of the host to L. migratoria. In both choice and no-choice experiments, locusts preferred EF (endophyte-free) plants to EI (endophyte-infected) plants, and the weight of the second instar locusts fed on EI plants was significantly lower than those fed on EF plants. Endophyte infection did not induce enough alkaloids produced to resistant herbivore. However, endophyte infection did significantly decrease the palatability of the host on one hand, which was manifested by lower concentration of soluble sugar and essential amino acids (such as Thr, Lys, His, Val, Leu, Phe and Met) in EI plants than those in EF plants. On the other hand, endophyte infection significantly increased the defense of the host, which was manifested by higher activity of polyphenol oxidase (PPO) and phenylalanin ammonialyase (PAL), and higher concentration of lignin and total phenolic in EI plants when compared with EF plants. The results supposed that the herbivore resistance of El grass was more related to indexes mentioned above than alkaloids.MJ treatment significantly inhibited growth of both El and EF plants, but effects of MJ treatment on herbivore resistance were different between EI and EF plants. For EF plants, MJ treatment significantly increased the activity of PPO and PAL, and significantly enhanced their resistance to locusts. For El plants, however, MJ treatment had no significant influence on PPO activity, and PAL activity also increased less than in EF plants. MJ treatment did not contribute to locust resistance of El plants. It is suggested that endophyte might not rely on MJ defense pathway.After clipping, the concentration of soluble sugar and essential amino acid such as Ile significantly decreased in El plants, while the concentration of total phenolic and lignin significantly increased. Meanwhile, the weight of the second instar locusts fed on El plants were less than those fed on EF plants. That is to say, clipping treatment further improved locust resistance of EI plants. As for EF plants, the concentration of soluble sugar and essential amino acids such as Thr, Lys, His and Val significantly increased after clipping. Although total phenolic in the shoot and root increased, the degree was much lower than those in El plants. The weight of the second instar locust increased significantly after clipping. That is to say, clipping treatment made EF plants more sensitive to locust. Thus, clipping treatment further strengthened locust resistance advantage of El plants over EF plants.