国家自然科学基金No.41201511;湖南省教育厅重点项目No.10A049;湖南省农业厅重点项目No.20172;湖南省研究生科创基金No.CX2012B288 Supported by the National Natural Science Foundation of China No.41201511,the Key Project of Hunan Provincial Education Department No.10A049,the Key Project of Hunan Provincial Agriculture Department No.20172 and the Hunan Provincial Science Create Fundation of Graduate Student No.CX2012B288