This work was supported by the National Key Technologies
R&D Program during the 12th Five-Year Plan of China
(2013BAD11B03-8), the National Basic Research Program of
China (973 Program, 2012 CB955904), the Natural Science
Foundation of Shanxi Province, China (2013011039-3),
the Agricultural Science and Technology Innovation
Program of CAAS, the Earmarked Fund for Modern AgroIndustry
Technology Research System, China (CARS-3-1-
24) and Shanxi Agricultural University Doctoral Scientific
Research Fund, China