ABSTRACT
Li Xiande, Researcher in the Institut National de la Recherche Agronomique (INRA), 63-65 Bd de Brandebourg, 94205, Ivry sur Seine, France. He would like to express his sincere thanks to Claude Aubert of INRA for his encouragement, support and help. Thanks are also due to Peter Ho and Jacob Eyferth for their constructive comments on the early version of this article. The author takes full responsibility for the opinions expressed.
