1. a Division of Agronomy and Soil Science , University of New England , Armidale , N.S.W. , 2351 , Australia E-mail:
2. b Plant Breeding Institute , The University of Sydney , Narrabri , N.S.W. , 2390 , Australia
3. c Division of Agronomy and Soil Science , University of New England , Armidale , N.S.W. , 2351 , Australia