Agronomic comparison of two sets of SSD barley lines differing for the ym4 resistance gene against barley mosaic viruses Jacques Le Gouis, Louis Jestin, Frank Ordon, Denis de Froidmont, Denis Béghin, Jean-Louis Joseph and Fernand Froidmont Agronomie, 19 2 (1999) 125-131 DOI: 10.1051/agro:19990205