Complexity in evaluating resistance of barley (Hordeum vulgare L) to 2 pathotypes of BYDV-PAV: allelic variability at the Yd2 gene locus BA Chalhoub, A. Sarrafi and HD Lapierre Agronomie, 15 7-8 (1995) 507 DOI: 10.1051/agro:19950744