Bdv1: a gene for tolerance to barley yellow dwarf virus in bread wheats

Barley yellow dwarf (BYD) is the most economically important and widespread virus disease of small grain cereals in the world. The North American bread wheat (Triticum aestivum L. emend. Thell.) cultivar Anza and several other International Maize and Wheat improvement Center (CIMMYT) wheats have shown tolerance to BYD. Anza and nine other tolerant wheats were studied to understand the genetic basis of tolerance. The tolerant wheats were intercrossed and crossed with the susceptible wheats |Bobwhite' and/or |Bagula'. Parents and the [F.sub.1], and [F.sub.2] generations were tested during 1990 in the field near Toluca (State of Mexico) with the MAV-Mex serotype of barley yellow dwarf virus. Seventy-two individual [F.sub.2]-plant-derived [F.sub.3] lines from each cross were classified in the field during 1991, together with the parents and [F.sub.1]'s, with the same serotype. The intercrosses among tolerant parents failed to segregate, and the observed distribution of [F.sub.3] lines in the crosses of tolerant and susceptible wheats was in ac. cordance with a monogenic segregation ratio. We conclude that the tolerance of Anza and the other nine wheats is due to a common, partially effective and partially dominant gene, designated as Bdv1. Bdv1 could have originated in the Brazilian cultivar Frontana and should be considered a durable source, because of its deployment in numerous CIMMYT wheats worldwide.