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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 F1 and F2 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 F2‐plant‐derived F3 lines from each cross were classified in the field during 1991, together with the parents and F1's, with the same serotype. The intercrosses among tolerant parents failed to segregate, and the observed distribution of F3 lines in the crosses of tolerant and susceptible wheats was in accordance 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.

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. 1998. Yield, quality and stress tolerance of barley mixtures in central Alberta. Can. J. Plant Sci. 78: [429][430][431][432][433][434][435][436]. Intraspecific mixtures may be a means of enhancing the genetic variability of modern crops while retaining the advantages of yield, quality, and stress tolerance of modern cultivars. Two-and three-way barley (Hordeum vulgare L.) mixtures of the cultivars Abee, Noble, Tukwa and Virden, were studied at Botha, Lacombe and Olds, Alberta, from 1992 to 1994. Treatments consisted of the four cultivars as monocrops and in 6 two-way and 3 three-way mixtures grown at a seeding rate of 250 seeds m -2 . Tukwa as a monocrop had the highest rank and best stability for grain yield of all the treatments. Grain yields of the mixtures usually fell between the yields of the respective monocrops and were often better than the weighted mean yield of the monocrops indicating that many mixtures were more effective at using resources than the monocrops. Of the mixtures, Tukwa:Noble, Tukwa:Abee:Virden and Noble:Virden had the best rankings and stability for grain yield. Test weights, kernel weights, percent thins, lodging, disease incidence and protein content of the mixtures were intermediate to those of the monocrops. Mixtures containing the two-rowed cultivar Abee had higher test weight and protein content than mixtures composed of only sixrowed cultivars. Lodging and disease ratings were lower for the mixtures composed of only six-rowed cultivars than those with Abee. In these intraspecific barley mixtures, Virden was often the most competitive cultivar while Tukwa was the least. Competitive ability was not associated with yield potential, tillering, or row-type. Le poids spécifique, le poids des grains, le pourcentage de grains minces, les cotes de gravité de la verse et des maladies et la teneur en protéine dans les mélanges étaient à mi-chemin entre ceux des cultures pures correspondantes. Les mélanges comportant le cultivar à deux rangs Abee produisaient un grain de poids spécifique et de teneur en protéine supérieurs à celui des mélanges formés exclusivement d'orge à six rangs. En revanche, ces derniers affichaient des cotes de gravité plus basses pour la verse et pour les maladies. Dans ces mélanges intraspécifiques, Virden était souvent le cultivar le plus et Tukwa le moins compétitif. La compéti-tivité n'était cependant pas associée avec les potentialités de rendement ni avec le tallage ou le nombre de rangs de grain de l'épi.

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