Marker-assisted selection for virus and low temperature tolerance in barley.

The soil-borne barley yellow mosaic virus (BaYMV), the aphid-borne barley yellow dwarf virus (BYDV) and the seed-borne fungus Pyrenophora graminea (leaf stripe) are the most serious diseases for the barley crop in Southern Europe environments, where mildew and other foliar diseases have a relatively small or not significant effect on yields. The development of barley cultivars resistant to the three diseases is thus an urgent objective of barley breeding for the area, in a context of increasing organic farming for cereals. Nevertheless, breeding for multiple diseases encounters several economical and technical problems, and cultivars resistant to the former diseases are not yet available. The bottlenecks of barley breeding for resistance to BYDV are the availability of sources of resistance, mainly based on semi-dominant Yd2 gene, and the labour-intensive inoculation test made with infected aphids. Availability of resistant germplasm and inoculation test are easier for BaYMV and, in relative terms, also for leaf stripe resistance. In this view, two schemes of marker-assisted selection (MAS) have been followed to develop high yielding advanced lines: an assisted pedigree by introducing the two virus resistances, and a "gene pyramiding" scheme to introduce four loci of resistance - two to leaf stripe, and one each to BYDV and BaYMV. STS and SSR markers have been selected for the aim and applied to segregating progenies together with phenotypic selection for agronomic traits.Results of the two MAS processes are here presented, including yield performances of the advanced breeding lines.