2011 Annual Report 1a.Objectives (from AD-416) The objectives of this project are. 1)conduct a QTL analysis of fire blight resistance in the Malus sieversii GMAL4593 mapping population;. 2)identify M. sieversii-specific SNPs to add additional markers to the genetic map of M. sieversii; and. 3)establish plantings of M. sieversii in Washington and West Virginia for the identification of additional sources of fire blight resistance in the future. 1b.Approach (from AD-416) Molecular map for Malus sieversii GMAL4593 mapping population is being developed. Fire blight resistance of population will be determined and used with the molecular map to identify a new genetic locus (QTL) conditioning resistance to fire blight in apple. New plantings of 192 M. sieversii accessions will be established in two distinct environments (Washington and West Virginia) in collaboration with Dr. Kate Evans, Washington State University, for future identification of new sources of fire blight resistance. 3.Progress Report Fire blight of apple is a devastating disease that can kill young trees outright. The limited number of effective management practices available to growers makes it difficult to slow the progress of fire blight epidemics. Although host plant resistance is one of the most effective and sustainable options for managing this disease, sources of fire blight resistance from wild apple species with small, bitter, or astringent fruit have negative effects on fruit quality that are difficult to overcome by conventional breeding methods. Wild Malus sieversii, previously collected by USDA-ARS in Kazakhstan, is an excellent source of disease resistance for apple breeding because of its large and palatable fruit facilitate rapid development of new varieties with superior eating quality. In order to identify genomic regions in M. sieversii associated with resistance to fire blight, over 725 molecular markers were screened in a population (194 individuals) resulting from a cross between 'Royal Gala' apple and M. sieversii PI631981. Replicate plants of the population were accessed for fire blight resistance in the greenhouse (2008) and the field (2010, 2011). Molecular markers associated with fire blight resistance were identified in two genomic regions. This genetic map will now be integrated with the apple genome sequence and expressed sequence tag databases to identify candidate fire blight resistance genes within these genomic regions. After validation, markers for the resistance genes will be made available to U.S. tree fruit breeding programs to facilitate the development of fire blight resistant apple and pear cultivars by marker assisted breeding.