The Homoeologous Regions on Long Arms of Group 3 Chromosomes in Wheat and Barley Harbour Major Crown Rot Resistance Loci

Crown rot (CR), caused by various Fusarium species, has become an important cereal disease worldwide and growing resistant varieties is an essential strategy to reduce the $A80 mil annual loss from CR in Australia. To facilitate the breeding of resistant varieties, we have screened 2514 wheat and 1059 barley genotypes and identified several lines with high levels of CR resistance in each crop. Initially focused on two wheat and one barley resistance sources, we have identified major QTL with unprecedented magnitudes. Two wheat QTL explain between 35% (LOD 7.6) and 49% (LOD 10.8) and the barley QTL explains up to 63% (LOD 14.8) of the phenotypic variance. One of the wheat QTL has been further assessed in four validation populations, and the presence of this QTL alone reduces CR severity by 33% on average. Surprisingly, all of the three major CR QTL are located in similar regions on the long arms of the homoeologous group 3 chromosomes, the two wheat QTL on 3BL and the barley QTL on 3HL. The possible homoeologous relationship between the 3BL wheat QTL and the 3HL barley QTL warrants further investigation. Relative rearrangements between 3H and 3B chromosomes are unknown, although the relative distances between the different QTL and the centromeres seem to be different. Compared with the barley QTL, the 3BL wheat QTL seems to be more distally located. However genetic distance can be affected by many factors including the use of different populations, thus the differences in genetic distances between the two different genera may have only limited value. The physical map of wheat chromosome 3B, which was recently made available as the first such resources for wheat, would make such a study much easier. Results will be presented on the detection, genetic analysis and mapping of these new sources of CR resistance.