Isolation and Characterisation Of MLO Orthologues From Roses

Powdery mildew is a major disease of economic importance in cut and pot roses caused by the obligate biotrophic fungus Podospaera pannosa. As an alternative to conventional resistance breeding strategies utilising single-dominant genes or QTLs, mildew resistance locus O (MLO)-based resistance might offer some advantages. In dicots such as Arabidopsis, pea and tomato, loss-of-function mutations in MLO genes confer high levels of broad-spectrum resistance. This resistance is characterized by durability and recessive inheritance. We have isolated and characterised four MLO homologues from a large rose EST collection isolated from leaves. These genes are phylogenetically closely related to other dicot MLO genes that play a role in powdery mildew susceptibility. Therefore, they are candidates for MLO genes involved in rose powdery mildew interactions. Two of the four isolated genes contain all of the sequence signatures considered to be diagnostic for MLO genes. We mapped all four genes to three linkage groups and conducted first analyses of alternative alleles. Aim of our work is a reverse genetics approach to select rose plants that are homozygous for loss of function in one or more MLO genes.