Functional characterization of fire blight resistance in malus fusca fine mapping, cloning and characterization of fire blight resistance genes from Malus fusca

Fire blight (FB), caused by the gram‐negative bacterium, Erwinia amylovora (Ea), is the most important bacterial disease on pome fruit worldwide including apple. Although the use of antibiotics as a control measure has been successful to some degree, their application is unwanted, forbidden or strictly regulated in many countries due to the threats they pose to the environment. Hence, there is the need for an alternative means of control. Recently, research has shown that genetic resistance can play a vital role in the management of fire blight disease. In different wild species of Malus, several potential sources to FB resistance have been identified and as a result, some wild apple accessions have been utilised as sources of resistance. Consequently, different quantitative trait loci (QTLs) for FB resistance have been identified by Peil et al. 2007; Durel et al. 2009, and Parravicini et al. 2011 and also by Calenge et al. 2005; Khan et al. 2006; in wild apple accessions and cultivated apple (Malus x domestica) respectively. These QTLs exhibit different levels of resistance to the disease. With the aim of identifying, isolating and characterizing resistance to fire blight from the wild species M. fusca, we report here the first results of QTL analysis and marker development for fine mapping. F1 progenies of Malus fusca x Idared were grafted and inoculated in the greenhouse with E. amylovora strain Ea222 in two consecutive years. DArT, SSR and SNP markers were developed and used to establish a genetic map and to perform QTL analysis. A major QTL could be localised on LG10. Two DArT markers were closely linked to the QTL. Four SSR markers linked to resistance were developed using the reference sequence of Golden Delicious for fine mapping the QTL. This research is in progress and additionally a bacterial artificial chromosome (BAC) library of M. fusca will be screened with SSRs flanking the QTL.