DNA markers for newly discovered genetic loci Phr3 and Phr4 , conferring resistance to white rust in Chrysanthemum morifolium

Chrysanthemum white rust, caused by Puccinia horiana, poses a serious threat to chrysanthemum (Chrysanthemum morifolium) production. The development of resistant cultivars is of great interest to breeders. Owing to the polyploid nature and complex inheritance patterns of chrysanthemum, efficiently utilising resistance genes in breeding programmes has been challenging. However, in recent years, DNA markers linked to resistance have been developed. Although multiple resistance sources have already been identified in chrysanthemum, this study aimed to discover additional resistance genes. We identified two previously unknown resistance genetic loci, Phr3 and Phr4. The genetic locus Phr3 conferred resistance to a relatively broad range of races. Although the resistance spectrum conferred by Phr4 was limited, it represents the resistance found in the important Japanese standard-type cultivar ‘Jimba’ and is expected to be useful in the development of progeny cultivars. We developed DNA markers linked to Phr3 and Phr4, enabling marker-assisted selection and gene pyramiding for rust resistance.