Inheritance of resistance to brown leaf spot disease in gentians

Brown leaf spot caused by Mycochaetophora gentianae is a serious disease on gentian in Japan. Previous studies revealed that Gentiana triflora cultivars were susceptible to M. gentianae and that G. scabra cultivars and their interspecific hybrid cultivars were resistant. We subsequently analyzed the mode of inheritance of resistance to M. gentianae in gentians using several populations derived from crosses between G. scabra and G. triflora. Parental G. scabra and G. triflora lines, F-1 and BC1 plants were inoculated with a conidial suspension and assessed for susceptibility to M. gentianae. All tested F-1 plants were resistant to M. gentianae, indicating that the resistance of G. scabra was inherited dominantly. Segregation ratios in backcross progenies using G. scabra line OK fit the Mendelian ratio of 1:1, showing the involvement of a single dominant locus. These results indicate that the resistance to M. gentianae in G. scabra line OK is controlled by a single dominant allele designated as gentian brown leaf spot resistance (GBLS-1). Finding this allele should facilitate future breeding efforts to develop resistant gentian cultivars.