Improvement of Bremia differential hosts: development of lettuce lines with monogenic resistance

When testing the virulence of Bremia strains, some of the differential host genotypes (HDBs) present problems. This project aimed to replace some of these HDBs with Lactuca sativa-type lines exhibiting monogenic resistance. Lines derived from the F3 generation [CGDM16 x F1 (Cg x LSE18/57)] were selected to replace, on the one hand, the HDB reported as susceptible, Cobham Green (Cg), and, on the other hand, the HDBDm16 lines currently available (L. serriola LSE18/57 or CGDM16, a Cobham Green Dm16). The resistance of Cobham green (Rcg) was counter-selected through tests with the Serr84/99 strain. To replace Ninja (R36 = Dm3+Dm4+Dm11+Rsal-1) and Discovery (R37 = Dm7+Rsal-1), a selection of Rsal1 lines was carried out from the F3 generation (Discovery x Angie) by back-selecting against Dm7 from Discovery and Dm6 from Angie. The selected lines yield results consistent with 14 UPOV strains. The material is currently being finalised between the partners with a view to proposing improved HDBs to the IBEB in 2011.