Genetic analysis of factors for resistance to downy mildew ( <i>Bremia lactucae</i> ) in species of lettuce ( <i>Lactuca sativa</i> and <i>L. serriola</i> )

Abstract

Simultaneous genetic analysis of resistance in species of lettuce (Lactuca sativa and L. serriola) and a virulence in Bremia lactucae were made to characterize the genetic basis of resistance to downy mildew in 11 host cultivars and accessions. Four new downy mildew resistance genes (Dm13, Dm14, Dm15 and Dm16) were characterized. Other resistance phenotypes were conditioned by combinations of these or previously described Dm genes. New resistance genes, Dm 16 (from LSE/18), Dm14 (from Gelber Winterkonig) and Dm15 (from PIVT 1309), mapped to Dm linkage group I (Dm1, Dm2, Dm3 and Dm6) while Dm13 from Pennlake segregated independently of the three previously characterized linkage groups and therefore belongs to a fourth linkage group. Characterization of new resistance genes requires simultaneous consideration of host and pathogen genetics.