Resistance to Bremia lactucae in natural populations of Lactuca saligna from some Middle Eastern countries and France

The results of the first detailed screening of a resistance to Bremia lactucae in naturally growing populations of Lactuca saligna are presented here. In total, 146 accessions from 25 populations of L. saligna originating in Israel (N = 136), France (N = 8), Jordan (N = 1) and Turkey (N = 1) were tested at seedling stage for their resistance to 10 highly virulent isolates (races) of B. lactucae from Lactuca sativa (DEG2, Bl:5, Bl:15, Bl:16, Bl:17, Bl:18, Bl:21, Bl:22, Bl:24 and Bl:25). Our study strongly supports the suggestion that L. saligna is indeed generally highly resistant to B. lactucae. However, our results provide evidence that at least at a seedling stage L. saligna may not be a non-host plant for B. lactucae, as was hypothesised for approximately the last 30 years. Some accessions expressed a differential (i.e. race-specific) response, which accords with other recently published data for this Lactuca species. Furthermore, some geographical differences in race-specific resistance were observed, too. Tests performed at an adult-plant stage, however, did not prove race-specificity of the respective accessions. To summarise, what is behind the race-specific character of the responses observed at a seedling stage is still uncertain, as is its comparability with the race-specific resistance of some other Lactuca species such as L. sativa or L. serriola. The presence of plant stage-dependent resistance, governed by a combined effect of different quantitative trait loci in young and adult plants of L. saligna, is discussed.