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.