Resistance in natural populations of three wild Lactuca species from Israel to highly virulent Californian isolates of Bremia lactucae

Seedlings of 213 accessions representing 9, 14, and 10 Israeli natural populations of the wild Lactuca serriola, L. saligna, and L. aculeata, respectively, were initially screened for their resistance to a pathotype CAVIII isolate of Bremia lactucae. All 60 L. serriola accessions were susceptible while all 83 accessions of L. saligna were resistant. Out of the 69 L. aculeata accessions, 36 (52.2 %) were resistant. From those resistant accessions, 56 L. saligna and 23 L.aculeata accessions were then tested at the seedling stage for their reaction against five highly virulent isolates originating from California and representing the two current major pathotypes and a novel type of B. lactucae; true leaves of adult plants were also tested with two out of these five isolates. Our study supports previous observations that L. saligna is highly resistant to B. lactucae. However, our results provide additional evidence that L. saligna may not be an absolutely non-host plant for B. lactucae at least at a seedling stage, which is in agreement with other recent data for this species. Sixteen (69.6 %) out of the 23 L. aculeata accessions expressed resistance against all isolates tested, even in seedling stage as well as in true leaves of adult plants. This study is probably the first report of detailed screening of resistance to some B. lactucae isolates in natural populations of L. aculeata. These patterns of resistance reactions show that L. aculeata, a species within the primary lettuce gene pool, should be considered as an attractive source of germplasm for resistance breeding of cultivated lettuce (L. sativa).