New Wild Lactuca Genetic Resources with Resistance Against Bremia lactucae

Abstract

A total of 1027 genotypes of wild Lactuca spp. (L. serriola, L. saligna, and L. aculeata), originating from Israel, Jordan, East Turkey, Armenia, Kazakhstan, China, and various other countries in Europe were screened for resistance to the lettuce downy mildew (Bremia lactucae Regel). The genotypes of L. serriola (N = 962); L. saligna (N = 43); and L. aculeata (N = 22) were tested at the seedling stage with two isolates of B. lactucae (race Bl-21 and Isr-74) isolated from cultivated lettuce in Italy and Israel, respectively. Altogether, the isolates possess virulence against 17 out of 20 Dm genes/R-factors composing the established differential set of lettuce lines/varieties. They could therefore be used for preliminary detection of the presence of new resistance factors. A total of 83 and three genotypes of L. serriola and L. saligna, respectively, were resistant to infection by each of the two isolates alone as well as to the infection by a mix of the two isolates. These genotypes probably carry previously unknown resistance, and therefore could be suitable for exploitation by breeders and further detailed research. The wild progenitor of lettuce, L. serriola, and related species harbor significant untapped genetic resources for lettuce improvement.

Phenotypic and histological expression of different genetic backgrounds in interactions between lettuce, wild Lactuca spp., L. sativa × L. serriola hybrids and Bremia lactucae

“…In this study, all resistant accessions were characterized by some degree of haustorial formation, at a level significantly different from the compatible controls (Table 5), the exception again being L. saligna, where development of haustoria was not recorded. The existence of qualitative as well as quantitative resistance in L. saligna is expected (Jeuken and Lindhout, 2002;Lebeda et al, 2002;Beharav et al, 2006).…”

“…The latter approach would be particularly effective if the different Rfactors determined different resistance mechanisms. The exploitation and utilization in lettuce breeding of wild Lactuca germplasm offers a source of resistance genes which may determine different resistance mechanisms Beharav et al, 2006).…”

“…Lactuca saligna is variable in terms of mechanisms of resistance to B. lactucae Beharav et al, 2006). Lebeda and Reinink (1994) reported for the first time a very low frequency of HR in L. saligna (CGN 05271) inoculated with race NL5.…”

Rationalization of genes for resistance to Bremia lactucae in lettuce

“…In addition, many other sources of resistance have been identified in germplasm screens but have yet to be characterized genetically (e.g. Bonnier et al 1994;Lebeda and Zinkernagel 2003;Beharav et al 2006). As more resistance genes are characterized from these and other sources, it is likely that several hundred genes with efficacy against B. lactucae will be identified that will require a coordinated, rational nomination process.…”

Evolution and Genetic Population Structure of Prickly Lettuce (Lactuca serriola) and Its RGC2 Resistance Gene Cluster

“…The wild and cultivated lettuces are sexually compatible and lettuce geneticists and breeders have made extensive use of this wild species, mainly for disease resistance, including resistance against downy mildew caused by Bremia lactucae (Crute 1992;Lebeda et al 2002;Beharav et al 2006). At least eight functional resistance genes (R-genes) with different specificities against downy mildew have been mapped to the RGC2 cluster, the major cluster of R-genes in lettuce (Farrara et al 1987;Kesseli et al 1994).…”