New resistance against downy mildew and lettuce mosaic potyvirus in wild Lactuca spp

New European isolates of B. lactucae and of LMV are able to overcome the disease resistance genes used in commercial varieties. Wild Lactuca spp. constitute a large pool for new genes. Several new re- sistance genes against European B. lactucae isolates were identified in wild Lactuca species and intro- duced in L. sativa lines. The resistance from two L. virosa accessions was efficient against every isolate. The results suggested at least 2 dominant genes in each accession controlled the resistance (2 independent in one accession, two tightly linked in the other one). A complete stable resistance was observed in artificial tests with absence of spores. Therefore, this resistance was assumed to be comparable to Dm gene. The spectra of resistance of lines derived from two L. saligna were similar with resistance from cv. Ninja. This mechanism seems more complex than Dm gene with apparition of late and sparse sporulation on many plants in some segregating populations. This late sporulation was also observed in some commercial varieties and other INRA resistant lines derived from L. serriola. In a large collection of different Lactuca spp., one L. virosa (PIVT1398), was identified as resistant to different European LMV isolates overcoming mo11 or mo12 genes. A study of L. virosa segregating F2 population suggested one major dominant gene for this resistance. Mo3 was proposed to designate this gene. Its expression in heterozygous plant was variable with different isolates. Its expression was consistent with a dominant gene against LMV-0, but incomplete dominant gene against LMV-13 (necrotic phenotype). The introgression of this gene in L. sativa is in progress despite several difficulties. An accumulation in one genotype of several resistance genes against each disease could be a strategy to increase the durability of these new genes