|Ryder, Edward - USDA-COLLABORATOR|
Submitted to: Lettuce Workshop and Leafy Vegetable International Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: March 19, 2004
Publication Date: September 1, 2004
Citation: Hayes, R.J., Ryder, E.J. Breeding lettuce cultivars with high resistance to lettuce mosiac virus. Lettuce Workshop and Leafy Vegetable International Conference Proceedings. 2004. No page numbers. Technical Abstract: Lettuce mosaic virus (LMV) is a serious disease of lettuce causing leaf mottling and stunting. Management practices include lettuce-free planting periods, seed indexing, and planting resistant cultivars. Most resistant cultivars carry recessive mo-1e, or mo-1g alleles that reduce virus accumulation, but still exhibit disease symptoms. Highly resistant genotypes that rarely exhibit symptoms have been identified. These include genotypes combining dominant Mi with mo-1e, and the recently identified PI 226514. The objectives of this research were to 1) determine the inheritance of high resistance in PI 226514, 2) determine the relationship between high resistance alleles in PI 226514 and mo-1e, and 3) characterize virus accumulation in susceptible (Sus), resistant (Res), and highly resistant (HRes) genotypes. Seedlings were inoculated with LMV at the 3-4 leaf stage using green peach aphids and observed for symptoms 14-21 days after inoculation (DAI). The numbers of Sus, Res, and HRes (asymptomatic) plants were tabulated and analyzed using chi-square. Six F2 populations were tested: A (226514 tinge leaf (tn) x Salinas, HRes x Sus), B (226514 tn x Salinas 88, HRes x Res), C (226514 green leaf (gr) x Salinas, HRes x Sus), D (226514 gr x Salinas 88, HRes x Res), E (Salinas x [99-1441-2-2 (226514 tn x Salinas)], Sus x HRes), F (Salinas 88 x 99-1441-2-2, R x HR). Twelve plants of each parent plus 01-754-3 (HRes from Mi mo-1e), Vanguard (S), and Vanguard 75 (Res) were tested for LMV with ELISA at 14, 21, 28, and 35 DAI. F2 progeny from A and E fit a 12 Sus: 3 Res: 1 HR segregation ratio, while F2 progeny from B and F fit a 3 Res: 1 HRes ratio. Among F3 families from A, no S plants were found in progeny derived from HRes and R F2 plants, and only 1 HRes F2 parent plant had F3 progeny segregating Res and HRes. Conversely, F3 progeny from Sus F2 plants were all Sus, segregating Sus:Res, or Sus:Res:HRes. F2 progeny from C and D had Sus:Res:HRes and later determined to be Res, and HRes progeny in C and D were likely escapes. Susceptible and R genotypes had positive ELISA results starting at 14 DAI, and increased with each sampling date. No positive ELISA results were obtained for 99-1441-2-2 and 01-754-3. High resistance in PI 226514 tn appears to result from two nuclear recessive genes, one allelic to mo-1e, and another that interacts with mo-1e to result in high resistance. High resistant breeding lines derived from PI 226514 and with the Mi mo-1e gene combination reduced virus accumulation below that of current resistant cultivars. Further research includes identifying PCR based molecular markers linked to HRes genes and developing HRes lettuce cultivars.