|Wintermantel, William - Bill|
Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/23/2004
Publication Date: 12/11/2004
Citation: Grube, R.C., Wintermantel, W.M., Hand, P., Aburomia, R., Pink, D.A., Ryder, E.J. Genetic analysis and mapping of resistance to lettuce dieback: a soilborne disease caused by tombusviruses. Journal of Theoretical and Applied Genetics. 2005. v. 110. p. 259-268. Interpretive Summary: Several cultivated modern and heirloom lettuce varieties and wild relatives of lettuce were screened for susceptibility to the disease lettuce dieback, which is caused by soilborne viruses of the family Tombusviridae. Of the 241 genotypes tested, 76 remained symptom-free and were therefore classified as resistant to dieback. Overall, modern varieties wee as likely to be resistant as heirloom or more primitive germplasm. There were differences between lettuce types, however. Modern iceberg lettuces wee uniformly resistant, while modern romaine lettuces were uniformly susceptible. A single dominant gene was found to be responsible for resistance in both modern iceberg lettuces and in recently released resistant romaine germplasm. Our data revealed that these are likely to be the same gene. We identified the location within the lettuce genome for Tvrl, the gene in iceberg lettuces, and found molecular markers near the gene, that may help breeder's select resistant plants without disease screening.
Technical Abstract: A diverse collection of modern, heirloom and specialty cultivars, Plant Introduction (PI) accessions, and breeding lines of lettuce were screened for susceptibility to lettuce dieback, which is a disease caused by soilborne viruses of the family Tombusviridae. Of the 241 genotypes tested in field experiments, 76 remained symptom-free in infested fields and were therefore classified as resistant to dieback. Overall, resistance genotypes were as prevalent in modern cultivars as in heirloom or primitive germplasm. Within modern germplasm, however, crisphead (iceberg) cultivars were uniformly resistant, while romaine cultivars were uniformly susceptible. Using enzyme-linked immunosorbent assay (ELISA), tombusviruses were detected in leaves of some resistant plants that were grown in infested fields or that were inoculated as seedlings in the growth chamber, suggesting that symptom-free plants are not immune to viral infection. The inheritance of resistance was studied for both 'Salinas', a modern crisphead cultivar, and PI 491224, the progenitor of recently released romaine germplasm with resistance to lettuce dieback. Data showed that resistance was conferred by a dominant allele at a single locus in both genotypes. The tombusvirus resistance locus from 'Salinas', Tvrl, was mapped in an intraspecific L. sativa population to a location that corresponds to linkage group 2 on the consensus map of Lactuca. The largest cluster of resistance genes in lettuce, the Dm1/Dm3 cluster, is found on this linkage group, however, the precise position of Tvrl relative to this cluster has not yet been determined. To our knowledge, Tvrl is the first Tombusvirus resistance gene identified for any plant host.