EVALUATION, ENHANCEMENT, GENETICS AND BREEDING OF LETTUCE, SPINACH, AND MELON
Location: Crop Improvement and Protection Research
Title: Development of molecular markers for marker-assisted selection in lettuce (Lactuca sativa).
Submitted to: Acta Horticulture Proceedings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 22, 2009
Publication Date: May 26, 2010
Citation: Simko, I., Pechenick, D.A., Mchale, L.K., Truco, M.J., Ochoa, O.E., Michelmore, R.W., Scheffler, B.E. 2010. Development of molecular markers for marker-assisted selection in lettuce (Lactuca sativa). Acta Horticulture Proceedings, Year 2010, volume 859, pages 401-408.
Interpretive Summary: Since the early 1990’s a previously uncharacterized dieback disease of lettuce has been observed throughout the main producing areas of California and Arizona. Symptoms of the disease include mottling, yellowing, and necrosis of older leaves, and stunting and death of plants. The disease affects romaine and leaf type lettuce often leading to 60% or more crop loss. The disease is caused by two closely related Tombusviruses: Tomato bushy stunt virus (TBSV) and Lettuce necrotic stunt virus (LNSV). We employed a combination of genetic linkage mapping and association mapping to pinpoint location of the single, dominant, resistance gene on chromosome 2 and to develop markers for marker-assisted selection. The newly developed marker showed match with resistant phenotype when tested on a set of 68 lettuce accessions from different horticultural types. The marker was introduced into our lettuce-breeding program.
Lettuce dieback disease is widespread in commercially grown romaine and leaf-type lettuces, but not in iceberg-type cultivars. The disease is caused by two closely related Tombusviruses: Tomato bushy stunt virus (TBSV) and Lettuce necrotic stunt virus (LNSV). A single dominant gene (Tvr1) on chromosomal linkage group 2 has been found to be responsible for the resistance observed in modern iceberg lettuces. A population of 192 F8 RILs developed from crosses between the susceptible romaine cultivar ‘Valmaine’ and the resistant iceberg cultivars ‘Salinas 88’ and ‘Salinas’ was used to pinpoint the position of the resistance gene with EST-based molecular markers. Nine markers closely linked to the Tvr1 gene were subsequently tested for association with resistance in a set of 68 accessions from all horticultural types of lettuce. Sequencing of the marker that matched precisely with resistance revealed the presence of three haplotypes in L. sativa, two of them associated with resistance. High-resolution DNA melting analysis, which allows detection of all three haplotypes in a single analysis, was successfully applied to study the marker-trait association. Results confirmed the usefulness of the marker for marker-assisted selection in all types of cultivated lettuce.