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United States Department of Agriculture

Agricultural Research Service

Research Project: Genetic Enhancement of Lettuce, Spinach, Melon, and Related Species

Location: Crop Improvement and Protection Research

Title: Identification of QTLs conferring resistance to downy mildew in legacy cultivars of lettuce

Authors
item Simko, Ivan
item Atallah, Amy
item Ochoa, Oswaldo -
item Antonise, Rudie -
item Galeano, Carlos -
item Truco, Maria -
item Michelmore, Richard -

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 18, 2013
Publication Date: October 7, 2013
Citation: Simko, I., Atallah, A.J., Ochoa, O., Antonise, R., Galeano, C., Truco, M.J., Michelmore, R. 2013. Identification of QTLs conferring resistance to downy mildew in legacy cultivars of lettuce. Scientific Reports. DOI:10.1038/srep02875.

Interpretive Summary: Downy mildew, caused by the biotrophic oomycete Bremia lactucae Regel, is one of the most economically important diseases of cultivated lettuce worldwide. Lettuce can be infected by the pathogen at any developmental stage, from young seedlings to mature plants. Infected plants develop yellow to pale green lesions that eventually become necrotic due to secondary pathogens following the breakdown of the biotrophic interaction. B. lactucae infection leads to lower marketable yield and to higher harvest-related expenses owing to the need to remove infected leaves. Chemical control of downy mildew with metalaxyl-based fungicides is possible, but ineffective against insensitive pathotypes. We developed a population of recombinant inbred lines (RILs) originating from a cross between these two legacy cultivars, constructed a linkage map, and identified two QTLs for resistance on linkage groups 2 (qDM2.1) and 5 (qDM5.1). These QTLs determined resistance under field conditions in California and the Netherlands. The same QTLs determined delayed sporulation at the seedling stage in laboratory experiments. The genes conferring resistance to downy mildew will be introgressed into modern lettuce cultivars using marker-assisted selection.

Technical Abstract: Many cultivars of lettuce (Lactuca sativa L.), the most popular leafy vegetable, are susceptible to downy mildew disease caused by Bremia lactucae. Cultivars Iceberg and Grand Rapids that were released in 18th and 19th century, respectively, have high levels of quantitative resistance to downy mildew. We developed a population of recombinant inbred lines (RILs) originating from a cross between these two legacy cultivars, constructed a linkage map, and identified two QTLs for resistance on linkage groups 2 (qDM2.1) and 5 (qDM5.1). These QTLs determined resistance under field conditions in California and the Netherlands. The same QTLs determined delayed sporulation at the seedling stage in laboratory experiments. Haplotypes conferring elevated resistance at both QTLs originate from cultivar Iceberg. The haplotypes conferring resistance to downy mildew will be introgressed into modern lettuce cultivars using marker-assisted selection.

Last Modified: 7/25/2014
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