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ARS Home » Pacific West Area » Salinas, California » Crop Improvement and Protection Research » Research » Publications at this Location » Publication #323293

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

Location: Crop Improvement and Protection Research

Title: Genetics of resistance against lettuce downy mildew

Author
item Parra, Lorena - University Of California
item Ochoa, Oswaldo - University Of California
item Mchale, Leah - The Ohio State University
item Christopoulou, Marilena - University Of California
item Simko, Ivan
item Michelmore, Richard - University Of California

Submitted to: Plant and Animal Genome Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/14/2015
Publication Date: 1/9/2016
Citation: Parra, L., Ochoa, O.E., Mchale, L.K., Christopoulou, M., Simko, I., Michelmore, R. 2016. Genetics of resistance against lettuce downy mildew. Plant and Animal Genome Conference Proceedings. Available: https://pag.confex.com/pag/xxiv/webprogram/Paper19545.html.

Interpretive Summary: Lettuce (Lactuca sativa) is one of the most valuable vegetable crops in the U.S. Downy mildew (DM), caused by Bremia lactucae, is the most important foliar disease of lettuce worldwide, which decreases the quality of the marketable portion of the crop. The use of resistant varieties carrying dominant genes (Dm genes) is the most effective method for controlling this disease; however, pathogen variability has led to the rapid defeat of individual Dm genes. Over 50 Dm genes and resistance factors have been identified and nominated by multiple groups; these have been rationalized to remove redundancies. Many resistance genes have been introgressed from wild species by repeated backcrosses to cultivated lettuce resulting in numerous near-isogenic lines (NILs). Whole genome sequencing of donor and recurrent genotypes and their NILs was used to identify the chromosome segments introgressed from wild species. Combined with genetic information, this has located the candidate chromosomal positions for resistance genes as well as additional introgression segments. In addition, adult plants of some lettuce varieties exhibit field resistance that provides partial resistance to B. lactucae. To determine the genetic basis of field resistance, two populations of recombinant inbred lines originating from crosses between a field resistant cultivar and a susceptible cultivar (Grand Rapids x Salinas and Iceberg x PI491224) have been evaluated for DM severity and genotyped using Genotyping-By-Sequencing for quantitative trait loci (QTL) analysis. Marker-assisted gene pyramiding of multiple Dm genes in combination with QTLs for field resistance provides the opportunity for more durable resistance to B. lactucae.

Technical Abstract: Lettuce (Lactuca sativa) is one of the most valuable vegetable crops in the U.S. Downy mildew (DM), caused by Bremia lactucae, is the most important foliar disease of lettuce worldwide, which decreases the quality of the marketable portion of the crop. The use of resistant varieties carrying dominant genes (Dm genes) is the most effective method for controlling this disease; however, pathogen variability has led to the rapid defeat of individual Dm genes. Over 50 Dm genes and resistance factors have been identified and nominated by multiple groups; these have been rationalized to remove redundancies. Many resistance genes have been introgressed from wild species by repeated backcrosses to cultivated lettuce resulting in numerous near-isogenic lines (NILs). Whole genome sequencing of donor and recurrent genotypes and their NILs was used to identify the chromosome segments introgressed from wild species. Combined with genetic information, this has located the candidate chromosomal positions for resistance genes as well as additional introgression segments. In addition, adult plants of some lettuce varieties exhibit field resistance that provides partial resistance to B. lactucae. To determine the genetic basis of field resistance, two populations of recombinant inbred lines originating from crosses between a field resistant cultivar and a susceptible cultivar (Grand Rapids x Salinas and Iceberg x PI491224) have been evaluated for DM severity and genotyped using Genotyping-By-Sequencing for quantitative trait loci (QTL) analysis. Marker-assisted gene pyramiding of multiple Dm genes in combination with QTLs for field resistance provides the opportunity for more durable resistance to B. lactucae.