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ARS Home » Pacific West Area » Salinas, California » Crop Improvement and Protection Research » Research » Publications at this Location » Publication #314762

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

Location: Crop Improvement and Protection Research

Title: Resistance to downy mildew in lettuce ‘La Brillante’ is conferred by dm50 gene and multiple QTL

Author
item Simko, Ivan
item Ochoa, Oswaldo - University Of California
item Pel, Mathieu - Enza Zaden
item Tsuchida, Cayla - University Of California
item Forcada, Carolina - University Of California
item Hayes, Ryan
item Truco, Maria - University Of California
item Antonise, Rudie - Keygene Nv
item Galeano, Carlos - University Of California
item Michelmore, Richard - University Of California

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/23/2015
Publication Date: 9/15/2015
Citation: Simko, I., Ochoa, O.E., Pel, M.A., Tsuchida, C., Forcada, C.F., Hayes, R.J., Truco, M.J., Antonise, R., Galeano, C.H., Michelmore, R.W. 2015. Resistance to downy mildew in lettuce ‘La Brillante’ is conferred by dm50 gene and multiple QTL. Phytopathology. 105:1220-1228.

Interpretive Summary: Cultivated lettuce (Lactuca sativa L.) is susceptible to downy mildew disease. This disease can infect lettuce plants at any developmental stage, causing yellow to pale green lesions that eventually become necrotic. Severe downy mildew infection results in loss of yield. We previously determined that Batavia type lettuce cultivar La Brillante has a high level of field resistance to the disease in California. Testing of a mapping population developed from a cross between the cv. Salinas 88 and cv. La Brillante in multiple field and laboratory experiments revealed at least five loci conferred resistance in ‘La Brillante’. The presence of a new dominant resistance gene (designated Dm50) that confers complete resistance to specific isolates was detected in laboratory tests of seedlings inoculated with multiple diverse isolates. This Dm gene is, however, ineffective against the isolates of B. lactucae prevalent in the field in California and the Netherlands. A quantitative trait locus (QTL) located at the Dm50 chromosomal region was detected when the amount of disease was evaluated a month before harvest maturity. Four additional QTLs for resistance to B. lactucae were identified. Markers linked to significant QTLs will facilitate introduction of these resistance loci into commercial cultivars of lettuce.

Technical Abstract: Many cultivars of lettuce (Lactuca sativa L.) are susceptible to downy mildew, a nearly globally ubiquitous disease caused by Bremia lactucae. We previously determined that Batavia type cultivar La Brillante has a high level of field resistance to the disease in California. Testing of a mapping population developed from a cross between the cv. Salinas 88 and cv. La Brillante in multiple field and laboratory experiments revealed at least five loci conferred resistance in ‘La Brillante’. The presence of a new dominant resistance gene (designated Dm50) that confers complete resistance to specific isolates was detected in laboratory tests of seedlings inoculated with multiple diverse isolates. Dm50 is located in the major resistance cluster on linkage group 2 that contains at least eight major, dominant Dm genes conferring resistance to downy mildew. This Dm gene is, however, ineffective against the isolates of B. lactucae prevalent in the field in California and the Netherlands. A quantitative trait locus (QTL) located at the Dm50 chromosomal region (qDM2.2) was detected, though, when the amount of disease was evaluated a month before plants reached harvest maturity. Four additional QTLs for resistance to B. lactucae were identified on linkage groups 4 (qDM4.1 and qDM4.2), 7 (qDM7.1), and 9 (qDM9.2).