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United States Department of Agriculture

Agricultural Research Service

Research Project: Evaluation, Enhancement, Genetics and Breeding of Lettuce, Spinach, and Melon

Location: Crop Improvement and Protection Research

Title: Mapping dominant negative mutation for triforine sensitivity in lettuce and its use as a selectable marker for detecting hybrids.

Authors
item Simko, Ivan
item Hayes, Ryan
item Truco, Maria -
item Michelmore, Richard -

Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 27, 2011
Publication Date: October 22, 2011
Citation: Simko, I., Hayes, R.J., Truco, M.J., Michelmore, R.W. 2011. Mapping dominant negative mutation for triforine sensitivity in lettuce and its use as a selectable marker for detecting hybrids. Euphytica. 182(2):157-166.

Interpretive Summary: Lettuce (Lactuca sativa L.) is a highly inbred species from the family of Compositae (Asteraceae) with a compound autogamous floral structure that makes manual cross-hybridization less than 100% reliable. The current method of cross-pollination that is most frequently used in breeding programs involves washing the recipient flowers to remove the pollen followed by transfer of the pollen from donor flowers. However, results of emasculation can be quite variable and self-fertilization may occur. Therefore, accurate testing of F1 hybrids is necessary to eliminate offspring resulting from self-pollination. In this study we investigate the use of triforine as a selectable marker for detecting hybrids. We mapped a single recessive gene (tr) that confers insensitivity of lettuce to triforine to linkage group 1 of the integrated genetic map of lettuce. The reaction to triforine can be used as a marker for detecting hybrids originating from a cross between phenotypically similar parents with different responses to triforine treatment. It also provides an indication of genotypes for which applications of triforine-containing fungicides are inappropriate.

Technical Abstract: Some lettuce cultivars are highly sensitive to triforine, an inhibitor of sterol biosynthesis found in some commercial systemic fungicides. First symptoms of a sensitive reaction are usually observed within 24 to 48 hours after treatment and include severe wilting, necrosis and rapid plant death. We mapped a single recessive gene (tr) that confers insensitivity of lettuce to triforine to linkage group 1 of the integrated genetic map of lettuce. The occurrence of insensitivity is not uniform across horticultural types of lettuce. While over 80% of green-romaine lettuce cultivars tested were sensitive, most cultivars of all other lettuce types were insensitive to triforine. All accessions of wild Lactuca spp. were insensitive to triforine. Allelism tests using F1 and F2 progeny revealed that sensitive cultivars of all horticultural types likely carry the same Tr gene. The dominant allele for sensitivity found in cultivated lettuce probably had a monophyletic origin. The reaction to triforine can be used as a marker for detecting hybrids originating from a cross between phenotypically similar parents with different responses to triforine treatment. It also provides an indication of genotypes for which applications of triforine-containing fungicides are inappropriate.

Last Modified: 8/1/2014
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