Page Banner

United States Department of Agriculture

Agricultural Research Service

Title: Qtl Analysis of Field Resistance to Lettuce Downy Mildew

Authors
item Pink, D - HORT RES INTL, UK
item Hand, P - HORT RES INTL, UK
item Mcclement, S - HORT RES INTL, UK
item Lynn, J - HORT RES INTL, UK
item Grube, Rebecca
item Schut, J - RZ, THE NETHERLANDS
item Van Der Arend, A J M - NZ, THE NETHERLANDS

Submitted to: Eucarpia Conference on Lettuce and Leafy Vegetables
Publication Type: Proceedings
Publication Acceptance Date: September 20, 2002
Publication Date: N/A

Interpretive Summary: Resistance to downy mildew is a major target in lettuce breeding programmes. Resistant varieties of lettuce have been developed using individual major genes that confer immunity to the pathogen. Historically, rapidly following the release of resistant varieties, races of the downy mildew pathogen that are not controlled by these genes have appeared. Alternative forms of resistance exist which are apparently non-race specific and are likely to be more durable. However, the resistance is often quantitative, or controlled by many genes with small effects, which are difficult to use in breeding programs. We are interested in developing technology to more easily select this quantitatively inherited resistance using molecular markers. We have conducted replicated field trials for downy mildew field resistance using genetic populations segregating for quantitative resistance. The trials took place at sites in the U.K., U.S.A. and NETHERLANDS. Some lines were tested at all sites, to obtain estimates of between-site environmental variation. Phenotypic assessents of disease were made. Mean disease scores were combined with molecular marker information for genetic analysis. The identification of genes for field resistance will be of benefit to breeders who wish to introduce field resistance instead of, or in combination with, major gene resistance.

Technical Abstract: Resistance to downy mildew is a major target in lettuce breeding programmes. Breeders have generally chosen to utilize resistances determined by single dominant genes (Dm genes) since these are easier to handle in a breeding programme. However this resistance has inevitably broken down. Alternative forms of resistance exist which are apparently non-race specific and are likely to be more durable. However the resistance is often quantitative and difficult to select for by phenotypic assessment. We are interested in developing technology to allow marker assisted selection for quantitatively inherited resistance to pests and diseases. We have conducted replicated field trials for downy mildew field resistance using F6 SSD lines from our mapping population of cv. 'Saladin' x cv. 'Iceberg'. The trials took place at sites in the U.K., U.S.A. and The Netherlands. Some SSD lines were tested at all sites, to obtain estimates of between-site environmental variation. Phenotypic assessments of disease were made and subjected to REML analysis. Mean disease scores were combined with molecular marker information for QTL analysis using marker regression. The identification of QTL for field resistance will be of benefit to breeders who wish to introduce field resistance instead of, or in combination with, qualitative Dm gene resistance.

Last Modified: 9/21/2014
Footer Content Back to Top of Page