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Theor Appl Genet. 2007 Oct;115(6):735-46. Epub 2007 Sep 8.

A high-density, integrated genetic linkage map of lettuce (Lactuca spp.).

Truco MJ, Antonise R, Lavelle D, Ochoa O, Kozik A, Witsenboer H, Fort SB, Jeuken MJ, Kesseli RV, Lindhout P, Michelmore RW, Peleman J.

Department of Plant Sciences, University of California, Davis, CA 95616, USA.
An integrated map for lettuce comprising of 2,744 markers was developed from seven intra- and inter-specific mapping populations. A total of 560 markers that segregated in two or more populations were used to align the individual maps. 2,073 AFLP, 152 RFLP, 130 SSR, and 360 RAPD as well as 29 other markers were assigned to nine chromosomal linkage groups that spanned a total of 1,505 cM and ranged from 136 to 238 cM. The maximum interval between markers in the integrated map is 43 cM and the mean interval is 0.7 cM. The majority of markers segregated close to Mendelian expectations in the intra-specific crosses. In the two L. saligna x L. sativa inter-specific crosses, a total of 155 and 116 markers in 13 regions exhibited significant segregation distortion. Data visualization tools were developed to curate, display and query the data. The integrated map provides a framework for mapping ESTs in one core mapping population relative to phenotypes that segregate in other populations. It also provides large numbers of markers for marker assisted selection, candidate gene identification, and studies of genome evolution in the Compositae.
PubMed: 17828385

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Theor Appl Genet. 2008 Nov 13. [Epub ahead of print]

The genomic architecture of disease resistance in lettuce.
McHale LK, Truco MJ, Kozik A, Wroblewski T, Ochoa OE, Lahre KA, Knapp SJ, Michelmore RW.

Genbank and The Compositae Genome Project database, containing over 42,000 lettuce unigenes from Lactuca sativa cv. Salinas and L. serriola accession UC96US23 were mined to identify 702 candidate genes involved in pathogen recognition (RGCs), resistance signal transduction, defense responses, and disease susceptibility. In addition, to identify sequences representing additional sub-families of nucleotide binding site (NBS)-leucine-rich repeat encoding genes; the major classes of resistance genes (R-genes), NBS-encoding sequences were amplified by PCR using degenerate oligonucleotides designed to NBS sub-families specific to the subclass Asteridae, which includes the Compositae family. These products were cloned and sequenced resulting in 18 novel NBS sequences from cv. Salinas and 15 novel NBS sequences from UC96US23. Using a variety of marker technologies, 294 of the 735 candidate disease resistance genes were mapped in our primary mapping population, which consisted of 119 F(7) recombinant inbred lines derived from an interspecific cross between cv. Salinas and UC96US23. Using markers shared across multiple genetic maps, 36 resistance phenotypic loci, including two new loci for resistance to downy mildew and two quantitative trait loci for resistance to anthracnose were positioned onto the reference map to provide a global view of the genomic architecture of disease resistance in lettuce and to identify candidate genes for resistance phenotypes. The majority but not all of the resistance phenotypes were genetically associated with RGCs.
PubMed: 19005638

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Theor Appl Genet. 2011 May 13. [Epub ahead of print]

The inheritance of resistance to Verticillium wilt caused by race 1 isolates of Verticillium dahliae in the lettuce cultivar La Brillante.
Hayes RJ, McHale LK, Vallad GE, Truco MJ, Michelmore RW, Klosterman SJ, Maruthachalam K, Subbarao KV.

Verticillium wilt of lettuce caused by Verticillium dahliae can cause severe economic damage to lettuce producers. Complete resistance to race 1 isolates is available in Lactuca sativa cultivar (cv.) La Brillante and understanding the genetic basis of this resistance will aid development of new resistant cultivars. F(1) and F(2) families from crosses between La Brillante and three iceberg cultivars as well as a recombinant inbred line population derived from L. sativa cv. Salinas 88 La Brillante were evaluated for disease incidence and disease severity in replicated greenhouse and field experiments. One hundred and six molecular markers were used to generate a genetic map from Salinas 88 La Brillante and for detection of quantitative trait loci. Segregation was consistent with a single dominant gene of major effect which we are naming Verticillium resistance 1 (Vr1). The gene described large portions of the phenotypic variance (R (2) = 0.49-0.68) and was mapped to linkage group 9 coincident with an expressed sequence tag marker (QGD8I16.yg.ab1) that has sequence similarity with the Ve gene that confers resistance to V. dahliae race 1 in tomato. The simple inheritance of resistance indicates that breeding procedures designed for single genes will be applicable for developing resistant cultivars. QGD8I16.yg.ab1 is a good candidate for functional analysis and development of markers suitable for marker-assisted selection.
PubMed: 21567237

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