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

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.

Differentiation of nearly identical germplasm accessions by a combination of molecular and morphologic analyses.

Polymerase chain reaction (PCR) based random amplified polymorphic DNA (RAPD) markers were used to study the extent of redundancy (duplication of genetic materials) within a genetic resources collection. Nine nearly phenotypically and identical accessions of butterhead lettuce (Lactuca sativa L.) were assayed for their genetic identities. A nonuniform, heterogeneous butterhead line and a crisphead cultivar were added for population comparison. PCR amplification using 13 oligonucleotide primers generated 93 polymorphic bands. The percentage of segregating bands was used to determine within-line variation; values ranged from 0.0 to 12.0%, except for the nonuniform line at 22.6%. Between-line similarity was measured using similarity coefficients and ranged from 0.919 to 0.985. The relationship between the crisphead accession and a composite of all butterhead accessions was 0.84. Selfed progeny of each line were measured for morphological uniformity. The variation obtained from these biological data was compared with variation detected at the DNA level and each was positively correlated. Results demonstrate that RAPD analyses may serve as a major source of information for separation of closely related accessions, especially when integrated with phenotypic measures.