Mapping morphological genes relative to molecular markers in lettuce (Lactuca sativa L.).

Two F2 populations were generated by crossing morphologically diverse genetic stocks in order to map 10 morphological traits relative to polymerase chain reaction-based molecular markers (RAPDs). Using one segregating population generated from crossing the experimental line, 'dwarf-2', with the butterhead cultivar, 'Saffier', the dwarf phenotype conditioned by the dwf2 locus was mapped using bulked segregation analysis to within 38 cM of the Adh3 locus. Using the second segregating population generated by crossing two experimental lines, 87-25-1M x 87-109M, nine traits [white seed (w), brown seed (br), salmon flower colour (sa), pale yellow flower colour (pa), virescent juvenile leaf colour (vi), plump involucre (pl), yellow seed (y), one of two complementary genes for anthocyanin expression (C or G) and anthocyanin spotting (Rs)] were linked to RAPD loci, but only six of them could be placed on an existing genetic map of lettuce generated by analysis of cv.

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.

The endogenous gibberellins of dwarf mutants of lettuce.

The gibberellin (GA) content of E-1, a tall genotype of early flowering lettuce (Lactuca sativa L.), and of three selected GA-responsive dwarfs, dwf1, dwf2, and dwf2(1), has been determined using (13)C-labeled internal standards and gas chromatographymass spectrometry (GC-MS). In the shoots of the E-1 parent, GA(1), 3-epi-GA(1), GA(3), GA(5), GA(8), GA(19), GA(20), GA(29), and GA(53) were identified by full scan GC-MS and Kovats retention indices.

Phenotypic characterization of lettuce dwarf mutants and their response to applied gibberellins.

Four monogenic, recessive dwarf mutants of lettuce (Lactuca sativa L.), previously isolated from a population induced by ethyl methanesulfonate, were compared with the normal genotype (E-1) for plant height, weight, leaf area, as well as hypocotyl length and root length. These nonallelic dwarfs (dwf1, dwf2, and dwf3) exhibited reduced hypocotyl length, smaller, dark green leaves, and reduced stem length.