ABSTRACT
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. 'Calmar' x cv. 'Kordaat'. A tenth trait, golden yellow (gy), remained unlinked. Approximately a third of the RAPD markers analysed segregated in both the 87-25-1M x 87-1090M and 'Calmar' x 'Kordaat' populations. In the genomic regions with multiple segregating loci in common, their relative orders and distances were mostly conserved. In one instance, linkage detected in the present study consolidated two separate groups on the earlier genetic map.
ABSTRACT
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.
ABSTRACT
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. Another mutant, dwf2, allelic with dwf2, exhibited an intermediate phenotype. Epidermal cells on hypocotyls and mature leaves were counted for both normal E-1 and dwf2 plants. The total number of epidermal cells per unit area for hypocotyls and for leaves from these plants was very similar, implying the dwarf's smaller size was due to an inhibition of cell expansion and not due to decreased cell divisions. Both dwarf and normal hypocotyls elongated normally in response to exogenous gibberellin A(3) (GA(3)). In the rosette stage, only E-1 and dwf2 responded similarly to lower concentrations of GA(3), while the other dwarfs required higher concentrations to respond. Hypocotyls of dwf2 and E-1 elongated equally with applied ent-kaurenol, ent-kaurenoic acid, GA(53)-aldehyde, GA(53), GA(19), GA(20), and GA(1) indicating that the biochemical block in dwf2 occurs at a very early step in the GA-biosynthetic pathway.
ABSTRACT
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. Purification by immunoaffinity chromatography selective for 13-hydroxy GAs, was necessary for GA identification. Relative to the parent E-1, the concentrations of GA(1), GA(8), GA(20), and GA(29) in the shoots of dwf2 plants were reduced to about 10% and in shoots of dwf2(1) plants to less than 50%. In dwf1 the levels of GA(1), GA(8), and GA(29) were also reduced to less than 50% of the parent E-1, but the level of GA(20) was fivefold higher than in E-1. Plant height was correlated with the endogenous levels of GA(1) and GA(8).
