BLATTNER, FRANK R.*, DIRK FISCHER, NIKOLAI FRIESEN, SVEN POLLNER, AND KONRAD BACHMANN. Department of Taxonomy, Institute of Plant Genetics and Crop Plant Research (IPK), D-06466 Gatersleben, Germany. - Molecular markers in Allium,range of application and taxonomic consequences.
DNA polymorphisms are the markers of choice for the identification and
characterization of plants. They are an integral part of the plant and
they are not subject to environmental modification. There are
relatively reliable generally applicable methods to obtain large
samples of markers from any species of plant. However, each marker
system samples a different fraction of the genome and therefore has a
different resolving power, range of applicability and probability of
homology. Standard measures (e.g., genetic distance) are dependent on
the marker system and on the group under study. Taxa of similar rank
may differ greatly in the variability of molecular marker systems.
This is illustrated with examples from the genus Allium.At the
IPK, a unique living collection of about 300 species of the genus,
many collected at type localities, and a large collection of
accessions of the cultivated species has been studied with a range of
molecular markers: isozymes, RAPDs, ITS-sequences, PCR-RFLPs of
variable regions of chloroplast DNA, and genome in situ hybridization
(GISH). Molecular marker studies have necessitated changes in the
subgeneric classification of the genus but have confirmed the
monophyly of most sections within subgenera. The origin of various
cultivated groups has been elucidated, especially where material of
native origin was available, since garden-grown Alliumare very
liable to genetic introgression. Introgression in nature between
species from various sections has been demonstrated. Microsatellite
primers have been developed for the characterization of individual
accessions of Allium cepaand for molecular genetic mapping
experiments.
Key words: Allium, chloroplast DNA, hybridization, ITS, phylogeny, RAPD