GAILING, OLIVER*, FRANK R. BLATTNER, AND KONRAD BACHMANN. Department of Taxonomy, Institute of Plant Genetics and Crop Plant Research (IPK), D-06466 Gatersleben, Germany. - Isolation of closely linked markers for the evolutionary reduction of inner microsporangia within the asteracean genus Microseris.
The reduction of inner (adaxial) pollen sacs (microsporangia = MS) is
a common derived character for the three asteracean species
Microseris bigelovii, M. pygmaeaand M. elegans. The
genetic of this reduction was determined in the F6 inbred population
of an interspecific cross between M. douglasiiwith 4 MS and
M. bigelovii with 2 MS by the cosegregation with molecular
markers (AFLPs). One major gene and four modifying genes could be
mapped as quantitative trait loci (QTLs). Three of those modifying
genes had only an effect on the homozygous recessive (2 MS) genotyp of
the major gene. 2 MS were produced only if at least 5 alleles of those
modifying genes determined the 2 MS phenotype. We isolated one plant
with the heterozygous genotype of the major gene and the homoyzgous
recessive 2 MS genotype in all the modifying genes. The 87 offspring
of this plant showed a visible 3:1 segregation in normal fertile
plants with 4 MS and small sterile plants with 2 MS in a more or less
homozygous genetic background. Thus AFLP markers closely linked with
the MS locus can be isolated. In order to test many markers in respect
of their cosegregation with the MS locus, DNA bulks of 10 plants with
the 2 MS phenotype and 10 plants with the 4 MS phenotype will be
screened with about 1000 AFLP primer combinations. After having tested
444 Eco/ Mse primer combinations the MS locus could be mapped in an
intervall of 4 Centimorgan between two flanking markers. Those markers
will be transferred into codominant SCARs (Sequence Characterized
Amplified Regions). Recombinants between those markers can be used to
narrow the F7 population of about 2000 plants that segregate for the
MS locus to about 160 plants for the fine mapping. With the isolation
of markers closely linked to the MS gene (or the gene itself) we have
the tools to explain the evolution of this diagnostic character in
detail.
Key words: anther evolution, evolutionary genetics, Microseris, microsporangia