SEIJO Jose Guillermo
congresos y reuniones científicas
Origin of polyploids in the Rhyzomatosae and Caulorhizae sections of Arachis (Leguminosae).
LAVIA, G.; A. ORTIZ; SEIJO, JG
Simposio; Generation Challenge Programme workshop Reference sets of food crop germplam for international collaboration.; 2008
Generation Challenge Program
mmm ORIGIN OF POLYPLOIDS IN THE RHIZOMATOSAE AND CAULORRHIZAE SECTIONS OF ARACHIS (LEGUMINOSAE) Lavia G.I., A.M. Ortiz and J.G. Seijo Section Rhizomatosae includes one diploid (A. burkartii) and three tetraploid species (A. glabrata, A. pseudovillosa and A. nitida), while section Caulorrhizae includes two species, A. pintoi (with two cytotypes 2x and 3x) and A. repens (2x); all with x=10. Arachis glabrata and A. pintoi produce forage of high quality and several commercial cultivars have been released. In an attempt to test the genetic origin of the polyploids in these sections, classical and molecular cytogenetic studies have been carried out. Meiotic analysis in A. glabrata revealed chromosome association which ranged from 20 II to 4II + 8IV suggesting an autotetraploid origin, although populations may have different diploidization degrees. Chromosome pairing in the 3x A. pintoi also showed a high proportion of trivalents, indicating that it may be an autotriploid clone. Within section Rhizomatosae, the tetraploids presented centromeric DAPI+ heterochromatic bands in the whole complement, two (A. glabrata) or three (A. nitida) pairs of 45S rDNA and, two pairs of 5S rDNA loci (all in different chromosomes). However, the diploid A. burkartii showed bands in all (except one) pair of chromosomes, four pairs of 45S rDNA loci (two synthenic) and, one pair of 5S rDNA loci. The later co-localize with one pair of 45S rDNA loci. These results showed that A. burkartii is not a good candidate as a genome donor of the tetraploid species, and that the autotetraploid nature of the species may be arguable. Concerning Caulorrhizae section, the classical cytological analysis has demonstrated that the morphology of 30 chromosomes of the triploid A. pintoi reflect three identical chromosome sets. Physical mapping of rDNA genes has revealed one cluster of 45S rDNA and two of 5S rDNA per haploid complement. The number, position and size of the ribosomal clusters in each complement of the triploid were identical to those observed in the diploid cytotype. Therefore, the bulk of evidence demonstrated that the 3x cytotype may have originated by autopolyploidy.