CYTOGENETICS OF EXPERIMENTAL HYBRIDS WITHIN THE ACHILLEA-MILLEFOLIUM POLYPLOID COMPLEX (YARROW)

Successful crossing experiments between the tetraploids Achillea ceret anica-4x, A, collina, A. distans subsp. styriaca, A. pratensis, and th e octoploid A. monticola, all from the A. millefolium agg. (Compositae ), are reported. Chromosomes were studied in 514 out of 883 hybrid pla nts obtained from 13 crossings. F-1-offspring from tetraploid parents was generally tetraploid, but some combinations produced up to 30% of aneuploid, near-pentaploid, and even hexaploid F-1-individuals. A back cross and a F-2-progeny consisted of normal tetraploids. A reciprocal F-1-combination involving a tetraploid parent with one B-chromosome sh owed an increase of B-chromosomes in the F-1, when the male transmitte d the B (69.2%), and a decrease, when the female had the B (33.3%). Ma inly hexaploid offspring resulted from a reciprocal F-1-cross between tetraploid and octoploid parents.