EFFECT OF RYE A-CHROMOSOME AND B-CHROMOSOME ON MEIOTIC ASSOCIATION OFHORDEUM-MARINUM SSP GUSSONEANUM (4X) CHROMOSOMES IN INTERGENERIC HYBRIDS

Chromosome association at metaphase I was studied in PMCs of eight H. marinum ssp. gussoneanum (4x) x rye hybrids. Differences in the levels of association separated six hybrids with 2n = 23 including 14 Hordeu m, 7 rye A and 2 rye B chromosomes into two groups of three plants eac h, a ''low association'' group with means of 0.03(III) + 4.43(II) (1.5 5 rings + 2.88 rods) + 5.10(I) and 6.03 chiasmata/cell, and a ''high a ssociation'' group with means of 0.01(IV) + 0.03(III) + 6.40(II) (3.55 rings + 2.85 rods) + 1.13(I) and 10.04 chiasmata/cell. The low number of plants studied prevents a safe estimate of the number of genes inv olved, but the significant difference between groups suggests the pres ence in the rye genome of two major genes, or two genotypes, for contr ol of meiotic chromosome association. In two additional hybrids with 2 n = 25, one of each above-mentioned group, the presence of two extra r ye B chromosomes raised chiasma frequencies by ca 1.5, indicating a pr omoting effect on chromosome association. The level of Hordeum chromos ome association in the ''high association'' group and the observation of up to 7 Hordeum ring bivalents in some cells agree with an autoploi d origin of H. marinum ssp. gussoneanum (4x). Hordeum and rye chromoso mes formed a few heterogenomic bi-and trivalents. Most rye A chromosom es formed univalents, but 2.7 % were included in associations. Rye B c hromosomes generally formed rod bivalents. The use of genome analysis in its traditional sense is discussed.