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Experimental results demonstrated clearly that the dominant Ph1 allele of chromosome 5B of wheat affects the homologous pairing of rye chromosomes. A rye-wheat monotelosomic 5BL addition line was produced and used for meiotic studies. Compared with 14-chromosome control plants, the 5BL addition to rye causes an increase in univalents and rod bivalent formation, i.e., a significant reduction of chiasma frequency (11.21 chiasmata per pollen mother cell). The 5BL telosome itself does not associate with any of the rye chromosomes. Thus, the double dosage of 5BL, present in hexaploid or octoploid triticale, could be one of the main causes of pairing failure of the rye genome.Key words: chromosome pairing, Ph1 locus, wheat, rye, rye-wheat addition.

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Wheat chromosome 3B when added to the rye genome causes resistance to powdery mildew of rye (Erysiphe graminis DC. f.sp. secalis Marchal) as the result of the action of the gene Rpm1. Wheat chromosome 3B also carries the gene Got-B3 for glutamate oxaloacetate transaminase. In two independent, vegetatively reproduced additions of 3B to rye, the extra wheat chromosome appeared to have been lost spontaneously, but both genes were still present. The rye chromosome into which the genes had been transferred could not be identified. Chromosome 3R appeared to be morphologically unchanged, no telomeric heterochromatin normally present in any rye chromosome had disappeared, and no wheat B-genome centromeric heterochromatin was observed. At meiosis the chiasma frequency was reduced, resulting in the frequent formation of one univalent pair, and occasionally two univalent pairs. No specific chromosome pair was preferentially involved. The wheat genes could not be transferred to the progeny by selfing nor by reciprocal back-crossing, but gametes without these genes were functional. The plants were semisterile.Key words: wheat chromosome addition, rye, somatic translocation, univalents, mildew resistance.

Hordeum bulbosum chromosomes 1Hb, 4Hb, 6Hb, and 7Hb were identified in five monosomic and one double monosomic H. vulgare – H. bulbosum substitution using 11 isozyme systems. In all substitutions analyzed, diagnostic isozyme bands for H. bulbosum chromosomes were found in the same isozyme systems and zones having diagnostic value for the homoeologous H. vulgare chromosomes. However, bands that are normally diagnostic for the 3Hv region appeared in one 6Hv substitution and in one selfed progeny from another 6Hv substitution.Key words: Hordeum vulgare, Hordeum bulbosum, alien chromosome substitutions, isozymes, chromosome identification, homoeologous relationships.