THE SIGNIFICANCE OF CHROMOSOME ASSOCIATION IN AN ADVANCED POPULATION OF TETRAPLOID RYE

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Abstract
Chromosome pairing was studied in a population of tetraploid spring rye (Secale cereale L.) 20 yr after the chromosomes were doubled. Cytogenetically the population was heterogeneous as revealed by significant differences between plants for chiasma frequency, the proportions of regular MI cells [percent of pollen mother cells without univalents] and regular quartets. Compared to early C [n.a.] generations meiotic behavior in the population improved by an increase in quadrivalent frequency, mainly at the expense of trivalents and univalents. Quadrivalent frequency failed to correlate with all other meiotic features; bivalent frequency had significant positive correlations with the features of meiotic regularity including chiasma frequency. The average quadrivalent frequency in the population was considerably less than that of inbred lines. Disomic association dominated the chromosome association pattern in this random mating population; in inbred materials the chromosome association pattern is predominantly tetrasomic. This was supported by a test against the theoretically expected chromosome association pattern in a true autotetraploid.