MONOSOMICS OF AVENA BYZANTINA C. KOCH. I. KARYOTYPE AND CHROMOSOME PAIRING STUDIES

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Abstract
Five monosomic lines resistant to Helminthosporium victoriae were isolated from the variety Victor-grain'' and examined for their karyotypes and chromosome pairing behavior under different controlled environments. Karyotype analyses of the missing chromosomes inlines 19-3-1 andl36-2-l revealed that they were the same and designated as Median - 3(M-3). By the same analysis, monosomic lines 213-3-1 and 473-6-6 were designated as sub-terminal (ST-7) and ST-17 respectively, while the critical chromosome in line 221-7-8 was sub-median (SM) and can be either SM-12 or 13. Three pairs of satellited chromosomes were observed. Meiotic behavior was normal for disomics and monosomics in all monsomes and in nulli-somes of monosome ST-17. Plants nullisomic for ST-7 and SM-12 or 13 showed asynapsis and desynapsis respectively. Perhaps, ST-17 should be assigned to the A genome. Genes on it control the homologous pairing of all the chromosomes, but more specifically of 14 chromosomes from the A genome; where as the gene(s) on the short arm of SM-12 or 13, controls to a greater degree the latter steps in the pairing process of the 28 chromosomes from the C and D genomes to which it belongs. ST-17 has no effect on chromosome pairing.

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