Populations of C. aquatica (2n=10) are characterized by numerical and structural variations in chromosomes. Translocation hybridity, polysomy and polyploidy are often encountered, sometimes even as intraplant variation (P. N. Rao, 1976, Theoret. Appl. Genet. 48:179-184). In 314 trisomic plants isolated during a cytogenetic analysis of the species, the frequency of occurrence of different types of trisomics, their meiotic behavior and transmission of the trisomic character to the progeny were studied. In 147 of them the extra chromosome remained as univalent while the rest of the chromosomes formed 5 bivalents. 58 primary trisomics, 97 translocation trisomics and 12 tertiary trisomics were found. That all the 5 possible trisomics were encountered is evidenced by the differences in size and extent of heteropycnosis of the extra chromosome. The short chromosome trisomic was as frequent as the trisomic for the long chromosome. In all, trisomy involving the nucleolar chromosome was found in 66 cases. In translocation and tertiary trisomics, the higher associations involved up to 8 chromosomes in the former and 5 chromosomes in the latter. The extra chromosome, when unpaired with other chromosomes, frequently paired within itself forming a ring. All the plants were pollen fertile to some extent, and a majority of them showed reasonable seed set. Transmission frequency of the extra chromosome to the progeny was variable (1.4% to 47.7%) and occurred both through male and female gametes in all the categories of trisomics.
Panuganti N. Rao
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