Indira Gandhi Agricultural University

Karyological studies in Coix and maize

--S. K. Katiyar, G. Chandel, R. Kumar* and J. K. S. Sachan*

*Indian Agricultural Research Institute, New Delhi

The study of karyotype has been realized as an aid to evolutionary significance and taxonomic classification. So far the least effort has been made to study the chromosomes of Coix and their comparison with Zea chromosomes. Therefore, the present investigation was carried out to standardize the cytological technique of mitotic chromosomes, construct the somatic karyotypes of Coix spp. present in the Indian subcontinent and establish chromosomal relationships within and between different species of Coix and with maize.

When 28 distinct collections of Coix from different geographical regions were studied for their somatic chromosome number, it was found that different populations of Indian origin largely fell into two major groups, i.e., (i) those with a chromosome complement of 2n=10 (Coix aquatica) and (ii) those with a chromosome complement of 2n=20 (C. lacryma jobi). Four collections showed deviations from the exact multiple of the basic number; the deviations were later found to be due to the presence of B-chromosomes in variable frequency in C. aquatica. Our results for different genotypes within species further revealed considerable intervarietal differences with respect to total chromosome complement, relative chromosome length, arm ratio, centromeric index and number of satellited chromosomes in Coix. Observations showed one pair of metacentric and four pairs of submetacentric, and four pairs of metacentric and six pairs of submetacentric chromosomes in Coix aquatica and C. lacryma jobi, respectively. Coix aquatica and C. lacryma jobi had two and five pairs of satellited chromosomes, respectively. Somatic karyotype analysis also showed that C. aquatica (2n=20) not only has fewer chromosomes, but also has the smallest genome at metaphase (33.25um long, with a mean chromosome length of 6.64um). The total genomic lengths of C. lacryma jobi and Z. mays were 80.82um and 87.43um, respectively.

Critical comparison of arm ratios and relative chromosome lengths of C. aquatica and C. lacryma jobi along with other morphological characteristics of chromosomes reveals that the genomes in the two species are quite different, however, the genomes of cultivated and wild Coix within C. lacryma jobi have shown a high degree of similarity. Qualitative features of maize karyotypes are relatively uniform. The karyotype of maize is symmetrical, however, it is entirely different from that of Coix. The chromosome number and pairs of chromosomes with secondary constriction are also different, indicating clearcut differences in the genomes of Coix and maize.

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