A new cytotype in Coix gigantea
-- P. Gayen, Rajesh Kumar and J.K.S. Sachan

The genus Coix (tribe Maydeae, family Gramineae) is an Asiatic wild relative of maize. Spontaneous occurrence of aneuploidy and structural heterozygosity (Gayen, et al., MNL 68:68, 1994) is not a new event in this genus. Coix gigantea is one of the five species known to be present in this genus. Cytologically this species is well known, with three cytotypes (2n=10, 2n=20 and 2n=40) on the basic number x=5 (Celarier, Cytologia 22:160-183, 1957; Goldblatt, Index to Plant Chromosome Numbers, 1984). Recently, a new stable cytotype with n=6 and 2n=12 has been reported in C. gigantea (Christopher and Jacob, Cytologia 56:265-268, 1991).
In a naturally occurring population of Coix from Talegaon, Pune (Coix-28), we observed chromosome number 2n=18 with more than 95% pollen fertility in all the 23 plants tested. The plants were meiotically checked for chromosome number and meiotic abnormalities, if any. In diakinesis and metaphase I (Fig. 1a), 9 bivalents were clearly observed. There was no meiotic abnormality at any stage of meiosis. Somatic chromosome number was also consistently found to be 2n=18 in all the root tips examined (Fig. 1b). Two pairs of chromosomes had secondary constrictions in mitotic metaphase. In diakinesis (Fig. 1c) two bivalents were attached to the nucleolus. Out of a total of 483 cells studied in diplotene and diakinesis in 23 plants, no additional nucleoli were observed in any cell.

Fig. 1. (a) Nine bivalents in metaphase I; (b) Eighteen chromosomes in somatic metaphase; (c) Nine bivalents in diakinesis with two bivalents attached to the nucleolus.

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