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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