The genus Coix is an Asiatic member of the tribe Maydeae of the grass family. C. aquatica Roxb. and C. gigantea Koen. are two of the three conventionally recognized species under the genus, though the morphological distinction between them seemed arbitrary.Watt (1904) considered the two as gigantea-aquatica complex and treated C. aqutica as a variety of C.gigantea, the latter applied to plants met with chiefly on the mountainous regions while the former to plants occurring on the banks of rivers and margins of ponds, marshes etc. Mimeur (1951) and Bor (1960) recongnized them as two separate species, however, Bor pointed out that the only reliable feature separating the two species by the habitat and that it should not be difficult to devise experiments to show whether C. aquatica is really a distinct species or only an ecotype of C. gigantea. Studies of chromosome numbers, karyomorphology and meiotic behavi our in C. aquatica (2n=10) and C. gigantea (2n=20, 40) (see Reeves and Mangelsdorf 1935, Mangelsdorf and Reeves 1939, Darlington and Janaki Ammal 1945, Venkateswarlu and Chaganti 1955, 1973, Koul 1970, Nirodi 1955, Venkateswarlu and Rao 1975, 1976, Rao 1973, 1976, Sapre et al. 1985 showed that the two are good and valid species. While pachytene chromosome morphology did not reveal any similar chromosomes in the complements of the two species (Venkateswarlu et al. 1976), chromosome associations in spontaneous hybrids indicated some homologies between them (Sapre et al. 1985). In order to have a clear understanding of the inter and intragenomic homologies and species divergence, interspecific hybrids of C. aquatica and C. gigantea were obtained artificially and studied. The results are reported here.
Materials and methodsThe two species are monoecious and cross pollinated in nature. Therefore, for crossing, two pot grown plants of both the species, were kept in one muslin bag and, after flowering commenced, male portions of the spike were removed once in 2 days in C. aquatica so that the seeds formed on it could be crossed with the pollen parent C. gigantea. Aceto-carmine squash preparations were used for cytological analyses.C. aquatica has thin culms, narrow leaves, glabrous leaf sheaths and pyriform fruit cases (ripe capsular spathes enclosing the pistillate spikelet) the latter with mouth obliquely cut and drawn out into a beak. In contrast, C. gigantea has broader leaves and thicker culms; lower leaf sheaths beset with reddish glands each with a bristle like hair (as found by Nirodi 1955) and fruit cases pyriform with a gaping mouth, flat on one side with an inconspicuous transverse constiriction and a prominent vertical fold. In a cytological analysis of C. gigantea, two cytological races, one 2n=20 and the other with 2n=18 forming 10 and 9 bivalents respectively were isolated (Rao 1973). Both the races were used for crossing with C. aquatica. C. aquatica and C. gigantea are referred as Ca and Cg in the text.
