Interspecific Chromosome Homologies in Coix lacryma-jobi L. and C. gigantea Koen. (Maydeae)

Abstract

Interspecific hybrids between Coix lacryma-jobi (2n=20 and its colchicine induced autotetraploid 4n=40) and C. gigantea (2n=20) were obtained and inter- and intragenomic chromosome homologies were studied. The diploid hybrid between C. lacryma jobi (2n=20) and C. gigantea displayed PMCs with chromosome numbers, 2n=19 and 20 even within the same anther. At meiosis, frequently 10 bivalents, and occasionally a chain each of 4 and 3 chromosomes and upto 2 univalents per cell were found. Two bridges with fragments were found at anaphase I. In the triploid hybrid between C. lacryma-jobi (4n) and C. gigantea (2n), a stable chromosome number of 3n=30 was found. Chromosomes mostly paired as trivalents. Higher associations of 4 chromosomes (not more than one per cell) were also found. The occurrence of bivalents in diploid hybrids and trivalents in triploid hybrids, despite the fact that the C. lacryma-jobi genome is in the duplicated state in the latter, indicates strong homologies between the genomes of the two species. However, the genomic divergence is reflected in the occurrence of univalents and formation of higher associations at prophase I and bridges and fragments at anaphase I, which indicate that the two genomes are separated at least by 2 translocations and 2 inversions. Judging from the basic number of 5 in the genus, the two species are considered tetraploids and it is believed that they arose from a common stock through polyploidy, differentiated subsequently through chromosomal repatterning. The occurrence of intragenomic bivalents in C. gigantea was deduced from chromosome associations in triploid hybrids. This shows that the haploid complement of 10 chromosomes of gigantea (as also lacryma-jobi) has two genomes, each of 5 chromosomes, which have partial homologies between them.