Chromosome Pairing in Induced Autotetraploid Chionachne Koenigii (Spreng.) Thw.

SUMMARY

Chionachne koenigii (Spreng.) Thw. (2 n=20), an asiatic relative of maize, occurs in India, Sri Lanka, China, Celebes and Australia. Colchicine induced autotetraploids (4 n=40) had inflorescences, bracts, pollen, stomata and seeds larger than those of diploids. They exhibited fewer quadrivalents (mostly rings and chains) and more bivalents. Other meiotic irregularities commonly associated with autotetraploids were met with. The progenies showed only 4 n=40 over many generations. A few white lethal seedlings occurred only in the progenies of tetraploids in each of c₂ to C⁹ generations. Genetic segregation for albinism as per expectation indicates absence of preferential pairing between any particular two chromosomes of a set of 4 homologues and occurrence of random separation of two-by-two chromosomes during meiosis. The reduction in multivalent frequency was apparently not due to environmental effects or limitation of chiasmata but may be due to restriction of the number of points where pairing is initiated as well as paucity of partner exchanges between the 4 homologues, so that bivalents were formed more frequently. Whether these phenomena are genotypically controlled is not known. The prevalent bivalent pairing, lack of complex quadrivalent types and occurrence of euploid progenies imply that the tetraploid is somewhat stabilized by regulation of its meiosis.