Chromosome instability in Coix gigantea Koen. (Maydeae)

Abstract

In Coix gigantea Koen. (2n = 20), six of the plants that survived in the progenies raised from seed collected from Madhya Pradesh showed wide intraplant variation in chromosome number and behaviour. The chromosome number varied from 2n = 7 to 29. Higher configurations involving up to 10 chromosomes were found, though associations of 3 and 4 chromosomes were more prevalent. Univalents were also fairly common. Further, chromosome fragments ranging from one to three per cell were found in several of the cells. Similar variations in chromosome number and fragments were also observed in tapetal cells. Chromosomal associations and chiasma frequency were studied in each of the chromosome classes. Laggards, ranging from one to five were observed at anaphase I and II. Pollen grains were polymorphic and completely sterile, and there was no seed set. The instability was considered as part of the genomic plasticity, coupled with polyploidy, serving to enlarge the cytogenetic diversity in the species. However, it occurs in this population to levels beyond the tolerance limits of the genome affecting the fitness of the individual.Key words: Coix, chromosomal variation.