CHROMOSOME EVOLUTION IN CERTAIN GENERA OF BRASSICEAE

Chromosome studies were carried out on 28 species and varieties belonging to 18 genera of Brassiceae after evolving special pretreatment techniques. In general the tribe is characterised by a graded karyotype with medium to short chromosomes and constrictions mainly median to submedian in position. In the subtribe Brassicinae, eight genera with chromosomes ranging from 14 to 36 in the somatic nuclei have been studied. Different base numbers have been observed and the same genus often shows more than one number. Intraspecific variations are on record. Four genera under the subtribe Raphaninae investigated have chromosome numbers ranging from 2n=16 to 60. In the subtribe Cakilinae, 2n=16 chromosomes are present in two species of a genus investigated. In the subtribes Vellinae and Moricandiinae 2n=16, 28 and 36 chromosomes have been observed. In the tribe Brassiceae, various base numbers namely, 6, 7, 9 and 10 have been observed but it is difficult to determine which one is more primitive. In evolution, polyploidy has been encountered in many cases. Aneuploidy is even more frequent. Gene mutation has been responsible for stabilisation and diversification of genera. The role of structural alteration of chromosomes is comparatively less in the diversification of major taxonomic units. © 1979, Japan Mendel Society, International Society of Cytology. All rights reserved.