Karyomorphological analysis and cytotypic diversity in natural populations of Costus speciosus Koen. ex Retz.

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• 作者：Debasree Lodh (1)
  Surochita Basu (1)
  
• 关键词：Costus ; Cytotypic diversity ; Karyomorphology ; Chromosomal and genomic versatility ; Reproductive limitations ; Evolutionary mechanism ; Speciation
• 刊名：The Nucleus
• 出版年：2013
• 出版时间：December 2013
• 年：2013
• 卷：56
• 期：3
• 页码：155-162
• 全文大小：597 KB
• 作者单位：Debasree Lodh (1)
  Surochita Basu (1)
  
  1. Department of Botany, Tripura University, Suryamaninagar, 799022, Tripura, India
  
• ISSN：0976-7975

文摘

Costus speciosus Koen. ex Retz. occurs in shady areas, grows wild and exhibit multiple cytotypes in mixed deciduous forests of the east Indian state of Tripura. Chromosome counts of the cytotypes reveal differences in chromosome number i.e. 2n--8, 27, 36, commensurate with the diploid, triploid, tetraploid status. Detailed chromosome analysis of the cytotypes reveal heterogeneity in size, form and number of primary and secondary constricted chromosomes within similar (2 pairs in diploid, 8 pairs in triploid and 3 pairs and 5 pairs of secondary constricted chromosomes in green and red tetraploid respectively), and between dissimilar ploidy level cytotypes. This is suggestive of the incidence of chromosome structural alterations. The latter coupled with polyploidy appears to have played prominent role in evolution of this species. Sporadic occurrence of chromosomal variation i.e. 2X type, encountered in a tetraploid cytotype possibly generates fixable intra-specific variation sustained through vegetative propagation. Karyomorphological studies correlated with morphological studies and cytogenetic background provides insight into role of chromosomal and genomic versatility in diversification of the species. Evolutionary mechanism centre over diploids and mixed occurrence of diploid, triploid and tetraploid in natural populations. However, the tetraploids predominate owing to wide adaptability and better reproductive ability. Diploids and triploids are less represented due to reproductive limitations and multiplication of triploids is limited to vegetative means. Changes in cell size, cell morphology, nuclear-chromatin association and flowering phenology have been attributed to growth feature and adaptive efficiency of the polyploids, especially the tetraploid. Exploitation of resources and dwindling forest cover maximally harm the diploid. Therefore, strategic conservation of the diploid cytotypes that are pivotal for evolution and speciation in the group is needed.