Abstract
Ten Citrus (Linnaeus, 1753) species of North-East India have been karyo-morphologically analysed. All studied species had 2n=18 chromosomes without any evidence of numerical variation. All the chromosomes were found to be of metacentric and sub-metacentric in all the species; the morphology of the chromosomes showing size difference only. Symmetrical karyotype which does not have much difference in the ratio of longest to shortest chromosome in all the species was observed. Three species, Citrus grandis (Osbeck, 1757), Citrus reticulata (Blanco, 1837) and Citrus medica (Linnaeus, 1753) are identified as true basic species from asymmetry studies of karyotypes as they reflect on the primitive nature of their genomes. Citrus indica (Tanaka, 1937)occupies a special taxonomic position within the genus Citrus as a progenitor for other cultivated species.
Highlights
The genus Citrus is economically very important and is known for its juice and pulp throughout the world
The data related to chromosome complements/karyotypes have been presented in Table 2 and illustrated in Fig. 1 and 2 and it is amply clear that among the 10 species of Citrus presently studied, two species namely C. jambhiri Lushington, 1910 and C. limon Linnaeus, 1753 were characteristic in having exclusively sub-metacentric chromosomes in the chromosomes complements
It was more intriguing to record that two metacentric pairs were observed in C. reticulata and C. latipes as metacentrics while one pair of metacentric were recorded in remaining 6 species
Summary
The genus Citrus is economically very important and is known for its juice and pulp throughout the world. In India, there are 30 species of Citrus (Singh and Chadha 1993) of which at least nine species are available throughout India, while 17 species are confined to North-Eastern India. It is reported that nine species are found in the southern region of India, six species in the north-western India while a single species is observed in central region of the country (Singh and Chadha 1993). The north-east region of India is known for its rich diversity in Citrus germplasm, reflected in 17 species, 52 cultivars and 7 probable natural hybrids which are found in the region (Bhattacharya and Dutta 1956). Citrus plants growing in deep forests undisturbed by biotic factors have been reported from the region, bestowing this area with a special status of “treasure house” of Citrus germplasm and highlighted the lack of our knowledge about the same (Sharma et al 2004)
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