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Alterations in the basic chromosome numbers as a means of speciation in Labiatae
Author(s) -
Singh T. P.
Publication year - 1995
Publication title -
feddes repertorium
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.24
H-Index - 25
eISSN - 1522-239X
pISSN - 0014-8962
DOI - 10.1002/fedr.19951060112
Subject(s) - biology , ploidy , chromosome number , chromosome , botany , genetics , karyotype , gene
Statistical data revealed that among the cytologically studied species of Labiatae, 41.99% are the true diploids (2χ). Tetraploids (27.38%) are the most common among the euploids observed in the family, while the euploids of higher orders were quite low ranging from 8.12 to 0.10%. The various genera, except a few, were suggested to prefer lower chromosome numbers and ploidy to a limited level. Significantly lower percentage of euploid spp. of odd numbers (10.38%) than those of even numbers (43.51 %) exhibited their preference for the cytologically convenient polyploids. Among the genera cytologically studied, 37.11% were the true diploids where existence of polyploids has not yet been reported. Again among the 28 monotypic genera, 75% are true diploids. On the other hand, genera possessing only higher euploids and no diploids (2χ) are only 14.43 % of the species studied. These data suggested a strong urge among Labiatae herbs to keep both the chromosome number and ploidy level within a cytologically workable limit. The most common primary and secondary base chromosome numbers were found to be 8, 9 and 17, represented by 42.86%, 33.78%, and 20.62% of the species, respectively. It was observed that secondary numbers arose as a result of the combinations between dissimilar primary numbers and the doubling of the same number for producing secondary numbers was rare. Acquiring new genes from the combinations of heterogeneous numbers was considered one of the reasons. The high percentages of two combinations (8 + 7 and 9 + 8) were perhaps due to the prevalence of the primary base numbers χ = 7,8 and 9 among the species. The species possessing only primary base numbers opt for the multiplication of their basic sets for speciation. On the other hand, the latter is achieved by creating new base numbers (by the combinations of dissimilar primary numbers) in the species having only secondary numbers, while both the factors were operative among the species containing both primary and secondary numbers. The synthesis of new base numbers, especially secondary ones, might have effected speciation i n Labiatae and this might be true for other families of plants, it was suggested.