Comparison of common cytotypesof Andropogon gerardii(Andropogoneae, Poaceae)

Abstract

Many plant species contain populations with more than one polyploid cytotype, but little is known of the mechanisms maintaining several cytotypes in a population. Andropogon gerardii cytotypes were compared to evaluate different models of autopolyploid cytotype coexistence. The enneaploid (90 chromosome, 9x) cytotype was found to be larger and taller than the hexaploid (60 chromosome, 6x) cytotype. Seed production is significantly more efficient in hexaploids, but seed production per area was not significantly different. The two cytotypes are not exomorphologically separable in the field because of great plasticity in response to environmental variation and wide variation within each cytotype. These data suggest cytotypic variation is maintained by natural selection.

Meiotic Studies in Some Species of <i>Pennisetum</i> Pers. (Poaceae) from the Western Himalayas

“…According to Turesson (1930), the morphological variations are more common in the wild taxa due to their widespread distribution, whereas Stebbins (1950) inferred that differences in morphological characteristics are dependent upon the change of environment, genetic recombination and mutations. In the presently studied species, different intraspecific cytotypes show variation in macro-and microscopic characters, possibly related to the variation in chromosome numbers as reported earlier in Andropogon gerardii (Keeler and Davis 1999), Dactylis (Amirouche and Misset 2007) and Centaurea stoebe (Španiel et al 2008), thus justifying the population-based studies, especially from previously unexplored areas of the Western Himalayas known as an active centre of plant biodiversity. Cytological studies At present, detailed meiotic studies have been carried out for 22 accessions belonging to seven species of the genus Pennisetum.…”

Chromosomal and morphological studies of diploid and polyploid cytotypes of Stevia rebaudiana (Bertoni) Bertoni (Eupatorieae, Asteraceae)

“…Keeler and Davis (1999) noted differences in the size of Andropogon gerardii, a species with hexaploid (2n = 6x = 60) and enneaploid (2n = 9x = 90) cytotypes, in which the biggest individuals had the highest chromosome number. Because of the different plant sizes, the production of seeds per unit area was equivalent for both cytotypes, but was more efficient in hexaploids.…”

“…In Andropogon gerardii, a species with hexaploid (2n = 6x = 60) and enneaploid (2n = 9x = 90) cytotypes, differences in plant size have been observed, and although seed production per unit area is the same in both cytotypes, it is more efficient in hexaploids (Keeler and Davis, 1999). In some species of coffee with different numbers of chromosomes, higher levels of ploidy generally produce larger stomatal cells with a greater number of chloroplasts (Boaventura et al, 1981).…”

Morphometric and Cytological Analysis of Different Cytotypes of <i>Dioscorea deltoidea</i> Wall., 1850 (Dioscoreaceae) from North-Western Indian Himalayas

“…In the presently studied species, different intraspecific cytotypes show variation in macro-and microscopic characters attributed to the variation in chromosome numbers as reported earlier in Andropogon gerardii (Keeler and Davis 1999), Dactylis (Amirouche and Misset 2007) and Centaurea stoebe (Španiel et al 2008). This increase in the ploidy level is correlated with slight gigantism for some of the features such as macro-morphological characters like plant height, number of leaves per plant, and size of leaf or micro-morphological characters as size, density, and index of stomata.…”