Nuclear genome size analysis of Agave tequilana Weber

Flow cytometric analysis of DNA content was performed using nuclei isolated from internal basal parts of young leaves in 8 varieties of Agave tequilana. The distributions of nuclear DNA content showed that more than 85% of leaf nuclei were in G(0)/G(1) phase of the cell cycle. Nuclei with DNA content higher than 4C were not detected, indicating the absence of endopolyploidy. A. tequilana varieties lineno, azul listado, azul, moraleno, xiguin, and pata de mula were found to be diploid (2n =2x = 60). These diploid varieties displayed a 2.5% variation in 2C DNA content, which ranged from 8.304 pg for var. lineno to 8.517 pg for var. pata de mula. No statistically significant differences were detected among all diploid varieties considered. This observation demonstrates that Agave belongs to plant taxa with a stable genome size. The mean 1C(x) value (DNA amount of monoploid chromosome set x) calculated for diploid cultivars was equal to 4.202 pg DNA. Triploid var. bermejo (2n = 3x = 90) had 2C = 12.513 pg DNA, i.e. approximately three times the 1C(x) value. 2C DNA amounts of tetraploid (4x) and pentaploid (5x) var. chato were equal to 16.01 pg and 20.11 pg DNA, respectively. These values are also multiples of the 1C(x) value, indicating a relationship between ploidy level and 2C DNA content. Nevertheless, the 1C(x) values calculated for tetraploids and pentaploids were lower than the 1C(x) value determined for diploids. This observation indicates a loss of certain DNA sequences after polyploidization. The results obtained form a basis for the application of flow cytometry in taxonomy, breeding and biotechnology of Agave tequilana.