Nuclear genome size and cytotype analysis in Agave cupreata Trel. & Berger (Agavaceae)

This study is a cytogenetic characterization by karyotyping and a determination of the DNA content by flow cytometry of wild populations of Agave cupreata from the Guerrero State, Mexico. Three of the studied populations were diploids (2n = 2x =60) and one population had tetraploid (2n = 4x = 120), pentaploid (2n = 5x = 150) and hexaploid (2n = 6x = 180) plants. Diploid populations had three different structural cytotypes. One population showed polyploid cytotypes. A. cupre-ata showed a bimodal karyotype of 10 large + 50 small chromosomes in diploids; 20 large + 100 small chromosomes in tetraploids and 25 large + 125 small chromosomes in pentaploids. In diploids, they had secondary constriction in one pair of the large chromosomes and, in the fourth or fifth large homologous chromosome groups, in polyploid plants. The arm ratio, the proportion of different types of large and small chromosomes, the mean of genome length and the asymmetry index of karyotypes clearly varied among diploid and polyploid cytotypes. The pattern of variation among Agave cupreata populations is probably due to rearrangements in the large and small chromosomes of the complement. The diploid populations displayed a 0.63% variation in 2C DNA content. The mean 2C DNA content was 7.88 pg; 1Cx value = 3.94 pg in diploids of Agave cupreata. Tetraploids had 2C = 16.54 pg DNA, i.e. approximately four times the 1Cx value; 2C DNA amounts of pentaploid and hexaploid were equal to 20.42 and 23.92 pg DNA, respectively. These values are also multiples of 1Cx value, indicating a relationship between the ploidy level and the 2C DNA content. The results shown are basic and useful information to develop biotechnology and breeding approaches for Agave cupreata. � 2012 Dipartimento di Biologia Evoluzionistica, Universit� di Firenze