Genome size and karyotype analysis of Agave aktites Gentry (Agavaceae) from Sonora, Mexico

Abstract

Genome size and karyotype structure of 2 wild populations of Agave aktites Gentry from Las Bocas and San Carlos, Sonora, Mexico were determined. Nuclear DNA content of leaf tissue was measured through flow cytometry, and chromosomes were observed in mitotic metaphase of root tips. All individual plants studied in both populations are diploids (2n= 2x= 60). The mean 2C nuclear DNA content was 8.404 pg; 1Cx= 4 120 million of base pairs. All plants of the 2 populations of A. aktites show a bimodal karyotype consisting of 10 large + 50 small chromosomes and corresponded to 46m+6st+8t; they also have a pair of large telocentric chromosomes with secondary constriction. The arm ratio was different in pair numbers 7, 8, 14 and 16 of the small chromosome group and there are morphological differences in these chromosomes between the 2 populations studied. These chromosome rearrangements may be due to spontaneous heterozygous chromosomal exchange and they are evidence that the genome of A. aktites is in active process of differentiation among populations that could lead to speciation. These analyses are fundamental for understanding the intraspecific genetic diversity in A. aktites and establishing in situ and ex situ conservation strategies for this species.