Nuclear genome size and cytotype analysis in Agave parviflora Torr. subsp flexiflora Gentry (Asparagales, Asparagaceae)

摘要

This study presents the cytogenetic characterization by karyotyping and a determination of the DNA content by flow cytometry of wild adult plants, plants grown from seeds of wild plants and bulbils of Agave parviflora subsp. flexiflora from Bacadehuachi to Nacori Town, Sonora, Mexico. The analyzed plants were diploids (2n = 2x = 60) and had three different structural cytotypes. The cytotype observed in wild adult plants was 44m + 4sm + 10st + 2t, the cytotype found in plants grown from seeds was 48m + 8st + 4t and the cytotype displayed by bulbils was 44m + 2sm + 14st. Agave parviflora subsp. flexiflora showed a bimodal karyotype of 10 large + 50 small chromosomes. All diploid plants had a secondary constriction in one pair of the large chromosomes. 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 all three diploid cytotypes. The pattern of variation among all the types of plants is probably due to rearrangements in the large and small chromosomes of the complement. Differences in the amount of nuclear 2C DNA = 8.20 pg in diploid wild adult plants and 8.21 pg in bulbils were significantly different when compared to 2C DNA = 8.07 pg of diploid plants grown from seeds. The different types of plants displayed 1.7% variation in the 2C DNA content and the mean 2C DNA content was 8.16 pg; 1Cx value = 4.08 pg. The results here reported consist of basic and useful information to set conservation strategies and breeding approaches for Agave parviflora subsp. flexiflora.