Nuclear genome size, ploidy level and endopolyploidy pattern in six species of Opuntia (Cactaceae)
2016
Palomino, G. | Martínez, J. | Méndez, I. | Muñoz-Urías, A. | Cepeda-Cornejo, V. | Pimienta-Barrios, E.
This study describes the haploid chromosome number (n), recombination index (RI), ploidy level and DNA content by DNA flow cytometry of six Opuntia (prickly pear) species from Mexico. Opuntia heliabravoana was diploid (2 n =2 x = 22, x = 11) with RI = 26; O. jonocostle , O. matudae and O. oligacantha were hexaploid (2 n = 6 x = 66) with RI = 74, 71, and 83, respectively; and O. hyptiacantha and O. tomentosa were octoploid (2 n = 8 x = 88) with RI = 99 and 103, respectively. The 2C DNA content was 3.81 pg in Opuntia heliabravoana. For hexaploid species 2C DNA content was : O. jonocostle = 5.84, O. matudae = 5.91 and O. oligacantha = 5.98 pg. The octoploid species O. hyptiacantha and O. tomentosa showed 2C DNA = 7.39 and 7.43 pg, respectively. The 1C x = 1.91 pg for diploid O. heliabravoana was 52% higher than the hexaploid species (mean 1C x = 0.99 pg) and 48% higher than the octoploid species (mean 1C x = 0.93 pg). These results suggest a loss of some DNA sequences after polyploidization in these Opuntia species. All accessions showed endopolyploidy, defined by the presence of nuclear populations of 2, 4 and 8C in cells of the stem parenchyma. The presence of endopolyploidy and polyploidy in prickly pear provide these plants with adaptive advantages in arid and semiarid environments. These results provide useful guidelines to set conservation strategies and breeding approaches for Opuntia species.
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