Sexual diploid and apomictic tetraploid races in Thrasya petrosa

ACUÑA, CARLOS A.; MARTÍNEZ, ERIC J.; QUARIN, CAMILO L.

AUSTRALIAN JOURNAL OF BOTANY

CSIRO PUBLISHING

Lugar: Collingwood, Vic. 3066 Australia; Año: 2005 vol. 53 p. 479 - 484

0067-1924

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:EN-GB;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Thrasya petrosa (Trin.) Chase is the most widespread species of a grass genus indigenous to the New World. Genetic systems in diploid (2n = 2x = 20) and tetraploid (2n = 4x = 40) races of T. petrosa were investigated. The diploid race exhibited embryological development typical of sexual reproduction, but failed to produce seed due to self-incompatibility, while the tetraploid showed embryological pathways characteristic of facultative apomixis. Consequently some ovules showed a normal meiotic embryo sac; others had one to several aposporous sacs, and finally there were ovules bearing one or more aposporous sacs beside the meiotic one. An uniform progeny test assisted by molecular markers confirmed that the main reproductive mode for the tetraploid race was apomixis, despite some sexual reproductive structures observed by cytoembryological analyses. The chromosome pairing patterns at meiosis suggested that autoploidy was the genetic origin of the tetraploid races of T. petrosa. In addition, the close relationship between Thrasya Kunth and Paspalum L. previously supported by phylogenetic analyses is further sustained by the particular genetic system shared by both genera. The system involves co-specific sexual self-incompatible diploids and apomictic, pseudogamous, and self-compatible polyploids.