Transferring genes blocked by apomictic reproduction in several tetraploid Paspalum species to an elite group of sexual plants.

NOVO PE.; ESPINOZA F; URBANI MH; QUARIN C; ACUÑA CA; GALDEANO F

Zavalla, Rosario

Seminario; Advances in Apomixis Research 2018; 2018

Apomixis is a reproductive system for cloning plants by means of seeds. In the last three decades, scientists put considerable efforts into finding the sound molecular bases of genetic control of apomixis with the specific target of transforming sexual crops into apomictically reproducing ones. The findings seem to be still insufficient to achieve any concrete result for engineering apomixis in major crops. Meanwhile, basic findings from classical genetic studies are available for harnessing the trait in plant improvement through breeding in some forage grass genera in which apomixis naturally occurs in some species as is the case for genus Paspalum. Most species of the genus are multiploid with a sexual diploid (2x) cytotype and apomictic polyploid (mainly tetraploid, 4x) conspecific cytotypes. Although some degree of residual sexuality may be observed in some particular plants of the tetraploid cytotype, a completely sexual reproducing individual has never been found in natural apomictic populations of any 4x cytotype. If the diploid cytotype is experimentally tetraploidized, and the recovered sexual autotetraploid is crossed with a natural apomictic 4x counterparts, the hybrids are fertile, and allosyndetic pairing occurs between chromosomes of the tetraploidized sexual female parent and the natural apomictic 4x cytotype. The hybrids segregate for the reproductive mode. Basic genetic findings indicate that self-pollination of a sexual 4x plant or sexual×sexual cross-pollination always produce sexual progenies; sexual×apomictic crosses always segregate for reproductive mode; and apomictic plants always generate apomictic progenies. Technically, now the flow cytometric seed analysis greatly facilitates the assessment of the reproductive mode for a large number of individual of Paspalum species. We recombined 52 selected sexual hybrids obtained from crosses between two sexual tetraploidized genotypes of P. plicatulum and nine natural apomictic tetraploid accessions that belong to six different species. Six hundred plants obtained from mixed seed of the 52 mutually fertile sexual hybrids were established in the field to form a sexual synthetic tetraploid population. Thirty six plants were selected based on general agronomic performance (vigor, growth habit, leafiness, healthy foliage). Further selection was performed on these 36 plants based on animal preference, seed production, ergot resistant, cold tolerance, and regrowth after flowering. Thus, a fairly allogamous and very heterogeneous population of nearly 20 plants was separated in order to check their agronomic performance as female parents. Theoretically, these plants contain a variable mixture of genetic factors recombined from nine natural apomictic tetraploid accessions that belong to six different species, except the genetic determinants for apomixis. The formation of testcross progenies of each one of these plants with two apomictic accessions of P. guenoarum let to the selection of a few sexual perennial plants based on their merit to produce heterotic hybrids for agronomic traits. Any heterotic apomictic hybrids in these testcross progenies or in future progenies with other apomictic parents could be advanced to further testing toward a new cultivar development.