The reproductive mode of tetraploid Paspalum malacophyllum and its incidence in breeding programs

HOJSGAARD DIEGO H.; MARTÍNEZ ERIC J.; QUARIN CAMILO L.

Buenos Aires, Argentina

Simposio; 6th International Symposium on the Molecular Breeding of Forage and Turf; 2010

The reproductive mode of tetraploid Paspalum malacophyllum has been established by different authors through cytoembryological protocols and with dissimilar results. The species was controversially classified as sexual or apomictic, obligate or facultative. The aim of this work was the re-examination of the reproductive mode in the species analyzing five selected accessions of P. malacophyllum through three different methodological ways: cytoembryology, flow cytometry single seed analysis (FCSS), and progeny test with AFLP markers. Embryo sac observation in mature ovules indicated that the five accessions were facultative apomictic because sexual as well as aposporous embryo sacs were observed. The degree of sexuality varied from 7.2 to 73 %, with an average of 40 %. The FCSS analysis indicated that the sexual way to form seed was poorly effective and varied from 9.6 to 11.7 % among the five accessions. Finally, progeny tests by AFLP, using fifty individuals obtained from seeds through free pollination of each accession, demonstrated that all progenies have originated through apomixis. Each progeny showed band patterns identical to the mother plant. These results support the viewpoint that tetraploid P. malacophyllum reproduces constitutively by facultative apomixis. The expression of apomixis or sexuality varies during the reproductive cycle: there is a high expression of sexuality at flowering as judged by the proportion of ovules bearing sexual embryo sacs. The sexual expression decreases at seed stage probably due to limited efficiency of sexual ovules to develop seeds. Moreover, at the end of the reproducing cycle, only apomictically developed descendants seem to be successful. Some strong selective pressure against sexuality might be acting to avoid the establishment of new recombinant individuals. These data are discussed considering previous reports and through their implication on breeding programs.