Genetic variability, ploidy levels and reproductive mode in wild populations of Paspalum denticulatum

SARTOR ME, CL QUARIN, F ESPINOZA

Buenos Aires, Argentina

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

Genetic variability, ploidy levels and reproductive mode in wild populations of Paspalum denticulatum.   Sartor, M.E., Quarin, C.L. and F.Espinoza   Instituto de Botánica del Nordeste (IBONE), Facultad de Ciencias Agrarias, Universidad Nacional del Nordeste (UNNE) - CONICET, CC 209, (3400) Corrientes, Argentina.   Email: mariasartor@agr.unne.edu.ar   Paspalum denticulatum Trin. is a valuable forage grass of the native alluvial pasturelands in western Brazil, Paraguay and northern Argentina. Since facultative apomixis and autotetraploidy have been reported in the species, other ploidy levels and reproductive modes may be expected. The aims of this work were: to establish ploidy levels, reproductive behavior, and genetic variability in three wild populations of P. denticulatum by using flow cytometry and AFLP markers. Measurement of DNA content in leaves cells, indicated that two entire populations of 60 and 73 individuals were uniformly conformed by tetraploids (2n=4x=40), while the third population (52 individuals) showed diploid, triploid, and tetraploid cytotypes, though diploids predominated. This is the first report of diploid and triploid cytotypes for this species. The study of reproductive behavior by flow cytometric seed screen showed that diploid individuals reproduced exclusively by sexuality showing a 2/3 embryo/endosperm ratio (n+n/n+n+n). However, the 4x individuals from these populations, pure and mixed, were facultative apomictic showing both 2/3 and 2/5 embryo/endosperm ratios (n+n/n+n+n and 2n+0/2n+2n+n, respectively). Triploid plants also reproduce by apomixis with a 3:8 embryo/endosperm ratio. In this case, the embryo had 2n=30 (2n+0) and the endosperm was formed by two unreduced polar nuclei (2n+2n) plus a sperm nucleus with 20 or nearly-20 chromosomes. Data from AFLP analyses revealed a maximal genetic diversity in the mixed population, where all individuals, diploids, triploids, and tetraploids showed different genotypes. In contrast, the genetic diversity for the two pure tetraploid populations was very low with predominance of one or two genotypes in each population. The species behaves as an agamic complex. The finding of sexual diploid constitutes the first step in a plant breeding program dealing with apomictic polyploid grasses. The results suggest that gene flow occurs among cytotypes, probably through recurrent autopolyploidization.