ANALYSIS OF 2X, 3X AND 4X CYTOTYPES DISTRIBUTION AND EVALUATION OF EST-SSR MARKERS FOR DETERMINING POPULATION GENETIC STRUCTURE OF PASPALUM UNISPICATUM SCRIBN. & MERR.

SARTOR ME; GRUBER LM; SIENA LA; ORTIZ, JPA; URBANI M; QUARIN CL; ESPINOZA F

Bahia Blanca, Argentina

Workshop; IV Ciclo de seminarios sobre avances en la caracterización genética y molecular de la apomixis en gramíneas forrajeras; 2014

Universidad Nacional del Sur/CERZOS, CONICET

Paspalum unispicatum is distributed from Mexico to Argentina. Although it has been described as a tetraploid (4x), diploid (2x) and triploid (3x) cytotypes have been found in the Chaco phytogeographic region in Argentina. The aim of this study was to examine the distribution and frequency of the different cytotypes in natural populations and test the utility of wheat EST-SSR markers for determining the genetic structure of natural populations. EST-SSR markers had been transferred to Paspalum species and used to perform a preliminary comparative mapping and phylogenetic analysis in the genus. However they have not been use yet for evaluating the genetic structure of natural populations in Paspalum. A minimum of 29 and a maximum of 68 individual were collected in each of six populations: Avia Terai (P1), Colonia José Mármol (P2) and El Boquerón (P3) in Chaco province, Ibarreta (P4) and Pozo del Tigre (P5) in Formosa province and Metán (P6) in Salta province, all in Argentina. The ploidy level of each plant was determined by flow cytometric analysis in leaves. To evaluate the genetic structure, three EST-SSR primer combinations were tested in a total of 87 individuals from five out of the six populations studied: P1 (13 individuals), P2 (12 individuals), P3 (15 individuals), P4 (32 individuals) and P5 (15 individuals). Cluster analysis was performed by the UPGMA method based on genetic distances (1-Jaccard). Ploidy level analysis showed that P1 and P3 were constituted by 2x plants, while P6 contains only 4x. In the remaining populations a high proportion of triploids were recorded. While P4 was exclusively 3x, 75% of individuals from P2 were 3x and 25% were 2x; and ,75% were 3x and 25% were 4x in P5. A total of 34 informative markers were obtained, with an average of 11.33 bands per primer pair. Cluster analyses allowed differentiate six groups of individuals. Interestingly enough, individuals were not grouped according to their population origin, since in all groups, plants from at least two different populations were found. Based on ploidy level, one cluster included only 3x, and the others included individuals with different ploidy levels: three clusters were formed by 2x and 3x individuals, one was formed by 3x and 4x and the last one included 2x, 3x, and 4x. Diploids included in the last cluster belong to the 2x population which is nearest from the 3x-4x population. Our results indicate that P. unispicatum is a multiploid species. The central east Chaco phytogeographic region, in Argentina, appeared to be the center of origin for the species. Triploidy in combination with apomixis, would constitute a successful system of adaptability. Moreover, the variability analysis with EST-SSR suggests that populations are not genetically isolated and that there is gene flow between them from 2x to 4x, where 3x would be acting as a bridge for the genetic exchange. The system would work by transferring the variability from 2x to 4x by fertilization of unreduced gametes of 3x with reduced gametes of 2x.