The generation of genetic diversity within the Paspalum notatum agamic complex

DAURELIO, L.D.; ESPINOZA, F.; QUARIN, C.L.; PESSINO, S.C.

Carlos Paz, Argentina.

Congreso; XXXVIII Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular.; 2002

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB)

Paspalum notatum is a subtropical grass organized as an agamic complex including races of variable ploidy level and characteristic reproductive behaviour. Diploids are sexual while polyploids give rise to clonal seeds through aposporous apomixis. RAPD markers were used to analyse the genetic structure of three natural populations of the species: i) diploids reproducing sexually (R2X); ii) sympatric apomictic tetraploids collected in the vicinity of the diploids (R4X); iii) allopatric apomictic tetraploids growing in isolation (C4X). About thirty individuals from each population were analysed. Chromosome-counting allowed verification of the ploidy levels on each plant. The obligate apomictic reproductive mode was confirmed in the tetraploid populations by the use of molecular markers in progeny tests. Genotypic and genetic variation indexes inferred from the molecular data revealed a dissimilar diversity rate between the tetraploid groups R4X and C4X. Tetraploids coexisting with diploids (R4X) showed a significantly higher intrapopulation variability with respect to those growing in isolation (C4X).  Jaccard´s similarity coefficients for interval measure within and between populations were used to produce a cluster diagram using the unweighted pair-group method (UPGMA) from which possible ancestral relationships among groups were established. Our observations strongly support the hypothesis presuming the periodic generation of novel tetraploid clones from the interaction between R4X individuals and the neighbouring R2X diploids.