FERTILITY OF BRACHIARIA-RUZIZIENSIS IN INTERSPECIFIC CROSSES WITH BRACHIARIA-DECUMBENS AND BRACHIARIA-BRIZANTHA - MEIOTIC BEHAVIOR, POLLEN VIABILITY AND SEED SET

Colchicine induced tetraploid (2n = 4x = 36) Brachiaria ruziziensis were used as female parent in crosses with apomictic tetraploid species (2n = 4x = 36) Brachiaria decumbens and Brachiaria brizantha. Tetraploid B. ruziziensis pollinated with B. decumbens set significantly more seed than selfed or crossed with B. brizantha. The crossability between B. ruziziensis and B. decumbens is also better than between B. ruziziensis and B. brizantha. In addition, hybrid seedlings obtained in crosses involving B. brizantha are more frequently lethal. All the viable F, hybrids are tetraploid with 36 chromosomes. Meiotic chromosome behaviour suggest that the three species belong to the same genomic group and therefore the same agamic complex. Chromosome associations at metaphase I do not allow to identify fertile and sterile hybrids. The interspecific hybrids averaged a lower fertility than their female parent, but some hybrids were more fertile than their apomictic male parent.