CYTOGENETICS AND REPRODUCTION OF PASPALUM-DASYPLEURUM AND ITS HYBRIDSWITH P-URVILLEI AND P-DILATATUM SSP FLAVESCENS

Paspalum dasypleurum has the southernmost distribution of the Paspalum species in South America. It is a sexual, self-fertile tetraploid wit h 40 chromosomes that pair as 20 bivalents at meiosis. This is the fir st report concerning its cytology and reproductive behavior. Morpholog ically, this species belongs to the Dilatata group and was crossed wit h two other tetraploid taxa of the same group: Paspalum urvillei (Vase ygrass) and Paspalum dilatatum ssp. flavescens (yellow-anthered Dallis grass), both with the genome formula II JJ. Crossability between P. di latatum ssp. flavescens (female) and P. dasypleurum (male) was 0.8%, a nd their hybrids showed regular meiotic behavior with 20 bivalents. Al l hybrids were male-sterile, but approximately 8% of the spikelets set seed after backcrossing with pollen from either parent. Crossability between P. dasypleurum (female) and P. urvillei (male) was 53.9%, and their hybrids had regular meiotic behavior with 20 bivalent at diakine sis and metaphase I. All hybrids had indehiscent anthers, and none pro duced seed when selfed. Backcrosses to P. dasypleurum set a mean of 4. 8% seed, and 18.6% (mean of five F-1 plants) to P. urvillei. The regul ar meiotic chromosome pairing in P. dilatatum ssp. flavescens x P. das ypleurum and P. dasypleurum x P. urvillei hybrids indicated that P. da sypleurum has the I and the J genomes that were previously described f or tetraploid biotypes of P. dilatatum and for P. urvillei. The abilit y of the hybrids to produce seed following backcrossing suggests that gene exchange through hybridization may be a feasible method for plant improvement among these species.