Intra- and Interspecific Hybridization between Dallisgrass and Vaseygrass

Two sexual tetraploid (2n = 4x = 40) biotypes of dallisgrass (Paspalum dilatatum Poir.) were crossed with vaseygrass (P. urvillei Steud.) (2n = 4x = 40) to investigate their genomic relations and determine the feasibility of gene exchange between these forage grasses. There are some morphological differences between the dallisgrass biotypes. They are referred to as P. dilatatum (F) and P. dilatatum (V) in this study. These biotypes also were crossed to investigate their relations. Cytologically, P. dilatatum (F), P. dilatatum (V), and P. urvillei behaved as allotetraploids, averaging 19.94, 19.97, and 20 bivalents per metaphase I cell, respectively. Crossability between P. dilatatum (F) and P. dilatatum (V) was 19.2%. The intraspecific hybrids had regular meiotic chromosome pairing, averaging 19.94 bivalents per cell. Thus P. dilatatum (V) apparently has the same genomes (II JJ) as the P. dilatatum (F) biotype. Crossability between P. dilatatum (F) and P. urvillei was low (1.2%). Chromosome pairing in the hybrids was regular averaging 19.96 bivalents per cell, indicating that P. dilatatum (F) and P. urvillei share the same genome formula (II JJ). Seed set in the hybrids was low ranging from 1.4 to 2.1%. Crossability between P. dilatatum (V) and P. urvillei was 19.3%. The hybrids exhibited similar meiotic behavior as the previous hybrids averaging 19.88 bivalents per cell. Fertility was investigated for six P. dilatatum (V) ✕ P. urvillei F₁ hybrids and seed set ranged from 0.3 to 18.8% among them. Seed set increased in the F₂ and backcross progenies. Some backcross plants exhibited similar seed set as the parental species. Findings from this study strongly implies that gene exchange between tetraploid P. dilatatum biotypes and P. urvillei is possible. Cooperative investigation of the Facultad de Ciencias Agrarias, Universidad National del Norddeste, and the Consejo National de Investigaciones CientÍficas y Técnicas de la República Argentina.