Interspecific Tetraploid Hybrids between Two Forage Grass Species: Sexual Paspalum plicatulum and Apomictic P. guenoarum

The Plicatula group of the grass genus Paspalum contains about 30 species. Most are tetraploid and reproduce by apomixis, though some of them contain sexual diploid races. We crossed a sexual colchicine-induced autotetraploid plant of brownseed paspalum (Paspalum plicatulum Michx.) with apomictic tetraploid P. guenoarum Arechav., also from the Plicatula group. Crossability was 35% and the progeny showed morphological characteristics intermediate to those of the parents but resembling more the male parent. The random amplified polymorphic DNA (RAPD) analysis showed that the whole progeny amplified bands that were specific of the male parent, confirming its hybrid origin. Meiotic chromosome behavior of hybrids exhibited primarily bivalent and quadrivalent associations similar to those of the two parents. This suggests that natural tetraploid P. guenoarum shares the same basic chromosome set with that of autotetraploid P. plicatulum, and both species probably originate from the same ancestral species. Fourteen out of 23 hybrids reproduced only sexually, while nine were obligate or highly apomictic. Seed set ranged from 11 to 55% among the hybrids. Our results open the possibility of exchanging genes at the tetraploid level in breeding programs of P. plicatulum and P. guenoarum. This possibility is based on their rate of crossability, the degree of fertility among the hybrids, the segregation observed for the reproductive mode in the F1 progeny, and the very simple procedure flow cytometry seed screen (FCSS) used to determine the reproductive mode for each hybrid.