Intra- and Interspecific Incompatibility in Brachiaria ruziziensis Germain et Evrard (Panicoideae)

Abstract

An introgression program aiming at transfering apomixis from tetraploid species Brachiaria decumbens (B.d) and Brachiaria brizantha (B.b) into the genome of the sexuate diploid Brachiaria ruziziensis (B.r), an interesting forage crop, started in our laboratory (Gobbe and al., 1983). Its first step was the obtention of autotetraploid plants of B.r. The second step was to cross them with the apomictic tetraploid species. As self-seed-set is generally very low in B.r, about 1–7 % in both diploids and tetraploids, these interspecific crosses were not preceded by emasculation (a very uneasy operation in Brachiaria). A few seeds were obtained, but most of these were self-seeds (Ndikumana, 1985). To investigate the reason of this and to localize precisely the interspecific barrier in Brachiaria, self-incompatibility and interspecific incompatibility in the progamic phase were studied and compared. For this purpose, we observed pollentube growth after self- and cross-intraspecific pollinations and interspecific pollinations of emasculated flowers of diploid and tetraploid B.r.

This work is part of a doctorate thesis to be presented by M. Ngendahayo