Interspecific hybridization between Brassica napus and Brassica rapa ssp. chinensis genotypes through embryo rescue and their evaluation for crossability

Abstract

The genus Brassica contains several important crop species that are used for a variety of purposes. Brassica napus and Brassica rapa are the most important ones for their use as oilseed crops. In Brassica , interspecific hybridization is a potential and useful method for transferring valuable traits between species of commercial interest. For breeding Brassicas resistant to some diseases, i.e. clubroot, attempts of transferring resistant genes (CR) through interspecific hybridization have also been reported. The main step in the introgression process is the production of interspecific hybrids between the two species. However, the cross-incompatibility occurring in wide hybridization might hamper the possibility of obtaining hybrid progenies. For that reason, the crossability study is essential and may give an insight into the cross-compatibility relationship among the species, the direction of success of crossing, and the crossability barriers of some combinations, if any. In the present study, interspecific reciprocal crosses between B. napus and B. rapa ssp. chinensis genotypes were carried out in order to determine their crossability and to produce their F1 hybrids. Crossability was analyzed based on the pollen germination index (PGI) and the development of hybrid embryos in in vitro cultures. It was observed that the unilateral interspecific incompatibility occurred in crosses between B. napus × B. rapa ssp. chinensis. When B. napus cultivars were used as a maternal parent, pollen grains of B. rapa germinated well on the stigmas, while only a small number of pollen tubes could elongate near the ovules, resulting in a low development of hybrid embryos. Using the B. rapa ssp. chinensis as the pistillate parent in the crosses, it was found that the crossability was relatively higher than that in the case of the reciprocal cross. This resulted in a greater number of embryos obtained. Generally, it was concluded that the selection of parental components for hybridization is an important step for obtaining breeding success.