Efficient resynthesis of oilseed rape (Brassica napus L.) from crosses of winter types B. rapa x B. oleracea via simple ovule culture and early hybrid verification

Resynthesis of Brassica napus is an important tool for the broadening of genetic diversity as well as crop cultivar improvement in oilseed rape. To the best of our knowledge, this is the first study focusing on the crossability, regeneration, and early verification of hybrids between diploid winter turnip rapes (Brassica rapa ssp. oleifera f. biennis), as the female component, and diploid winter curly kales (Brassica oleracea convar. acephalla var. sabellica). Pollination efficiency, mean embryo regeneration per bud and siliqua, as well as their relationships were evaluated in ovule cultures of twenty-four different one-sided crosses between six accessions of B. rapa and four accessions of B. oleracea. Successful germination of the embryos was achieved in 23 combinations. The mean number of embryos per bud reached 0.34. The most productive cross, Svalofs Duro x Kapral, yielded 2.7 embryos per bud in the best replication. A significant and positive correlation (r = 0.26*) was detected between the pollination efficiency (i.e., setting of siliquae) and the number of embryos per siliqua. In the majority of crosses, procedures implemented exhibited better results than in similar published experiments on spring Brassica genotypes, and provides a simplified and less laborious method. The hybrid nature of all regenerants was verified via flow cytometry. The use of bulked samples for analysis was reliable due to highly significant differences in relative DNA content between all hybrid combinations and their respective parental components. Chromosome counting and morphological assessment further corroborated the results of the flow cytometric analysis.