Unravelling the secrets of wide hybridization among the brassica species

Abstract Pre-fertilization barriers in Brassica and related species pose a significant challenge in interspecific and intergeneric hybridization, hindering the successful transfer of desirable genetic traits crucial for crop improvement. Pollen germination, pollen tube growth, and the tube's capacity to reach and fertilise the ovule are among multiple stages at which these obstacles may appear. This study focuses on identifying such pre-fertilization barriers and assessing meiotic abnormalities during microsporogenesis in interspecific hybrids of Brassica species. Pre-fertilization parameters such as pollen germination percentage, pollen tube growth, and pollen tube abnormalities were thoroughly examined. In interspecific hybrids, the mean pollen tube germination percentage was highest for B. carinata × B. nigra (33.67 ± 11.35) and lowest for B. carinata × B. napus (18.68 ± 6.62), whereas it was highest for B. napus × B. carinata (33.06 ± 13.41) in reciprocal crosses. B. carinata × B. nigra had the highest mean pollen tube growth (21.23 ± 5.33), followed by B. carinata × B. napus (10.18 ± 3.17), while B. nigra × B. carinata had the lowest mean growth among reciprocals (21.39 ± 7.53). Pollen tube abnormalities such as coiling, bending, hairpin shapes, tube tip swelling, bifurcation, multiple tube emergence, and misdirected growth were observed. The highest incidence of abnormalities occurred when B. carinata was used as a pollen parent with B. napus. Further observations using fluorescent microscopy revealed pre-fertilization incompatibilities in the stylar and ovule regions. Crossability data revealed varying percentages of seed set (ranging from 0% in B. nigra × B. carinata and B. rapa × B. carinata to 25.64% in B. carinata × B. nigra) and siliqua set (from 33% in B. carinata × B. napus to 72% in selfed B. carinata). Additionally, meiotic analysis revealed abnormalities such as improper alignment during M-I, M-II, A-I, A-II, and Telophase, indicating cytological instability in some hybrids. Correlation study further established the association among all of these traits. This study highlights critical reproductive and cytological barriers affecting hybrid success in Brassica, offering valuable insights for breeders. By identifying suitable parent combinations and understanding hybridization limitations, it supports more efficient transfer of traits and the development of diverse, improved lines for future breeding programs.