Systemic development of a complete set of monosomic alien addition lines of Raphanus sativus in natural Brassica napus and detection in breeding for clubroot resistance

Brassica napus, as an important oil crop, boasts great biomass and considerable yield. Nonetheless, short agricultural history, limited genetic resources and susceptible to a multitude of biotic and abiotic stressors make the improvement of B. napus an urgent task. Monosomic alien addition lines (MAALs) created by interspecific hybridization have become a great pursuit for many researchers, because they are expected to be valuable genetic stocks to transfer favorable traits from wild species to crops. Herein, a complete set of B. napus-Raphanus sativus (radish) MAALs (AACCR_1–9, 2 n = 39) was developed after screening thousands of backcrossing individuals between the synthesized allootacploid (AACCBBRR, 2 n = 72) and B. napus cv. “Youyan” (AACC, 2 n = 38) using PCR amplification with a set of R chromosome specific primers and multi-color fluorescence in situ hybridization. These MAALs exhibit a wide range of morphological variations, which have resulted in many desirable agronomic traits, including more seeds per silique, longer and wider silique, longer pod beak and heavier seeds weight, which can be used for further improvement of Brassica napus. A higher transmission rate of alien R chromosome via male gamete than female gamete was generally observed in MAALs, and a widespread homoeologous exchange (HE), including a bias of homoeologous chromosome pairing between C genome and R chromosome, was detected in the MAALs with the frequency of homoeologous chromosome pairing (HEP) ranging from 26.73 % (AACCR6) to 91.96 % (AACCR7). Three unequal segregation patterns (20:19, 21:18, 23:16) in anaphase I were also observed using dual FISH. In addition, the clubroot resistance tests revealed that AACCR5 was resistant to Plasmodiophora brassicae pathotypes and other two lines (AACCR7 and AACCR9) may have minor gene resistant to the clubroot disease. Overall, these MAALs are pivotal for enhancing the genetic diversity and for the innovation of excellent germplasm resources for genetic improvement of B. napus.