Cytokinins (CKs) are phytohormones that promote cell division and differentiation. However, the regulation of CK distribution and homeostasis in Brassica napus is poorly understood. Here, the endogenous CKs were first quantified by LC-ESI-MS/MS in rapeseed tissues and visualized by TCSn::GUS reporter lines. Interestingly, the cytokinin oxidase/dehydrogenase BnaCKX2 homologs were mainly expressed in reproductive organs. Subsequently, the quadruple mutants of the four BnaCKX2 homologs were generated. Endogenous CKs were increased in the seeds of the BnaCKX2 quadruple mutants, resulting in a significantly reduced seed size. In contrast, overexpression of BnaA9.CKX2 resulted in larger seeds, probably by delaying endosperm cellularization. Furthermore, the transcription factor BnaC6.WRKY10b, but not BnaC6.WRKY10a, positively regulated BnaA9.CKX2 expression by binding directly to its promoter region. Overexpression of BnaC6.WRKY10b rather than BnaC6.WRKY10a resulted in lower concentration of CKs and larger seeds by activating BnaA9.CKX2 expression, indicating that the functional differentiation of BnaWRKY10 homologs might have occurred during B. napus evolution or domestication. Notably, the haploid types of BnaA9.CKX2 were associated with 1000-seed weight in the natural B. napus population. Overall, the study reveals the distribution of CKs in B. napus tissues, and shows that BnaWRKY10-mediated BnaCKX2 expression is essential for seed size regulation, providing promising targets for oil crop improvement.

Oilseed rape (Brassica napus) has significant heterosis and Ogura CMS is a major way to use it. Ogura CMS has the advantages of complete and stable male sterility and easy-to-breed maintainers. Therefore, to breed better restorers has become an important goal for this system. Incidentally, clubroot is a soil-borne disease that is difficult to control by fungicidal chemicals, and it has been the main disease of oilseed rape in recent years in China, severely restricting the development of the oilseed rape industry. At present, the most effective method for controlling clubroot disease is to cultivate resistant varieties. One Ogura CMS restorer line (R2163) has shown much better combining ability, but lacks the clubroot disease resistance. This study was carried out to improve R2163 through marker-assisted backcross breeding (MABB). The resistant locus PbBa8.1 was introduced into the restorer R2163, and we then selected R2163R with clubroot disease resistance. Using the new restorer R2163R as the male parent and the sterile lines 116A and Z11A as the female parent, the improved, new resistant hybrids Kenyouza 741R and Huayouza 706R performed well, providing strong resistance and good agronomic traits. This work advances the utilization of heterosis and breeding for clubroot disease resistance in B. napus.

为了探究油菜品种油蔬两用的适宜栽培方式、筛选出适宜湖北省栽培的油蔬两用早熟油菜(Brassica napus L.)品种,以19个甘蓝型油菜品种、1个白菜薹品种和1个红菜薹品种为材料,研究了密度和肥力对菜薹品种产量的影响.试验设置高密度低肥力(移栽密度为10.8万株/hm2,无外施复混肥)、高密度高肥力(移栽密度为10.8万株/hm2,抽薹前增施1次复混肥,施用量约600 kg/hm2)和低密度高肥力(移栽密度5.4万株/hm2,抽薹前增施1次复混肥,施用量约300 kg/hm2)3种处理.结果表明,在21个品种中,与低密度相比,高密度处理下4个品种增产极显著,8个品种增产显著,6个品种增产不显著,3个品种减产;与低肥力相比,高肥力处理下9个品种增产显著或极显著,7个品种减产显著;6个表现较晚熟的油菜品种平均产薹量在高密度条件下比低密度增加61.21％,在高肥力条件下比低肥力增加49.50％;13个早熟品种平均产薹量在高密度种植下比低密度增加31.53％,而在高肥力条件下与低肥力没有显著变化.由此可知,增加种植密度有助于提高油菜品种菜薹产量,而肥力对菜薹产量的影响因品种而异.