Improved application of tribenuron-methyl as a chemical hybridizing agent with forchlorfenuron for rapeseed hybrid breeding

Chemicals or agents that can induce plant male sterility are considered chemical hybridizing agents (CHAs) and are quite useful for plant hybrid breeding. Tribenuron-methyl (TBM) can effectively induce male sterility in rapeseed plants. However, applications of TBM in rapeseed breeding practices have not been reported. Here, treatment with the CHA referred to as CHA-TBM, which contained 0.1–0.9 mg/L TBM, induced male sterility in all 22 tested rapeseed inbred lines. However, the highest induced male sterile rates in the tested rapeseed lines were only approximately 54–57% together with poisoned rates of approximately 36–39%, which were resulted from two treatments of CHA-TBM containing 0.5 mg/L TBM at an interval of 9 days beginning at the floral bud stage (FBS) of 2.0–3.5 mm. Such male sterile rates and poisoned rates caused by CHA-TBM indicated that TBM is not an ideal CHA for rapeseed hybrid breeding. The results of many screening experiments showed that forchlorfenuron can alleviate the toxic effects of TBM on rapeseed plants. Two treatments with the CHA referred to as CHA-TBM-FCF, which contained 0.6 mg/L TBM and 2.1 mg/L forchlorfenuron, at an interval of 9 days beginning at the FBS of 2.0–3.5 mm induced male sterility in approximately 96–98% of plants of all the 22 tested rapeseed inbred lines and poisoned only approximately 2–4% of the tested plants. The CHA-TBM-FCF treatment did not affect pistil fertility of the rapeseed plants, and had no carry-over influence on stamen fertility of the rapeseed hybrids produced with this CHA. Some rapeseed hybrids were successfully produced using CHA-TBM-FCF (e.g., Qinrong 1, Qinrong 2, Qinyou 19, Qinyou 33, Qinzayou 4 and Qinzayou 5). The hybridity values of the F1 seeds of the rapeseed hybrids produced using CHA-TBM-FCF were determined to be approximately 93–98% with the simple sequence repeat (SSR) marker techniques. Together, the results indicate that CHA-TBM-FCF containing TBM and forchlorfenuron at suitable concentrations is an ideal CHA for rapeseed hybrid breeding.