Abstract：Inorderto clarifythe effects ofdifferent gibberellin treatments on flowering dynamicsand outcrossingsituation of rice sterile lines，thecombinationsof Zao6A×Zao5.1 ，Jingkang1 and Chuanzhong 3A × Zhongzhong R16O7 were used as materials. The treatments included no gibberellin control（CK），spraying 22.5 g/hm² gibberellin at the M stage of young panicle differentiation of sterile lines（S1），spraying 15.0g/hm² gib

berellin at the M stage of young panicle differentiation of sterile lines and spraying 90.0g/hm² and 75.0g/hm² gibberellin at 7：00 and 19：00 on the day of 10% heading（S2），spraying 75.0g/hm² ， 45.0g/hm² and 45.0g/hm² gibberellin on the day of 20% heading and the next two days（S3）.The effects of different treatments on flowering dynamics，plant morphology，paniclestructure，stigmaexsertionrateandyieldcompositionof sterile lineswereanalyzed.Theresults showed thattheflowering periodoftheparentsofthethreecombinations inCKwasshiftedby5-6d.Theflowering indexof the three combinations under S1 treatment was 73.33%-85.71% ，and the flowering indexunder S2 treatment and S3 treatment was43.75 % -66.67 % .The plant height of the three sterile lines of S2 treatment and S3 treatment was significantly higher thanthatofS1treatmentandCK，andthelengthsoftheinvertedlstinternode，inverted2ndinternodeandinverted3rdinternodeof the three sterile linesofS2 treatmentand S3 treatment were significantlylongerthanthoseofS1treatmentand CK.The paniclerateofthethreesterilelinesfromlowto highwasS3treatment，S2treatment，S1treatmentand CK.The unilateralstigma exsertionrate，bilateralstigmaexsertionrateandtotal stigmaexsertionrateofthethreesterilelinesunder S3treatment were significantlyhigherthan thoseunder theotherthree treatments.Among them，the bilateral stigma exsertion rate of S3 treatment increased by 9 6.20%-140.03% compared with CK. There were no significant differences in the numberof efectivepanicles，the numberof grains per panicle and1Ooo-grain weight among the three sterile lines.The seedsetingrateandtheoreticalyieldof thethreecombinationsunderS3treatmentandS2treatmentweresignificantlyhigher thanthoseofS1treatmentand CK.Onthewhole，the decreaseofflowering index caused byflowering perioddeviationof parents is the mainfactorforthedecreaseofoutcrossingrateof hybridseed production.S3treatmentcan efectivelyimprove the flowering index and improve the outcrossing situation of sterile lines.

Key Words：hybrid rice；mechanized seed production；gibberelin；sterile lines；flowering period；outcrossing seed setting rate

水稻是中国第一大口粮作物，有 60% 以上的人口以稻米为主食[1]。目前中国杂交水稻的种植面积约占水稻种植面积的 50% 。因此，杂交制种是保障中国水稻生产乃至粮食安全的重要要素。但居高不下的制种成本是限制杂交水稻大面积推广应用的一大难题。机械化生产是降低制种成本的有效措施，但机械化制种加大了花期不遇的风险，这导致传统制种向机械化制种转型受到限制[2-3]。因此，如何促进亲本花期相遇进而提高制种产量是杂交水稻机械化制种的关键[4-5]。杂交水稻制种的核心在于亲本间的异花授粉过程，亲本花期相遇程度是决定异交结实率的关键因素，并显著影响制种产量[6]。此外，不育系的穗层结构、柱头外露状况等异交态势也会对制种产量产生重要影响[7]

赤霉素（GA3）是常用的生长调节激素，能协调杂交水稻制种亲本的异交态势，提高花期相遇程度[8]，但赤霉素喷施效果受喷施时期与剂量的交互影响。不育系破口期或始穗期喷施可缩短出穗时间，始穗期喷施可有效解除包颈，灌浆期喷施能够改善柱头活力[9]。黄益峰等[0]研究发现，赤霉素用量达到一定阈值后，进一步增施对制种产量的提升效应趋于平缓，且不同喷施时期和剂量组合的制种产量具有显著差异[7]。此外，赤霉素对不同播差期（两亲本播种期之差）组合的调控效果存在明显差异。播差期 ⩾10d 的亲本需分次高剂量喷施赤霉素以延长花期重叠窗口，而播差期 lt;5d 的亲本则需要精准低剂量赤霉素即可调控亲本抽穗同步性和优化柱头外露率[1I-I2]。……