砧木对果树树体的生长发育、果实产量和品质有着重要的影响，目前矮化砧木在世界主要苹果生产国中得到了广泛的应用。本课题组研究表明，玉米素对苹果自根砧致矮有重要调控作用，同时在矮化砧木玉米素合成基因IPT5b启动子上存在着INDEL突变，且这个突变与砧木致矮性紧密相关。为此，本研究拟以IPT5b多态位点作为突破口，以八棱海棠×M9杂交后代为材料，通过遗传连锁分析该INDEL插入对砧木矮化性状的影响，进一步利用启动子活性检测、稳定转化等证明该INDEL插入是否通过在转录水平调控IPT5b表达来决定砧木致矮性，并对IPT5b上游转录调控进行分析。最终明晰IPT5b启动子上INDEL插入的生物学意义及其上游调控路径，从而为从分子辅助育种手段加速苹果砧木改良、培育具有自主知识产权的优良矮化砧木品种提供基因储备和理论指导。

Grafting is widely used in cultivated horticultural plants, not only for improving their adaptability and tolerance of salinity, cold and drought, but also for controlling adequate growth and development of the scion.Dwarfing apple rootstocks are widely used in the world. Our reseached showed dwarfing effect is caused by inherently poor root cytokinin biosynthesis in dwarfing rootstock. Specifically, an IPT5b mutant allele with INDEL insertion in the promoter exhibited dwarfing effect. There’re three major parts in our project. 1) Association between the IPT5b allele and dwarfing effect by analyzing segregating progeny. 2 ) An INDEL insertion in the Promoter of IPT5b alters its expression. 3) The upstream regulation of IPT5b.