两个小麦赤霉病关联QTL座位上稀有抗性等位基因的解析和育种基础研究

Fusarium head blight (FHB) in wheat can cause severe yield reduction and accumulation of mycotoxin in grains. Attributing to the Fhb1 gene, Sumai3 has been extensively used in wheat breeding programs for improvement of FHB resistance. Unfortunately, our previous studies suggested that most varieties, including Sumai3, carry FHB-susceptible quantitative trait loci (QTL) on the chromosome arms of 2DS and 4BS, which are probably the causal loci that incur accumulations of toxins such as DON in the grains of Sumai3 after infection by the Fusarium complex. The FHB-resistant alleles at the two QTL were rarely presented in natural germplasm resources and were detected out predominantly in Chinese and Japanese wheat landraces. Chinese wheat landrace Caizihuang carries a resistant allele at the QTL on 2DS and the Japanese wheat landrace Tokai66 carries a resistant allele at the QTL on 4BL, and both varieties show a high level of resistance to FHB and low toxin accumulation in the grains. However, these two resistant alleles have been not accessed in breeding programs. This project is going to create the corresponding mapping populations, to fine map the two resistant QTL, to identify the candidate genes at the two QTL, to develop functionally diagnostic markers, and to decipher their effects on the resistance to toxin accumulation, and on agronomic and yielding traits. The expected achievements of this project would find out potentially novel genes for FHB improvement in breeding programs, and would also be extremely useful in efficient detection and elimination of the susceptible alleles at the two chromosomal loci mentioned above, thus would facilitate the efficiency of improving FHB resistance in wheat.

赤霉病可造成小麦严重减产并在籽粒中积累真菌毒素。苏麦3号主要因携带Fhb1基因而广泛用于抗赤霉病育种。我们前期研究发现，包括苏麦3号在内的大部分品种在2DS和4BL染色体臂上携带感赤霉病QTL，且苏麦3号受赤霉菌感染后籽粒中仍然积累较高的DON毒素。我国小麦地方品种菜籽黄和日本小麦地方品种Tokai66高抗赤霉病和抗毒素积累，它们在2DS和4BL染色体臂上分别携带相应的抗病等位变异，这两个抗病等位基因在自然种质中频率极低，因此在育种中尚未得到有效利用。本项目拟在此基础上，配置相应作图群体，开展这两个抗病QTL的精细作图，筛选可能的候选基因，设计功能性分子标记，解析其在抗毒素积累、农艺和产量性状等方面的效应。研究结果不仅能挖掘新的抗赤霉病基因，为培育高抗赤霉病新种质提供重要基因资源，同时有利于育种过程中高效检测并剔除上述两个位点上的感病等位变异，为提高抗赤育种效率和品种抗性水平提供更多选择。

由禾谷镰刀菌引起的小麦赤霉病可造成小麦严重减产并在籽粒中积累真菌毒素。苏麦3号因携带Fhb1基因而广泛用于抗赤霉病育种。但包括苏麦3号在内的大部分品种在2DS和4BL染色体臂上携带感赤霉病QTL。我国小麦地方品种菜籽黄和日本小麦地方品种Tokai66高抗赤霉病，它们在2DS和4BL染色体臂上分别携带相应的抗病等位变异QFhb.czh_2DS与QFhb.tki_4B。本项目主要开展这两个抗病QTL的精细作图，设计位点鉴别标记，解析其在抗毒素积累等方面的效应，并筛选可能的候选基因。表型精准鉴定、精细作图群体构建以及高通量分子标记开发是实现精细定位和图位克隆的前提。依托该项目，我们发明了新的赤霉病接种鉴定方法“基部穗轴注射法（简称BRII），该法最大的优点是不论在大田或温室环境，接种后均无需采取保湿措施，发病的湿度条件由植株自身体内水分来保证，解决了传统单花滴注法鉴定需要套袋或喷雾、喷水等保湿的问题。在宁7840/Clark群体中，利用BRII方法接种，能够稳定检测到宁7840的2DS染色体上也携带该感病QTL，同时发现该感病QTL对Fhb1有显著抑制作用，单倍型分析表明该QTL来自苏麦3号。进一步通过构建菜籽黄/苏麦3号分离群体并筛选目标QTL杂合子构建了次级分离群体，将QFhb.czh_2DS定位于17.0-23Mb, 开发了目标QTL的鉴别标记Indel.2DS-1。Tokai66在QFhb.tki_4BL位点上携带抗性等位变异，利用亲本重测序和高通量蛋白组分析，鉴定到QFhb.tki_4BL的候选基因TaG3LEA-25，在接种后48小时内Tokai66穗部TaG3LEA-25被明显诱导，而在Clark材料中则不被赤霉菌诱导。通过亲本重测序发现亲本在起始密码子ATG上游约1000bp左右出现一个SNP变异位点，在抗病材料Tokai66中的位点是“C”， 而在感病材料Clark中为“T”，说明TaG3LEA-25受到赤霉菌的诱导可能与该位点存在关联，我们根据该变异设计了位点鉴别标记CAPs。上述阶段性成果为培育高抗赤霉病新种质提供重要基因资源，同时有利于育种过程中高效检测并剔除上述两个位点上的感病等位变异，为提高抗赤育种效率和品种抗性水平提供更多选择。