Dwarfing Genes Rht-B1b and Rht-D1b Are Associated with Both Type I FHB Susceptibility and Low Anther Extrusion in Two Bread Wheat Populations

It has been well documented that dwarfing genes Rht-B1b and Rht-D1b are associated with Type I susceptibility to Fusarium head blight (FHB) in wheat; but the underlying mechanism has not been well delineated. Anther extrusion (AE) has also been related to Type I resistance for initial FHB infection, where high AE renders FHB resistance. In this study, two doubled haploid populations were used to investigate the impact of the two dwarfing genes on FHB resistance and AE, and to elucidate the role of AE in Rht-mediated FHB susceptibility. Both populations were derived by crossing the FHB susceptible cultivar ‘Ocoroni F86’ (Rht-B1a/Rht-D1b) with an FHB resistant variety (Rht-B1b/Rht-D1a), which was ‘TRAP#1/BOW//Taigu derivative’ in one population (the TO population) and ‘Ivan/Soru#2’ in the other (the IO population). Field experiments were carried out from 2010 to 2012 in El Batán, Mexico, where spray inoculation was adopted and FHB index, plant height (PH), and AE were evaluated, with the latter two traits showing always significantly negative correlations with FHB severity. The populations were genotyped with the DArTseq GBS platform, the two dwarfing genes and a few SSRs for QTL analysis, and the results indicated that Rht-B1b and Rht-D1b collectively accounted for 0–41% of FHB susceptibility and 13–23% of reduced AE. It was also observed that three out of the four AE QTL in the TO population and four out of the five AE QTL in the IO population were associated with FHB resistance. Collectively, our results demonstrated the effects of Rht-B1b and Rht-D1b on Type I FHB susceptibility and reducing AE, and proposed that their impacts on Type I FHB susceptibility may partly be explained by their effects on reducing AE. The implication of the relationship between the two dwarfing genes and AE for hybrid wheat breeding was also discussed.

已有充分文献证实，矮秆基因（dwarfing genes）Rht-B1b与Rht-D1b与小麦赤霉病（Fusarium head blight, FHB）I型感病性（Type I susceptibility）相关，但其潜在机制尚未得到清晰阐释。花药外露率（Anther extrusion, AE）同样与赤霉病初始侵染的I型抗性（Type I resistance）相关，较高的花药外露率可赋予植株赤霉病抗性。本研究借助两个双单倍体群体（doubled haploid populations），探究上述两个矮秆基因对小麦赤霉病抗性及花药外露率的影响，并阐明花药外露率在Rht介导的赤霉病感病性中的作用。两个群体均由赤霉病感病品种‘奥科罗尼F86（Ocoroni F86）’（基因型为Rht-B1a/Rht-D1b）与赤霉病抗病品种杂交获得，该抗病品种的基因型为Rht-B1b/Rht-D1a；其中一个群体（记为TO群体）的抗病亲本为‘TRAP#1/BOW//太谷衍生系’，另一个群体（记为IO群体）的抗病亲本为‘Ivan/Soru#2’。2010至2012年在墨西哥埃尔巴坦（El Batán）开展田间试验，采用喷雾接种（spray inoculation）法，对赤霉病病情指数（FHB index）、株高（plant height, PH）及花药外露率进行调查评估；上述株高与花药外露率两个性状，均与赤霉病严重度呈显著负相关。本研究采用DArTseq GBS平台对两个群体进行基因分型，并结合两个矮秆基因及数条简单序列重复（Simple Sequence Repeats, SSRs）标记开展数量性状位点（Quantitative Trait Locus, QTL）分析。结果显示，Rht-B1b与Rht-D1b共同解释了0~41%的赤霉病感病性变异，以及13~23%的花药外露率降低幅度。研究同时观察到，TO群体的4个花药外露率QTL中有3个、IO群体的5个花药外露率QTL中有4个，均与赤霉病抗性相关。综上，本研究结果明确了Rht-B1b与Rht-D1b对小麦赤霉病I型感病性及花药外露率降低的调控效应，并提出二者对赤霉病I型感病性的影响，可部分通过其降低花药外露率的效应得以解释。本研究还探讨了这两个矮秆基因与花药外露率的关联在杂交小麦育种中的应用价值。