Mapping of Ug99 stem rust resistance in Canadian durum wheat

Stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), has potential to cause major yield losses in durum wheat. Development of durum cultivars with improved resistance to stem rust is a sustainable option for effective control of this disease. This study was conducted to identify genomic regions associated with resistance to Ug99-derived Pgt races using a doubled haploid (DH) mapping population produced from a cross between the resistant experimental line A9919-BY5C and the moderately susceptible cultivar ‘Strongfield’. The parents and DH lines were phenotyped for adult plant disease severity and infection response at Njoro, Kenya, for four years, and for seedling reaction to race TTKSK in a containment facility near Morden, Canada. Composite interval mapping using 612 SNP and DArT markers indicated four significant QTL for resistance to stem rust on chromosomes 1B, 4A, 5B, and 6A. A major and stable QTL from A9919-BY5C was identified on the short arm of chromosome 6A (6AS), which accounted for 71% of variation explained for seedling resistance and up to 46% for field resistance. This QTL mapped near the Sr8 locus and may be Sr8155B1, or a novel gene at the same location. Another QTL for adult plant resistance from A9919-BY5C was mapped on chromosome 1B that explained up to 14% of the phenotypic variation and likely is Sr14. Two minor QTL were identified in ‘Strongfield’ on chromosomes 4A and 5B that were inconsistent over years. Markers associated with the 6AS and 1B QTL can be used to proactively stack resistance to Ug99-derived races of Pgt into Canadian durum wheat.由小麦秆锈菌（Puccinia graminis f. sp. tritici，Pgt）引发的秆锈病，对硬粒小麦存在造成重大产量损失的风险。培育抗秆锈病能力优化的硬粒小麦品种，是实现该病害有效防控的可持续路径。本研究以抗秆锈育种品系A9919-BY5C与中度感病品种‘Strongfield’杂交创制的双单倍体（doubled haploid，DH）作图群体为材料，旨在鉴定与Ug99衍生Pgt生理小种抗性相关的基因组区域。研究团队分别在肯尼亚Njoro地区，对双亲及DH群体开展了为期四年的成株期病情严重度与侵染反应表型鉴定；同时在加拿大莫登附近的隔离设施内，完成了对TTKSK小种的苗期反应鉴定。利用612个单核苷酸多态性（Single Nucleotide Polymorphism，SNP）与多样性阵列技术（Diversity Arrays Technology，DArT）标记开展复合区间作图分析，在1B、4A、5B及6A染色体上共检测到4个与秆锈病抗性相关的显著数量性状位点（Quantitative Trait Locus，QTL）。其中，来自A9919-BY5C的一个主效且稳定的QTL被定位在6A染色体短臂（6AS）区域，该位点可解释苗期抗性71%的表型变异，对田间抗性的表型变异解释率最高可达46%。该QTL与Sr8基因座紧密相邻，推测其为Sr8155B1或是位于同一区域的新型抗性基因。另一个源自A9919-BY5C的成株期抗性QTL被定位在1B染色体上，其表型变异解释率最高可达14%，该位点极有可能为已知抗性基因Sr14。此外，在感病亲本‘Strongfield’中还检测到2个分别位于4A和5B染色体上的微效QTL，但这两个位点的抗性表型在不同年份间稳定性较差。与6AS和1B染色体上QTL连锁的分子标记，可用于前瞻性地将Ug99衍生Pgt生理小种的抗性基因聚合到加拿大硬粒小麦品种中，为硬粒小麦抗秆锈病育种提供有力的技术支撑。