Steffenson B J, Case A J, Pretorius Z A, Coetzee V, Kloppers F J, Zhou H, Chai Y, Wanyera R, Macharia G, Bhavani S, Grando S
First, second, sixth, and seventh authors: Department of Plant Pathology, University of Minnesota, St. Paul 55108; third author: Department of Plant Sciences, University of The Free State, Bloemfontein, Republic of South Africa 9300; fourth and fifth authors: Pannar Seed (Pty) Ltd., P.O. Box 19, Greytown, Republic of South Africa 3250; eighth and ninth authors: Kenyan Agricultural and Livestock Research Organization, Njoro, Kenya; tenth author: International Maize and Wheat Improvement Center, Apdo. Postal, 6-641, 06600, Mexico, D.F.; and eleventh author: International Center for Agricultural Research in the Dry Areas, P.O. Box 114/5055, Beirut, Lebanon 1108-2010.
Phytopathology. 2017 Aug;107(8):950-962. doi: 10.1094/PHYTO-11-16-0400-R. Epub 2017 May 24.
The emergence of widely virulent pathotypes (e.g., TTKSK in the Ug99 race group) of the stem rust pathogen (Puccinia graminis f. sp. tritici) in Africa threatens wheat production on a global scale. Although intensive research efforts have been advanced to address this threat in wheat, few studies have been conducted on barley, even though pathotypes such as TTKSK are known to attack the crop. The main objectives of this study were to assess the vulnerability of barley to pathotype TTKSK and identify possible sources of resistance. From seedling evaluations of more than 1,924 diverse cultivated barley accessions to pathotype TTKSK, more than 95% (1,844) were found susceptible. A similar high frequency (910 of 934 = 97.4%) of susceptibility was found for the wild progenitor (Hordeum vulgare subsp. spontaneum) of cultivated barley. Additionally, 55 barley lines with characterized or putative introgressions from various wild Hordeum spp. were also tested against pathotype TTKSK but none was found resistant. In total, more than 96% of the 2,913 Hordeum accessions tested were susceptible as seedlings, indicating the extreme vulnerability of the crop to the African pathotypes of P. graminis f. sp. tritici. In total, 32 (1.7% of accessions evaluated) and 13 (1.4%) cultivated and wild barley accessions, respectively, exhibited consistently highly resistant to moderately resistant reactions across all experiments. Molecular assays were conducted on these resistant accessions to determine whether they carried rpg4/Rpg5, the only gene complex known to be highly effective against pathotype TTKSK in barley. Twelve of the 32 (37.5%) resistant cultivated accessions and 11 of the 13 (84.6%) resistant wild barley accessions tested positive for a functional Rpg5 gene, highlighting the narrow genetic base of resistance in Hordeum spp. Other resistant accessions lacking the rpg4/Rpg5 complex were discovered in the evaluated germplasm and may possess useful resistance genes. Combining rpg4/Rpg5 with resistance genes from these other sources should provide more durable resistance against the array of different virulence types in the Ug99 race group.
茎锈病病原体（小麦条锈菌）在非洲出现的广泛致病型（如Ug99种族组中的TTKSK）威胁着全球小麦生产。尽管已经开展了大量研究工作来应对小麦面临的这一威胁，但对于大麦的研究却很少，尽管已知TTKSK等致病型会侵染大麦作物。本研究的主要目的是评估大麦对TTKSK致病型的易感性，并确定可能的抗性来源。通过对1924多个不同栽培大麦品种进行TTKSK致病型的苗期评估，发现超过95%（1844个）的品种易感。栽培大麦的野生祖先（野生大麦亚种）也表现出类似的高易感频率（934个中有910个 = 97.4%）。此外，对55个具有来自不同野生大麦物种特征性或推测性渗入的大麦品系也进行了TTKSK致病型测试，但未发现有抗性的品系。总共，测试的2913个大麦品种中有超过96%在苗期易感，这表明该作物对小麦条锈菌的非洲致病型极度易感。总共分别有32个（占评估品种的1.7%）栽培大麦品种和13个（1.4%）野生大麦品种在所有实验中均表现出持续的高抗至中抗反应。对这些抗性品种进行了分子检测，以确定它们是否携带rpg4/Rpg5，这是已知在大麦中对TTKSK致病型高度有效的唯一基因复合体。在测试的32个抗性栽培品种中，有12个（37.5%）对功能性Rpg5基因检测呈阳性，在13个抗性野生大麦品种中有11个（84.6%）呈阳性，这突出了大麦属抗性遗传基础的狭窄。在评估的种质资源中发现了其他缺乏rpg4/Rpg5复合体的抗性品种，它们可能拥有有用的抗性基因。将rpg4/Rpg5与来自其他来源的抗性基因结合，应该能够提供对Ug99种族组中一系列不同毒力类型更持久的抗性。
