Assessment of genetic biodiversity of durable disease resistance in African wheat genotypes leading to the development of markers for wheat breeding

小麦茎锈病和条锈病是小麦的主要真菌病害。直到1999年，通过推广抗病小麦品种，有效地控制了茎锈病。1999年，东非出现了一种新的致病小种，UG99，它摧毁了小麦作物。UG99现在已经在阿拉伯半岛被检测到，这显示出人们对锈病病原体在世界各地传播的熟悉程度。UG99现在预计将在不久的将来蔓延到北非、中东、巴基斯坦和印度的主要小麦种植区。条锈病也主要是通过部署抗性基因来控制的，虽然可以获得一些有效的抗病来源，但过去的历史表明，这种疾病可以造成多么严重的破坏。上世纪80年代，东非又出现了一种新的致病小种S。不到四年，这场竞赛就蔓延到了南亚。据估计，它在途中造成了价值10亿美元的小麦生产损失。这种疾病也正在获得新的领域。1996年，它首次出现在南非。2002年，它从东澳大利亚州蔓延到西澳大利亚州，并再次在北美西海岸造成严重问题。作为全球锈病倡议的一部分，在肯尼亚和埃塞俄比亚进行的研究表明，目前种植的大多数小麦品种都对UG99感病，就像1980年代S的新条锈病小种一样。因此，对于这两种疾病，我们必须不断寻找新的抗源。该方案将筛选约翰·因内斯中心小麦种质馆藏的大量非洲小麦品种。该种质包括从埃塞俄比亚、肯尼亚、赞比亚、南非、苏丹、突尼斯和摩洛哥收集的300份小麦种质。这些小麦品种将在英国和非洲的田间试验以及JIC的温室试验中进行抗茎和条锈病评估。DNA标记将被用来在分子水平上定义这些基因型之间的差异程度，并将这种差异与茎和条锈病的遗传抗性差异联系起来。古老的欧洲小麦品种Cappelle Desprez(CD)在整个20世纪60年代的S和70年代的S期间一直在欧洲种植，并在此期间保持了对条锈病的田间抗性。自2001年以来，CD对条锈病的抗性在南非的种植条件下被证明是有效的。细胞遗传学研究表明，CD中的一些染色体参与了对条锈病的抗性，这表明了复杂的遗传控制。因此，很明显，充分了解CD持久抗条锈病的遗传学对于确保其有效转移到非洲小麦品种是至关重要的。将进行一项遗传和图谱研究，以确定导致这种极其有用的抗药性来源的基因。英国JIC的L博士和R Prins博士与南非UFS的Z Pretorius教授之前的合作，从南非品种Kariega与感条锈病小麦鳄梨的杂交中获得了一个巨大的加倍单倍体群体。这项研究在Kariega中发现了两个抗条锈病的主效基因；位于2B染色体上的一个新的、未鉴定的抗性和位于7D染色体上的一个抗性被认为是持久的抗锈病复合体，Yr18/Lr34。然而，识别这两个抗性的标记仍有一段距离，在标记辅助选择育种策略中需要使用更接近的标记。两种新的标记方法将被应用于精细定位2B和7D条锈性；NBS-轮廓(van der Linden等人。2004年)，以及根据在表达基因中发现的核苷酸多态开发的标记(Liu和Anderson，2003)。参考文献：Liu&Anderson(2003)Genome 46：817-823；Van der Linden等人。(2004)标签109：384-393

Stem and stripe rust are major fungal diseases of wheat. Until 1999 stem rust was effectively controlled through the deployment of resistant wheat cultivars. In 1999 a new, virulent race of this pathogen, Ug99 appeared in Eastern Africa, devastating the wheat crop. Ug99 has now been detected in the Arabian Peninsula, showing the all too familiar ease with which rust pathogens spread around the world. Ug99 is now predicted to spread to the major wheat growing areas of North Africa, the Middle East, Pakistan and India in the very near future. Stripe rust is also primarily controlled through the deployment of resistance genes, and while some effective sources of resistance to this disease are available past history recalls how devastating this disease can be. In the 1980's a new virulent race of stripe rust again appeared in Eastern Africa. Within four years this race had spread to Southern Asia. On its way it was estimated to have caused a loss in wheat production valued at 1 billion US dollars. This disease is also gaining new territories. It appeared in South Africa for the first time in 1996. In 2002 it spread from Eastern to Western Australia, and it is again causing significant problems along the western coast of North America. Research undertaken in Kenya and Ethiopia, as part of the Global Rust Initiative, has shown that most of the currently grown wheat cultivars are susceptible to Ug99, as was the situation with the new stripe rust race in the 1980's. Therefore, for both diseases, it is imperative that we are constantly on the search for new and novel sources of resistance. This programme will screen an extensive collection of African wheat genotypes held within the John Innes Centre Wheat Germplasm Collection. This collection consists of 300 wheat accessions collected from Ethiopia, Kenya, Zambia, South Africa, Sudan, Tunisia and Morocco. These wheat genotypes will be assessed for resistance to stem and stripe rust in field trials in the UK and Africa, and in greenhouse tests at JIC. DNA markers will be used to define the extent of the variation between these genotypes at the molecular level, and relate this variation to the differences in genetic resistance seen for stem and stripe rust. An old European wheat cultivar, Cappelle Desprez (CD) was grown in Europe throughout the 1960's and 1970's and during this period maintained its field resistance to stripe rust. The stripe rust resistance in CD has proven effective under South African growing conditions since 2001. Cytogenetic studies have implicated a number of chromosomes in CD as contributing to the stripe rust resistance, suggesting a complex genetic control. It is therefore clear that a full understanding of the genetics of the durable stripe rust resistance in CD is essential to ensure its effective transfer to African wheat cultivars. A genetic and mapping study will be undertaken to identify the genes contributing to this extremely useful source of resistance. A previous collaboration between Dr. L Boyd, JIC, UK and Dr R Prins and Prof. Z Pretorius, UFS, South Africa generated a large Doubled Haploid population from the cross between the South African cultivar Kariega and the stripe rust susceptible wheat AvocetS. This study identified two major genes for resistance to stripe rust in Kariega; a new, uncharacterised resistance on chromosome 2B and a resistance on chromosome 7D believed to be the durable rust resistance complex, Yr18/Lr34. However, the markers identifying these two resistances are still some distance, and closer markers are required for use in Marker Assisted Selection breeding strategies. Two new marker approaches will be applied to fine map the 2B and 7D stripe rust resistances; NBS-profiling (van der Linden et al. 2004) and markers developed from nucleotide polymorphisms found within expressed genes (Liu and Anderson, 2003). References: Liu & Anderson (2003) Genome 46:817-823; Van der Linden et al. (2004) TAG 109:384-393