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

条锈病和秆锈病是小麦的主要真菌病害。直到1999年，通过使用抗锈小麦品种，茎锈病得到了有效控制。1999年，这种病原体的一个新的毒性小种Ug 99出现在东非，摧毁了小麦作物。现在在阿拉伯半岛发现了Ug 99，这表明锈病病原体在世界各地传播的速度非常容易。据预测，Ug 99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，虽然对这种疾病有一些有效的抗性来源，但过去的历史回顾了这种疾病的破坏性。20世纪80年代，东非又出现了一种新的条锈病毒力小种。四年后，这场比赛蔓延到了南亚。据估计，这场风暴在途中造成了价值10亿美元的小麦产量损失。这一疾病也在扩大新的领域。1996年首次出现在南非。2002年，它从东澳大利亚蔓延到西澳大利亚，并再次造成严重的问题，沿着北美西海岸。在肯尼亚和埃塞俄比亚进行的研究，作为全球锈病倡议的一部分，已经表明，目前种植的大多数小麦品种对Ug 99敏感，就像20世纪80年代新的条锈病小种的情况一样。因此，对于这两种疾病，我们必须不断寻找新的和新颖的耐药性来源。这一方案将筛选约翰·英纳斯中心小麦种质收藏所收藏的大量非洲小麦基因型。该收集包括从埃塞俄比亚、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。这些小麦基因型将在英国和非洲的田间试验以及JIC的温室试验中评估对茎锈病和条锈病的抗性。DNA标记将用于在分子水平上确定这些基因型之间的变异程度，并将这种变异与茎锈病和条锈病的遗传抗性差异联系起来。一个古老的欧洲小麦品种，Cappelle Desprez（CD）在整个20世纪60年代和70年代在欧洲种植，并在此期间保持其对条锈病的田间抗性。自2001年以来，在南非的种植条件下，CD的抗条锈性已被证明是有效的。细胞遗传学研究表明CD中的许多染色体有助于抗条锈性，这表明存在复杂的遗传控制。因此，很明显，充分了解CD持久抗条锈病的遗传学是确保其有效转移到非洲小麦品种的关键。将进行一项遗传和绘图研究，以确定促成这种极其有用的抗性来源的基因。英国JIC的L Boyd博士和南非UFS的R Prins博士和Z Pretorius教授之前的合作从南非栽培品种Kariega和条锈病易感小麦AvocetS之间的杂交中产生了一个大型加倍单倍体群体。这项研究确定了Kariega抗条锈病的两个主要基因;染色体2B上的一个新的、未表征的抗性和染色体7 D上的一个抗性，据信是持久的锈病抗性复合体，Yr 18/Lr 34。然而，鉴定这两种抗性的标记仍有一定距离，需要更近的标记用于标记辅助选择育种策略。两种新的标记方法将用于精细定位2B和7 D条锈病抗性; NBS-谱分析（货车der林登et al. 2004）和从表达基因内发现的核苷酸多态性开发的标记（Liu和安德森，2003）。参考文献：Liu和安德森（2003）基因组46：817-823;货车德林登等人（2004）TAG 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