Background

Rice blast, caused by the fungus Pyricularia oryzae, represents the most damaging fungal disease of rice worldwide. Utilization of rice resistant cultivars represents a practical way to control the disease. Most of the rice varieties cultivated in Europe and several other temperate regions are severely depleted of blast resistance genes, making the identification of resistant sources in genetic background adapted to temperate environments a priority. Given these assumptions, a Genome Wide Association Study (GWAS) for rice blast resistance was undertaken using a panel of 311 temperate/tropical japonica and indica accessions adapted to temperate conditions and genotyped with 37,423 SNP markers. The panel was evaluated for blast resistance in field, under the pressure of the natural blast population, and in growth chamber, using a mixture of three different fungal strains.

Results

The parallel screening identified 11 accessions showing high levels of resistance in the two conditions, representing potential donors of resistance sources harbored in rice genotypes adapted to temperate conditions. A general higher resistance level was observed in tropical japonica and indica with respect to temperate japonica varieties. The GWAS identified 14 Marker-Traits Associations (MTAs), 8 of which discovered under field conditions and 6 under growth chamber screening. Three MTAs were identified in both conditions; five MTAs were specifically detected under field conditions while three for the growth chamber inoculation. Comparative analysis of physical/genetic positions of the MTAs showed that most of them were positionally-related with cloned or mapped blast resistance genes or with candidate genes whose functions were compatible for conferring pathogen resistance. However, for three MTAs, indicated as BRF10, BRF11–2 and BRGC11–3, no obvious candidate genes or positional relationships with blast resistance QTLs were identified, raising the possibility that they represent new sources of blast resistance.

Conclusions

We identified 14 MTAs for blast resistance using both field and growth chamber screenings. A total of 11 accessions showing high levels of resistance in both conditions were discovered. Combinations of loci conferring blast resistance were identified in rice accessions adapted to temperate conditions, thus allowing the genetic dissection of affordable resistances present in the panel. The obtained information will provide useful bases for both resistance breeding and further characterization of the highlighted resistance loci.

中文翻译：

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全基因组关联研究在田间和控制条件下对粳稻的稻瘟病抗性

背景

由稻瘟病菌引起的稻瘟病是全世界稻米中最具破坏性的真菌病。利用水稻抗性品种代表了控制该病的实用方法。欧洲和其他几个温带地区种植的大多数水稻品种都严重缺乏了稻瘟病抗性基因，因此在适应温带环境的遗传背景中鉴定抗性来源成为当务之急。基于这些假设，使用311个温带/热带粳稻和in稻进行了水稻抗稻瘟病的全基因组关联研究（GWAS）。适于温和条件并具有37,423个SNP标记的基因型。使用三种不同真菌菌株的混合物，在自然爆炸种群的压力下以及在生长室中评估该板的抗爆炸性。

结果

平行筛选鉴定了在两种条件下均显示高水平抗性的11个种质，表示在适应温带条件的水稻基因型中具有抗性来源的潜在供体。在热带观察到一般较高的电阻水平粳稻和籼相对于温带粳稻品种。GWAS确定了14个标记特质协会（MTA），其中8个是在田间条件下发现的，6个是在生长室筛选下发现的。在这两种情况下均确定了三个MTA。在田间条件下专门检测了5种MTA，而在生长室接种中则检测了3种。对MTA的物理/遗传位置的比较分析表明，它们中的大多数与克隆或定位的抗药性基因或功能可赋予病原体抗性的候选基因在位置上相关。然而，对于三个MTA，分别表示为BRF10，BRF11-2和BRGC11-3，未发现明显的候选基因或与抗瘟QTL的位置关系，这增加了它们代表抗爆炸新来源的可能性。

结论

我们通过田间和生长室筛选确定了14种MTA的抗爆炸性。在这两种条件下总共发现了11种显示出高水平抗性的种质。在适应温度条件的水稻种质中鉴定到了赋予抗瘟性的基因座组合，因此可以进行基因组中遗传上可承受的抗性的遗传分离。获得的信息将为抗性育种和突出显示的抗性基因座的进一步表征提供有用的基础。