Department of Crop Genetics, John Innes Centre, Norwich Research Park, Norwich, UK.
Universidade de Passo Fundo, Passo Fundo, RS, Brazil.
BMC Plant Biol. 2020 Aug 27;20(1):398. doi: 10.1186/s12870-020-02592-0.
Wheat blast, caused by Magnaporthe oryzae Triticum (MoT) pathotype, is a global threat to wheat (Triticum aestivum L.) production. Few blast resistance (R) genes have been identified to date, therefore assessing potential sources of resistance in wheat is important. The Brazilian wheat cultivar BR 18-Terena is considered one of the best sources of resistance to blast and has been widely used in Brazilian breeding programmes, however the underlying genetics of this resistance are unknown.
BR 18-Terena was used as the common parent in the development of two recombinant inbred line (RIL) F populations with the Brazilian cultivars Anahuac 75 and BRS 179. Populations were phenotyped for resistance at the seedling and heading stage using the sequenced MoT isolate BR32, with transgressive segregation being observed. Genetic maps containing 1779 and 1318 markers, were produced for the Anahuac 75 × BR 18-Terena and BR 18-Terena × BRS 179 populations, respectively. Five quantitative trait loci (QTL) associated with seedling resistance, on chromosomes 2B, 4B (2 QTL), 5A and 6A, were identified, as were four QTL associated with heading stage resistance (1A, 2B, 4A and 5A). Seedling and heading stage QTL did not co-locate, despite a significant positive correlation between these traits, indicating that resistance at these developmental stages is likely to be controlled by different genes. BR 18-Terena provided the resistant allele for six QTL, at both developmental stages, with the largest phenotypic effect conferred by a QTL being 24.8% suggesting that BR 18-Terena possesses quantitative resistance. Haplotype analysis of 100 Brazilian wheat cultivars indicates that 11.0% of cultivars already possess a BR 18-Terena-like haplotype for more than one of the identified heading stage QTL.
This study suggests that BR 18-Terena possesses quantitative resistance to wheat blast, with nine QTL associated with resistance at either the seedling or heading stage being detected. Wheat blast resistance is also largely tissue-specific. Identification of durable quantitative resistances which can be combined with race-specific R gene-mediated resistance is critical to effectively control wheat blast. Collectively, this work facilitates marker-assisted selection to develop new varieties for cultivation in regions at risk from this emerging disease.
由稻瘟病菌（Magnaporthe oryzae Triticum，MoT）引起的小麦穗疫病是全球小麦（Triticum aestivum L.）生产的威胁。迄今为止，已鉴定出少数几个抗穗疫病（R）基因，因此评估小麦的潜在抗性来源很重要。巴西小麦品种 BR 18-Terena 被认为是抗穗疫病的最佳来源之一，已在巴西的育种计划中广泛使用，但该品种的抗性遗传基础尚不清楚。
BR 18-Terena 被用作与巴西品种 Anahuac 75 和 BRS 179 两个重组自交系（RIL）F 群体的共同亲本。利用测序的 MoT 分离株 BR32 对幼苗期和抽穗期进行抗感鉴定，观察到超亲分离。为 Anahuac 75×BR 18-Terena 和 BR 18-Terena×BRS 179 群体分别制作了包含 1779 和 1318 个标记的遗传图谱。在第 2B、4B（2 个 QTL）、5A 和 6A 染色体上鉴定到与幼苗期抗性相关的 5 个数量性状位点（QTL），在 1A、2B、4A 和 5A 染色体上鉴定到与抽穗期抗性相关的 4 个 QTL。尽管这两个性状之间存在显著的正相关，但幼苗期和抽穗期 QTL 没有共定位，这表明这两个发育阶段的抗性可能由不同的基因控制。BR 18-Terena 为两个发育阶段的 6 个 QTL 提供了抗性等位基因，其中一个 QTL 赋予的表型效应最大，为 24.8%，表明 BR 18-Terena 具有数量抗性。对 100 个巴西小麦品种的单倍型分析表明，已有 11.0%的品种携带与鉴定出的抽穗期 QTL 中的一个或多个相似的 BR 18-Terena 单倍型。
本研究表明，BR 18-Terena 对小麦穗疫病具有数量抗性，在幼苗期或抽穗期检测到与 9 个 QTL 相关的抗性。小麦穗疫病抗性在很大程度上是组织特异性的。鉴定出可与特定 R 基因介导的抗性相结合的持久数量抗性，对于有效控制小麦穗疫病至关重要。总的来说，这项工作促进了标记辅助选择，以开发用于防治这一新兴疾病的新品种。
