Unlocking the genetic potential of the root system, rhizosheath mucilage and microbiome of wheat (Triticum aestivum L.)

全球人口不断增加，对气候的预测将对作物生产构成挑战，化肥和杀虫剂的有害使用意味着我们需要在对环境影响最小的情况下提高目前正在耕种的土地的生产力。小麦是全球作物产量的第二大贡献者，在两个半球的纬度范围内都有种植。小麦的根系是植物表现的关键决定因素，但由于研究地下器官的挑战，根在育种中被忽视。来自文献的证据表明，在高产和有压力的环境中，水分和养分的吸收往往是次优的。促进将根系特征纳入育种计划，并制定增强根系功能的作物管理战略，可能是提高产量潜力和稳定性，同时将投入降至最低的关键。为了填补根系-根际-产量互作的知识空白，本研究分成三个战略领域：根系构型(RSA)、根系分泌物和根际微生物1)在Avalon x Cadenza双单倍体(AXC)定位群体中的RSA的遗传定位确定了苗木种子根角、根长和生长速率的数量性状基因座(QTL)。可复制的QTL与根角相关，定位在3A和4D染色体上，解释了7%的表型变异。经过广泛的根部表型鉴定，在种群分布的两端显示表型的尾巴被带到田间试验。2)根分泌物代表植物固定碳的显著损失，但它们被认为与植物水分状况、营养、盐胁迫、微生物相互作用和根鞘的发育有关。用酶联免疫吸附分析法(ELISA)定量测定AXC尾叶根鞘中高分子量多糖的含量，确定基因型对分泌的影响，并研究与RSA的潜在相互作用。3)对AXC尾叶根鞘内微生物种群的元基因组学研究发现，同一物种的不同品系之间微生物群落组成存在差异。根据表型(分泌水平、RSA、产量)分组的品系表明，高产品系的微生物群与低产品系的不同。分泌的多糖水平与微生物群的差异有关。总体而言，这项研究提出了一种新的、多方面的研究，从田间的苗木到成熟的植物，因为全面的作物改良方法比不太可能发现“银弹”更有说服力。

An increasing global population, projections of climates that will challenge sufficient crop production, and a detrimental use of fertiliser and pesticides mean that we need to increase the productivity of land currently under cultivation with minimal impact on the environment. Wheat is the second largest contributor to global crop production and is cultivated across a range of latitudes across both hemispheres. The wheat root system is a crucial determinant of plant performance, yet roots are overlooked in breeding due to the challenge of studying organs below ground. Evidence from the literature indicate that water and nutrient uptake are often suboptimal in high yielding and stressed environments. Facilitating the incorporation of root system characteristics into breeding programmes and developing crop management strategies that enhance root function could be key to increasing yield potential and stability, while minimising inputs. To fill the knowledge gap on root-rhizosphere-yield interactions the research presented here falls into three strategic areas: root system architecture (RSA), root secretions and the rhizosphere microbiome.1) Genetic mapping of RSA in the Avalon x Cadenza Doubled Haploid (AxC) mapping population identified quantitative trait loci (QTL) for seedling seminal root angle, length and growth rate. Replicable QTLs were associated with root angle and mapped to chromosomes 3A and 4D, explaining 7% of phenotypic variation. After extensive root phenotyping, the tails displaying phenotypes at the extremes of the population distribution were taken forward for field trials. Correlations between seedling root phenotypes and the root and canopy phenotypes of mature plants grown in the field were calculated.2) Root secretions represent a significant loss of fixed carbon from the plant, yet they are thought to confer benefits in relation to plant water status, nutrition, salinity stress, microbial interactions and the development of the rhizosheath. Enzyme-linked immunosorbent assays (ELISAs) were used to quantify the amount of high molecular weight polysaccharides in the rhizosheath of AxC tails, determine the influence of genotype on secretion and investigate potential interactions with RSA.3) A metagenomics study of the microbial population within the rhizosheath of AxC tails uncovered differences in microbial community composition between lines of the same species. Lines grouped according to phenotype (level of secretion, RSA, yield) showed that the microbiome of high-yielding lines differed from that of low-yielding lines. The level of secreted polysaccharides was associated with differences in the microbiome.Overall, this research presents a novel, multi-faceted study of the root system, from seedling to mature plant in the field, as a holistic approach to crop improvement is more robust than the unlikely discovery of a "silver bullet".