Abstract Modelling and limited data suggest that crops with deeper and longer roots capture more soil resources and yield more when water is available deeper in soil profiles. Interest has grown in the development of new cultivars with deeper roots. This study provides data from three field experiments to help researchers and breeders continue to assess the value of selecting for deeper roots for yield and water use efficiency gains. We asked: do genotype groups with shoot phenotypes easily selectable in pre-breeding programs express predictable root depth and length at time of grain harvest in the field? Do flowering time and shoot biomass predict deep roots measured directly in the field with coring, such that deeper roots are associated with more shoot growth and yield? Does genotype, including triticale versus wheat types, vary in rooting traits? Thirty-four wheats (Triticum aestivum L.) and two triticales (× Triticosecale) were drawn from ten ‘genotype groups’; selections from breeding programs and commercial cultivars that were distinguished on the basis of height, tillering, winter habit, and early vigour. These were grown at two independent sites and soil conditions in year 1 (experiment 1 and 2), with a subset of six wheats and two triticales repeated in year 2 at year 1 site (experiment 3). Above-ground biomass, flowering date, grain yield and root length and depth were measured with a high level of replication (four replicate plots and four soil cores per plot). Root length density was predicted from root counts obtained using the core-break method on 42 mm diameter, two m deep cores. A Bayesian multivariate mixed-effects model was used with fixed effects of the environment and random effects of genotype groups, genotypes and their interactions with the environment. Variation in rooting depth and length caused by environments was much larger than that caused by genotypes. Positive relationships between biomass, yield and root depth and length were observed across experiments and genotype groups (r = 0.62 for biomass and root depth, r = 0.61 for yield and root depth; r = 0.66 for biomass and root length, r = 0.53 for yield and root length), but the largest effects were driven by differences in soil and rainfall conditions between experiments. However, the smaller genetic effects on rooting depth and yield were positively correlated (r = 0.69). We did not find that easily selectable shoot traits like early vigour, tillering, and height reliably predicted in-field deeper rooting. Notably, the two triticales were 74 % more likely to have a deeper rooting and 82 % more likely to have less total root length, than spring wheats. We conclude that deeper and longer roots at maturity are (1) challenging to pre-select using shoot phenotype prior to field evaluation; (2) depend almost entirely on environment for expression in the field with small effects of genotype; and (3) can grow at no apparent 'cost' to shoot growth or yield and as such can remain a target for breeding.

中文翻译：

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在三个田间试验中生长的不同小麦和黑小麦基因型成熟时的根表型：与枝条选择、生物量、谷物产量、开花时间和环境的关系

摘要 建模和有限的数据表明，当土壤剖面更深的水可用时，根系更深更长的作物捕获更多的土壤资源，产量更高。人们对开发具有更深层次的新品种的兴趣日益浓厚。这项研究提供了来自三个田间试验的数据，以帮助研究人员和育种者继续评估选择更深的根以提高产量和用水效率的价值。我们问：在预育程序中容易选择具有枝条表型的基因型组是否在田间谷物收获时表达可预测的根深和长度？开花时间和枝条生物量是否可以预测直接在田间取芯测量的深根，这样更深的根与更多的枝条生长和产量有关？基因型，包括黑小麦与小麦类型，生根性状不同？从十个“基因型组”中抽取了 34 种小麦 (Triticum aestivum L.) 和两种小黑麦 (× Triticosecale)；根据高度、分蘖、冬季习性和早期活力区分的育种计划和商业栽培品种的选择。这些在第 1 年（实验 1 和 2）的两个独立地点和土壤条件下种植，第 1 年地点（实验 3）在第 2 年重复了 6 种小麦和两种小黑麦的子集。地上生物量、开花日期、谷物产量和根长和深度以高水平重复测量（四个重复样地和每个样地四个土壤核心）。根长密度是根据在 42 毫米直径、2 米深的核心上使用核心断裂方法获得的根数来预测的。贝叶斯多元混合效应模型用于环境的固定效应和基因型组、基因型及其与环境相互作用的随机效应。环境引起的生根深度和长度的变化远大于基因型引起的变化。在实验和基因型组中观察到生物量、产量和根深度和长度之间的正相关关系（生物量和根深度 r = 0.62，产量和根深度 r = 0.61；生物量和根长度 r = 0.66，r = 0.53 用于产量和根长），但最大的影响是由实验之间土壤和降雨条件的差异驱动的。然而，对生根深度和产量的较小遗传效应呈正相关（r = 0.69）。我们没有发现像早期活力、分蘖、和高度可靠地预测了田间更深的生根。值得注意的是，与春小麦相比，这两种小黑麦的生根较深的可能性高 74%，总根长较短的可能性高 82%。我们得出结论，成熟时更深、更长的根是（1）在田间评估之前使用芽表型进行预选择具有挑战性；(2)在田间表达几乎完全依赖环境，基因型影响小；(3) 可以在没有明显的芽生长或产量“成本”的情况下生长，因此可以继续作为育种目标。我们得出结论，成熟时更深、更长的根是（1）在田间评估之前使用芽表型进行预选择具有挑战性；(2)在田间表达几乎完全依赖环境，基因型影响小；(3) 可以在没有明显的芽生长或产量“成本”的情况下生长，因此可以继续作为育种目标。我们得出结论，成熟时更深、更长的根是（1）在田间评估之前使用芽表型进行预选择具有挑战性；(2)在田间表达几乎完全依赖环境，基因型影响小；(3) 可以在没有明显的芽生长或产量“成本”的情况下生长，因此可以继续作为育种目标。