Abstract：
We evaluated root system architecture (RSA) of a set of 58 historical spring wheat cultivars from Pakistan representing 105 years of selection breeding. The evaluations were carried out under control and water-limited conditions using a high-throughput phenotyping system coupled with RhizoVision Explorer software. The cultivars were classified into three groups based on release year as cultivars released pre-1965, released between 1965 and 2000, and cultivars released post-2000. Under water-limited conditions a decline in 20 out of 25 RSA component traits was observed in pre-1965 cultivars group. Whereas cultivars released after the 1965, so-called green revolution period, showed a decline in 17 traits with significant increments in root length, depth, and steep angle frequency which are important root traits for resource-uptake under water-limited conditions. Similarly, cultivars released after 2000 indicated an increase in the number of roots, depth, diameter, surface area, and steep angle frequency. The coefficient of correlation analysis showed a positive correlation between root depth and yield-related traits under water-limited conditions. We also investigated the effects of green-revolution genes (Rht1) and some phenology-related genes such as DRO1, TaMOR, TaLTPs, TaSus-2B on RSA and identified significant associations of these genes with important root traits. There was strong selection pressure on DRO1 gene in cultivated wheat indicating the allele fixed in modern wheat cultivars is different from landraces. The expression of DRO1, and TaMOR were retrieved from an RNAseq experiment, and results were validated using qRT-PCR. The highest expression of DRO1 and TaMOR was found in Chakwal-50, a rainfed cultivar released in 2008, and MaxiPak-65 released in 1965. We conclude that there is a positive historic change in RSA after 1965 that might be attributed to genetic factors associated with favored RSA traits. Furthermore, we suggest root depth and steep angle as promising traits to withstand water-limited environments and may have implications in selection for breeding.
摘要：
我们评估了来自巴基斯坦的58个历史春小麦品种的根系结构（RSA），这些品种代表了105年的选择育种。使用结合RhizoVisionExplorer软件的高通量表型鉴定系统在对照和限水条件下进行评价。根据释放年份将品种分为三组，分别是1965年之前释放的品种，1965年至2000年之间释放的品种和2000年之后释放的品种。在限水条件下，在1965年前的品种组中观察到25个RSA成分性状中有20个下降。而在1965年，即所谓的绿色革命时期后发布的品种，显示17个性状下降，根长显著增加，深度,和陡角频率是水分限制条件下资源吸收的重要根系性状。同样，2000年后释放的品种表明根数增加，深度,直径,表面积,和陡峭的角度频率。相关系数分析表明,在限水条件下,根深与产量相关性状呈正相关。我们还研究了绿色革命基因（Rht1）和一些物候相关基因，如DRO1，TaMOR，TaLTPs,TaSus-2B在RSA上，并确定了这些基因与重要根性状的显着关联。栽培小麦中DRO1基因存在强大的选择压力，表明现代小麦品种中固定的等位基因不同于地方品种。从RNAseq实验中检索DRO1和TaMOR的表达，并使用qRT-PCR对结果进行验证。DRO1和TaMOR的最高表达在2008年发布的雨养品种Chakwal-50和1965年发布的MaxiPak-65中发现。我们得出的结论是，1965年以后RSA发生了积极的历史性变化，这可能归因于与偏爱的RSA性状相关的遗传因素。此外，我们建议根深和陡峭的角度是有前途的性状，可以承受水限制的环境，并可能对育种选择产生影响。
