Zhu Yong-He, Weiner Jacob, Yu Ming-Xi, Li Feng-Min
State Key Laboratory of Grassland Agro-ecosystems, Institute of Arid Agroecology, School of Life Sciences Lanzhou University Lanzhou Gansu Province China.
Department of Plant and Environmental Sciences University of Copenhagen Frederiksberg Denmark.
Evol Appl. 2018 Dec 26;12(4):733-743. doi: 10.1111/eva.12749. eCollection 2019 Apr.
Root system characteristics determine soil space exploration and resource acquisition, and these characteristics include competitive traits that increase individual fitness but reduce population performance. We hypothesize that crop breeding for increased yield is often a form of "group selection" that reduces such "selfish" traits to increase population yield. To study trends in root architecture resulting from plant breeding and test the hypothesis that increased yields result in part from group selection on root traits, we investigated root growth and branching behavior in a historical sequence of wheat () cultivars that have been widely grown in northwestern China. Plants were grown in gel-filled chambers to examine growth angles, numbers, and lengths of seminal roots, and in soil-filled chambers under eight soil resource levels for fractal analysis of root system architecture. Yield in field was evaluated at standard and low planting densities. Newer cultivars produced higher yields than older ones only at the higher sowing density, showing that increased yield results from changes in competitive behavior. Seminal root number and growth angles were negatively correlated with yield, while primary seminal root length was positively correlated with yield. Roots of higher-yielding modern varieties were simpler and less branched, grew deeper but spread less laterally than modern varieties. The fractal dimension of root branching was negatively correlated with the yield of cultivars at all resource levels. Root:shoot ratio was negatively correlated with yield under high soil resource levels. The results are consistent with the hypothesis that the success of wheat breeding for higher yields over past 100 years in northwestern China has been in part due to unconscious group selection on root traits, resulting in smaller, less branched, and deeper roots, suggesting a direction for further increases in crop yield in the future.
根系特征决定了对土壤空间的探索和资源获取，这些特征包括一些竞争性状，这些性状会增加个体适合度但降低群体表现。我们假设，提高产量的作物育种通常是一种“群体选择”形式，它会减少此类“自私”性状以提高群体产量。为了研究植物育种导致的根系结构趋势，并检验产量增加部分源于对根系性状的群体选择这一假设，我们调查了在中国西北广泛种植的一系列历史小麦（）品种的根系生长和分支行为。植株种植在装有凝胶的培养室中以检查胚根的生长角度、数量和长度，并种植在装有土壤的培养室中，设置八个土壤资源水平以进行根系结构的分形分析。在标准和低种植密度下评估田间产量。仅在较高播种密度下，较新的品种产量高于较旧的品种，这表明产量增加源于竞争行为的变化。胚根数和生长角度与产量呈负相关，而初生胚根长度与产量呈正相关。高产现代品种的根系更简单、分支更少，比现代品种扎根更深但横向扩展范围更小。在所有资源水平下，根系分支的分形维数与品种产量呈负相关。在高土壤资源水平下，根冠比与产量呈负相关。这些结果与以下假设一致：在中国西北过去100年里，小麦高产育种的成功部分归因于对根系性状的无意识群体选择，从而产生了更小、分支更少且扎根更深的根系，这为未来进一步提高作物产量指明了方向。
