Cassava is an important source of food security and livelihoods for millions of consumers daily. Water deficit conditions are one of the major factors that affect the development of root system architecture (RSA) and consequently, crop productivity, and yet, due to its long maturity periods and bulky storage root systems, RSA studies in cassava are uncommon. The objective of this study was to identify traits that are responsible for the variability and plastic responses of cassava in response to drought at the juvenile stage of growth. Eight cassava genotypes were grown in soil-filled pots under well-watered and droughted conditions for up to 45 days and multivariate analyses employed to determine the major contributory traits to variability and the relative distance plasticity index (RDPI) was computed to evaluate plasticity. There were significant genotypic variations for most of the traits measured. Drought generally inhibited root production and development and the degree of inhibition was between 2 and 22%. Regardless of the soil moisture condition, traits which differentiated the RSA included root biomass, root numbers, root branching density, and total root length, and these were also the important contributory traits to variability under well-watered soil conditions. Important contributory traits to variability traits under drought were shoot-related traits such as leaf area and shoot biomass, and also root system traits such as nodal root number, root biomass, diameter and branching density. Phenotypic plasticity was found in most traits where the number, branching density and diameter of upper nodal roots presented the highest RDPI. These traits corresponded with the traits contributing greatly to variation. Plastic responses of cassava to drought were dependent on trait and genotype. It is concluded that upper nodal roots-related traits could have importance in breeding cassava to better tolerate water deficit conditions. The secondary growth and ability to maintain or increase the upper nodal root count or density under limited soil moisture may be related to good growth and yield performance of cassava under drought conditions. Upper nodal roots could be used to screen and select cassava genotypes adapted to drought at the juvenile stage but as a potential indirect selection strategy, the persistence and pertinence of these traits and their relationship with yield and yield components under drought conditions in the field must be confirmed.

中文翻译：

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幼年木薯 (Manihot esculenta Crantz) 植物响应土壤湿度降低的可变性和可塑性的因果芽和根系统性状。

木薯是数百万消费者日常粮食安全和生计的重要来源。缺水条件是影响根系结构（RSA）发育进而影响作物生产力的主要因素之一，然而，由于其成熟期长和根系储存体积大，木薯的RSA研究并不常见。本研究的目的是确定导致木薯在幼年生长阶段应对干旱的变异性和塑性反应的性状。八种木薯基因型在浇水良好和干旱的条件下在充满土壤的盆中生长长达 45 天，并采用多变量分析来确定对变异性有主要影响的性状，并计算相对距离可塑性指数 (RDPI) 以评估可塑性。大多数测量的性状都存在显着的基因型变异。干旱普遍抑制根系的产生和发育，抑制程度在2%~22%之间。无论土壤湿度条件如何，区分 RSA 的性状包括根生物量、根数、根分枝密度和总根长，这些也是水分充足的土壤条件下变异的重要贡献性状。干旱条件下变异性状的重要贡献性状是与枝条相关的性状，例如叶面积和枝条生物量，以及根系性状，例如节根数量、根生物量、直径和分枝密度。在大多数性状中都发现了表型可塑性，其中上部节根的数量、分枝密度和直径呈现出最高的RDPI。这些性状与对变异有很大贡献的性状相对应。木薯对干旱的塑料反应取决于性状和基因型。结论是，上部节根相关性状对于育种木薯以更好地耐受缺水条件可能具有重要意义。在有限的土壤湿度下，次生生长和维持或增加上部节根数或密度的能力可能与木薯在干旱条件下良好的生长和产量表现有关。上部节根可用于筛选和选择幼期适应干旱的木薯基因型，但作为潜在的间接选择策略，必须确定这些性状的持久性和针对性及其与田间干旱条件下产量和产量组成部分的关系。确认的。