Key message

Walnut production in California depends on the performance of three clonal hybrid rootstocks, and this study provides evidence that roots of genotype RX1 exhibit unique properties to cope with water stress induced by drought.

Abstract

Three hybrid genotypes RX1 (Juglans microcarpa × J. regia), Vlach and VX211 (both J. hindsii × J. regia) are the most commonly used rootstocks for walnut production in California. These rootstocks provide various levels of disease resistance, but their performance under drought is unknown. Based on our findings on xylem stress physiology of native walnut species, we hypothesize that hybrid genotypes originating from wild species native to drier habitats will exhibit superior root performance under drought stress. Using a whole-plant experimental approach, we evaluated root and canopy physiological characteristics of 2-year-old tree saplings of RX1, Vlach and VX211 under two soil moisture treatments (‘control’ 70–90% and ‘drought’ 20–40% w/w soil moisture). In control saplings, root biomass was twofold smaller in RX1 as compared to VX211, but root system hydraulic conductance (K_ro, predominantly cell-to-cell pathway) was more than 50% greater in RX1 and Vlach as compared to VX211. The relatively low K_ro of VX211 was related to a larger number of root cortical cell layers and endodermis development. In drought-stressed saplings, root biomass was reduced by 27% (P < 0.05) in VX211 but no significant reduction in root biomass was detected in RX1 and Vlach. Maintenance of root biomass under drought in RX1 and Vlach was associated with an 80% decrease in K_ro, a threefold increase in leaf intrinsic water-use efficiency, and maintenance of leaf turgor as compared to control conditions. Drought-induced reductions in K_ro were linked to the formation of a multiseriate root endodermis in all three genotypes.

中文翻译：

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可作为砧木购得的核桃基因型（RX1，Vlach，VX211）对干旱的生理响应的比较研究

关键信息

加利福尼亚州的核桃生产取决于三种克隆杂交砧木的性能，这项研究提供了证据表明基因型RX1的根表现出独特的特性以应对干旱引起的水分胁迫。

抽象

三混合基因型RX1（胡桃叶榕 ×  J.核桃），瓦拉几和VX211（二者J. hindsii  ×  J.核桃）是加利福尼亚核桃生产中最常用的砧木。这些砧木提供各种水平的抗病性，但是在干旱下其表现尚不清楚。根据我们对天然核桃树种木质部胁迫生理的发现，我们假设源自干旱和干旱生境的野生物种的杂种基因型在干旱胁迫下将表现出优异的根系表现。使用整株植物的实验方法，我们评估了两种土壤水分处理（“控制” 70-90％和“干旱” 20-40％）对RX1，Vlach和VX211的2岁树苗的根和冠层的生理特性。 w / w土壤水分）。在对照树苗中，RX1的根生物量比VX211小两倍，但根系水力传导率（K _ro，主要是细胞间通路）在RX1和Vlach中比VX211高出50％以上。相对低的ķ _RO VX211的是有关根皮质细胞层和内皮层发展的更大的数字。在干旱胁迫的幼树中， VX211的根系生物量减少了27％（P <0.05），但在RX1和Vlach中未检测到根系生物量的显着减少。干旱胁迫下在RX1和瓦拉几根生物量的维护用在80％的下降相关联ķ _RO，在叶固有水分利用效率增加了三倍，和叶子的膨压的维护相比，控制的情况。在干旱导致减少ķ _RO 在所有三种基因型中都与多序列根内胚层的形成有关。