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Grapevine root growth under water stress and its relationship to root water uptake

Abstract : The subject of adaptation to climate change has become one of the most important contemporary topics in grapevine. Much focus has been placed on the understanding of rootstocks effects on scion growth, nutrient uptake, and tolerance to stress, with the ultimate goal of developing novel rootstocks that facilitate adaptation to a changing climate. The purpose of this thesis is to examine how differences in drought resistance between genotypes could result largely from differences in their ability to maintain root growth under stress. A better understanding of how root structure, growth, and water uptake respond to stress will allow us to better understand what aspects of root physiology contribute to drought tolerance. Previous research focused on root water uptake in grapevine suggested that root water uptake could be tightly coupled to a root’s instantaneous rate of growth (see Gambetta et al. 2013). This observation implies that differences in drought resistance between genotypes could result largely from their ability to maintain root growth under stress. Two grapevine rootstocks with contrasting drought resistance capacity, Riparia Gloire de Montpellier (RGM) and 110 Richter (110R), were selected to study in this thesis. RGM is considered as sensitive to drought, while 110R is highly resistant to drought (Carbonneau 1985). The thesis examined the relationship between root growth and drought resistant capacity by assessing root growth rate, hydraulic conductivity across two rootstock varieties subjected to water deficit. The role of aquaporin gene expression (via qPCR and RNAseq) and their contribution to root hydraulic conductivity were analyzed in fine roots in order to obtain a better understanding on the mechanisms involved in the regulation of root water uptake and hydraulic conductivity across development and in response to water deficit.Prolonged water stress treatment decreased plant water potential. Individual root growth is very heterogeneous, although drought treatment reduces root elongation on average, individual root growth rate still varies enormously. High level of water stress significantly reduced average root growth rate for both RGM and 110R. Globally, average root growth rate showed a decreased trend over plant development. Soil temperature is also a factor that affects root growth. For both RGM and 110R, under both well-watered and water-stressed conditions, average daily root growth rate was positively correlated with average daily soil temperature. Under well-watered conditions, higher root growth rates were constantly observed in 110R compared to RGM, which could be one possible explanation for the higher capacity in drought resistance of 110R.Root hydraulic conductivity (Lpr) was influenced by both water stress treatment and plant developmental stage. Generally, for both RGM and 110R, Lpr was significantly reduced under water stress in early stage. In mid and late stages, no significant differences in Lpr were observedIVbetween well-watered and water-stressed plants. Changes in individual root Lpr in response to pre-dawn leaf water potential (ᴪpredawn) were investigated as well. Lpr showed a fast drop in the beginning of water stress treatment when ᴪpredawn was higher than -0.5 MPa. However, with ᴪpredawn getting more negative, e.g. from -0.4 MPa to -2.0 MPa, the range of Lpr values measured in our study maintained constant. Lpr of well-watered plants decreased as well even though their ᴪpredawn was maintained at a high level (< 0.1 MPa) during the period of the experiment. [...]
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Li Zhang. Grapevine root growth under water stress and its relationship to root water uptake. Vegetal Biology. Université de Bordeaux, 2017. English. ⟨NNT : 2017BORD0893⟩. ⟨tel-02488828⟩

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