Root age distribution: how does it matter in plant processes? A focus on water uptake

Aims and background Root growth creates a gradient in age at both the scale of the single root, from distal to proximal parts, but also at the root system level when young branch roots emerge from the axis or new nodal roots are emitted that may reach same soil domain as older roots. It is known that a number of root functions will vary with root type and root tissue age (e.g. respiration, exudation, ion uptake, root hydraulic conductance, mucilage release…) and so will the resulting rhizosphere properties. The impact of the distribution of root demography with depth, and related functions, on the overall functioning of the root system is fundamental for an integration of processes at the root system scale. Scope and conclusion Starting from methods for measuring root demography, we discuss the availability of data related to root age and its spatial distribution, considering plant types (monocot/dicot, perennial/annuals) which may exhibit different patterns. We then give a detailed review of variation of root/rhizosphere properties related to root age, focusing on root water uptake processes. We examine the type of response of certain properties to changes in age and whether a functional relationship can be derived. Integration of changing root properties with age intomodelling approaches is shown from 3D models at the single plant scale to approaches at the field scale based on integrated root system age. Functional structural modelling combined with new development in non-invasive imaging of roots show promises for integrating influence of age on root properties, from the local to whole root system scales. However, experimental quantification of these properties, such as hydraulic conductance variation with root age and root types, or impact of mucilage and its degradation products on rhizosphere hydraulic properties, presently lag behind the theoretical developments and increase in computational power

Genetic control of water use efficiency and leaf carbon isotope discrimination in sunflower (Helianthus annuus L.) subjected to two drought scenarios.

High water use efficiency (WUE) can be achieved by coordination of biomass accumulation and water consumption. WUE is physiologically and genetically linked to carbon isotope discrimination (CID) in leaves of plants. A population of 148 recombinant inbred lines (RILs) of sunflower derived from a cross between XRQ and PSC8 lines was studied to identify quantitative trait loci (QTL) controlling WUE and CID, and to compare QTL associated with these traits in different drought scenarios. We conducted greenhouse experiments in 2011 and 2012 by using 100 balances which provided a daily measurement of water transpired, and we determined WUE, CID, biomass and cumulative water transpired by plants. Wide phenotypic variability, significant genotypic effects, and significant negative correlations between WUE and CID were observed in both experiments. A total of nine QTL controlling WUE and eight controlling CID were identified across the two experiments. A QTL for phenotypic response controlling WUE and CID was also significantly identified. The QTL for WUE were specific to the drought scenarios, whereas the QTL for CID were independent of the drought scenarios and could be found in all the experiments. Our results showed that the stable genomic regions controlling CID were located on the linkage groups 06 and 13 (LG06 and LG13). Three QTL for CID were co-localized with the QTL for WUE, biomass and cumulative water transpired. We found that CID and WUE are highly correlated and have common genetic control. Interestingly, the genetic control of these traits showed an interaction with the environment (between the two drought scenarios and control conditions). Our results open a way for breeding higher WUE by using CID and marker-assisted approaches and therefore help to maintain the stability of sunflower crop production

Sunflower and climate change: Possibilities of adaptation through breeding and genomic selection

Due to its ability to grow in different agroecological conditions and its moderate drought tolerance, sunflower may become the oil crop of preference in the future, especially in the light of global environmental changes. In the field conditions, sunflower crop is often simultaneously challenged by different biotic and abiotic stresses, and understanding the shared mechanisms contributing to two or more stresses occurring individually or simultaneously is important to improve crop productivity under foreseeable complex stress situations. Exploitation of the available plant genetic resources in combination with the use of modern molecular tools for genome-wide association studies (GWAS) and application of genomic selection (GS) could lead to considerable improvements in sunflower, especially with regard to different stresses and better adaptation to the climate change. In this chapter we present a review of climate-smart (CS) traits and respective genetic resources and tools for their introduction into the cultivated sunflower, thus making it the oil crop resilient to the extreme climatic conditions and well-known and emerging pests and diseases. © Springer Nature Switzerland AG 2019