Abstract
Genetic studies of response to water deficit in adult trees are limited by low throughput of the usual phenotyping methods in the field. Here, we aimed at overcoming this bottleneck, applying a new methodology using airborne multispectral imagery and in planta measurements to compare a high number of individuals.An apple tree population, grafted on the same rootstock, was submitted to contrasting summer water regimes over two years. Aerial images acquired in visible, near- and thermal-infrared at three dates each year allowed calculation of vegetation and water stress indices. Tree vigour and fruit production were also assessed. Linear mixed models were built accounting for date and year effects on several variables and including the differential response of genotypes between control and drought conditions.Broad-sense heritability of most variables was high and 18 quantitative trait loci (QTLs) independent of the dates were detected on nine linkage groups of the consensus apple genetic map. For vegetation and stress indices, QTLs were related to the means, the intra-crown heterogeneity, and differences induced by water regimes. Most QTLs explained 15-20% of variance.Airborne multispectral imaging proved relevant to acquire simultaneous information on a whole tree population and to decipher genetic determinisms involved in response to water deficit.
Highlights
According to current climate change models for the 21st cen tury, an increase in global mean temperatures is expected, with longer or more frequent episodes of extreme temperatures and drought, notably in the Mediterranean basin (IPCC, 2014)
Models related to phenotypic values in (A) well-watered trees (WW) and waterstressed trees (WS), and (B) models related to differential index (DI) were built
normalized difference vegetation index (NDVI) appeared the most stable vegetation index, independent of the environment and acqui sition conditions whereas other spec tral indices chosen proved to be sensitive to drought, with a G×D interaction revealed for visible atmospherically resistant index (VARI), simple ratio pigment index (SRPI), TsTa and Water Deficit Index (WDI)
Summary
According to current climate change models for the 21st cen tury, an increase in global mean temperatures is expected, with longer or more frequent episodes of extreme temperatures and drought, notably in the Mediterranean basin (IPCC, 2014). Climate change will lead to reconsideration of bree ding programmes for many crops, and optimization of water. Plants have developed various mechanisms to cope with drought that depend on the duration and intensity of the water deficit, and their responses occur at different temporal and spatial scales, from cell to whole tree level (Jones et al, 2002). Efficiency of stomatal regulation is variable according to species and Tardieu and Simonneau (1998) have shown that plants display contrasting transpiration behaviours (isohydric vs anisohydric) in response to drought. At the intra-specific level, genetic vari ability of stomatal regulation has been highlighted in apple (Massonnet et al, 2007; Liu et al, 2012) and grapevine (Marguerit et al, 2012; Coupel-Ledru et al, 2014)
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