Experimental design
The MAGIC population was grown in three different geographical regions
(France, Israel and Morocco) and four specific stress treatments were
applied. Trials were conducted in order that in a given trial any stress
treatment was applied aside a control trial (Supplemental Table 1).
Treatments consisted in water deficit (WD), two levels of salinity –
considered here as low salinity (LS) and high salinity (HS) – and high
temperature (HT) stress. Water deficit was applied by reducing the water
irrigation of about 70% and 30% according to the reference
evapotranspiration in Israel in 2014 and 2015, respectively and by 50%
in Morocco in 2015. Salinity treatment was managed as described in Diouf
et al. (2018) and the average electrical conductivity of the substrate
(Ec) in Morocco 2016 was 3.76 and 6.50 dS.m-1 for LS
and HS, respectively; while the Ec in the control condition in Morocco
2015 was about 1.79 dS.m-1. For HT stress, plants were
sown during the late spring and phenotyped in the summer 2014 in Israel
(HIs14) and summer 2017 in France (HAvi17). During HT treatments,
greenhouse vent opening was managed all along the entire growing season,
with opening the vent only when temperatures rose up to 25°C. Average
mean (respectively maximal) temperatures calculated on daily (24 hours)
measurements were of 26°C (respectively 34°C) for HAvi17 and 33°C
(respectively 48°C) for HIs14. Besides stress treatments, local
conventional cultural conditions were applied for control treatments as
described in Diouf et al., (2018).
Environments were considered as any combination of a geographical
region, a year of trial and an applied treatment (Supplemental Table 1).
Climatic sensors were installed in the greenhouses and climatic
parameters recorded hourly in all environments. From the climatic
parameters, seven environmental covariates were defined (Supplemental
Figure 1) including temperature parameters (mean, minimal and maximal
daily temperatures and thermal amplitude), the sum of degree-day (SDD),
the vapour-pressure-deficit (Vpd in kPa) and the relative humidity (RH)
within the greenhouse. To characterize the environments, every covariate
was calculated during the period covering flowering time of the
population on the fourth truss. Indeed, phenotypic data analyzed here
were mostly recorded on the fourth and fifth trusses (Supplemental Table
2). Hierarchical clustering was performed with ‘FactoMineR’ R package
(Lê et al., 2008) using the environmental parameters to group
environments according to their similarity regarding the
within-greenhouse climatic conditions.
The MAGIC population, the eight parental lines and the four first
generation hybrids (one hybrid per two-way cross) were evaluated for
fruit weight (FW) by measuring the average FW of the third and/or fourth
plant truss in each environment. Phenotypic data were recorded across
the different environments for nine supplemental traits related to fruit
quality – fruit fruit firmness (firm) and soluble solid content (SSC);
plant phenology – flowering time (flw), number of flowers (nflw) and
fruit setting (fset); plant development – stem diameter (diam), leaf
length (leaf) and plant height (height) and fruit number (nfr). Details
about the phenotyping measurements are in Supplemental Table 2. At least
two plants per MAGIC line were replicated in each environment except in
Avi17 (control condition) where the average phenotype was recorded from
single plant measurements. Parents and hybrids had more replicates per
genotype (at least two) and served as control lines to measure
within-environment heterogeneity.