Relationships between root system morphology
and biomass production under nitrogen
deficiency in grafted tomato
Lequeue Gauthier and Draye Xavier
Université catholique de Louvain - Earth and Life Institute - Agronomy
Croix du Sud 2, bte L7.05.11,1348 Louvain-la-Neuve, Belgium
contact: [email protected]
Introduction and objectives
Results
This project aims to improve our understanding of the architectural
response of the tomato (S. lycopersicon) root system to low nitrogen
input and to assess the quantitative genetic variability of this response in
order to develop rootstocks that enhance the agronomic stability and
sustainability of tomato under low nitrogen.
A very large variability was observed for all recorded traits in the
population, as illustrated for the third replicate on Table 1. Broad sense
heritabilities ranged from 0.32 to appreciable values of 0.73. They were
similar or lower at low N compared to high N, except for the evolution of
the N status (slope of a linear regression of plant N on time) where H2
was higher at low N. No differences were found for the shoot:root ratio at
low N
Material and Methods
A large-scale phenotyping experiment has been conducted on a
population of 140 recombinant inbred lines (RILs) from a cross between
Solanum lycopersicum var. cerasiforme and S. pimpinellifolium. RILs were
used as rootstocks, and grafted with a common scion, in order to isolate
the underground contribution to biomass production under low N.
Table 1. Variance analysis and heritabilities
Trait
N level
nG
F
P<F
H2
Maximum root depth
0.8
132
2.77
<0.0001
0.64
13
139
2.54
<0.0001
0.60
0.8
132
2.20
<0.0001
0.54
0.38
N status evolution
Root dry mass
Root fresh mass
Root:shoot ratio
Shoot dry mass
Shoot fresh mass
Fig 1 : Schematic representation of the aeroponic
box (Ligeza A. and al., 2011. Aeroponics as a tool
for
high
throughput
phenotyping.
”plant
phenotyping workshop”, Juelich, Germany).
Three-week old RIL-scion plants produced by Unigenia (Spain) were
acclimated in aeroponics for one week after whole root system excision
(fig. 1). They were then grown for two weeks under both low N (0.8 mM,
n=3) and high N (13 mM, n=3). Individual plant N status has been
monitored every two days using a Multiplex® (FORCE-A, Orsay, France).
At the end of the experiment, a highresolution image of the root system
has been acquired and the root and shoot fresh and dry biomass have
been measured. The maximum root depth was extracted from a first step
image analysis. The whole experiment has been replicated three times.
Perspective
A more detailed analysis of root system images is currently carried out to
generate additional root shape parameters that should approach root
system architecture using model-based methods (fig. 3). In addition,
xylem sap collected at harvest is being analysed for major hormones
(ABA, ACC, auxin, cytokinins, jasmonic acid, salicylicacid) and elements
(cations and anions, C, N, O). The final dataset will be used for the QTL
analysis of root system architecture and biomass production to identify
the underlying traits contributing to low N tolerance.
13
139
1.62
<0.0001
0.8
132
1.95
<0.0001
0.49
13
139
2.11
<0.0001
0.52
0.8
132
3.83
<0.0001
0.73
13
139
3.41
<0.0001
0.71
0.8
132
1.01
0.44
0.01
13
139
1.92
<0.0001
0.48
0.8
132
1.47
0.004
0.32
13
139
2.24
<0.0001
0.55
0.8
132
2.11
<0.0001
0.52
13
139
2.71
<0.0001
0.63
Two-way analyses of variances revealed highly significant genotype x
treatment interactions, indicating that the best performing genotypes at
low N do not necessarily perform better at high N. Genotype x replicate
interactions were also highly significant, and most likely due to an
observed sprinkler heterogeneity in the root space.
A graphical analysis of genotypic means revealed
the pronounced effect of N level on most traits
(Fig. 2). The shoot fresh weight and its genetic
variance were dramatically increased under high
N and revealed that high performance at high N
is not synonymous to high performance at low N.
The N effect, however, was much less
pronounced on the shoot dry weight.
Fig. 2. Mean genotypic values
as a function of N level.
N affected root biomass and maximum root length opposite to shoot
biomass, with an increased root allocation under low N. However, the
root:shoot ratio indicated that a small number of genotypes responded in
contrasted ways.
The most dramatic response to N was obviously that of the N evolution,
which was highly superior at high N compared to low N. There were
however no genetic correlations between the N evolution at low and high
N, which was consistent with the results of the two-way variance
analyses.
Conclusions
This segregating RIL population, used as rootstock, revealed interesting
shoot responses to the root genotype, suggesting the validity of the
approach
Reasonably large values of heritability were found for root traits, and
seemed to induce lower, but still large values of heritability for shoot traits
(despite the use of a unique scion), demonstrating the strong imprint that
root traits may have on shoot traits.
Fig. 3. Model based reconstruction of root systems.
Top: two contrasting root system (observed).
Bottom: simulated avatars of the same root systems.
Root traits and N evolutions displayed the less correlations between low N
and high N, indicating that genetic improvement might require
development of specific genotypes for specific environments.
Acknowledgments:
This research has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 289365