Model assisted phenotyping of rice response to vegetative drought : case study of a collection of 203 tropical japonica genotypes

Context:

Context:

Drought impact on plant early vigour limits its establishment, resource acquisition and thus final yield. This is a major issue for rice

crop, in particular in upland ecosystems. The response of rice early vigour to drought is complex as it involves numerous traits. These traits regulate water and carbohydrates source (assimilation, water uptake) and sink (tillering, developmental rate, leaf size, growth, transpiration) relations (Luquet et al. 2008). Japonica group has a great partially unexploited genetic diversity of adaptation to drought and should provide favorable alleles to this traits.

Objective:

Objective:

Using a combined approach based on plant modelling and sugar analysis, we phenotype the regulation of water and C

source-sink relations by a vegetative drought. We present here the first experimental results and modeling applications

Perspectives

Perspectives

Two-segmented regression and model optimization are promising methods to dissect genotype discrimination parameters, the application on the 203 genotypes is underway. We will associate morphogenetic and physiological process-based parameters with sugar contents in source and sink organs to discriminate genotypes. We also want to perform a genetic association study using available SNP markers (2011) to determine markers and alleles of interest for rice response to drought.

References:

References:

Luquet D., Dingkuhn M., Kim, Tambour L., Clément-Vidal A. Functional plant biology, 33 (4) : 309-323.

Luquet D., Clément-Vidal A., Fabre D., This D., Sonderegger N., Dingkuhn M. 2008. Functional plant biology, 35 (8) : 689-704.

Genotype distribution for four measured variables

EcoMeristem model: water and C source-sink processes controlling rice vegetative morphogenesis

under drought

•Component traits (parameter values) optimized for genotype discrimination on 21 genotypes:

Model assisted phenotyping of rice response to vegetative drought:

case study of a collection of 203 tropical japonica genotypes

Drought onset by dry-down when leaf 6 appears (FTSW*_=1).

Transpiration & stress monitored by gravimetry.

Morphological measurements at FTSW= 1 and FTSW= 0.2: 1st_{leaf size, seed dry weight, tiller and leaf number,}

haun index, last formed leaf size, final shoot dry weight, and sugar (soluble, starch) contents at FTSW=0.2.

*_{FTSW: Fraction of Transpirable Soil Water}

Modelling application

•Description of a response pattern to FTSW using a two-segment model.

•Optimization with Ecomeristem (Luquet et al. 2006): model of water and C source-sink processes controlling rice vegetative morphogenesis under drought.

•Greenhouse experiment (CIRAD, Montpellier, France) •203 tropical japonica cvs.

•3 replications (temporal) •2 treatments: dry-down/ irrigated •1l pots (no rooting differences)

Materials and Methods

Materials and Methods

Results and Interpretations

Results and Interpretations

°C.d(ftsw 02-f tsw 1) F re q u e n c y 0 50 100 150 200 250 300 0 4 0 8 0 cm/leaf rank F re q u e n c y 0 5 10 15 20 0 4 0 8 0 nb/°C F re q u e n c y 0.000 0.005 0.010 0.015 0.020 0.025 0 4 0 8 0 g/°C F re q u e n c y 0.000 0.004 0.008 0.012 0 1 0 0 2 0 0

Phyllochron Leaf size

Tiller number SDW

Irrigated Stressed

M.C. Rebolledo*, M. Forest, C. Seranuch, J.-C. Soulié, L. Rouan, M. Dinkguhn, D. Fabre, D. Luquet

CIRAD French Agricultural Research Center for International Development, Biological Systems: Agro-ecological Adaptation and Varietal Innovation. Montpellier, France.

*[email protected] G164 FTSW 0.0 0.2 0.4 0.6 0.8 1.0 1.2 T ra n s p ir a tio n ra te (g /c m 2 ) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Bp 0.77 R2 0.88 G60 T ra n s p ir a tio n ra te (g /c m 2 ) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Bp 0.8 R2 _0.80 G18 T ra n s p ir a ti o n ra te (g /c m 2 ) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Bp 0.86 R2 _0.96 G200 FTSW 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Bp 0.67 R2 _0.82 G175 FTSW 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Bp 0.41 R2 0.66 G172 FTSW 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Bp 0.43 R2 0.43 G171 FTSW 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Bp 0.38 R2 _0.47 G119 Bp 0.86 R2 _0.81 G143 Bp 0.86 R2 _0.69 G156 Bp 0.76 R2 _0.65 G162 Bp 0.69 R2 _0.86 G59 Bp 0.8 R2 _0.87 G43 Bp 0.40 R2 _0.94 G38 Bp 0.46 R2 _0.87 G29 Bp 0.72 R2 _0.88 Predicted values Observed values

Two-segment models illustrate varietal differences in the control of transpiration.

Measured variables show genotypic variation in morphological responses to drought.

One curve model of normalized leaf transpiration response to FTSW

•Water stress affects final shoot dry weight (SDW) through:

–Changes in developmental rate (phyllochron, tiller number), –Changes in organ size (last ligulated leaf size).

•ANOVA on 203 genotypes for 7 variables shows genotype, treatment, and (temporal) replication effects.

•Application to 15 genotypes and two repetitions.

•Breakpoints varied from 0.4 to 0.85 across genotypes:

Eg. G59 with a higher value than G43 is less able to maintain

a higher transpiration during the drying cycle.

MGR 8 10 12 14 16 18 n u m b e r o f g e n o ty p e s 0 1 2 3 4 5 6 7 Parameter value 0 1 2 3 0 1 2 3 4 5 6 7 Phyllochron 50 60 70 80 90 100 0 2 4 6 8 EpsiB 2 3 4 5 6 7 0 1 2 3 4 5 6 ThresLER 0.0 0.4 0.8 1.2 0 2 4 6 8 ThresTransp 0.3 0.6 0.9 1.2 0 1 2 3 4 5 6 7 Ict MGR: Meristem Growth Rate ThresLER: FTSW

threshold for leaf expansion reduction ThresTransp: FTSW threshold for transpiration reduction Ict: Carbon supply/demand ratio Phyllo: Phyllochron EpsiB: Conversion coefficient

These parameters are both describing

physiological processes and genotypic variability.

(indica)

–Significant range of values (need to enlarge the range for ThresLER),

–No significant correlation between EcoMeristem parameters