Rice (Oryza sativa. L) genetic diversity for early vigor and drought ...

Introductionestimation. The identification of relevant process based traits for genetic studies was thus a majorchallenge during the last decades for ecophysiologists (Dingkuhn et al. 2006; Tardieu et al. 2010).Recently some approaches proved their relevance for phenotyping process based traits on a largenumber of genotypes. This is the case of high throughput imaging methods that enable a rapidcharacterization of plant growth dynamics or water status (Berger et al. 2010). The application ofmodeling also showed its relevance to phenotype process based traits using the parameters ofequations formalizing plant response to environmental variables to differentiate genotypes; suchparameters are thus genotypic and less prone to GxE than corresponding measured variables(Dingkuhn et al. 2006; Tardieu et al. 2010). This was pioneered by Reymond et al. (2004) using asimple model (with 3 equations) predicting maize leaf expansion rate (LER) response toenvironmental variables related to drought conditions (leaf temperature, vapor pressure deficit andsoil water potential). Indeed consistent associations of Quantitative Trait Loci (QTL) and modelparameters were reported for hundreds of genotypes in maize populations with different geneticbackgrounds and across environments (Welcker et al. 2011).The interest of metabolomics for plant phenotyping has been less explored (Fernie et al. 2009),although they might reveal genotypic variation for growth and adaptation strategies (Stitt et al. 2010)or for physiological traits (Ishimaru et al. 2007). The role of non structural carbohydrates (NSC) asmarkers of genotypic growth pattern was demonstrated: on Arabidopsis, Sulpice et al. (2009)reported a negative correlation between seedling growth and starch accumulation and on Medicagotrucatula Vandecasteele et al. (2011) reported a negative correlation between seedling vigor andsucrose:rafinose ratio. Meanwhile in a preliminary study on 200 rice sativa genotypes grown underwell watered conditions Luquet et al. (2008b) reported that early vigor was associated to low NSCconcentration in the plant. Metabolic component traits demonstrated also their interest todiscriminate genotypes for drought response mechanisms (Shao et al. 2009; Verslues et al. 2011),rice vegetative growth (Cabuslay et al. 2002). This suggests the relevance of exploring the geneticdiversity for NSC during rice vegetative growth.OBJECTIVES, OVERVIEW OF THE CHAPTERS AND THE METHODOLOGYWithin Genphen and Orytage projects, extensive phenotypic data sets were generated with athreefold purpose (i) identify traits contributing to rice growth and adaptation strategies (to droughtin particular) and their diversity, (ii) characterize physiological and/or genetic linkages among traits,and their GxE; and (iii) detect QTLs and related favorable alleles for studied traits using a chip ofabout 1 million SNP markers for association genetics studies. Genetic studies are planned for June2012 when the chip of SNPs markers will be available.17