Résumé
Abstract:Context and purpose of the studyMerlot grapevine is the second wine cultivar most planted in the world and especially in the Bordeaux wine region.This cultivar has many advantages in producing high quality wine; however, in the last decade, climate change hasincreased the sugar concentration in berries at harvest and shortened the maturation cycle. If this has been up tonow a great opportunity to improve wine quality profile, we are touching the tipping point. High sugarconcentration at harvest induces high alcool content in wine which can negatively impact wine quality. There aremany viticultural and oenological practices possible to limit this effect. In this study we focus on plant materialthrough intra-varietal diversity of Merlot cultivar.Material and methodsThis study is based on three years of phenotyping a private collection of Merlot including 55 accessions and 3ENTAV-INRA® registered clones. Each genotype is present in four blocks of 6 vines in the experimental plot. Amongthis collection, two extreme genotypes for sugar concentration, selected on 3 years of phenotyping, werephenotyped again on the fourth year at a larger scale. Separated individual berries were collected at 5 stages fromgreen hard berries to mature berries. Sugar and organic acids were mearsured on each berry to compare bothmaturation cycles and to select triplicates of synchronized individual berries before transcriptomic analysis. Pairended RNAseq reads were then aligned on high quality Merlot assembly and the counting table of gene expressionwas produced.ResultsExtreme genotypes have an average of 17g.L-1 difference in sugar concentration at harvest which approximatelyrepresents 1%vol of alcool in wine after fermentation. Whilst as expected thousands of genes were differentiallyexpressed according to the advancement of ripening, statistical analysis only revealed 28 differentially expressedgenes between the two genotypes throughtout all developmental stages and gives an insight on genes potentiallyinvolved in the control of sugar concentration. Selection among intra-varietal diversity therefore appears as a toolto immediate adaptation but also offers possibilities in gene detection of very specific agronomical traits.