Breeding strategies for wine grapesFrom genetic analysis of agronomic traits to wine sensory evaluation stars

Abstract

The main objectives of this research were the analysis of the genetic basis of agronomic traits in wine grape, the assessment of the influence of berry size in the oenological composition of segregating progenies and clones; and the sensory evaluation of wines derived from Graciano × Tempranillo selections. Two segregating progenies derived from Grenache × Tempranillo (130 genotypes) and Graciano × Tempranillo (151 genotypes) were evaluated for 26 agronomic traits, including berry, flower, seed, phenology and productivity characters from 2014 to 2017, assessing the influence of sex at the phenotypic level. All traits except berry shape showed transgressive segregation and large phenotypic variability in both progenies, essential for the selection of new genotypes with improved attributes. Female plants showed significant differences in flower shape and diameter, number of seeds, and flowering and veraison onset dates when compared with hermaphrodites in both genetic backgrounds. Eleven red-berry and eleven white-berry genotypes were pre-selected in the Grenache × Tempranillo population, based on berry weight, cluster weight, acidity and ripening date. In order to investigate the major regions controlling 26 agronomic traits, Quantitative Trait Loci (QTL) analyses were conducted in two (Graciano × Tempranillo) and up to four seasons (Garnacha × Tempranillo); assessing the influence of Sex locus. Parental and consensus genetic maps were developed for the Grenache × Tempranillo progeny, genotyped using GBS (genotype-by-sequencing) methodology, with 1300 informative markers. The consensus map covered 1540 cM distributed in 19 linkage groups, with an average interval length of 1.2 cM between markers. Significant and reproducible QTL were detected for berry and flower morphology, must composition, productivity and phenology; and candidate genes were found within the confidence intervals of several identified QTL. Moreover, a QTL region in LG2 was identified for flower-morphology, seed, productivity traits, and phenological stages, confirming the influence of flower sex in the genetic determinism of these characters. Influence of berry size on wine composition was studied in two Tempranillo segregating progenies in Rioja and in Pinot noir clones grown in Marlborough region, New Zealand. Consistently, wines derived from small berry genotypes presented higher proportions of phenolic compounds and deeper colour, obtaining higher quality scores. Pinot Noir clones presented differences in berry morphology and nitrogen compounds independently of the subregion studied. Besides, environmental conditions and rootstock were found to influence these parameters. Aiming at the selection of genotypes suitable for future climatic conditions, sensory and physicochemical evaluation of wines derived from twelve pre-selected Graciano × Tempranillo hybrids were conducted in two distinct vintages: 2017 and 2018. Two early-ripening selections, were consistently perceived as higher quality than Graciano and Tempranillo in both years. Furthermore, two late ripening selections provided distinct sensory characteristics valuable for the necessary diversification of the wine market. Results of this research reveal novel insights into the genetic control of relevant traits for wine grapes, and will be useful for breeding new genotypes with better quality features. This is the first physicochemical and sensorial evaluation of young red wines elaborated with Tempranillo intraspecific hybrid grapes. Selected genotypes were able to produce quality wines with great sensory variability, confirming that intraspecific hybridization is a useful tool to improve traditional varieties and meet new consumer demands.