The kinetics of grape ripening revisited through berry density sorting

Abstract

Aim: In this study, ripening and heterogeneity in density-sorted berries were investigated, with the aim of more clearly understanding the kinetics of water uptake and sugar, acid and anthocyanin accumulation in the fruit of a new, disease-resistant hybrid.Methods and results: The 3184-1-9N hybrid, grown in a semi-arid climate in the South of France, was used. Its genotype is the result of several backcrosses of a Muscadinia ´ Vitis vinifera F1 hybrid with several V. vinifera varieties. From the end of the green plateau to the over-ripening stage, single berries were sampled weekly and sorted by density, to monitor the advancement of ripening and the heterogeneity of grapevine fruit development at population level. Fruit firmness, density, fresh weight, primary metabolite content (sugars and organic acids), secondary metabolite content (anthocyanins), potassium content and pH were measured in berries from each density class. The data showed that softening and hexose accumulation occurred before fruit pigmentation. Based on malic acid and anthocyanin concentration relative to sugar concentration in density-sorted grapes, malic acid breakdown or dilution was promoted and anthocyanin accumulation reduced in late- or slow-ripening berries. In the different population structures in two experimental plots, berries with similar sugar concentration showed considerable heterogeneity in terms of volume and anthocyanin content, whereas pH, potassium content and acid content showed much more homogeneous kinetics.Conclusions: During ripening, analysis of density-sorted berries provides useful information about sugar concentration heterogeneity and its relation with organic acid and anthocyanin content. The stage at which grapes can be considered ripe may be precisely determined through periodic determination of mean berry volume or weight, to detect the cessation of phloem unloading and the onset of berry shrivelling. However, ripening and shrivelling berries generally coexist in the harvested population. Asynchronous berry development and berry weight heterogeneity greatly complicate determination of the timing of developmental events that are regulated at the single-berry level. Therefore, analysis of individual berries would seem to be an indispensable component of investigations of berry growth and development.Significance and impact of the study: Plotting water uptake and solute accumulation relative to sugar accumulation (as an internal clock) provides an original way to display grapevine fruit development data. Analysis of density-sorted berries has identified the relatively invariant fruit features, such as the minimum concentration of tartaric acid, the stability of potassium accumulation and pH, and conversely, the huge variations in berry size.

Vitis vinifera L. Diversity for Cations and Acidity Is Suitable for Breeding Fruits Coping With Climate Warming

“…In this study, PCA analysis showed that sugars and K + are orthogonal at both developmental stages (Figure 7). The lack of univocal relationship between sugar and K + accumulation during the phloem unloading period was recently reported by Bigard et al (2019). This result is now confirmed from a genetic point of view.…”

“…Obviously, the concept of developmental stage remains equivocal in such heterogeneous samples. Indeed, a phenological stage must be defined by intrinsic physiological parameters, such as the onset and the arrest of sugar loading, which may occur at different harvest dates or brix, according to the genotype (Bigard et al, 2019;Shahood et al, 2019).…”

“…Recently, Bigard et al (2019) pointed out the impossibility to unambiguously define developmental stages in unsynchronized berry populations. Attempts were made to compare genotypes more precisely by sorting berries at precise physiological stages, i.e.…”

“…Recently, Bigard et al. (2019) pointed out the impossibility to unambiguously define developmental stages in unsynchronized berry populations.…”

“…(A) shows the level of acidity in all collected samples as a function of the sum of major osmotica (Glucose + Fructose + Malate + Tartrate). (B) shows the volume of the fruits for the varieties Aramon and Cinsault, and the microvine 114 and 119 fruit growth expressed as 1/tartaric acid concentration(Bigard et al, 2019). Black square shows the position of green stage samples.…”