Guest blog post by Dr Emilio Cervantes
Grape seeds have a characteristic oval or pear-like shape. It has been long recognised that this form is variable, and that, in general, wild-type seeds are smaller and more rounded, while the seeds of cultivated varieties tend to be more elongated in one side, or pear-shaped.
Recently, seeds belonging to 38 cultivars stored in the collection of IMIDRA were classified in ten morphological groups, each corresponding to a new morphological model. The models are geometric figures defined by equations, and similarity to each model is evaluated by quantification of percent of the area shared by the two figures, the seed and the model (J index).
The groups thus defined were: Listán Prieto, Albillo Real, Moscatel, Doña Blanca, Hebén, Tortozón, Sylvestris, Teta de Vaca, Airén and de Cuerno.
An article just published in the open-access, peer-reviewed Viticulture Data Journal by the same research groups at IRNASA-CSIC, Department of Mathematics of Salamanca University and IMIDRA, presents an analysis of the curvature – the degree of variation in the points of a curve – in the apex of the cultivars. A set of points along the surface of the seed image are marked and used to obtain the Bézier curves corresponding to seed profiles. The curvature values along the curves are then calculated in Mathematica and represented. Then, the cultivars are classified according to the variation of their curvature and distribution of maximum curvature values. The groups formed based on the curvature analysis are related to the classification based on geometrical figures.
The results show the peduncles of Vitis seeds can be ordered in three groups: 1) Acute, with a unique point of maximum curvature; 2) Plane, with two equivalent points of maximum curvature, and 3) Intermediate. According to this result, the groups based on geometric models are divided by the curvature analysis in two series:
The seeds in most of the cultivars had their pedicels flat at their apex. In consequence, representations of Bézier of their profiles had a plane form with two maximum curvature values. This type was observed in a total of 23 cultivars, including all but one of the 23 cultivars in four groups, and with the addition of Airén. The cultivars with a flat pedicel are predominant in groups Listán Prieto (Listán Prieto and Tortozona Tinta), Albillo Real (Alarije, Albillo Real, Cayetana Blanca, Graciano, Juan García and Tempranillo), eleven of the twelve cultivars of group Moscatel (all of them except Moscatel de grano menudo), the three cultivars of group Doña Blanca (Doña Blanca, Monastrell and Pedro Ximénez) and Airén.
The seeds with an acute apex belong to six cultivars in four groups: Hebén (Macabeo and Zalema, but not Hebén itself), Tortozón (Imperial and Tortozón), Airén (Mazuela) and de Cuerno.
The morphological difference between the seeds of wild grapes and cultivars of Vitis has been known for a long time, but biochemical and structural properties associated with these types remain to be investigated. Considering that lignin is an important component of the cell walls, it is possible that adaptation to agricultural conditions is associated with changes in lignin composition. Pedicel thickening and lignin synthesis may be increased in the cultivars that have their beaks plane in comparison with those varieties that present acute beaks.
Cervantes E, Martín-Gómez JJ, Espinosa-Roldán FE, Muñoz-Organero G, Tocino Á, Cabello Sáenz de Santamaría F (2021) Seed apex curvature in key Spanish grapevine cultivars. Viticulture Data Journal 3: e66478. https://doi.org/10.3897/vdj.3.e66478