Microstructure of Croatian Wild Grapevine (Vitis vinifera subsp. sylvestris Gmel Hegi) Pollen Grains Revealed by Scanning Electron Microscopy

Wild grapevine (Vitis vinifera subsp. sylvestris Gmel Hegi) is dioecious with male and female plants, whereas domesticated grapevine is mostly hermaphrodite with self-fertile hermaphrodite flowers. The pollen morphology of wild grapevine has been poorly studied. There is no detailed palynological study of V. sylvestris in Croatia and neighboring countries. Here, scanning electron microscopy (SEM) was used to analyze the pollen of V. sylvestris from male and female individuals growing at two natural sites in Croatia. The selective APT3 marker was used to confirm the flower phenotype with the genetic background. SEM analysis showed that the pollen grains of V. sylvestris were isopolar and radially symmetrical, with foveolate perforated ornamentation, regardless of the flower type of the individuals. All male flowers were 3-colporate and prolate in shape, whereas female individuals varied from subprolate to spheroidal and had inaperturate pollen grains. Pollen shape, dimensions and exine ornamentation proved very informative, and here we address the most polymorphic traits in the analyzed V. sylvestris individuals. Principal component analysis (PCA) and clustering based on pollen morphology variables clearly differentiated individuals by their flower type, and no grouping specific to population was observed, pointing to the conserved pollen structure of V. sylvestris. The results indicate the need to continue the palynological study of V. sylvestris and serve as a good phenotypic basis for functional genetic studies on genes involved in pollen morphology and function.