Somatic Embryogenesis and Embryo-to-Plant Conversion in Different Grapevine Genotypes: two Different Bottlenecks for Plant Production

Abstract Somatic embryogenesis (SE) represents a central regeneration system for the implementation of new breeding technologies in grapevine ( Vitis spp.). However, its practical use remains constrained by genotype dependence, prolonged developmental timelines, and variability associated with explant type and culture conditions. This study evaluated SE and embryo-to-plant conversion across fifteen recalcitrant European genotypes and hybrids from Italy, Spain, Portugal, and Hungary using anthers and ovaries cultured on three induction media, followed by embryo germination. Ovaries generally exhibited higher responsiveness to SE than anthers, the PIV medium showed the broadest effectiveness, although the genotype was the primary determinant of the SE process. Noteworthy, differences in embryogenesis competence did also emerge among clones of Nebbiolo cultivar highlighting intra-cultivar variability effects. By extending the duration of callus culture beyond the conventional evaluation windows and using a two-media induction protocol, the embryogenesis success increased in several genotypes, suggesting that premature callus elimination may underestimate SE potential. Regeneration experiments confirmed that the embryo-to-plant transition was the second critical step of the process. For instance, Kadarka was a cultivar with low aptitude to SE and high regeneration efficiency, whereas other genotypes displayed poor embryo germination. Overall, all fifteen recalcitrant grapevine genotypes produced SE although plant regeneration was not achieved in Graciano and Fernão Pires. The results support a two-bottleneck-based model of grapevine regeneration controlled by genotype. Inefficiencies in the embryo-to-plant conversion constitute a highly limiting factor for downstream plant breeding applications, underscoring the need for genotype-specific optimization strategies able to address both embryogenic induction and regeneration efficiency.