Revised dominance hierarchy for S-alleles in Corylus avellana L.

Pollen-stigma compatibility was studied in cultivars and more than 1800 seedlings of the European hazelnut (Corylus avellana L). Four new S-alleles were identified, bringing the total to 25 unique alleles within C. avellana. The new alleles are the recessive alleles in ‘Tonda di Giffoni’ and ‘Segorbe’ (S₂₃), in ‘Neue Riesennuss’ (S₂₅), in ‘Gasaway’ (S₂₆), and a dominant allele in a seedling of Turkish origin (S₂₄). Dominance relationships in 233 of the possible 300 pairs of alleles were determined in both pistil and pollen. All alleles exhibited independent action in the pistil, whereas in the pollen either dominance or codominance was exhibited. The dominance hierarchy of alleles in the pollen was revised in light of the new information obtained. All 25 alleles have been assigned to a level in the hierarchy that is linear and now has eight levels. S₆ and S₉ were reassigned to lower levels in the hierarchy. Thirteen of the alleles are on the level of S₁, while S₄, S₆, S₁₁, and S₂₃ occupy unique positions in the hierarchy. Improved pollen tester clones were identified for several S-alleles. The alleles in 55 cultivars were determined. The alleles identified in ‘DuChilly’ (S₁₀ S₁₄) did not agree with previous reports. Four cultivars have the same alleles as ‘Römische Nuss’ (S₁₀ S₁₈) and are morphologically indistinguishable from it: ‘Frutto-grosso’, ‘Istarski Okrogloplodna’, ‘Payrone’, and ‘Romai’. ‘Belle di Giubilino’ and ‘Tonda di Biglini’ are both S₁ S₁₀ and appear to be synonyms for the same cultivar.