Self-compatible seedlings of the cutleaf hazelnut

The cutleaf hazelnut [Corylus avellana L. f. heterophylla (Loud.) Rehder] is an ornamental form with strongly dissected leaf morphology. Its stigmas express incompatibility allele S,,, but none of the other 25 S-alleles was detected with fluorescence microscopy. Three seedlings from a cross of the cutleaf hazelnut and VR6-28 lacked S-20 and were investigated further. Each expressed an allele from the parent VR6-28 (S-2 S-26), S-26 in OSU 562.031 and OSU 562.048 and S-2 in OSU 562.049. S-2 and S-26 are low in the dominance hierarchy, so we expected the new allele from the cutleaf hazelnut to be expressed in their pollen. Unexpectedly, fluorescence microscopy showed that pollen of all three selections was compatible on their cutleaf parent and on each other, and furthermore, self-pollinations showed the excellent germination and long parallel tubes in the styles that are typical of a compatible pollination. Controlled self- and cross-pollinations in the field verified the self-compatibility of two selections. Cluster set for self-pollinations was very high (75-90%) and within the range observed for compatible cross-pollinations. Furthermore, the frequency of blank nuts was low (<10%). The second allele in the cutleaf hazelnut is designated S-28, and its presence in seedlings of 'Cutleaf' is indicated by the absence of S-20, Controlled pollinations in the field also showed that selection OSU 562.069 (S-2 S-28) from the cross 'Cutleaf' x 'Redleaf #3' was self-compatible. Fluorescence microscopy showed that two additional seedlings were self-incompatible [OSU 367.052 (S-1 S-28) and OSU 367.076 (S-6 S-28)] while a third [OSU 706.071 (S-9 S-28)] was self-compatible. Self-compatibility may be limited to genotypes that combine S-28 with a second allele that is low in the dominance hierarchy.