Progress on pollen-stigma compatibility in Corylus (hazelnuts): a review

The genus Corylus is an important member in the Betulaceae family of the order Fagales. Self-incompatibility is one of the choke points in breeding and hazelnut production. This reviewe describes, the progress on pollen-stigma compatibility in Corylus, including basic reproductive characteristics, S-alleles testing and their applications, inter-specific hybridization, self-compatibility in wild species, and recent molecular research on the genetic mechanism of compatibility. Compared with other species, progress on pollen-stigma compatibility (sporophytic self-incompatibility, SSI) in Corylus is slow, especially those in the Brassicaceae family. De novo approaches should be used to target the unique reproductive characteristics of hazelnuts. The continuous improvement of technological platforms based on molecular biology should broaden the pathways in investigating compatibility in Corylus. In addition, research should be conducted on overcoming selfand crossincompatibility, and approaches based on biological, chemical, and physical principles should be introduced. Both theoretical and practical study of compatibility in Corylus should be devoted to change the self-incompatibility trait into a benefit in the species evolvement and nut quality establishment.