First steps in hardy geranium breeding: focus on pollen conservation, stigma receptivity and overcoming seed dormancy

M. Akbarzadeh, J. Van Huylenbroeck, S. Werbrouck, E. Dhooghe
Getting a new combination of desirable traits in a plant is the main goal of every breeder. Hardy geranium (Geranium sp.) is categorized as a famous perennial garden plant that has many fans all over the world. Although there are a significant number of hardy geranium varieties available worldwide, there is still room for improvement in the assortment especially in terms of flowering time, flower size and plant architecture. Today, geranium breeders use classical breeding methods such as hybridization to create and release new cultivars. For successful hybridization, male fertility, female receptivity and seed germination are vital. Therefore, this study focused on these three different aspects: pollen conservation, stigma receptivity and breaking seed dormancy. Since there is diversity in flowering period and sometimes no overlap between interesting species, different methods of pollen conservation were tested. For this purpose, we stored pollen of 4 different genotypes at 4 different temperatures (4, -20, -80 and -196°C) for 0, 1, 7, 30, 60 and 90 days of storage duration. Pollen quality was measured by FDA staining. The results showed that pollen from G. macrorrhizum ‘White Ness’ and G. × cantabrigiense ‘Biokovo’ are sensitive to low temperatures (-80 and 
-196°C), whereas pollen from G. × oxonianum ‘Katherine Adele’ and G. sylvaticum ‘Album’ on the other hand, showed high preservation at low temperatures. To find the best stage for stigma receptivity, crosses were performed at different stigma ages and evaluated using aniline blue staining. Pollen tubes were able to successfully reach the oocytes when the stigma was moderately old or old, but never germinated when the stigma was too young. In addition, breaking the seed dormancy in vivo was investigated by cold treatment. Our data showed that the best way to break seed dormancy was 90 days at 5°C. These data will give Geranium breeders new opportunities for hybridization.
Akbarzadeh, M., Van Huylenbroeck, J., Werbrouck, S. and Dhooghe, E. (2023). First steps in hardy geranium breeding: focus on pollen conservation, stigma receptivity and overcoming seed dormancy. Acta Hortic. 1368, 251-258
DOI: 10.17660/ActaHortic.2023.1368.33
aniline blue, Geranium, Geraniaceae, germination, hybridization, vernalization

Acta Horticulturae