The flowering dynamics and breeding system in Magnolia ×soulangeana ‘Hongyun’

Abstract

Magnolia soulangeana ‘Hongyun’ is an ornamental tree used for landscaping. It has an attractive shape and produces abundant showy flowers. However, the fruit set rate of ‘Hongyun’ is low under natural pollination condition. In this study, we examined the basic characteristics of its breeding system. The results showed that the flower of ‘Hongyun’ is hermaphroditic, with both pistil and stamen being fertile. The pollen-ovule ratio (P/O) ranged from 3,205.78 to 6,244.21, and the outcrossing index (OCI) was 4. Comparing with different pollination treatments, we found that there was no fruit set under direct bagging, bagging after emasculation, and no bagging and non-pollination after emasculation. Furthermore, the fruit set rate under the geitonogamy treatment was lower than that under the xenogamy treatment, indicating low self-compatibility. Therefore, when combined with the numerical value of P/O and OCI, we infer that the breeding system of ‘Hongyun’ is partially self-compatible, outcrossing, and demands pollinators. In particular, ‘Hongyun’ presents a mass-flowering pattern. Furthermore, there is the phenomenon of secondary opening and closing in the flowering process of a single flower. The stigma receptivity and pollen viability of a flower are the strongest when it is slightly blooming during the first flowering. Strangely, the anther wall dehiscence occurs during the second flowering, which may guarantee that ‘Hongyun’ maintains a morphological dichogamy status to avoid self-fertilization. Overall, the unique flowering dynamics is closely related to the type of breeding system in ‘Hongyun’. Group planting will be the best way to promote better reproductive success of ‘Hongyun’ under garden planting conditions.