Evaluating Sterility of a Late-Flowering Ornamental Tung Oil Tree (Aleurites fordii)

We recently identified an Aleurites fordii seedling with ornamental potential that shows late flowering, approximately 4 weeks delayed, and does not produce normal drupes, which are toxic and a nuisance to lawn mowers since they are large (5-8 cm) and heavy. The ornamental and landscape industries could benefit from a small (4-6 meter), deciduous landscape tree that has no known insect or disease problems, has uniform growth habit, tolerates diverse soil conditions and drought, is readily propagated, and has a tropical flair with large, heart-shaped leaves and Catalpa-like blooms. Clusters of approximately 60 flowers open before the leaves in early spring and have 5 to 7 ivory petals with pink to red throats. Flowers are monoecious and both male and female flowers are visible on the late-flowering selection. Staminate male flowers produce visible pollen but staining and microscopy measurements show a high percentage of large, heavily-stained pollen grains mixed with unstained normal-sized pollen. Genome size comparisons using a flow cytometer do not suggest ploidy differences between the late-flowering selection and plants in our tung oil germplasm collection. Tung oil trees are not self-sterile and flowering times for normal trees and the late-flowering selection overlap slightly. However, male sterility combined with late-flowering could account for the lack of drupes. Two-way controlled crosses were made between seven bud-grafted clones of the late-flowering selection and seven random plants from the tung-oil tree germplasm collection to confirm sterility. Cold-hardiness evaluations of bud-grafted clones are underway since previous literature indicates hardiness only in USDA cold-hardiness zones 8 to 10, which would limit the potential of this tree.