The New Zealand Plant Producers nursery industry organisation (NZPPI) is leading a request for a sale ban exemption in Auckland, New Zealand for several Japanese flowering cherry cultivars attributed to Prunus serrulata and claimed to be sterile. NZPPI Biosecurity and Technical Manager Kathryn Hurr reports for Commercial Horticulture.
The Japanese flowering cherry research project, Project Sakura, was launched last year with pollination scientists from Plant & Food Research – Dr David Pattemore and Dr Melissa Broussard – along with Murray Dawson from Manaaki Whenua Landcare Research and Vance Hooper of Magnolia Grove Nursery.
Several Prunus species are invasive in New Zealand and Japanese flowering cherries including P. serrulata, P. serotina and P. campanulata are due to be banned from sale in the Auckland Region from September 1, 2022, under the Auckland Council Regional Pest Management Plan.
Two cultivars of Prunus campanulata are exempted from the sale ban (‘Mimosa’ and ‘Pink Clouds’). NZPPI is hoping for the same success with the Prunus serrulata cultivars.
There is anecdotal evidence that cultivated forms of Japanese flowering cherry rarely bear fruit but there is not much specific literature on which cultivars are sterile. We are hoping that these cultivars are unlikely to produce lots of fruit and be “weedy” in the environment, and then apply to Auckland Council to have them exempted from the ban. This would mean these cultivars could continue to be propagated and sold in Auckland.
Flowering cherries are a popular street tree in subdivisions and home gardens. There are over 200 varieties around the world.
Project delays
Last year the Project Sakura researchers looked at six serrulata cultivars to compare them with the wilding type Prunus serrulata found in Auckland. They collected 10 flowers from each cultivar and the Auckland wilding type and sent them to Plant & Food Research in Hamilton to determine:
- Number of stamens
- Number and morphology of pistils
- Presence of pollen in anthers.
Just as the project started, however, Auckland went into Level 4 lockdown due to COVID, followed shortly afterwards by Hamilton. We were able to collect the flowers and get them to Hamilton, however they had to be put in the freezer at PFR until the laboratory opened again so we were not able to look at stigma receptivity. Some further work is being scoped to undertake this research on some cultivars in spring.
Prunus ‘Shimidsu Sakura’ and ‘Kanzan’ were both found to be sterile and have been exempted from the ban. Flowers of both these cultivars had ovaries and styles replaced by a pair of leaflets and their pollen viability was poor.
Although the remaining cultivars did not show clear signs of female infertility and there was limited evidence of inviable pollen, further work is required to establish whether these cultivars are capable of producing viable seed.
Prunus ‘Shirotae’, ‘Amanogawa’, ‘Tai Haku’, ‘Kiku Shidare Sakura’ and ‘Ukon’ have been granted interim exemption by Auckland Council until September 1, 2023 while more research is done.
Reproduced with permission from Commercial Horticulture, April-May 2022.
