Exemptions sought to ban on sales of flowering cherries in NZ

Prunus ‘Shirotae’ cultivar, left, has been granted interim sales ban exemption by Auckland Council until September 1, 2023 while more research is undertaken. Right: Prunus ‘Kanzan’ cultivar was found to be sterile and is exempted from the Auckland Council’s pest management plan.

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.

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