News Japanese holly collection in the Bokrijk Arboretum is key to a co-creative breeding project

During covid times, Bokrijk has become a particularly popular walking destination, where visitors enjoy the open space, the historic setting of the Open Air Museum, and the lush greenery. That greenery is now receiving extra attention from scientists. The Bokrijk Arboretum in fact houses an exceptional collection of varieties of Ilex crenata or Japanese holly, a species often used as a substitute for boxwood. The plants in Bokrijk, together with plants from the Leen arboretum in Eeklo, are screened for useful properties, such as disease resistance and tolerance to less acidic soils. The aim is to use plant breeding to develop new cultivars that can be used even more widely in all kinds of gardens and are therefore less dependent on the right type of soil (acid - non-acid, heavy clay - sand, dry - wet).

This scientific project with ILVO and KU Leuven is being carried out at the request of ornamental plant cultivation company Plant Select, and therefore has a co-creative set-up with a view to accelerated innovation and added value creation. "This acceleration is necessary in order to be able to respond to an opportunity in the market, because breeding is usually a long process," explains researcher Esther Geukens.

Soft and snuggly holly

The small-leaved or Japanese holly (Ilex crenata) looks nothing like the classic spiny holly, but it does resemble boxwood enormously, without being bothered by fungal diseases or box moth infestations. It is therefore not surprising that, parallel to the search for disease and pest resistant boxwood, work is also being done on well-performing Ilex alternatives. At Plant Select, a leading Belgian company in the cultivation of Japanese holly, cultivation is on the rise. With Ilex crenata Blondie and Dark Green®, the company has its own selections of Japanese holly under the Ilex Select label, which have already found their way to the European market in millions of plants. For the expansion of the range of Ilex crenata, Plant Select is calling on the experience in ornamental plant breeding at ILVO and on the expertise within KU Leuven.

Valuable collections

Researcher Esther Geukens : "Within this study we are grateful to be able to use of the Ilex crenata collection in the Bokrijk Arboretum. In the meantime, material from nearly one hundred different Ilex crenata genotypes has been collected in the collections of Bokrijk and Het Leen in Eeklo, among others." Bokrijk is happy to cooperate with the study. "In our arboretum you will find one of the largest collections of the Ilex crenata in Europe. In addition, we are recognized as a testing ground by the American Holly Society. It is therefore natural that Bokrijk is happy to cooperate with this research as part of its social role," says Igor Philtjens, president of Bokrijk.

Sven Bronckaers, heritage gardener at Bokrijk, explains: "Our interest in holly arose in the 1980s when there was a need for shelter and an evergreen structure in the garden to better showcase the blooms of our Magnolia collection (one of our other reference collections). Meanwhile, the collection has grown to no less than 800 different holly species and cultivars. In addition to the well-known evergreens, there are numerous deciduous varieties with a very attractive fruiting on bare branches in winter. There are species with leaves from one centimeter long in dwarf forms of Ilex crenata to twenty centimeters long in Ilex latifolia. Ilex rugosa is a creeping, ground covering species, and there are many species that can grow into trees up to 20 meters high", says Sven.