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 Product renewal is commercially very important for ornamental tree nurseries, especially in the section of the visual attractive plants. Desired characteristics are winter hardness, compact growth, colour (of the flower) and variations in leave shape.
Of course, these characteristics are sensitive to the type of plant and trends. Resistant to diseases has become a very important criterion because of growing environmental concerns.
Novelties. Driven by a continuous search for novelties, the assortment in (ornamental) tree culture has expanded enormously the last years. The introduction of species of foreign origin has been a very important source of novelties. Nowadays, the introductions in the (ornamental) tree culture are the result of "a stroke of luck" in the populations of seedlings or spontaneous mutations. Since most of the (ornamental) trees are vegetatively multiplied (rather than produced from seed), mutations can lead to stable, new cultivars. New plant cultivars can also be developed by targeted crossing and selection schemes, which respond to the needs and demands of the consumer.
Three pillars. Plant breeding of ornamental plants leans on three pillars:
- Genetic variation: at the beginning of a breeding program one starts with a population of parent plants with a great variation in characteristics. These can be existing cultivars or wild species and also pre-breeding material (plants selected out of earlier breeding activities).
- Selection: within this population of parents the breeder chooses the plants with the desired features, accomplishes the crossings and afterwards selects the descendants with the desired characteristics. The promising descendants are tested and taken in as pre-breeding material.
- Recombination: the desired characteristics of the parents are combined in the descendants.
With these three pillars in mind, at the Institute for Agricultural and Fisheries Research in cooperation with BEST-select different tree nursery products are being bred, amongst them Hibiscus, Hydrangea, Malus, Ligustrum, Callicarpa, Buddleia, Viburnum, Ribes,...
Interspecific hybridisation. Interesting qualities are frequently present in "wild" species and not in commercially interesting cultivars or species. Crossing these "wild" species with the commercial species (interspecific hybridisation) can lead to pre-breeding material with added value.
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Although they offer new variations and provide the possibilities to introduce the desired characteristics, up till now these interspecific crossings have rarely been conducted using woody ornamental trees.
Interspecific hybridisation doesn't come by itself. Naturally present crossing barriers are often an obstruction to optimal use of the present biodiversity. The development of strategies (amongst them in vitro embryo rescue and polyploidisation techniques) to circumvent or break through these barriers is a interesting and important research theme.
A research program on interspecific hybridisation is being conducted at the Institute for Agricultural and Fisheries Research in cooperation with BEST-select. At this moment the research is mainly focused on the genus Hibiscus, Hydrangea, Buddleia and Ligustrum. The results of this research show that it is possible to create new cultivars within (ornamental) tree culture with improved characteristics using interspecific crossings and techniques that help to circumvent crossing barriers. Close cooperation between the research institute and the nursery sector is imperative to turn new introductions into successes on the market.
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