ISHS Acta Horticulturae 508: XIX International Symposium on Improvement of Ornamental Plants
SELECTION FOR VERTICILLIUM RESISTANCE IN NORWAY MAPLE (ACER PLATANOIDES) |
| Authors: | J.A. Hiemstra, H.M.C. Van Holsteijn |
| Abstract:
Verticillium wilt is an important problem in the cultivation of planting stock of shade trees, especially Norway maple (Acer platanoides), in The Netherlands. Affected trees usually consist of a cultivar on a (susceptible) seedling rootstock. In 1993 a research project (*) has been started which aims at increasing the resistance of maple planting stock through selection of resistant seedlings that can be developed into resistant clonal rootstocks or cultivars. Efficient methods for screening young maple plants for Verticillium resistance were developed. Soil inoculation, stem inoculation and root dip were tested on seedlings of different ages. Both root-dip of very young seedlings and stem inoculation of 1 to 2 years old plants proved to be very efficient and reliable inoculation techniques. Hence these two methods were adopted for use in large-scale selection experiments. Two experiments were carried out. First, 2000 1-year-old seedlings of four different seed origins were stem-inoculated. Symptom development was recorded and the best 40 plants were selected for vegetative propagation to allow a second test. In the second experiment about 17 000 very young seedlings were tested for resistance. Plants were grown from commercially obtained seed of several different geographic origins and inoculated (root-dip) 4–6 weeks after germination. Plants with symptoms of Verticillium wilt were discarded weekly. Again the plants that remained free of symptoms were selected for vegetative propagation. On average about one to two percent of the plants remained free of symptoms. No clear differences in selection percentage were observed between seedling groups of different origin. In fact, in the greenhouse experiment the variation between seedling groups of different origin was of the same order of magnitude as the variation between different seed batches of the same origin. Vegetative propagation of Norway maple through rooting of cuttings appeared to be extremely difficult. Now, after several years, some of the selected plants have been propagated successfully by either rooting of cuttings or tissue culture. The resulting clones will be used for resistance testing in 1997/1998. In the meantime, in order to allow a first test of the selected material, in 1996 buds of trees selected in the field-experiment as well as buds from non-selected (control) trees have been chip-budded on seedling rootstocks. In 1997 the resulting plants were stem-inoculated. The results showed a highly significant difference in disease index between the selected and the control group. Moreover, several of the selected clones remained virtually free of symptoms. (*) Supported financially by the Dutch Product Board for Horticulture. | |
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