Abstract
Garden rose varieties certified as ‘Toproos’ form the best choice for nurserymen and garden lovers in The Netherlands. However, these varieties had not been tested for fungus resistance before 1995. Therefore, 63 ‘Toproos’ varieties planted in 3 different locations during 3 years, unsprayed, were re-selected by Dutch Permanent Judging Committee (VKC) for resistance to black spot, mildew and rose rust, as well as for disease effects on new growth. Re-selection greatly contributed to the status of the certificate, as only 44 varieties (68%) proved to be satisfactory under prevailing conditions. Observations indicated horizontal resistance for each disease; despite annual variation in disease level, genotype-location interaction did not occur. New growth was significantly affected by black spot and rose rust. Varieties infected by black spot and rose rust were the same. The selected varieties form an excellent collection of progenitors in a breeding programme for horizontal resistance. To introduce new black spot and mildew resistant germplasm, interspecific crosses between recurrent flowering, tetraploid (2n=4x=28) Hybrid Tea varieties and non-recurrent, putatively vertically resistant selections from R.moschata (2x), R.bella (4x), R.acicularis (6x), R.nutkana (6x) and R.marginata (8x) were carried out. Most crosses resulted in F1-populations. Sofar, F2-back crosses have yielded seeds. Percentages between 10-40% of recurrent flowering F2-seedlings are expected. Resistance of recurrent F2-plants will be tested.
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