Developments in Breeding for Horizontal and Vertical Fungus Resistance in Roses

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.

Powdery Mildew on Roses: Pathotype Screening

“…As the genetic background of rose cultivars is very narrow, the introduction of wild species can not only be interesting for disease resistance, but for other characteristics as well. The difficulty in this breeding work is the ploidy of cultivars (mostly 2n=4x) that differs from these of most wild species (2n=2x to 8x) (De Vries, 2000;De Vries and Dubois, 1996;De Vries and Dubois, 2001;Gudin, 1995).…”

Colchicine induction of ‘Old Blush’ 2n pollen for the hybridization and breeding of tetraploid rose

“…Modern rose has highly heterozygous genetic characteristics and has been created through tens of thousands of repeated hybridizations between Chinese and European rose species ( Erlanson, 1938 ), involving bud mutations, mutagenesis, and molecular breeding for traits favorable for flower color, potpourri, thorns, disease resistance, and stress resistance. Hybridization is common in rose breeding and has a long application history and creating a very large seasonal population ( Vries & Dubois, 2001 ). One main issue in cross-breeding is that the hybrid genetic background of traditional varieties is narrow, and the utilization of genetic resources tends to be saturated after long-term breeding.…”

Antifungal Effectiveness of Nanosilver Colloid against Rose Powdery Mildew in Greenhouses

“…Powdery mildew, caused by Sphaerotheca pannosa var. rosae, is one of the most common and widespread fungal diseases of greenhouse and outdoor roses [1,2]. It mainly appear first on the under surface of young leaves in early summer and the infection spreads to stems, shoots and buds [1].…”