HortScience 14(6): 764-765. 1979
Spotless Gold, Spotless Yellow, and Spotless Pink Rose: Blackspot Resistant Breeding Lines1
Peter Semeniuk2
U.S. Department of Agriculture, Science and Education Administration, Agricultural Research, Beltsville, MD 20705

1 Received for publication June 29, 1979. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper must therefore be hereby marked advertisement solely to indicate this fact.
2 Research Horticulturist, Florist and Nursery Crops Laboratory, Horticultural Science Institute.

Here we report the first evidence of resistance of roses to the blackspot disease, Diplocarpon rosae Wolf. Blackspot is a major foliar disease of roses that causes severe losses to commercial and home gardeners. It spreads rapidly on susceptible cultivars, results in premature defoliation, and severely reduces yield and quality of this popular plant. Growers must make frequent applications of fungicides which are costly in labor and materials and environmentally undesirable. Stewart and Semeniuk (3) reported on the problems and techniques in transferring resistance to blackspot from the diploid species to garden roses (1, 2). The breeding lines Spotless Gold, Spotless Yellow, and Spotless Pink will be released for use as resistant parents in breeding programs. This germplasm should be valuable to breeders for its resistance to 7 isolates of D. rosae from Beltsville, Maryland, Tifton, Georgia, Ames, Iowa, Ithaca, New York, Delaware. Ohio, University Park, Pennsylvania, and Tyler, Texas. These roses have been released by the U.S. Department of Agriculture, Science and Education Administration. The developmental work was done by the Florist and Nursery Crops Laboratory at the Agricultural Research Center, Beltsville, Maryland.

Origin

Spotless Gold, Spotless Yellow, and Spotless Pink are the result of a breeding program begun in 1965 (3) to develop horticulturally suitable rose breeding lines with appreciable levels of resistance. They were selected from an F3 population derived from crosses between a tetraploid form of a blackspot resistant species (Rosa rugosa) and the commercial cultivars 'Goldilocks' and 'Chic'. Selections for disease resistance were made in the greenhouse following repeated inoculations of the F2 and F3 generations. Pollen fertility and seed set were comparatively good in all three cultivars.

Description

Spotless Gold, Spotless Yellow, and Spotless Pink showed no symptoms of rose blackspot in unsprayed field trials at Star Roses. Detached leaf tests (1) were used to explore seasonal variation in infection. Leaves of susceptible lines were highly infected in all detached leaf tests, whereas the 3 breeding lines showed virtually no infection at any season. The most significant attribute of Spotless Gold, Spotless Yellow, and Spotless Pink is their resistance to rose blackspot.

Spotless Gold (Fig. 1), an F3 selection from 'Goldilocks' x R. rugosa (tetraploid) has ovoid bud; flower medium in size (6.4 cm), double (25 petals), fragrant, yellow, Royal Horticultural Society Colour Chart Number 9A; solitary or few. The leaflets are 3 to 4 cm long, usually glossy, 5 per leaf, and green, 147A. The branches have sickle-shaped thorns, 12 per 10 cm stem section. Vigorous and bushy everblooming floribunda type of plant with exceptionally high rose blackspot resistance.

Spotless Yellow (Fig. 1), an F3 selection from 'Goldilocks' x R. rugosa (tetraploid), has ovoid bud; flower medium in size (7.6 cm); semi-double (10-15 petals), slightly fragrant, yellow, 7B; singly and cluster. The leaflets are 3 to 4 cm long, the number varies from 5 to 7 and are dark green, 137A. Everblooming floribunda type of plant with exceptionally high rose blackspot resistance.

Spotless Pink (Fig, 2), an F3 selection from 'Chic' x R. rugosa (tetraploid), has ovoid bud; flower large in size (10 cm), double (65-70 petals), fragrant, red, 38A; solitary or few. The leaflets are 4 to 5 cm long, semi-glossy green, 137B, usually 5-7 per leaf. Vigorous and bushy everblooming floribunda type of plant with exceptionally high rose blackspot resistance.

Availability

Small amounts of budwood are available for distribution to public and private researchers for use as a parental rose line upon written request to the Florist and Nursery Crops Laboratory, U.S. Department of Agriculture, Beltsville, MD 20705.

Literature Cited

  1. Palmer, J. G. and P. Semeniuk. 1961. Comparable susceptibility of 50 species and hybrid roses inoculated with blackspot fungus from plants field grown in Maryland in 1959. American Rose Annual, p. 125-133.
  2. Semeniuk, P. and T. Arisumi. 1968. Colchicine-induced tetraploid and cytochimeral roses, Bot. Gaz. 129(3): 190-193.
  3. Stewart, R. N. and P. Semeniuk. 1965. Report on rose research in the U.S. Department of Agriculture. American Rose Annual, p. 99-105.
Fig. 1. Spotless Yellow rose (left) and Spotless Gold (right). Fig. Spotless Pink rose.