Blackspot-Free Roses on Horizon
Beltsville, Md. — In four to eight years rose enthusiasts in several areas of the country can look forward to roses free of blackspot and the white residue often left by fungicides used to control this disease.
A U.S. Department of Agriculture scientist has developed three hybrid roses which are resistant to strains of the blackspot fungus native to areas in the East, South and Midwest. Peter Semeniuk, a research horticulturist with the department's Science and Education Administration, is now releasing budwood from the three cultivars (cultivated varieties) to interested commercial and amateur rose breeders.
While two of the cultivars will need further cross breeding to produce an acceptable garden rose, one cultivar, "Spotless Pink," already has a well-shaped bud, a full bloom of 60 to 70 petals, and semiglossy, dark green foliage. Semeniuk feels this rose could stand on its own merits, but "will leave that decision to commercial breeders."
If it is judged acceptable as is, the rose could reach the general market in three to four years. Otherwise it could take eight or more years before the offspring of "Spotless Pink" and the other two resistant parents, "Spotless Gold" and "Spotless Yellow," are available to the public.
Semeniuk estimates there may be as many as 50 to 100 strains of the blackspot fungus in the United States alone, but he chose seven strains that he had closely studied to test for resistance during his breeding program. The strains, which he maintained in the laboratory, had been cultured from infected leaves from Beltsville, Md.; University Park, Pa.; Ithaca, N.Y.; Tifton, Ga.; Tyler, Texas; Ames, Iowa; and Deleware, Ohio.
Because the new rose cultivars are resistant to these strains, "there is a good possibility that they will be resistant to some other strains," he said. "But we won't know for sure until after resistant roses are introduced and reports start coming in from growers around the country."
Andhra Pradesh Agricultural University (APAU) was established on June 12, 1964 at Hyderabad.
Breeding for disease resistance (p. 93)
Black spot is a major foliar disease of roses that causes severe losses to commercial and home gardens. The breeding lines ‘Spotless gold’ (Floribunda, F3 selection: Goldilocks x Rosa rugosa), ‘Spotless Yellow’ (Floribunda, F3 selection; Goldlocks x Rosa rugosa) and ‘Spotless Pink’ (Floribunda, F3 selection: Chic x Rosa rugosa) have been release for use a resistant parents in breeding programmes.
Americn Rose Annual, 68: 96-97 (1983)
Rose Breeding — Blackspot
In the rose breeding program, we are investigating ways and means by which the genes for blackspot resistance can be transferred to our garden roses. Progeny tests are the only feasible means of determining the genetic distribution of a pair of alleles from selfing or crossing resistant and susceptible roses. First generation (F1) seedlings between blackspot resistant breeding lines Spotless Pink, Spotless Gold, and Spotless Yellow crossed with susceptible Pink Radiance, Crimson Glory and Scarlet Knight were inoculated and evaluated to determine the genetic distribution of genes for resistance. The progeny from such crosses gave both resistant and susceptible types with the seedlings segregating into sharply defined groups of unequal numbers. Preliminary results indicate that it should be possible to incorporate blackspot resistance into our everblooming garden roses.
CybeRose note: 'Goldilocks', 'Chic', 'Crimson Glory' and 'Scarlet Knight' are derived remotely from Pernetianas. 'Radiance' has an "unnamed seedling" or two in its ancestry, so the precise lineage is not certain.