L. Panella and L. E. Hanson
Sugarbeet (Beta vulgaris L.) germplasm FC724 (Reg. no. GP-, PI 632251) was developed by the USDA-ARS, Fort Collins, CO, in cooperation with the Beet Sugar Development Foundation, Denver, CO. FC724 has high resistance to root-rotting strains (AG-2-2) of Rhizoctonia solani Kühn and good to moderate resistance to cercospora leaf spot caused by Cercospora beticola Sacc., but is beet curly top virus (BCTV) susceptible. FC724 was developed as a population from which to select monogerm O-type parent lines with enhanced rhizoctonia resistance. There is no CMS equivalent. FC724 was released in 2003 from seed production 19961014.
FC724 is an O-type germplasm with 12% green hypoctoyls (14/116 plants) and is segregating for monogerm (mm). It is a product of nine generations of cyclic mass selection for resistance to rhizoctonia root rot and two cycles of recurrent selection for high general combining ability. The approximate genetic contribution of the parents to the original population was 20% 611100-0, 17% FC 601/2 and 63% FC702 (Hecker and Gaskill, 1972). The original crosses were FC702 (Hecker and Gaskill, 1972) by selfed progeny lines from FC601/2 and from 611100-0. Breeding line 611100-0 was developed through a poly cross of several BCTV and leaf spot resistant lines: SLC122-0, US22/3 (PI 590708 -- Murphy et al., 1948), US201 (PI 590678), US22/4 (SL92 -- PI 610266 -- Coons et al., 1955), SL202 (F2 of US35/2 x US22/4). FC601/2 consisted of selected progeny lines from SL202 x SLC122‑0. Because the original crosses were made to male-sterile plants (genetic male sterility - aa), it is possible that FC724 is segregating for genetic male sterility, but no male sterile-plants were observed in the last seed production.
Hybrid tester lines were produced with Fort Collins breeding lines to test for general combining ability in 1974 and 1977. Remnant, selfed seed from superior lines was recombined after each cycle of testing. The population has gone through nine cycles of selection in the USDA-ARS rhizoctonia nursery in Fort Collins (Panella, 1998), has been O-type indexed to remove restorer genes, and has been selected for monogerm seed throughout the development process. The smallest population size was 19 plants.
FC724 exhibited excellent resistance to rhizoctonia root rot when tested under strong disease pressure (Ruppel et al., 1979). FC724's performance was not significantly different from the highly resistant check (FC705/1) (Hecker and Ruppel, 1985) in disease index (DI) ratings from 1998 through 2001, respectively (DI of 0 = no root rot and 7 = all plants dead). FC724 performed significantly better than the susceptible check (FC901/C817) (Gaskill et al., 1967). FC724 had mean disease indices (DI=s) of 2.3, 3.1, 3.1, and 1.7 (1998-2001, respectively), whereas the highly resistant check had DI=s of 2.7, 3.3, 3.1, and 1.6, respectively. Percentages of resistant plants (those rated 0 or 1) were 47, 16, 5, and 52 for FC724; 33, 22, 13, and 53 for the highly resistant check and 12, 12, 3, and 44 for the resistant check (FC703) (Hecker and Ruppel, 1977), (1998-2001, respectively).
FC724 also exhibited resistance to cercospora leaf spot when tested in an artificial epiphytotic (Ruppel and Gaskill, 1971). In 2 years of tests, it was significantly better than the susceptible check and not significantly different from the resistant check in 1 year and had significantly less resistance than the resistant check in the other. The following DI ratings (DI of 0 = no leaf spot and 10 = all plants dead) represent the most severe rating (last of three or four ratings each season). The DIs of FC724 were 4.0 and 3.2; DIs of the resistant check (FC504CMS/FC502-2//SP6322-0) (Coe and Hogaboam, 1971; Smith and Gaskill, 1979) were 2.8 and 2.9; DIs of the susceptible check (SP351069‑0) were 6.5 and 5.8, respectively. FC724 does not show tolerance to the BCTV.
In 2002, FC724 was planted in one-row plots, replicated six times at the USDA-ARS Fort Collins Research Farm, on May 3. Plots were 3.04 m long with 56 cm between rows and 20 to 25 cm within-row spacing. Roots were harvested on October 8 and sent to the Western Sugar Co. tare lab in Scotts Bluff, NE for analyses. The average sucrose concentration and sugar loss to molasses of three commercial varieties – Beta 6045, HM1955, Monohikari – was used as a standard for comparison. Sucrose concentration of FC724 was 96.3% of the standard, and in sugar loss to molasses, FC724 was 97.9% of the standard.
Breeder seed of FC724 is maintained by USDA-ARS and, for at least five years, will be provided in quantities sufficient for reproduction upon written request to Sugar Beet Research, USDA-ARS, Crops Research Laboratory, 1701 Center Ave., Fort Collins, CO 80526-2083. Seed of this release has been deposited in the National Plant Germplasm System, where it is available for research purposes, including development and commercialization of new lines or cultivars. The developing organizations request appropriate recognition of the source when this germplasm contributes to a new cultivar. U.S. plant variety protection will not be requested for FC724.
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Coons,G.H., F.V.Owen, and D.Stewart. 1955. Improvement of the sugar beet in the United States. Adv. Agron. 7:89-139.
Gaskill, J.O., C.L. Schneider, A.M. Murphy, and G.E. Coe. 1967. Breeding for combined resistance to leaf spot and curly top in sugar beet. J. Am. Soc. Sugar Beet Technol. 14:518-537.
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Hecker, R.J. and E.G. Ruppel. 1977. Registration of diploid and tetraploid FC 701/4 and FC 703 sugarbeet germplasm. Crop Sci. 17:678.
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Panella, L. 1998.Screening and utilizing Beta genetic resources with resistance to Rhizoctonia root rot and Cercospora leaf spot in a sugar beet breeding program. In: Frese, L., L. Panella, H. M. Srivastava, and W. Lange, (ed.). Int. Beta Genetic Resources Network. A report on the 4th Int. Beta Genetic Resources Workshop and World Beta Network Conf. held at the Aegean Agric. Res. Inst., Izmir, Turkey, 28 February ‑ 3 March, 1996. International Crop Network Series No. 12. pp 62-72 , Int. Plant Genetic Resources Inst, Rome.
Ruppel, E.G., C.L. Schneider, R.J. Hecker, and G.J. Hogaboam. 1979. Creating epiphytotics of Rhizoctonia root rot and evaluating for resistance to Rhizoctonia solani in sugarbeet field plots. Plant Dis. Rep. 63:518-522.
Ruppel, E.G., and J.O. Gaskill. 1971. Techniques for evaluating sugarbeet for resistance to Cercospora beticola in the field. J. Am. Soc. Sugar Beet Technol. 16:384-389.
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