Registration of Four Rhizoctonia Root Rot Resistant Multigerm Sugarbeet Germplasms, FC716, FC717, FC718 and FC719

SUGARBEET (Beta vulgaris L.) germplasms FC716 through FC719 (Reg. no. GP- through Reg. no. GP- )(PI 574627 through PI 574630) were developed by the USDA-ARS in cooperation with the Beet Sugar Development Foundation. Each of these germplasms was developed from genetically different and distinctive sources. These lines should provide resistance to root-rotting strains (AG-2-2) of Rhizoctonia solani K?hn and potential pollinators with combining ability for yield. They were released in 1992.

FC716 resulted from interpollination of 38 mother roots, which were selected for resistance to Rhizoctonia from three commercial hybrids, HH32 (66%), ACH-139 (24%), and 70MSH386 (10%). HH32 is a Rhizoctonia-resistant Holly Sugar Corporation hybrid, ACH-139 is a Rhizoctonia-resistant American Crystal Sugar Company hybrid, and 70MSH386 is a Rhizoctonia-resistant hybrid from the former Great Western Sugar Company. This initial population underwent five cycles of mass selection for Rhizoctonia root rot resistance. FC716 has excellent Rhizoctonia root rot resistance when tested under strong disease pressure (4). There were no significant differences between FC716 and resistant controls in disease index (DI) (2) or the percentage of healthy plants (4) (Table 1). It has low-medium leaf spot (caused by Cercospora beticola Sacc.) resistance and is susceptible to curly top virus. FC716 is diploid, multigerm, and easy bolting and has medium sucrose content. It is segregating for green hypocotyls (88%). All plants have the cytoplasmic factor for male sterility (CMS); about 80% of the plants are pollen fertile (non-O-type) and 20% CMS. The fertile plants include type 2, type 3, and type 4 pollen fertile plants. Nonetheless, it is a good pollen producer. It should have a low frequency of segregates for monogerm and O-type. Because FC716 originated from productive hybrids, it should have potential as a source of Rhizoctonia-resistant germplasm with high combining ability for sugar yield. Isolation plots had excellent seed set and FC716 could function as a pollinator or a source population from which to select pollinators, O-types or CMS females. It was released in 1992 as seed production 911028.

FC717 was derived from a cross between FC708 and ACH14. FC708 is a Rhizoctonia root rot resistant, monogerm O-type (3) and ACH14 is an American Crystal hybrid. Starting with the F₂ population, four cycles of mass selection for Rhizoctonia resistance were made and it has excellent Rhizoctonia root rot resistance when tested under strong disease pressure (Table 1.). It has low-medium Cercospora leaf spot resistance and is susceptible to curly top virus. FC717 is diploid, multigerm, and has medium sucrose content. It is segregating for green hypocotyl (17%). It should have a low frequency of monogerm and O-type segregates; it has normal cytoplasm, and is a good pollen producer. There are no combining ability data on FC717, but the line may have potential as a source for selection of resistant pollinators and/or monogerm O-types. It was released in 1992 as seed production 911031.

FC718 resulted from the interpollination of Rhizoctonia resistant selections from four USSR open-pollinated populations Ramonsk 06 (5 plants), Ramonsk 100 (2 plants), Verkhynyachsk 072 (1 plant), and Vladovsk 20 (1 plant). Ramonsk 06 has high sugar yield and wide adaptation. Ramonsk 100 was bred for high sugar content and clear juice purity. Verkhynyachsk 072 was bred for resistance to storage rot. Vladovsk 20 was bred for high root yield and powdery mildew (Erysiphe polygoni DC) resistance. The initial population of FC718 underwent eight cycles of mass selection for Rhizoctonia root rot resistance. FC718 has excellent Rhizoctonia root rot resistance when tested under strong disease pressure (Table 1.). FC718 is unrelated to any other FC releases. The resistance appears to be quantitative and reacts with the pathogen in the same manner as resistant germplasm from U.S. sources. It is susceptible to Cercospora leaf spot and curly top. FC718 is diploid and multigerm. It has relatively low sucrose content and is segregating for green hypocotyl (27%). FC718 is relatively vigorous and heterogeneous. It may have potential as a source from which to select pollinators with high combining ability for sucrose content and root yield. It was released in 1992 as seed production 911032.

FC719 resulted from a cross between Polish 2x-4-73 and Syn OP (FC702/5 X FC701/5, F₂). Polish 2x-4-73 is a monogerm selection from the high sucrose Polish line, PZHR₄. FC701/5 and FC702/5 are breeding lines further selected for Rhizoctonia root rot resistance out of Fort Collins lines FC701 and FC702 (1). The F₂ population underwent five cycles of mass selection for Rhizoctonia root rot resistance. FC719 has excellent Rhizoctonia root rot resistance when tested under strong disease pressure (Table 1) but it has little resistance to Cercospora leaf spot or curly top. FC719 is diploid and multigerm. It is relatively high in sucrose content and is segregating for green hypocotyl (71%). Because half of the genes in the source were from a high-sucrose Polish population that was unrelated to most U.S. germplasm, FC719 should have diverse variability for sugar yield combining ability. It was released in 1992 as seed production 911037.

Breeder seed of FC716, FC717, FC718, and FC719 is maintained by USDA-ARS and will be provided in quantities sufficient for reproduction upon written request to Sugarbeet Research, USDA-ARS, Crops Research Laboratory, 1701 Center Ave., Fort Collins, CO 80526-2081. We request that appropriate recognition be made of the source when this germplasm contributes to a new cultivar.

L. Panella*, E. G. Ruppel, and R. J. Hecker (5)

References and Notes

1. Hecker, R.J., and J.O. Gaskill. 1972. Registration of FC 701 and FC 702 sugarbeet germplasm. Crop Sci. 12:400.

2. Hecker, R.J., and E.G. Ruppel. 1977. Rhizoctonia root-rot resistance in sugarbeet: breeding and related research. J. Am. Soc. Sugar Beet Technol. 19:246-256.

3. Hecker, R.J., and E.G. Ruppel. 1981. Registration of FC 708 and FC 708 CMS sugar beet germplasm. Crop Sci. 21:802.

4. 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.

5. Research Geneticist, Plant Pathologist, and Research Geneticist (retired), USDA-ARS, Crops Research Lab., 1701 Center Ave., Fort Collins, CO 80526-2081. A joint contribution of USDA-ARS and the Beet Sugar Development Foundation.

Table 1. Disease index and the percent of healthy plants after infection by Rhizoctonia solani in an artificially created epiphytotic.

A scale of 0 to 7 was used, with 0 = no apparent infection and 7 = plant dead. A disease index (DI) was calculated for each plot from individual root ratings.

Plants in classes 0 and 1 were considered healthy and were used to calculate the percentage of healthy plants.

^*In all cases, significant differences ( = 0.05) occurred between the susceptible checks and each of the other lines. There were no significant differences among the resistant checks and the other lines. Values for % healthy were transformed to arcsin-square roots for analysis.