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Registration of FC709-2 and FC727 Sugarbeet Germplasms Resistant to Rhizoctonia Root Rot and Cercospora Leaf Spot.

Sugarbeet (Beta vulgaris L.) germplasms FC709-2 (Reg. no. GP200, PI 599668) and FC727 (Reg. no. GP-201, PI 599669) were developed by the USDA-ARS, Fort Collins, CO, in cooperation with the Beet Sugar Development Foundation, Denver, CO. These lines should provide excellent resistance to root-rotting strains (AG2-2) of Rhizoctonia solani Kuhn and moderate resistance to cercospora leaf spot (caused by Cercospora beticola Sacc.). They are potential pollinators or populations from which to select pollinators with combining ability for yield. FC709-2 and FC727 were released in 1998 from seed productions 9210124 and 951017, respectively.

FC709-2 is multigerm (MM), non-O-type, and pseudo-self-fertile, with 13% green hypocotyls. It is segregating, with approximately 19% male sterility. The sterility is most likely cytoplasmic, because plants had a range of anther types from white, shrunken anthers with no pollen production to full, yellow, dehiscent anthers with normal pollen. However, no progeny testing was done to confirm the basis of sterility. FC709-2 is the result of three cycles of selection within the line 871016. 871016 had one more cycle of selection for resistance to R. solani than its parent line, 841034. FC709 (1) was released as a composite of seed from 871016 and 841034. The first cycle of selection for FC709-2 was mass selection for resistance to rhizoctonia root rot in a nursery inoculated with R. solani (2). Seed was produced in bulk from surviving roots planted in a field isolation plot where they were reinoculated with R. solani. Seed from 28 plants was harvested. Some of this seed was planted into a disease-free nursery and, based on percent sucrose of individual roots, the 9.4% of beets with the highest sucrose (55 beets) were selected. The remaining seed from Cycle 1 was grown in a rhizoctonia-inoculated nursery, and three beets were selected. The three beets were increased in bulk along with the 55 beets selected for high sucrose. Seed was harvested from a total of 33 surviving plants. This Cycle 2 population underwent another cycle of mass selection for resistance to rhizoctonia root rot in an inoculated nursery (2). Seed from the 121 surviving plants was harvested in bulk to produce FC709-2.

FC709-2 had high resistance to rhizoctonia root rot when tested under strong disease pressure (2). Based on disease index (DI) ratings from 1994 through 1997, where a DI of 0 = no root rot and 7 = all plants dead, there were either no significant differences or FC709-2 performed better than the rhizoctonia-resistant controls. In these four years, the DI ratings for the resistant check (FC705-1) were 1.4, 1.4, 1.5, and 3.2, compared with 1.0, 1.5, 0.9, and 2.5 for FC709-2. FC709-2 was always significantly better than the susceptible control (FC901/C817//413). Of all lines tested, FC 709-2 had the lowest DI rating in the very severe epiphytotic of 1997. Percentages of resistant plants (those rated 0 or 1) were 86, 55, 100, and 49 for FC709-2, and 65, 58, 62, and 49 for FC705-1.

FC709-2 showed good resistance to cercospora leaf spot when tested in artificial epiphytotics (3). In three years of testing, it was significantly better than the susceptible control and not significantly different from the resistant control. The following DI ratings (DI of 0 = no leaf spot and 10 = all plants dead) are from the most severe rating (the last of three or four ratings each season). In 1994, 1995, and 1997, DI ratings of FC709-2 were 3.0, 4.3, and 4.2/3.5 (tested in two trials). Ratings of the resistant control (FC504CMS/FC502-2//SP6322-0) were 3.2, 3.5, and 3.8/2.9 for the same respective years, and ratings of the susceptible control (SP351069-0) were 4.5, 6.2, and 7.0/6.5. FC709-2 does not have tolerance to the beet curly top virus (BCTV). As with FC709, field testing of FC709-2 in California revealed a low frequency of plants with some resistance to rhizomania (R.T. Lewellen, personal communication); however, this germplasm is not recommended as a source for rhizomania resistance.

In a 1995 yield trial at Fort Collins, CO, with moderate drought stress, the sucrose yield of FC709-2 was 89% of `Beta 2398' and 66% of `Monohikari' and the percent sucrose was 102% of `Beta 2398' and 86% of `Monohikari'. FC709-2 has not been tested for combining ability. It was released for use as a pollinator for making rhizoctonia root rot- and cercospora leaf spot-resistant hybrids, or as a source population from which such pollinators can be selected.

FC727 is multigerm (MM), non-O-type, and has 51% green hypocotyls. FC727 resulted from crossing FC703 (4) (50% of the genetic contribution) to three high-sucrose sources: Polish A J, ZZ (16%), the Spanish line `Aula Del 13' (21%), and `American Crystal 67-436' (13%). FC727 is the result of eight cycles of mass selection for resistance to rhizoctonia root rot. Within four of these cycles, resistant roots were simultaneously selected for high sucrose of individual roots. The smallest population size was 26 plants and, on average, a selection intensity of 18% for sucrose was used.

FC727 has excellent resistance to rhizoctonia root rot when tested under severe disease pressure (2). There were no significant differences between it and rhizoctonia-resistant controls in DI ratings, and FC727 was significantly more resistant than the susceptible control (FC901/C817//413) from 1994 through 1997. FC727 had mean yearly Dis of 1.4, 1.7, 1.1, and 3.6 (1994- 1997), whereas the highly resistant control (FC705-1) had Dis of 1.4, 1.4, 1.5, and 3.2. Percentages of resistant plants (those rated 0 or 1) were 69, 41, 89, and 16 for FC727 and 65, 58, 62, and 49 for FC705-1.

FC727 has a moderate reaction to cercospora leaf spot. In three years of testing in an artificial epiphytotic of cercospora leaf spot (3), it was significantly more resistant than the susceptible control but, significantly more susceptible than the resistant control. The following DI ratings are from the most severe rating (last of three or four ratings each season). In 1994, 1995, and 1997, Dis of FC727 were 3.8, 4.5, and 4.8. Dis of the resistant control (FC504CMS/FC502-2//SP6322-0) were 3.2, 3.5, and 2.9. Dis of the susceptible control (SP351069-0) were 4.5, 6.2, and 6.5. FC727 does not have tolerance to BCTV.

FC727 had relatively good general combining ability for sucrose yield when used as a pollinator on several diverse CMS lines. FC727 has potential for use as a pollinator or a population from which to choose pollinators with good combining ability. It should contribute to the development of high-sucrose hybrids with resistance to rhizoctonia root rot.

Seed of FC709-2 and FC727 is maintained by the USDA-ARS and, for at least five years, 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 80526-2083. Seed of this release will be deposited in the National Plant Germplasm System, where it will be 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.

LEE PANELLA(*) (5)

References and Notes

(1.) Hecker, R.J., and E.G. Ruppel. 1988. Registration of rhizoctonia root rot resistant sugarbeet germplasm FC 709. Crop Sci. 28:1039-1040.

(2.) 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.

(3.) 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.

(4.) 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.

(5.) USDA-ARS, Crops Research Lab., 1701 Center Ave., Fort Collins, CO 80526-2081. A joint contribution of the USDA-ARS and the Beet Sugar Development Foundation. Registration by CSSA. Accepted 31 July 1998. (*) Corresponding author (lpanella@lamar.colostate.edu).
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Author:PANELLA, LEE
Publication:Crop Science
Date:Jan 1, 1999
Words:1362
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