The USDA Agricultural Research Service (ARS), in cooperation with the Beet Sugar Development Foundation (BSDF), announces the release of three sugarbeet germplasms. Each germplasm was developed from genetically different and distinctive sources. These lines should provide excellent resistance to root-rotting strains (AG-2-2) of Rhizoctonia solani and moderate resistance to leaf spot caused by Cercospora beticola. They are potential pollinators or populations from which to select pollinators with combining ability for yield. The germplasms were developed by ARS and BSDF in the research program of L. Panella and E. G. Ruppel at Fort Collins, Colorado.
FC725 is multigerm (MM), non O-type, self-sterile, and has 44 percent green hypocotyls. It resulted from the cross C37 x FC707/2. An F2 population of 25 individuals was random-mated and followed with four cycles of mass selection for resistance R. solani. Population size was maintained at 32 or more plants. The Rhizoctonia-resistant parent is a superior sib line of FC707, and the parent from the Salinas ARS sugarbeet breeding program (C37) combines resistance to bolting, curly top virus, and virus yellows.
FC725 had excellent resistance to Rhizoctonia root rot when tested under strong disease pressure. On a disease index (DI) scale of 0 to 7, with 0 = healthy and 7 = dead, FC725 was significantly more resistant to R. solani than the susceptible control (FC901/C817//413) in both 1993 (DI of 1.2 vs 3.0) and 1994 (DI of 1.4 vs 4.9). Likewise, percent healthy roots for FC725 vs the control was 74 vs 23 percent in 1993 and 76 vs 5 percent in 1994. FC725 also shows some resistance to Cercospora leaf spot. On a DI scale of 0 to 10, with 0 = no leaf spots and 10 = complete defoliation, FC725 was significantly better than the susceptible control (SP103569-0) in 1993 (DI of 4.3 vs 6.3) and 1994 (DI of 3.8 vs 4.5). FC725 was not tolerant of the curly top virus. FC725 can be used as a pollinator for making Rhizoctonia root rot- and Cercospora leaf spot-resistant hybrids or as a source population from which such pollinators may be selected.
FC726 is multigerm (MM), non O-type, self-sterile, and has 46 percent green hypocotyls. FC726 resulted from the cross FC703/3 x Permano. FC703/3 is a superior sib line of the Rhizoctonia- resistant line FC703. Permano is a fodderbeet with relatively high sucrose and medium Rhizoctonia root rot resistance, detected in the exotic germplasm screening program of R.J. Hecker. White roots were selected in the F2 generation, followed by four generations of mass selection for resistance to R. solani and three simultaneous generations of mass selection for high sucrose. The smallest population size was 17 roots and, on average, the highest 27 percent of the roots were selected for high sucrose. Permano was chosen as a parent because of its diverse origin (fodderbeet, not sugarbeet) and its relatively good Rhizoctonia resistance. Permano might represent another source of resistance to Rhizoctonia root rot, and crossing with the Rhizoctonia resistant parent FC703/3 could lead to transgressive segregants for Rhizoctonia resistance. This has not been tested; however, progress toward Rhizoctonia resistance has been rather rapid, indicating that transgressive segregants may have occurred. FC726 has relatively low sugar but has considerable vigor and represents a source of genetic diversity. FC726 had excellent resistance to R. solani when tested under strong disease pressure. FC726 was significantly better than the susceptible control in both 1993 (DI of 1.2 vs 3.0; 73 percent vs 23 percent healthy roots) and 1994 (DI of 1.5 vs 4.9; 67 percent vs 5 percent healthy roots). It had significantly better resistance to C. beticola than the susceptible control when tested in 1993 (DI of 3.5 vs 6.3) and 1994 (DI of 3.8 vs 4.5). FC726 did not show tolerance to the curly top virus.
FC728 is multigerm (MM), non O-type, self-sterile, and has the sterile cytoplasm. It has 26 percent green hypocotyls. FC728 resulted from a population derived of equal numbers of F1 plants (90) from three crosses: Mono-Hy A4 x FC708, Mono-Hy D2 x FC708, and Mono-Hy 309 x FC 708. True hybrids were selected with hypocotyl color as a marker. These F1s were interpollinated and underwent five generations of mass selection for resistance to R. solani. FC728 has a low frequency of segregants for monogermity (mm) and O-type. It has less than 15 percent male sterility. FC728 is vigorous and has relatively high sucrose. Population size was maintained at 28 plants or higher throughout the selection process. There are no combining ability data available, but, because of the productive hybrids as parents, FC728 should be a good source of parents with high combining ability. Because of the genetic background, it should also be possible to isolate monogerm, O-type, and CMS genotypes. When tested under strong disease pressure, FC728 had excellent resistance to R. solani. There were no significant differences between it and Rhizoctonia-resistant controls (FC703 and FC705/1) in DI ratings. FC728 was significantly more resistant to R. solani than the susceptible control in 1993 (DI of 1.1 vs 3.0; 82 percent vs 23 percent healthy roots) and 1994 (DI of 1.7 vs 4.9; 63 percent vs 5 percent healthy roots). FC728 showed moderate resistance to Cercospora leaf spot. It was significantly better than the susceptible control in 1993 (DI of 4.7 vs 6.3) and 1994 (DI of 3.5 vs 4.5). FC728 did not show tolerance to the curly top virus.
Breeder seed of FC725, FC726, and FC728 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 80526-2083. Genetic material 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 cultivars. We request that appropriate recognition be made of the source when this germplasm contributes to a new breeding line or cultivar.