The Agricultural Research Service, United States Department of Agriculture, in cooperation with the Beet Sugar Development Foundation, announces the release of FC712 (4X) tetraploid, multigerm sugar beet germplasm. This line was developed in the breeding program of L. Panella, Sugar Beet Research Unit, USDA-ARS, Fort Collins, Colorado. This line has excellent resistance to root-rotting strains (AG-2-2) of Rhizoctonia solani K?hn. It is also moderately resistant to leaf spot caused by Cercospora beticola Sacc. It is released as a tetraploid pollinator, or population from which to select tetraploid pollinators with resistance to rhizoctonia root rot and cercospora leaf spot. FC712 (4X) is released from seed production 971018.

FC712 (4X) (PI 607379) is tetraploid (2n = 4x = 36), multigerm (MM), non-O-type, pseudo-self-fertile, and has 4% green hypocotyls. It is a colchicine doubled version of FC712, which was registered in 1986. FC 712 was developed by combining the most rhizoctonia resistant germplasm in the USDA-ARS, Fort Collins, breeding program. One hundred thirty-eight colchicine treated seedlings with thickened or distorted hypocotyls were selected, transplanted, vernalized, and induced to flower. Pollen from approximately 100 plants was sized to determine ploidy and seed was harvested individually from 39 tetraploid C₀ plants. Five seeds of each mother plant were planted, vernalized, and induced to flower. Again, pollen was sized to confirm ploidy and 121 tetraploid plants from 36 of the original C₀ mother roots harvested for seed to produce the C₁. The C₁ seed was planted in the greenhouse and pollen sized to confirm ploidy level. The C₂ seed was harvested from 74 tetraploid plants. C₂ seed went through another cycle of seed production in the greenhouse, in which 100 plants were harvested to produce C₃ seed. This seed was tested in artificially created epiphytotics of rhizoctonia root rot and cercospora leaf spot, bulk increased in a field isolation plot in 1997 (234 plants), and the increased seed lot tested in 1998 and 1999.

FC712 (4X) exhibited excellent resistance to rhizoctonia root rot when tested under strong disease pressure. FC712 (4X) performance was equal or superior to rhizoctonia-resistant checks in disease index (DI) ratings in 1997 and 1999 (DI of 0 = no root rot and 7 = all plants dead). FC712 (4X) performed significantly better than the susceptible check (FC901/C817). FC712 (4X) had mean DI's of 2.9 and 3.0 (1997 and 1999), whereas the highly resistant check (FC705/1) had DI's of 3.2 and 3.3, respectively. Percentages of resistant plants (those rated 0 or 1) were 29 and 26 for FC712 (4X); and 49 and 22 for the highly resistant check.

FC712 (4X) also exhibited good resistance to cercospora leaf spot when tested in an artificial epiphytotic. In tests from 1998 and 1999, 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) represent the most severe rating (last of three or four ratings each season). In 1998 and 1999, DIs of FC712 (4X) were 3.3 and 3.5; DIs of the resistant control (FC504CMS/FC502-2//SP6322-0) were 2.8 and 2.7; DIs of the susceptible control (SP351069-0) were 5.8 and 6.3, respectively. FC712 (4X) does not show tolerance to the curly top virus.

Breeder seed of FC712 (4X) is maintained by USDA-ARS and will be provided in quantities sufficient for reproduction upon written request to Lee Panella(Lee.Panella@ars.usda.gov), Sugar Beet Research, USDA-ARS, Crops Research Laboratory, 1701 Center Ave., Fort Collins, CO 80526-2083. Genetic material of this release has been deposited in the National Plant Germplasm System where it will be available for research purposes, including development and commercialization of new varieties/cultivars. We request that appropriate recognition be made of the source when this germplasm contributes to a new cultivar. U.S. plant variety protection will not be requested for FC712 (4X).