Notice of Release of FC709-2 and FC727 Multigerm Sugarbeet Germplasms

The USDA Agricultural Research Service (ARS), in cooperation with the Beet Sugar Development Foundation (BSDF), announces the release of FC709-2 and FC727 multigerm sugarbeet germplasms. These lines should provide excellent resistance to root-rotting strains (AG-2-2) of Rhizoctonia solani K?hn and good to 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 are released from seed productions 9210124 and 951017, respectively.

FC709-2 is multigerm (MM), non O-type, pseudo self-fertile, and has 13% green hypocotyls. It is segregating with approximately 19% male sterility. Of 122 plants examined for pollen production, there were 8% Type 0, 11% Type 1 (both considered male sterile), 14% Type 2, and 67% Type 3. FC709-2 is the result of three cycles of selection within the most resistant population (871016) that went into FC 709. This population first was mass selected for resistance to Rhizoctonia root rot caused by R. solani, and surviving roots were increased in bulk in a field isolation plot where they also were re-inoculated with R. solani. Twenty-eight plants were harvested. Seed was split and planted into a disease-free nursery and a nursery inoculated with R. solani. Fifty-three roots were selected from the disease-free nursery based on percent sucrose of individual roots (highest 9.4%), and these were increased in bulk with three roots selected for Rhizoctonia resistance. Seed was harvested from a total of 33 surviving. This population underwent another cycle of mass selection for resistance to Rhizoctonia root rot, and the 121 surviving roots were harvested in bulk to produce the seed released as FC709-2.

FC709-2 had excellent resistance to Rhizoctonia root rot when tested under strong disease pressure. There were either no significant differences or FC709-2 performed better than the Rhizoctonia-resistant controls in disease index (DI) ratings from 1994 through 1997, respectively (DI of 0 = no root rot and 7 = all plants dead). FC709-2 was always significantly better than the susceptible control (FC901/C817//413). FC709-2 had mean disease indices (DI's) of 1.0, 1.5, 0.9, and 2.5 (1994-1997), whereas the highly resistant control (FC705/1) had DI's of 1.4, 1.4, 1.5, and 3.2, respectively. Of all lines tested, FC 709-2 had the lowest DI 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 the highly resistant check.

FC709-2 also showed good resistance to Cercospora leaf spot when tested in an artificial epiphytotic. In tests from 1994, 1995, and 1997, 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 (last of three or four ratings each season). The test from 1996 is excluded because, due to a non-uniform disease intensity, there were no significant differences among lines tested in that year. In 1994, 1995, and 1997, DIs of FC709-2 were 3.0, 4.3, and 4.17/3.5 (tested in two trials); DIs of the resistant control (FC504CMS/FC502-2//SP6322-0) were 3.2, 3.5, and 3.8/2.9; DIs of the susceptible control (SP351069-0) were 4.5, 6.2, and 7.0/6.5, respectively. FC709-2 does not show tolerance to the curly top virus. As with the parent line, FC709, field testing of FC709-2 in California revealed a very low frequency of plants that exhibit some resistance to rhizomania (R. T. Lewellen, personal communication). This germplasm is, however, not recommended as a source for rhizomania resistance.

In a yield trial with some drought stress (unpublished data), the sucrose yield (root weight x percent sucrose) of FC709-2 was 89% of 'Beta 2398' and 66% of 'Monohikar?', and the percent sucrose was 102% of 'Beta 2398' and 86% of 'Monohikar?'. FC709-2 has not been tested for combining ability. It is 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 the cross FC703 (50% of the genetic contribution) and three high sucrose sources - Polish AJ, -ZZ (16%), the Spanish line 'Aula Dei 13' (21%), and American Crystal's '67-436' (13%). The effective population size of the F₁ was 92 plants. FC727 is the result of eight generations of mass selection for resistance to Rhizoctonia root rot induced by R. solani and four simultaneous generations of mass selection of individual roots for high sucrose. The smallest population size was 26 roots and, on average, the highest 18% of the roots were selected for sucrose.

FC727 has excellent resistance to Rhizoctonia root rot when tested under strong disease pressure. There were no significant differences between it and Rhizoctonia resistant controls in DI ratings, and FC727 tested significantly better than the susceptible control (FC901/C817//413) from 1994 through 1997. FC727 had mean disease indices (DI's) of 1.4, 1.7, 1.1, and 3.6 (1994-1997), while the highly resistant control (FC705/1) had DI's of 1.4, 1.4, 1.5, and 3.2, respectively. Percentages of resistant plants (those rated 0 or 1) were 69, 41, 89, and 16 for FC727; and 65, 58, 62, and 49 for the highly resistant check.

FC727 has some resistance to Cercospora leaf spot. When tested form 1994 through 1997 in an artificial epiphytotic of Cercospora leaf spot, it was significantly better than the susceptible control but, also, significantly worse than the resistant control. The following DI ratings are from the most severe rating (last of three or four ratings each season). The year 1996 is excluded because, due to a non-uniform disease intensity, there were no significant differences among lines tested. In 1994, 1995, and 1997, DI's of FC727 were 3.8, 4.5, and 4.8; DI's of the resistant control (FC504CMS/FC502-2//SP6322-0) were 3.2, 3.5, and 2.9; DI's of the susceptible control (SP351069-0) were 4.5, 6.2, and 6.5, respectively. FC727 does not show tolerance to the curly top virus.

FC727 has relatively good general combining ability for sucrose yield when used as a pollinator on several diverse CMS lines (unpublished data). 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 synthesis of high sucrose hybrids with resistance to Rhizoctonia root rot.

Breeder seed of FC709-2 and FC727 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 varieties/cultivars. We request that appropriate recognition be made of the source when this germplasm contributes to a new cultivar.

Table 1.  These germplasms were tested in artificial epiphytotics of curly top virus (Kimberly, ID), Rhizoctonia root rot (Fort Collins, CO), and Cercospora leaf spot (Fort Collins, CO) for 2 yr.