|Notice of Release of FC721 and FC721CMS Sugarbeet Germplasms|
SUGARBEET (Beta vulgaris L.) germplasms FC721 (Reg. no. GP- , PI 594910) and FC721CMS (Reg. no. GP- , PI 594911 ) were developed by the USDA-ARS in cooperation with the Beet Sugar Development Foundation. They were released in 1996 from seed productions 931005HO and 931005HO1. These germplasms were released as sources of resistance to root-rotting strains of Rhizoctonia solani K?hn and incorporate moderate tolerance to the curly top virus and leaf spot caused by Cercospora beticola Sacc.
FC721 is a diploid, monogerm, O-type, self-fertile (Sf), sugarbeet germplasm resistant to root and crown rot caused by R. solani AG-2-2. It is relatively homogenous, easy bolting, and moderately tolerant to the curly top virus and Cercospora leaf spot caused by Cercospora beticola Sacc. FC721 segregates for hypocotyl color (39% rr) and genetic male sterility (aa). It is the O-type (maintainer line) of its CMS equivalent, FC721CMS, which is the BC10 with C718CMS (1) as the nonrecurrent parent. One parental component of FC721 was a population developed from selected S1 plants crossed to FC701 (2). The S1 progeny were from populations that had been developed (in the early 1950s), selected, recombined, and reselected from a number of curly top and leaf spot resistant sources that included SLC122-0, US 22/3 (3), US 22/4 (4), US 201 (5), SL 202, and US 35/2. The parent derived from these S1 selections x FC701 segregated for genetic male sterility. Twenty-three male-sterile plants were pollinated by 13 fertile plants from C718 (1) to produce the F1 from which FC721 was selected. C718 from the USDA-ARS sugarbeet breeding program in Salinas, CA is bolting resistant, moderately resistant to curly top, and has good combining ability for root and sucrose yield (1). The female parent combined sources of resistance to Rhizoctonia root rot, Cercospora leaf spot, and curly top virus.
F2 plants were selfed in the greenhouse and O-type indexed. Twenty-five O-type, S1 plants were bulk increased in the greenhouse. The resulting population underwent five cycles of mass selection for resistance to Rhizoctonia root rot concurrent with three cycles of mass selection for monogerm seedballs. The smallest population size during this selection process was nine plants.
In a 1994 replicated field evaluation for resistance to R. solani at Fort Collins, CO (6), FC721 and FC721CMS were not significantly different from each other or from the resistant check, but were significantly more resistant than the susceptible check. FC721 and FC721CMS had mean disease indices (DIs) of 1.8 and 2.3, compared with 1.8 and 4.9 for the resistant (FC703) and susceptible (FC901/C817//413) checks, respectively (DI of 0 = no root rot and 7 = all plants dead). Percentages of resistant plants (those rated 0 or 1) were 36, 36, 60, and 5 for FC721, FC721CMS, and the resistant and susceptible checks. The 1994 epiphytotic was severe and an excellent test of resistance to Rhizoctonia root rot. In the more moderate 1995 epiphytotic, DIs of 1.7, 1.7, 1.8, and 3.4 for FC721, FC721CMS, resistant and susceptible checks were obtained. Percentages of healthy plants (those rated 0 or 1) were 45, 43, 58 and 7 for FC721, FC721CMS, resistant check, and susceptible check, respectively. (Table 1)
FC721 and FC721CMS were tested in 1994 and 1995 in the Beet Sugar Development Foundation's curly top nursery in Kimberly, ID. Under the severe epiphytotic of 1994, FC721 and FC721CMS performed intermediately -- significantly poorer than the resistant control (Beta G6040), but significantly better than the susceptible control (FC718). FC721 and FC721CMS had mean DIs of 7.2 and 6.8, compared with 5.2 and 8.3 for the resistant and susceptible checks, respectively [Mumford's classification: 0 (= healthy) to 9 (= plant dead)]. In the more moderate 1995 epiphytotic, FC721 was not significantly different from the resistant check and FC721CMS was intermediate. FC721 and FC721CMS had mean DIs of 4.3 and 4.7, compared with 3.8 and 6.3 for the resistant and susceptible checks (L609), respectively. (Table 1)
FC721 and FC721CMS also show some resistance to Cercospora leaf spot when tested in an artificial epiphytotic (7). When tested in the mild epiphytotic of 1994, they were not significantly better than the susceptible control (SP351069-0) or significantly different from the resistant control (FC504CMS/FC502-2//SP6322-0). In 1995, which was more severe than 1994, FC721 and FC721CMS were intermediate in resistance (significantly different from both resistant and susceptible controls) with mean DIs of 4.5 and 4.7, compared with 3.5 and 6.2 for the resistant and susceptible checks (L609), respectively. (Table 1)
General combining ability of FC721 has not been tested. FC721 is proposed for use as an O-type population, with multiple disease resistance from which to select O-type monogerm parents for use in commercial three-way resistant hybrids.
Seed of FC721 and its CMS equivalent is maintained by the USDA-ARS and will be provided in quantities sufficient for reproduction upon written request to the corresponding author. We request that an appropriate recognition be made of the source when this germplasm contributes to the development of a new cultivar.
L. W. Panella* and E. G. Ruppel(8)
References and Notes
1. Lewellen, R.T., J.S. McFarlane, and I.O. Skoyen. 1978. Registration of 11 germplasm lines of sugarbeets. Crop Sci. 18:1100-1101.
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.
aDisease Index is based on Mumford's Classification: 0 (= healthy) to 9 (= plant dead)