|Registration of Rhizoctonia Root Rot Resistant Sugarbeet Germplasms FC715 and FC715CMS|
SUGARBEET (Beta vulgaris L.) germplasms FC715 (Reg. no. GP-148, PI 5774625) and FC715CMS (Reg. no. GP-149, PI 574626) were developed by the USDA-ARS in cooperation with the Beet Sugar Development Foundation. They were released in 1992 from seed productions 911026HO and 911026HO1. These germplasms were developed as sources of resistance to root-rotting strains of Rhizoctonia solani K?hn.
FC715 is a diploid, monogerm, O-type, pseudo-self-fertile, sugarbeet germplasm resistant to root and crown rot caused by R. solani AG-2-2. It is genetically heterogeneous, relatively vigorous, easy bolting, and moderately tolerant to Cercospora leaf spot (caused by Cercospora beticola Sacc.), with low to medium resistance to the curly top virus. It segregates for green hypocotyl (21%). It is the O-type (maintainer line) of its CMS equivalent, FC715CMS, which is the BC7 with ([FC504CMS X FC502-2] X 662119s1) X FC7081 as the nonrecurrent parent. The original population consisted of approximately 60 individuals. FC715 consists of S0 individuals developed via four cycles of mass selection for Rhizoctonia root rot resistance. The original source population of FC715 (300 mother roots) had gene contributions of 16% from FC5043, 16% from FC502/23, 16% from 662119s1, and 52% from FC708.
In our 1993 field evaluation for resistance to R. solani in a replicated, inoculated field experiment at Fort Collins, CO2, FC715 and FC715CMS were not significantly different from each other or from the resistant check but were significantly better than the susceptible check ([[alpha] = 0.05). FC715 and FC715CMS had mean disease indices (DI) of 1.3 and 1.0, compared with 1.3 and 3.0 for the resistant (FC705/1) and susceptible checks, respectively (DI of 0 = no root rot and 7 = all plants dead). Percentages of healthy plants (those rated 0 or 1) were 67, 84, 71, and 24 for FC715, FC715CMS, resistant check, and susceptible check, respectively. The 1993 epiphytotic was moderate in severity. From past experience, we would expect even greater differentiation between the resistant germplasms and the susceptible check under a more severe epiphytotic.
General combining ability (GCA) of FC715 was not tested; however, because it is heterogeneous, it should have potential for GCA improvement. FC715 is proposed for use as a diverse O-type population from which to select O-type monogerm parents for use in commercial three-way resistant hybrids.
Breeder seed of FC715 and its CMS equivalent is maintained by the 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 80526-2081. We request that an appropriate recognition be made of the source when this germplasm contributes to the development of a new cultivar.
E. G. Ruppel, R. J. Hecker, and L. W. Panella* 4