Registration of sugar beet genetic stocks FC308 (PI701378) and FC309 (PI700990)

Abstract

Sugar beet (Beta vulgaris L.) genetic stock lines FC308 (PI701378) and FC309 (PI700990) are two highly homozygous and phenotypically homogenous sources of resistance to two sugar beet pests. FC308 is resistant to sugar beet cyst nematode (Heterodera schachtii), but susceptible to Fusarium yellows, while FC309 is Fusarium yellows resistant, but sugar beet cyst nematode susceptible. These two populations were developed by the USDA-ARS in Fort Collins, CO, derived from unreleased USDA-ARS Salinas germplasm lines. Multiple field and greenhouse trials for Fusarium yellows and nematode resistance confirmed the uniform phenotypes of both lines for each disease. To enable molecular breeders to rapidly screen proprietary markers in silico, gene space assemblies for each line were also developed. Genome sequencing of individual plants from each line, as well as pooled sequencing of sub-populations of both lines indicated fixation of a previously reported genetic variant linked to sugar beet cyst nematode resistance in FC308. However, two previously reported variants linked to Fusarium resistance appear to be unlinked to the resistance found in FC309. Collectively, these two new genetic stocks should prove useful as sources of resistance to Fusarium yellows and sugar beet cyst nematode, as model genetic backgrounds for studying plant-pathogen interactions, and for mapping the resistance genes present in these lines.

A standard area diagram for Fusarium yellows rating in sugar beet (Beta vulgaris L.)

“…When using either SAD for Fusarium yellows assessment, the head breeder or researcher should describe to all individuals rating an experiment where the disease severity cutoff is for the research question of interest, especially when considering other potential Fusarium management tools. Typically, after 30 days, empirical evidence suggests that resistant plants that fall into BvFus-SAD-v2 <60% disease severity will recover from Fusarium oxysporum F-19 infection in the greenhouse when maintained at 28C (Todd et al, 2023, Webb et al, 2015). When conducting high-throughput screening in the greenhouse for Fusarium yellows resistance, pixel quantification using PlantCV may provide a cheap and easy image solution that is most comparable to human estimates from 20-100% disease severity on the BsFus-SAD-v2 scale.…”

“…Because soil-borne fungi are difficult to control with chemical fungicides, a major line of defense against Fusarium yellows in beet is resistant cultivars (El-Aswad et al, 2023). A limited number of sugar beet germplasm with improved resistance to Fusarium yellows has been developed by USDA-ARS pre-breeding programs (Panella et al, 2015, Todd et al, 2023), which have utilized wild germplasm from the USDA National Plant Germplasm System for Fusarium resistance trait discovery and introgression. Disease screening is an integral part of the pre-breeding process, highlighting the importance of reliable and repeatable resources to aid in disease screening.…”

A fully phased, chromosome-scale genome of sugar beet line FC309 enables the discovery of Fusarium Yellows resistance QTL

“…Seeds for USDA germplasm line FC309 (Todd et al, 2023) were planted and grown in 25°C, 16h day greenhouse conditions. Twelve individuals in differing growth stages were collected to maximize transcript discovery for RNA isolation for PacBio IsoSeq.…”

“…Untreated cotyledon and two-leaf stage seedlings were flash frozen in liquid nitrogen. Six eight-leaf stage plants were separated into root and shoot tissue types and flash frozen 30 days after inoculation with Fusarium oxysporum strain F19 as described in Todd et al (2023). Six additional Fusarium treated eight-leaf stage individuals were placed in a 4C room to vernalize for 190 days following the 30 days after inoculation period, separated by roots and shoots and flash frozen in liquid nitrogen 14 days after being removed from vernalization.…”

“…Thus, improved host plant resistance represents the primary tool for growers to limit financial impact from this disease. The recent release of the sugar beet genetic stock FC309 (Todd et al, 2023), which has robust resistance to Fusarium Yellows derived from the Bvm background, represents a resurrected effort to genetically fix Fusarium resistance for breeders, genetically map, and characterize the resistance mechanism(s) at the molecular level.…”