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Williams 82

Williams 82 is a public soybean cultivar developed by USDA-ARS and the University of Illinois by backcrossing a Phytophthora-resistance region from Kingwa into the cultivar Williams. It is the primary reference genome for soybean research.

Dated referenceLast reviewed: 2026-07-12Updated: 2026-07-12
Illustrative diagram · AgricultureID (original)

Record

Cultivar / variety
Variety of
Soybean
Botanical taxon
Glycine max
Type
Cultivar (self-pollinated pure line)
Breeding method
Backcross introgression (recurrent parent Williams; donor parent Kingwa)
Origin
United States
Breeder / institution
USDA-ARS and the University of Illinois
Registry status
Historical
Registries
  • USDA GRIN · United States · as of 2026-07-12Williams 82 is maintained in the USDA Soybean Germplasm Collection (Urbana, Illinois); specific accession identifiers are not reproduced here.
Adaptation
Maturity Group III, historically adapted to the central U.S. Corn Belt latitudes; maturity-group adaptation ties flowering and maturity to day length and latitude.
Intended use
Reference genome and genetic reference for soybean research, Public cultivar and breeding parent, Grain and oilseed production (historical)
Disease resistance
  • Carries the Rps1-k allele introgressed from the donor parent Kingwa, associated with race-specific resistance to certain isolates of Phytophthora sojae (Phytophthora root and stem rot). Rps genes are race-specific and can be overcome by other pathogen isolates.

Source-attributed claims for specific conditions; resistance can break down and is not a guarantee under all pathogen populations or environments.

Registry listing or variety protection is jurisdiction- and date-specific and does not by itself indicate current commercial availability, universal cultivation approval, patent status, or a recommendation.

Williams 82 is a public soybean cultivar developed by USDA-ARS and the University of Illinois. It was produced by backcrossing to introgress a Phytophthora root-rot resistance region (carrying the Rps1-k allele) from the donor parent Kingwa into the recurrent parent Williams, a Maturity Group III cultivar.

Williams 82 is best known as the soybean reference genome: an assembly of this cultivar was first reported in 2010 and it has since served as the main reference used by the soybean research community. It is maintained in the USDA Soybean Germplasm Collection.

Development

Williams 82 was derived by backcrossing: the cultivar Williams served as the recurrent parent, while a chromosomal region carrying the Rps1-k resistance allele was transferred in from the donor parent Kingwa. The aim was to add Phytophthora root-rot resistance to the Williams background while retaining most of Williams’ agronomic characteristics.

Role as the soybean reference genome

An assembled genome of Williams 82 was first reported in 2010 and became the standard reference for the soybean research community, underpinning gene annotation, comparative genomics, and marker development. Successive assemblies and analyses have continued to use Williams 82 as the primary reference cultivar.

Disease reaction

Williams 82 carries the Rps1-k allele introgressed from Kingwa, associated with resistance to certain isolates of Phytophthora sojae, the cause of Phytophthora root and stem rot. Resistance conferred by single Rps genes is race-specific: it is effective against some pathogen isolates and can be overcome by others, and its usefulness depends on the local pathogen population.

Scope & limitations

Geographic scope: Developed in the United States (USDA-ARS / University of Illinois); used worldwide as the soybean reference genome.

Climate context: Maturity Group III soybean; maturity-group adaptation is latitude- and day-length-dependent.

  • Williams 82 is a public reference cultivar and breeding parent rather than a current commercial variety; agronomic performance is environment-specific.
  • Rps1-k Phytophthora resistance is race-specific and can be overcome by other pathogen isolates; it should not be read as broad or durable resistance.
  • A precise release year is reported inconsistently across sources and is therefore not stated here.

Sources

This article draws on the following authoritative sources. See our sources & methodology for how they are selected.

  1. [1]GRIN-Global / National Plant Germplasm System (opens in a new tab)

    USDA Agricultural Research Service (ARS)

    Authoritative

    Cited for: Maintenance of Williams 82 in the USDA Soybean Germplasm Collection

    Type:
    Official registry
    Jurisdiction:
    United States / Global
    Accessed:
    2026-07-12
  2. [2]USDA ARS — Agricultural Research Service (opens in a new tab)

    USDA Agricultural Research Service (ARS)

    Authoritative

    Cited for: Development by Rps1-k backcross introgression and use as the soybean reference genome

    Type:
    Government agency
    Jurisdiction:
    United States
    Accessed:
    2026-07-12

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