The Kunitz Soybean Variety

Theodore Hymowitz

In 1917, T.B. Osborne and L.B. Mendel, researchers at the Connecticut Agricultural Experiment Station, demonstrated that unheated, raw soybean meal is inferior in nutritional quality to steam-heated soybean meal. Their research became the foundation for the development of the lucrative soybean processing industry and expanded the potential use of soybean meal as a high-protein feed. Physiologically, the ingestion of raw soybean meal by monogastric animals (for example, poultry or swine) causes pancreatic hypertrophy, a condition in which the pancreas enlarges and ultimately ceases to function.

Moses Kunitz, professor of biochemistry at New York's Rockefeller University, purified and characterized the predominant antinutritional factor in soybean seed in 1945. This factor, a trypsin inhibitor, bears his name and is inactivated during moist heat processing.

In 1968, the author and his colleagues at the Illinois Agricultural Experiment Station began to study the variations in and the genetics of the Kunitz trypsin inhibitor in soybean seed. Thousands of seed samples from the USDA soybean germplasm collection in Urbana, Illinois, and Stoneville, Mississippi, were screened for variation in the Kunitz trypsin inhibitor. Four different trypsin inhibitor (Ti) forms were discovered. Three of the forms identified as Tia, Tib, and Tic are distinguishable from one another by banding patterns produced on gels. The differences are due to amino acid substitutions in the protein. Genetic studies have revealed that the three forms are controlled by a co-dominant multiple allelic system at a single locus. All major soybean varieties grown in the United States contain the Tia form.

The fourth form, found in soybean germplasm samples PI 157440 and PI 196168, lacks the Kunitz trypsin inhibitor. The absence of the protein is inherited as a recessive allele to Tia, Tib, and Tic, and has been designated ti. Although other inhibitors may be present in the seed of PI 157440 and PI 196168, all experimental evidence from genetic, biochemical, and molecular studies indicates that the seeds of the two accessions lack the Kunitz trypsin inhibitor.

The Kunitz soybean variety was developed by backcrossing and is the progeny of an F2 plant selected from the fifth backcross, Williams 82(6) 5 PI 157440. Kunitz is similar to Williams 82 in all visible traits such as white flowers; tawny hairs; tan pods; and shiny, yellow seeds. Kunitz is resistant to many races of phytophthora rot, bacterial pustule, leaf spot, and powdery mildew. Kunitz is also similar to Williams 82 in yield performance, and in the seed's protein and oil content.

The advantages of the Kunitz soybean variety over other commercial varieties are as follows:

Theodore Hymowitz, professor of plant genetics, Department of Agronomy

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