Genetics of the kunitz trypsin inhibitor: An antinutritional factor in soybeans

The major trypsin inhibitor present in soybean seed [Glycine max (L.) Merrill] is the Kunitz trypsin inhibitor or soybean trypsin inhibitor A 2 (SBTI‐A 2 ). Four types of SBTI‐A 2 9 have been identified in the U.S. soybean germplasm collection. Three of the types designated Ti a , Ti b , and Ti c are electrophoretically distinguishable from one another by their different Rf values of 0.79, 0.75, and 0.83, respectively. The three types are inherited as codominant alleles in a multiple allelic system at a single locus. The fourth type which is the absence of SBTI‐A 2 is found in P.I. 157440 and P.I. 196168. The gene for the lack of SBTI‐A 2 is designated ti and is inherited as a recessive allele to the other three SBTI‐A 2 9 types. Ti a is the most common SBTI‐A 2 type in the germplasm collection. Linkage studies revealed that the SBTI‐A 2 protein is inherited independently of certain morphological characters and chemical components of seed. Potential applications of the SBTI‐A 2 types are discussed.