Association of the Brazil nut protein gene and Kunitz trypsin inhibitor alleles with soybean protease inhibitor activity and agronomic traits

The use of soybean [Glycine max (L.) Merr.] in animal feed without heat treatment may be possible by reducing protease inhibitors. The objectives of this study were to determine to what extent soybean protease inhibitors would be reduced genetically by combining the Brazil nut protein (BNP) gene from the transgenic line BX4P9341B6 with the ti allele for the Kunitz trypsin inhibitor from the cultivar Kunitz and their effect on agronomic traits. Soybean seed from 42 F-2-derived lines from the cross BX4P9341B6 X Kunitz were evaluated in replicated trials in 1995 for trypsin inhibitor (TI), chymotrypsin inhibitor (0) activity, and agronomic traits. There were six lines homogeneous for presence of the BNP gene and the Ti allele (BNP +, Ti), 18 lines homogeneous for presence of the BNP gene and the ti allele (BNP+, ti), six lines homogeneous for absence of the BNP gene and presence of the Ti allele (BNP-, Ti), and 12 lines homogeneous for absence of the BNP gene and presence of the ti allele (BNP-, ti). The mean TI activity of the BNP+, ti lines was 85.1% less than for the BNP-, Ti lines representative of conventional soybean cultivars. The mean CI activity of the BNP+, ti lines was 61.4% less than the BNP-, Ti lines. The means of the four genotypic classes were not significantly different (P > 0.05) for seed yield, maturity, lodging, and protein content. It should be possible to develop high-yielding cultivars with the BNP+, ti genotype that have major reductions in TI and CI activity.