INHERITANCE OF SOYBEAN SUSCEPTIBILITY TO AGROBACTERIUM-TUMEFACIENS AND ITS RELATIONSHIP TO TRANSFORMATION

The development of genetic transformation techniques for soybean [Glycine max (L.) Merr.] has been slow, but in a few cases transgenic plants have been obtained with Agrobacterium tamefaciens as the vector. Soybean genotypes with good agronomic characteristics and susceptibility to infection with A. tumefaciens would be desirable for transformation attempts. The objectives of this study were to determine the inheritance of susceptibility to A. tumefaciens and to determine if any relationship exists between gall formation on growing plants and transformation of cotyledonary tissue in vitro. In three experiments, susceptible parent 'Peking', resistant parent 'Clark', and the F-1, F-2, F-3, F-4, BC1P1, and BC1P2 progeny were inoculated at 12 sites at the V8 growth stage with A. tumefaciens wild-type strain A281. The distributions of galls per plant indicated quantitative inheritance of the susceptible gall formation response. However, because heritability was high (>0.50) and the number of genes controlling susceptibility was estimated as between two and three, this characteristic should be relatively easy to transfer to new genotypes. Immature zygotic cotyledons were excised from the same material, inoculated with strain A281 containing a plasmid holding the beta-glucuronidase (GUS) reporter gene, and induced to form somatic embryos. The frequency of somatic embryos exhibiting GUS activity was greater than 50% in the first and second embryo collection periods. It was not possible to predict which genotype would be useful for transformation attempts based on the plant rating of susceptibility.