INHERITANCE OF AGROBACTERIUM-TUMEFACIENS-INDUCED TUMORIGENESIS OF SOYBEAN

Soybean [Glycine max (L.) Merr.] genotypes differ widely in response to inoculation with wild-type strains of Agrobacterium tumefaciens (Smith and Townsend) Conn. The objective of this work was to study the inheritance of tumorigenesis in soybean so as to gain a better understanding of the A. tumefaciens-soybean interaction. A rapid, nondestructive assay for tumorigenesis was developed, which consisted of inoculating hypocotyls of partially etiolated seedlings at multiple wound sites. Four soybean genotypes were screened for tumorigenesis and each had a quantitatively distinct phenotype. 'Peking', a highly tumorigenic genotype, was crossed with two relatively non-tumorigenic genotypes, 'Century' and 'Thomas. The extent of tumor formation of F, plants was intermediate to that of the parents, while the F2 frequency distributions were continuous and no distinct phenotypic classes were observed. Variance component heritability on a plot basis was 0.30 for Peking x Century and 0.44 for Peking x Thomas, and on an entry-mean basis was 0.62 for Peking x Century and 0.76 for Peking x Thomas. The results indicate that tumorigenesis of soybean is a quantitative trait and heritability estimates were moderate to high. Thus, it should be possible to introgress tumor forming capacity into resistant genotypes. Such an approach may help alleviate genotype restrictions to genetic transformation.