INHERITANCE OF AGROBACTERIUM-TUMEFACIENS-INDUCED TUMORIGENESIS OF SOYBEAN

Soybean [Glycine max (L.) Merr.] genotypes differ widely in response t o inoculation with wild-type strains of Agrobacterium tumefaciens (Smi th and Townsend) Conn. The objective of this work was to study the inh eritance of tumorigenesis in soybean so as to gain a better understand ing 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 geno type, was crossed with two relatively non-tumorigenic genotypes, 'Cent ury' and 'Thomas. The extent of tumor formation of F, plants was inter mediate to that of the parents, while the F2 frequency distributions w ere continuous and no distinct phenotypic classes were observed. Varia nce component heritability on a plot basis was 0.30 for Peking x Centu ry and 0.44 for Peking x Thomas, and on an entry-mean basis was 0.62 f or Peking x Century and 0.76 for Peking x Thomas. The results indicate that tumorigenesis of soybean is a quantitative trait and heritabilit y estimates were moderate to high. Thus, it should be possible to intr ogress tumor forming capacity into resistant genotypes. Such an approa ch may help alleviate genotype restrictions to genetic transformation.