Genotypic Variability of Soybean Response to Agrobacterium Strains Harboring the Ti or Ri Plasmids

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Abstract
Diverse cultivars (24) of soybean and 3 lines of its annual wild progenitor G. soja Sieb et Zucc. were tested for their response to Agrobacterium strains harboring either the Ti (tumor-inducing) plasmid (pTi) from A. tumefaciens or the Ri (root-inducing) plasmid (pRi) from A. rhizogenes following uniform wounding and inoculation. Based upon gall weight at 8 wk postinfection, 3 G. max cultivars (Biloxi, Jupiter and Peking) and 1 G. soja line, Plant Introduction (PI) 398.693B, were judged highly susceptible to A. tumefaciens strain A348 (pTiA6), 10 genotypes moderately susceptible, 11 weakly susceptible and 2 nonsusceptible. Of 26 genotypes inoculated with strain R1000 (pRiA4b), only 7 responded in a clearly susceptible fashion by forming small, fleshy roots at internodal infection sites. Cotyledons excised from 1- or 3-day old seedlings of ''Peking'' and ''Biloxi'' also formed galls when infected in vitro with agrobacteria carrying either the Ti or Ri plasmid. Tumor lines established from cotyledon and stem galls induced by A. tumefaciens A348 (pTiA6) exhibited the T[tumor]-DNA borne traits of phytohormone-independent growth and octopine synthesis. DNA isolated from cultured tumors hybridized with labeled T-DNA probe.