Evidence for the existence of a universal crown-gall tumor initiation enhancer.

Tumor initiation of different dicotyledonous plant species inoculated with Agrobacterium tumefaciens B6 has been studied in vivo and in vitro. The tumor formation in weakly susceptible plants can be strongly enhanced by exogenously applied active extract fractions derived from highly susceptible Helianthus cotyledons. It is found that highly susceptible plants (Kalanchoë, Lycopersicon and Pinto beans) contain an active tumor initiation enhancer which is clearly similar to the compound(s) found in Helianthus cotyledons. No activity can be detected in extracts derived from weakly susceptible plants (Coleus, Phaseolus) or in those obtained from crown-gall tumor tissues.