Etiology, anatomy, and ultrastructure of false broomrape, a tumorous disease of tobacco

Abstract

False broomrape (FBR) is a tumorous disease that affects the roots of tobacco plants. The diseased roots developed tumors which are fleshy and usually whitish in color. Leaf-like structures from the hypertrophied tissues may emerge from the soil and develop chlorophyll. All attempts to identify the causal agent of false broomrape have been unsuccessful. FPR tumors were found to be 100% mechanically transmitted from the juice of tumor tissue to healthy roots. The disease is soil-borne and has no reported vector which transmits this disease. Three isolates of FBR obtained from Kentucky, Georgia, and North Carolina differed in their size and shape, but not in host range, thermal inactivation, aging at -20C, and dilution end point. The causal agent passed through filters that return small bacteria. It was diluted out at a concentration between 10⁻⁹ and 10⁻¹². Many crown gall tumors occur some distance from the point of inoculation. These tumors were found to be void of any causal agent. The causal agent of FBR tumor could be translocated in the steam and roots of tobacco plants, however, they never formed on any above ground parts of the plant. ...