Growth Substance in Crown Gall as Related to Time after Inoculation, Critical Temperature,

The importance of growth substances in the normal development of plant tissues has suggested that, when present in. unusual amounts, they may be more or less directly responsible for atypical and pathological growth. Attention has been directed especially to such growths as crown gall caused by Phytomonas tumefaciens (Smith and Town.) Bergey et al. Beta-indole-acetic acid and substances related in effect, like auxin-a and auxin-b in particular, have been considered the chemical means by which the bacteria induced this diseased overgrowth. The evidence for this has been presented and discussed by various workers. For example, beta-indole-acetic acid has been suggested with various degrees of emphasis by Nëmec (11)^ Brown, and Gardner (2), Link, Wilcox, and Link (^), and Berthelot and Amoureux (1) as the responsible stimulating agent produced by the bacteria. Locke, Riker, and Duggar (6) described symptoms on plants bearing crown gall as similar in several particulars to those induced by beta-indoleacetic acid. Limited trials by diffusion technique indicated that more growth substance is present in recently inoculated tomato stems than in control stems. However, trials with older galls and with extractions failed to show differences between gall and control tissue. In addition, Locke, Riker, and Duggar (7, 8) found that crown gall and related avirulent bacteria in peptone broth produced in similar amounts a substance acting like beta-indole-acetic acid in its sensitivity to acid and alkali, and that both healthy and diseased tomato tissue contained material likewise similar to this acid. Kraus, Brown, and Hamner (4) demonstrated the similarity in structure between galls induced by Phytomonas tumefaciens and beta-indole-acetic acid. The present investigations have been aimed at quantitative determinations of certain growth substances (1) that are found at progressive intervals following crown gall inoculation, (2) that are present in tomato stems grown both above and below the critical maximum temperature for crown gall formation, and (3) that diffuse from healthy and diseased tissue. A preliminary statement of some of this work has already appeared (13). With such studies it seemed possible to clarify the relation, if any, of growth substances such as beta-indoleacetic acid to the pathogenicity of crown gall bacteria.