Evidence for a Tumor-associated Factor Active in the Promotion of Crown-gall Tumor Growth on Primary Pinto Bean Leaves

The growth of crown-gall tumors on primary pinto bean leaves (Phaseolus vulgaris L. cv. “Pinto”) between day 3 and day 6 after inoculation was found to be proportional to the number of tumors on the leaves. Similar differences observed in the growth of tumors induced by adenine, methionine and asparagine requiring mutants of Agrobacterium tumefaciens (Smith and Town.) Conn appear to be due to the same phenomenon. Tumors induced by these auxotrophs thus show no obvious growth differences from those induced by the prototrophic strain despite the lower specific infectivity and the existence of a mutational lesion in these bacteria. A diffusible growth factor(s) produced by the tumor tissue is proposed to account for the relation between tumor number and early tumor growth.