Rhizobial-Induced Chlorosis in Soybeans: Isolation, Production in Nodules, and Varietal Specificity of the Toxin

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Abstract
Rhizobium japonicum induced chlorosis was found to be caused by a single, nonspecific, phytotoxic amino compound produced in the nodules of soybean-rhizobial associations. The phytotoxin was recovered in substantial quantities from young chlorotic leaves, but not in older, normal-appearing leaves of soybean plants. Addition of /ig quantities of the purified toxin to the putrient solution induced chlorosis in seedlings of susceptible soybean varieties. The amount of toxin required was less than the amount found in the nodules of single soybean plants. More than 4 times as much toxin was required to induce chlorosis in seedlings of resistant varieties. The resistant response of soybean varieties nodulated by pathogenic rhizobial strains was found to be associated with the prevention of phytotoxin synthesis or accumulation in the nodule. An unidentified amino acid accumulated to higher levels in nodules of soybean-rhizobial associations where the toxin was produced than in associations where it was not produced. No other differences in the kinds and amounts of free amino acids in the nodules were associated with toxin formation.

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