Role of the Root Nodule in the Bacterial‐Induced Chlorosis of Soybeans

Abstract Plant grafting experiments with chlorosis‐susceptible and chlorosis‐resistant varieties of soybean, observations on a difficultly‐nodulating experimental line, and isolations of bacteria from chlorotic plants were made in order to characterize more fully the bacterial‐induced chlorosis of soybeans. The plant grafts showed that an interaction between susceptible rootstocks and specific rhizobia was responsible for the onset of chlorosis. Top growth of chlorosis‐susceptible varieties showed no chlorosis when grown on resistant rootstocks; in the reverse graft, chlorotic top growth was obtained. Observations on the difficultly‐nodulating line showed that chlorosis developed only after root nodules were formed. No invasion of the aboveground parts of chlorotic plants by root‐nodule bacteria could be demonstrated. It was concluded that when certain strains of rhizobia invade and nodulate chlorosis‐susceptible varieties of soybean, some growth‐damaging or chlorophyll‐inhibiting factor is formed in nodular tissue.