Bacterial blight and bacterial pustule of soybean

Chao, Si-tsan
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Bacterial blight infection has been observed on leaves, and emerging cotyledons of soybeans, and the pustule infection on leaves, pods, and emerging cotyledons. The causal bacteria have been isolated from these infected tissues;Disease spots were caused by both blight and pustule bacteria together thus making the typical symptoms that were caused only by one or the other of the bacteria;Among the media employed both bacteria grew best on Wernham's buffered potato dextrose medium. The blight organism was rather difficult to isolate from invaded tissues but it was rather easy to differentiate from other species of bacteria and fungi by using this medium;Isolates of both blight pustule bacteria have been proven to be identical with those recorded in the literature by morphological and physiological studies and their pathogenicities were shown by inoculations on soybean;The blight and pustule organisms have been isolated from 16 and 17 months old seed respectively but not two-year old. They were found to be able to live on or in the seed. They would not all be killed by seed treatments of living inside the seed;Both blight and pustule organisms could remain viable in sterilized soil, put out of doers during winter, for at least 19 weeks. The blight organism did not lose its pathogenicity at all over 53 weeks of freezing when mixed with sterilized soil. The pustule bacteria were able to infect soybeans after 69 weeks in frozen sterilized soil although their pathogenicity was greatly weakened;Water suspensions made from soil, soybean debris and seeds, which had been left on the soybean field in September and were collected during the following spring, were sprayed on soybean plants grown in the greenhouse. Infections showed up on the inoculated plants, most of them being caused by the blight organism;From the results of field experiments during the growing season evidence points to the fact that the agents of the primary infections of blight and pustule of soybeans are seed, debris, and soil, whereas the leafhopper acts as the agent of secondary infections. For blight the importance of transmitting agents is in this order; soil, debris, leafhopper and seed, whereas for pustule it is seed, leafhopper, debris and soil.