ANTIBIOTICS FOR THE CONTROL OF VEGETABLE CROP DISEASES 



For many years the two most effective weapons against plant diseases 

 have been the breeding of resistant varieties and the use of chenaical sprays 

 or dusts. Both methods have been effective against diseases caused by 

 fungi, but neither has been very effective against bacterial diseases. Re- 

 cently, however, scientists have found that some of the same antibiotics 

 used in human naedicine are also capable of destroying various organisnns 

 which cause disease in plants. > 



Antibiotics thenaselves are a recent discovery. But for millions of 

 years soil microorganisms doubtless have been manufacturing these com- 

 plex substances for use against their own microbe enemies. Just before 

 World War II scientists isolated antibiotics and began using them against 

 the microbes which cause various diseases of animals and plants. Little is 

 known of the action of antibiotics except that they destroy or inhibit the 

 growth of certain organisms. Penicillin is an outstanding example of this 

 early work. 



At first antibiotics were scarce and expensive and were used only to 

 fight human ills. As the supply increased, they found a place in veterinary 

 medicine, animal nutrition, and plant pathology. Only in the last 5 years 

 has the use of antibiotics for the control of plant diseases begun to develop. 



With the discovery that certain antibiotics would kill disease-causing 

 bacteria in plants, came the discovery that they were systemic in their 

 action. Unlike earlier fungicides and bacteriacides, which formed a 

 protective coating over the plant's surface, most antibiotics are absorbed 

 by the plant and move to its various parts. Once antibiotics have entered 

 the plant, they are unaffected by rainfall and can move through the plant 

 to protect internal tissues against the disease-causing organisms, or 

 pathogen, and to destroy any organisms that have gained entrance. The 

 degree of translocation, or movement through the plant, varies with the 

 different antibiotics and with the plant treated, but all are systennic to 

 some degree. 



Many antibiotics have been tested by plant pathologists of the Agri- 

 cultural Research Service of the U.S. Department of Agriculture, of State 

 agricultural experiment stations, and of the pharmaceutical industry. 

 Only a few have demonstrated their usefulness as specific plant-disease 

 fighters. Of these few, streptomycin is the most effective in combating 

 vegetable diseases. ' 



STREPTOMYCIN 



Streptonnycin acts principally against disease-causing bacteria, but 

 it is also effective in combating certain fungi. The bacteria causing halo 

 blight of beans, bacterial spot of tomatoes , angular leaf spot of cucumbers, 

 seed piece decay and blackleg of potatoes all can be controlled by strepto- 

 mycin. In addition, the antibiotic controls the fungi causing downy mildew 

 of lima beans, late blight of tomatoes, and downy mildew of cucurbits. 



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