204 BACTERIA IN RELATION TO PLANT DISEASES. 



In 1891, Dr. Byron D. Halsted reported a widespread and destructive decay of pota- 

 toes in south New Jersey, part of which appeared to be due to bacteria. The potato tubers, 

 it is said, 



Developed well-formed ulcers, and slices of these quickly turned to almost a coal black, especially 

 near the surface beneath the skin, and over all rapidly grew [oozed?] an almost velvety layer, consist- 

 ing entirely of masses of bacteria. 



This entry probably belongs here, or if not here, then most likely under Basal Stem-rot. 



Early in 1892, Dr. Halsted published a bulletin from the Mississippi Experiment Sta- 

 tion giving an account of the Southern tomato-blight, as observed by him in that State in 

 1891. This disease he ascribed without hesitation to bacteria, basing his conclusions on 

 numerous microscopic examinations. Dr. Halsted noted the wilting of young leaves and 

 growing tips of the stem, the water-soaked appearance of certain tissues, the watery greenish 

 disorganized pith, the brown stain in the vascular system, and under the microscope in 

 freshly gathered material the presence of large numbers of bacteria, while all traces of fungi 

 were absent. Inoculations into growing plants failed. 



A blight of potatoes was also observed and studied by Dr. Halsted at Ocean Springs, 

 Mississippi. The above-ground signs were similar to those on the tomato. 



Below ground the stem is more or less darkened, in patches brown, and occasionally almost black. 

 The old "seed" potato is a soft rotten mass, and the few new potatoes usually small and decayed, 

 invariably at the stem end and almost always at the eye, appearing at first "watery" and afterward 

 brown. It is an interesting fact to be stated in passing that the earth adheres very closely to the 

 surface of the decaying portions. It seems evident from the extended study of these diseased potato 

 plants, hundreds being examined, that the rot passes from the main stem to the tubers, and probably 

 comes originally from the "bud." Often a lateral underground branch including its minute potatoes, 

 as large as peas, is entirely softened. Upon making halving sections of the tubers it is seen that the 

 most diseased portion is in a circle which includes the base of each eye. This portion is a soft, grow- 

 ing layer, rich in nitrogenous substances, and furnishes the avenue through which the disease spreads 

 from one eye to another. From this decayed tract a milky juice quickly accumulates upon the sec- 

 tion that is made up very largely of bacteria and contains no other form of fungus [consult this 

 Monograph, vol. I, pi. 24]. 



Dr. Halsted believes the disease is transmitted to the growing plant from the mother- 

 tuber. Cross-inoculations from potato to tomato in the field failed. The tomato-plants 

 were then full-grown. Direct infections under bell-jars in moist air succeeded. These were 

 made many times over and the checks usually remained sound. For this purpose Dr. 

 Halsted used slices of tomato-fruits and potato-tubers and also short pieces of tomato- 

 stems and potato-stems. The decay was rapid. The milky ooze from the potato rotted 

 tomato, and that from the tomato rotted potato, but under the same conditions melon- 

 tissues were also rotted when inoculated with this material, and Bacillus phytophthorus, 

 Bacillus melonis, or some similar organism must have been present. The disease as observed 

 in the field must, however, I think, have been due to Bacterium solanacearum. 



Several attempts were made to infect seedling tomatoes by planting them on soil con- 

 taining diseased material, by soaking seeds in it before planting, and by spraying infected 

 fluid on the plants, but as the results were not conclusive it is not necessary to make further 

 mention of them. 



According to a note by Director S. M. Tracy prefaced to this paper the losses from this 

 disease in Mississippi had been serious for several years, amounting in some cases to from 

 a quarter to half the plants. In 1890 the losses were widespread and severe. 



In 1891 the disease appeared at Ocean Springs, Mississippi, in the tomato fields on 

 May i. (In 1914, Rolfs found it for me on potato shoots at Gainesville, Fla. April 15.) 



In 1892, in Garden and Forest, Dr. Halsted reported occurrence of this southern tomato 

 disease in the north. The material was received from F. I/. Stevens, Syracuse, New York, 

 where 3 fields were affected. In the field most seriously injured about 3 per cent of the 

 plants were dead, 8 per cent badly affected, and many more showing traces when the 



