10 Walter H. Burkholder 



success in reducing the amount of disease by planting two-years-old seed. 

 Temperature, moisture, and the manner of storing the seed, no doubt play 

 an important part in such viability tests. 



Muncie (1917 b) and recently Patel (1929) have shown that Phyt. phaseoli 

 can overwinter also in the soil. One experiment has been conducted by 

 the writer on this phase of the subject, and, while not conclusive, is reported 

 here merely for what it is worth. This experiment differs from those of 

 Muncie and Patel in that it was conducted in the field, and, although 

 having a more practical bearing, it lacked the niceties of the laboratory 

 experiments. A plot 100 feet by 50 feet in size was planted to beans, and, 

 when germination had taken place and the seedling stage had passed, the 

 plants were inoculated heavily with the pathogene. All plants became 

 severely infected, and in the fall were not pulled and removed as is usually 

 the case in the sections growing dry shell beans. Thus the soil was much 

 more severely contaminated with the organism than is usual. Phyt. 

 flaccumfaciens probably was present, besides Phyt. phaseoli. In the follow- 

 ing spring the plot was plowed and again sown to beans. On either side, 

 plots of similar size were used as checks. In August, when counts were 

 made of the number of blighted plants in each plot, it was found that the 

 checks had slightly more diseased individuals than the treated plots had. 

 Continuous observations before this time had shown that the disease had 

 not originated in the treated plot and spread to the checks, but had 

 appeared simultaneously over the entire planted area. The disease had 

 come in on the seed, or had been brought in, in some other manner, from 

 the outside. This is merely a single experiment, and such conditions as 

 the amount of organic material in the soil, hydrogen-ion concentration, and 

 other related factors, might alter the case. 



The fact that the bacteria in the soil can survive a winter under New 

 York conditions is probably of no great importance. Rotation of crops 

 is practiced, and even in the western counties, where beans are grown as a 

 major crop, the rotation is seldom less than three years. Can the organism 

 survive for a period of that length? From observation, probably not, 

 since the disease is of no economic importance when seed from disease-free 

 fields is used for planting. 



Under New York conditions, infected seed introduce the pathogene into 

 a field in approximately 100 per cent of the cases. The life history of the 

 pathogene in relation to its host plant, then, may proceed in the following 

 manner: With the germination of the planted seed, the bacteria become 

 active, and their number in the cotyledons determines the severity of 

 early infection, weather conditions being favorable. With severely infected 

 seed the growing tip may be destroyed by the time the plant is above 

 ground, giving rise to the so-called snakeheads and frequently causing 

 the death of the seedling. This consequently reduces the chances of the 

 particular pathogene's continuing and infecting other host plants. In 



