Phyto'phtJiora Rot of Tomato 305 



The fact that the organism attains its maximum development at 

 a relatively high temperature in a humid atmosphere might explain 

 the outbreak of Phytophthora in Indiana in 1921. The disease appeared 

 at Lafayette during the first three days of August, 1921. The weather 

 conditions at Lafayette, as given by the U. S. Weather Bureau at 

 Indianapolis, show that for the last three days of July and the first 

 three days of August the mean temperature was 77.5 °F. The average 

 maximum temperature for the six days was 86.5 °F. which is equivalent 

 to 30.2 °C. The average minimum temperature for the six days was 

 68.5 °F. or 20.2 °C. The average maximum temperature was very favor- 

 able for the maximum development of the fungus, and the average 

 minimum temperature was high enough to permit good growth of the 

 organism. The record of precipitation for the last three days of July 

 and the first three days of August show that on July 30, there was 

 1.06 inches of rainfall, on August 2, 2.20 inches, and on August 3, 

 0.85 of an inch, or a total of 4.11 inches for the six days. This is 

 more than the average total rainfall for the entire month of July 

 or August. 



From the above data, it is quite evident that temperature and 

 moisture conditions were ideal for the development of the fungus, 

 especially the amount of soil moisture which is undoubtedly the most 

 important of the two factors. 



The records further show that the weather conditions for the months 

 of August and September were conducive to the continued development of 

 the disease. The average mean temperature for both months was above 

 normal, and the total precipitation was about double that of the normal 

 for these two months. In August it rained 0.01 of an inch or more on 

 ten different days and 0.01 of an inch or more on twelve different days 

 in September, supplying an abundance of soil moisture at all times. 



As previously stated, tomatoes were grown on the same ground in 

 1922 and no buckeye I'ot developed. The importance of the soil moisture 

 is again brought out when the records of the U. S. Weather Bureau are 

 consulted. During the months of July, August, and September, 1922, 

 the temperature at Lafayette averaged slightly above normal, but the 

 rainfall for the same months was far below normal, being 0.61 of an 

 inch below normal for July, 1.35 inches below normal for August, and 

 1.53 inches below normal for September. Thus it can be seen that the 

 most important factor in the development of the disease was lacking 

 in the summer of 1922. 



SUMMARY. 



A Phytophthora rot of tomato, eggplant and pepper fruits occurred 

 in the field at Lafayette, Indiana, in the late summer of 1921. 



The same fungus was repeatedly isolated from diseased fruits, and 

 successful inoculations were secured on eggplant and pepper with the 

 fungus isolated from tomato. Subsequent reisolations from inoculated 

 fruits were m.ade. 



The symptoms of the disease on tomato resemble very closely buckeye 

 rot of tomato as described by Sherbakoff, and the fungus agrees mor- 



20—25870 



