1022 Walter H. Burkholder 



EFFECT OF DRY ROOT-ROT ON THE YIELD OF THE BEAN CROP 



Few experiments have been conducted to determine the exact effect 

 of any plant disease on the yield of its host. For a crop that is subject to 

 numerous diseases, such information is frequently of extreme value. 

 This is true of the bean, in the case of which several pathogenes may 

 occur on the roots of the plants. One of these is the dry root-rot, and, 

 since inoculations can be controlled, an experiment to learn the effect 

 of this disease on the bean crop can readily be conducted. 



Since the black root-rot is so frequently associated with the dry 

 root-rot, it was considered advisable to determine the loss in yield result- 

 ing from each as well as from a combination of the two diseases. For 

 the sake of accuracy such an experiment should be repeated through 

 several seasons in order to avoid the effect of unusual weather conditions. 

 A preliminary experiment of this type was conducted in 1916. The 

 seed was not planted until July 20, and therefore the crop did not mature 

 before the early frost of that season. Plants in the rows inoculated 

 with Fusarium martii phaseoli were considerably dwarfed, but those 

 inoculated with Thielavia basicola could not be distinguished from the 

 check rows. A combination of the two, from all appearance, caused no 

 more injury than did F. martii -phaseoli alone. It was unfortunate that 

 the beans could not be harvested, inasmuch as the weather was especially 

 favorable for the effects of the disease to appear in the yield. 



In 1917 a more extensive experiment was conducted at Ithaca. The 

 weather conditions were very unfavorable for the dry root-rot, but were 

 advantageous for the bean plant. Marked losses, therefore, which would 

 be noted in average years or in years favorable for the disease, were not 

 obtained. Some interesting facts appeared in the experiment, and for 

 this reason the data, although incomplete, are set forth here. 



The plot at Ithaca used for the experiment was located on a low piece 

 of ground. The soil was a gravelly loam. In previous years the plot 

 had been in alfalfa, and no records show that it had ever been planted 

 to beans. It was likewise out of the bean area and the soil proved to be 

 free from the pathogene Fusarium martii phaseoli. The soil was likewise 

 free from Thielavia basicola, since all checks remained healthy even though 

 this organism is widely distributed and occurs on such hosts as alfalfa. 



The plan of the experiment was as follows: Plants in row 1 were 

 inoculated with Thielavia basicola; row 2 remained as a check; row 3 



