70 Walter H. Burkholder 



in pure culture is not always possible, and in the majority of cases is not 

 practicable. Too much time and labor would be consumed. If the 

 diseases could be distinguished one from another in the field on a symptom 

 basis, the problem would be greatly simplified. The extent to which the 

 symptoms could be used with certainty should be carefully examined and 

 set forth, together with their limitations. This is attempted in the 

 following discussion. 



It should be taken into consideration also that two or more of these 

 diseases may appear on the same plant. In New York, Phytomonas 

 phaseoli, Phyt. flaccumfaciens, and Phyt. medicaginis var. phaseolicola 

 sometimes intermingle in the field, and various combinations of these 

 organisms have been isolated from the same diseased individual. Under 

 such conditions a complication of symptoms is set up which is difficult to 

 untangle. Such cases, however, are more likely to be individual, and do 

 not often occur in a bean field. 



SYMPTOM BASIS 



In the foregoing descriptions of the various bacterial diseases, the most 

 striking and characteristic symptoms of each disease have been pointed 

 out and discussed. In the main these symptoms have been observed in 

 the field on the Red Kidney variety and have been produced on this 

 variety in the greenhouse for purposes of study. To a less degree they 

 have been observed on such common bean varieties as White Marrow, 

 Pea, Refugee, and a few other types found growing in the fields and gar- 

 dens of New York. More than a hundred varieties of Phaseolus vulgaris 

 may be obtained on the market which differ greatly in many of their 

 characters from the Red Kidney bean or the other varieties mentioned 

 above. It is not inconceivable, then, that the symptoms of the bacterial 

 diseases may vary considerably with the variety of beans affected. For 

 this reason it is considered best not to lay too much emphasis on indi- 

 vidual symptoms on unknown varieties when endeavoring to separate 

 these bacterial diseases in the field. The Red Kidney and Marrow beans 

 as they occur in New York are the types that are under discussion here. 



In considering these symptoms for use as diagnostic characters, certain 

 limitations should be noted. The chief of these limitations arises 

 through the fact that a pathogene may not always produce the 

 same type of symptoms on the bean plant. The disease-producing 

 organism may cause a distinct type of lesion on the leaf, the pod, and 

 other plant parts, but this will not hold in 100 per cent of the cases. Cer- 

 tain anomalies at times are found to exist. These anomalies are seldom 

 to be met with in the greenhouse, where conditions are fairly well con- 

 trolled, but are found more often in the field, where the environmental 

 factors surrounding the life of a diseased plant can only be guessed at. 

 The causes of these variations in types of lesions may be due primarily to 



