The Bacterial Diseases of the Bean 31 



symptoms 



General 



Since Phytomonas flaccumfaciens is primarily a vascular parasite and 

 invasion has a decided tendency to become systemic in nature, the general 

 symptoms of a diseased plant are the most pronounced. A stunting of an 

 infected plant takes place and, as a rule, quickly develops into a wilt. 

 It is this wilting of an infected plant, which is the most outstanding symp- 

 tom of the disease, that led Miss Hedges (1926) in first describing the 

 disease to give to it the common name wilt. At any stage in the develop- 

 ment of the plant the wilt may take place, from a seedling wilt to the wilt 

 of the entire plant bearing mature pods. Wilting of a part of the plant, 

 as a branch, also is not uncommon. Since the stalk and the branches of a 

 maturing bean plant are more or less woody in nature, the true flagging is 

 limited primarily to the leaves and the young growing shoots. Even the 

 leaf petioles seldom droop, but remain erect. Wilted leaves become dry 

 and brown, and, after several rains, very ragged. Sometimes the leaves 

 on an infected plant will not persist but will drop off. 



On the leaf 



As already stated, the wilt is the primary symptom of this disease, and 

 this is especially true with reference to the leaves. The leaflets may flag, 

 beginning at the tip or along the side. Such leaves fail to recover, dry up, 

 and turn brown, still persisting on the plant. A heavy wind or rain may 

 destroy these leaves completely or whip them to a very ragged condition. 

 In some cases, but less frequently, only a part of the leaf may wilt and die, 

 thus giving rise to a rather characterless lesion as shown in figure 5. 



In some plants, the vascular systems of which are infected, the leaflets 

 may turn somewhat yellow, dry up, and fall off. In such cases the main 

 petiole remains standing erect. 



On the stem 



There is probably only one type of lesion found on the stem of bean 

 plants infected with Phyt. flaccumfaciens. This is a stem girdle, or a 

 disease of the nodes. These lesions appear to be of endogenous origin, 

 the bacteria working their way out from an infected xylem along a leaf 

 trace. Such infected nodes turn red, and are greatly weakened so that 

 the plant is broken off easily during a windstorm. The stem girdle is not 

 peculiar to this disease, but may be caused by Phyt. phaseoli and possibly 

 by Phyt. medicaginis var. phaseolicola. 



On the pods 



Lesions produced on the pods by Phyt. flaccumfaciens occur along the 

 suture. The bacteria spread from the fibrovascular bundles, causing a 



