The Dry Root-Rot of the Bean 1005 



definite margin, or may occur as red streaks which frequently extend 

 to or above the surface of the ground. Later the diseased areas become 

 brown and longitudinal fissures appear in the cortex. 



As the disease progresses upward, the lower lateral roots and the end 

 of the taproot shrivel and become dry. Frequently, too, the main root 

 and the lower part of the stalk are found to be pithy. Above the dead 

 area new lateral roots are developed. These frequently push their way 

 through the diseased cortex and subsequently become diseased. Other 

 roots that are produced above the lesions may develop rapidly and become 

 abnormally large, to take the place of the diseased lower rootlets. 

 Occasionally one of these lateral roots takes the place of the taproot. 

 More frequently, however, these surface roots are small and very numerous, 

 and form a dense mat in the first inch or so of soil (Plate LVI, 2). As 

 a rule they do not become severely affected, and persist throughout the 

 entire growing season. On the other hand, in severe cases the entire 

 root system may be destroyed. 



ON THE PLANT ABOVE GROUND 



Although no lesions appear above ground, the effect of the loss of the 

 lower lateral roots and part of the taproot is very noticeable. This is 

 especially true during the latter part of the growing season. During 

 the first five to six weeks of growth a diseased plant may not be readily 

 detected unless in comparison with a healthy one. At this stage the 

 affected plant is slightly dwarfed but otherwise remains normal in appear- 

 ance so far as the parts above ground are concerned. The symptoms 

 of the disease are more evident at podding time. There is then an apparent 

 checking in growth of the entire plant. Few pods are formed, and the 

 remainder either fail to set, or drop in the early stages of their formation 

 (Plate LVII). The leaves of plants affected with the dry root-rot fre- 

 quently turn yellow and fall. This has given rise in some localities to the 

 name yellow-leaf, but it is a character which is not constant. Never- 

 theless, the diseased individuals mature earlier than do normal plants, 

 since they dry much more rapidly in the absence of an entire root system. 

 The seeds also in the few pods frequently are under size, and this con- 

 tributes to the loss in yield. 



In the true sense of the word this disease is not a wilt, as the leaves 

 or the tender parts of the plant seldom flag. In a few cases, however, 



