78 

 I. A Foot-rot of Wheat and its Causal Fungus 



SYMPTOMS 



As the name implies, the most obvious symptom is a rotting of the 

 basal portion of the stem of the wheat plant, that is, the lowesr portion 

 of the lowest internode. In earlier stages than that of actual rotting, 

 minute yellow or brown lesions occur on the stem (PI. VII), while 

 the roots, if diseased, are slightly yellowed and largely or quite devoid 

 of functional root-hairs. No weft of superficial mycelium or black incrus- 

 tation, such as is so frequently described in articles concerning take- 

 all, was seen. The diseased tissues, however, were invariably ramified 

 by an internal mycelium. Certain cases of diseased wheat came under 

 observation in which the plants had attained a nearly normal growth 

 and were eighteen inches high, when they suddenly died throughout. 

 In such cases there was a slight darkening of the lower node and a mycelial 

 invasion at this point. The opinion of those who observed this wheat 

 in the field was that the death was due to frost injury. It is probable 

 that the actual cause of death was foot-rot following the frost injury. 



FUNGI PRESENT 



Direct microscopic observation of the diseased tissues, in all cases 

 of foot-rot examined, revealed the presence of an internal hyaline or 

 faintly tinted mycelium in great abundance permeating the diseased 

 tissues. Mycelium of different character was also occasionally found, 

 but so inconstantly as apparently to have no actual relation to the disease. 

 Isolations of the fungi present in the diseased tissues were made by two 

 methods: 



1. Direct planting of bits of diseased tissue on poured agar (corn- 

 meal agar or wheat-straw agar). The diseased tissue was secured in as 

 clean condition as possible by stripping back the enclosing sheaths, ex- 

 cising the diseased part with sterile tools, and tearing it apart in a sterile 

 Petri-dish. 



2. Direct planting of similar bits of diseased tissue after surface- 

 sterilization in mercuric chloride (1-1000, 10 min.). 



Dilution plating was unsatisfactory owing to the paucity of conidia 

 and the presence of numerous soil bacteria, particularly "spreaders." 



As might be expected, the methods employed gave rise to colonies 

 of many genera and species, including Phyllosticta, Septoria, Fusarium, 

 Epicoccum, Alternaria, and Helminthosporium. A striking fact, however, 



