124 

 ETIOLOGY OF FOOT-ROT 



EVIDENCES OF ETIOLOGICAL RELATION OF H. NO. 1 



Constant Presence of the Pathogens 



In all cases of American foot-rot of wheat that have come under my 

 observation the rotten basal portion of the shoot bore and was to a large 

 extent occupied by a mycelium, which grew luxuriantly within the wheat 

 tissue though very sparfngly upon its surface, coursing lengthwise within 

 the diseased cells. This mycelium was hyaline, septate, vacuolate, irregular 

 in thickness, and, in short, agreed in all characters with those of H. No. 1 

 when growing in rotting wheat-tissue (page 105). 



Absence of other Constant Parasites 



No other organism which might be considered as a possible parasite was 

 present in any large number of cases in or on the wheat tissue. Amebae 

 and nematodes were present in great numbers in the soil, but appeared to 

 bear no relation to the rot of the wheat. Various fungi, as Fusarium (two 

 species), Rhizoctonia, Epicoccum, Alternaria, were occasionally found on 

 the roots or stems, but each only rarely, in a fraction of 1% of the cases, 

 and with no evidence of etiological relation to the rot of the stem. 



Identity of Pathogene proved by Culture 



Very numerous isolations were made by taking bits of tissue (1) from 

 diseased sheaths, (2) from diseased stem-lesions, and (3) by stripping away 

 the sheath, disinfecting the remaining surface with mercuric chloride and 

 taking out diseased bits, with precautions against contamination. All 

 such diseased bits were laid on the surface of corn-meal agar plates. Hun- 

 dreds of these were made, with the result that in practically every instance 

 the diseased bit gave rise to Helminthosporium conidia in general aspect 

 like those of H. No. 1. Other organisms, as mentioned, occasionally 

 occurred on these plates, but in only a small per cent, of instances. It 

 seems entirely conclusive that the mycelium constantly found in the rotting 

 basal portion of the diseased w r heat-stems is that of a Helminthosporium. 



Evidence of Infectiousness 



Several bags of soil that bore diseased wheat in 1919, near Granite 

 City, Illinois, were brought into our greenhouse in July, 1919. In this soil 

 was planted "Sultzer Pride" wheat, and the planting kept liberally watered. 

 At the end of some weeks the plants were removed, and on examination all 



