WILT-DISEASES OP TOBACCO. 269 



The disease, from what I could see and learn, was pretty well scattered throughout the district. 

 In a field of transplants there seemed no order in the plants attacked. The plants here and there 

 over the whole field kept going, and one could see plants in all stages of disease. 



The promiscuity of attack, the general symptons, and the presence of insects, especially hemip- 

 terous, first started me to wonder if there really was a bacterial disease present; insects play an im- 

 portant part in the dissemination of wilt diseases. 



Now, perhaps, all this idea about a bacterial disease is "wildfire," but it seems to me to require 

 investigation. There is one great objection, and that is the general dispersion of the disease in one 

 year, taking it for granted that this is the first year that it has been noticed. 



Mr. Bowhill made an investigation in the same section visited by Mr. Dewar, concern- 

 ing which he says: 



I made a careful examination of the diseased plants, and also dissected a great many of them. 

 In all the infected plants examined I found a small white, active larva with a black head. * * * 

 On making a complete bilateral section of an infected plant from the root upwards the ravages of 

 the maggot are easily discerned. The pith in portions is of a brownish colour, and in other parts it 

 is completely honeycombed. * * * 



Several infected plants were split open with a sterilized knife and cultures instituted on sterile 

 potatoes from the decolourized portions of the pith. * * * One larva was removed with steril- 

 ized forceps and placed in a tube of gelatine in order to observe what, if any, micro-organisms were 

 introduced by them into the pith and other portions of the stem during their meanderings. * * * 



Regarding the question as to whether there is also a blight disease amongst the tobacco in this 

 area, I am not prepared from the evidence in my possession to either affirm or deny such a contention, 

 but I must, however, state that I believe there is something else in addition to the larva already 

 dealt with. I have personally noticed, as well as having my attention drawn to the fact, that some 

 of the infected plants droop in one night, while others (supposed to be affected by the so-called blight 

 disease) appear to degenerate by degrees. In some instances the roots were found to be in an ad- 

 vanced state of decay. 



Mr. Bowhill obtained a variety of bacteria and fungi in his cultures, e. g., Bacillus 

 mycoides roseus, Bacillus megaterium, a slender bacillus unidentified, and some Mucors. 

 Regarding these he says: "I am of the opinion that their presence within the stems of 

 infected plants is due to external combinations caused by the destruction of the external 

 cuticle of the plant." 



Mr. Lounsbury concluded, after personally visiting various sections where the disease 

 prevailed, that the cause was the potato moth, combined in some cases with the action of 

 the gall worm. He refers to McKenney's description of the North Carolina tobacco wilt, 

 and also to the Japanese tobacco wilt, and has the following to say concerning the relation 

 of these two diseases to the Kat River wilt : 



These more serious tobacco diseases may be distinguished from the Kat River wilt, to judge 

 from the descriptions, by the more extensive blackening of the stalks, by black lines in the wood 

 marking the work of the fungus or bacterium in the sap channels, and by the earlier decay of the roots. 

 Perhaps, however, the only clearly distinguishing feature in many plants would be the presence 

 or absence of the causative bacterium or fungus. In all three troubles the pronounced symptom of 

 wilting appears to be due to a gradual stoppage of the flow of sap. 



Many growers will doubtless believe that they have one or the other of the foreign wilt diseases. 

 I can not deny the possibility of their being correct, but can say that I saw nothing which, in my mind, 

 justifies an opinion that the whole trouble is not due to the potato moth, assisted in a few places by 

 the gall worm. I failed to find evidence that would lead me to suspect fungi or bacteria as the 

 primary source. Although Mr. Dewar at first inclined to the idea of a true plant disease in addition 

 to injury through insects, he failed to substantiate his suspicions by his subsequent laboratory 

 examination of affected plants, and he had not learned at the time of similar trouble, due to potato 

 moth alone, in Rhodesia. Moreover, were the trouble an entirely new fungoid or bacterial disease, 

 it would probably not have appeared simultaneously over a large area, and would probably have 

 caused more uniform destruction wherever it appeared. Illustrations of the American and Japanese 

 diseases show plants in large patches wilting down all at once. However, should the developments of 

 future years in the Kat River Valley show my conclusions to be wrong, I shall have erred on the safe 

 side, since there are no practical remedies for the true wilt diseases. The potato moth and gall worm, 

 on the other hand, are pests that it should pay to combat by the measures discussed, irrespective of 

 the wilt; and growers are therefore urged to take action. 



[In this connection see account of African potato disease on p. 214.] 



