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BULLETIN" UIO, U. S. DEPARTMENT OF AGRICULTURE 



Aside from tobacco, the tomato is probably most vigorously 

 attacked. The symptoms on tomato are much like those on tobacco, 

 and this plant has been frequently used in experimental work in 

 preference to tobacco, for the reason that it is practically immune to 

 Thielavia root rot and consequently is a better index of brown root- 

 rot infection in some soils than the tobacco plant, particularly in 

 soils where the two diseases may be present. 



Fig. 10. — Influence of soil drying or aeration on the growth of tobacco plants : A, 

 In brown root rot soil dried in a thin layer one week ; B, in the same soil not 

 dried; G, in healthy soil (control) ; D, in healthy soil to which was added a small 

 quantity of washed timothy roots taken from brown root rot soil. Drying or 

 aeration of the soil seems to destroy rapidly the injurious agency which appears 

 to be located, at least in large part, in the organic matter of the soil 



The potato, eggplant, and pepper are apparently affected, but 

 much less so than tobacco or tomato, pepper especially being very 

 resistant to it. 



Many legumes belong in the susceptible group, although, again, 

 much variation is to be found. Cowpeas, soybeans, garden beans, 

 hairy vetch, and the common clovers belong to the group of mod- 

 erately susceptible plants. 



The common graminaceous crop plants were found difficult to 

 classif}^, but it may be said with certainty that, so far as evidence of 

 typical root lesions are concerned, oats, barley, wheat, and rye are 

 only very slightly, if at all, affected. Timothy should probably be 

 classified along with these related crops, although one could not 



