Feb. 17, 1923 
Cotton Rootrot in Arizona 
527 
being pulled up showed in abundance the characteristic mycelium of 
the rootrot fungus. Within 5 days four other inoculated plants died in 
the same characteristic manner, but by this time the soil on the sides of 
the trench had become so depleted of moisture that the disease was 
unable to make further progress. 
From the first inoculated plant which died (it was pulled up imme¬ 
diately after wilting), the mycelium was isolated and pure cultures were 
prepared after the method of Atkinson. 4 Bits of sterile cotton roots 
were used as the medium. After abundant growth had been obtained 
from one of these pure cultures on a layer of sterile cotton roots in moist 
chambers, the material was conveyed to another trench that had been 
prepared a few feet from the first. This material was then used to in¬ 
oculate 10 plants on one side of the trench, 4 plants being left as a con¬ 
trol. The 14 plants on the other side of the trench were treated with 
diseased roots as described above. The plants were kept well supplied 
with moisture and in 12 days they began dying almost simultaneously 
on both sides of the trench. By September 20, the disease had appeared 
in all but 4 or 5 of the plants on both sides of the trench, including the 
four control plants, which had been attacked one at a time by the inva¬ 
sion of the mycelium through the soil from the inoculated plants. By 
October 1, the mycelium had spread from the pure-culture treatment to 
the plants 3X feet away in the next row, and 4 of them had succumbed 
by this date. After seven weeks none of the plants which had been 
treated with spores showed any signs of distress. 
Spores collected from fresh fruiting mats were induced to germinate 
in distilled water and in artificial media after several days, but the re¬ 
sulting growth was extremely slow. After five weeks in the Van Tieghem 
cells the germ tubes have grown but two or three times longer than the 
diameter of the spores. The difficulty in inducing the spores to develop 
in artificial media and the failure to induce the disease by applying them 
to the roots of healthy plants is not surprising. If the conditions neces¬ 
sary for the development of spores were not very exacting, the enormous 
quantities in which they are produced would long since have made the 
distribution of the disease universal. 
It is of the utmost importance to determine as promptly as possible 
to what extent the promising results obtained in these local experiments 
are applicable in other regions. 
SUMMARY 
(1) At Sacaton, the fungus causing rootrot of cotton and alfalfa 
fruits abundantly in favorable seasons, the fruiting masses being identi¬ 
cal apparently with those described by Duggar. 5 
(2) The fungus spreads from a center in ever-widening circles after 
the manner of a fairy-ring fungus. 
(3) Plants have been inoculated successfully with pure cultures of 
the mycelium. 
(4) Spores are germinated with difficulty and have not been used 
successfully as a medium of inoculation. 
(5) The spread of the disease may be checked by the use of formalde¬ 
hyde. 
< Atkinson, G. F. method for obtaining pure cultures op pammel’s fungus of Texas root 
rot OF cotton. In Bot. Gaz., V. 18, p. 16-19. 1893. 
& Duggar, B f M op. cit. 
