Aug. 25, 1923 
Ophiobolus cariceti and Weakened Plants 
357 
lated ? Anyone who has tried to grow wheat in 5-inch pots, as Kirby 
did, under ordinary greenhouse conditions for considerable periods of 
time, knows how difficult it is to avoid weak, spindling, under-developed 
plants, and when one turns to his photograph (PI. II, fig. c) labeled 
“ Healthy and diseased plants after four months’ growth,” it is noted that 
the pot of “healthy” plants is so full of drooping, withered, and dead 
leaves as to make the plants appear decidedly unhealthy. Kirby be¬ 
lieves that the fungus also produces a seedling blight 8 for, speaking of field 
observations, he says (p. 68), “An accurate determination of the amount 
of damage caused by take-all was impossible because many of the plants 
were killed in the seedling stage.” And farther on, under “Symptoms,” 
he says, “The writer has not had the opportunity to study the disease 
through all its early stages in the field.” But what about the early 
stages in the inoculated pots? Although he inoculated when the seed 
was sown he notes no Ophiobolus symptoms until ten and a half weeks 
after inoculation ( p . 74). His work, therefore, can not be said to pre¬ 
sent a clear picture of the relationship of attack by Ophiobolus cariceti to 
the condition of the host. 
The increase in the percentage of infection on the lime plot in the 
writers’ experiment is in full accord with the work of Kirby and of others, 
although, as we have already noted, Ophiobolus was able to attack plants 
growing in acid soil. Of course the relationship of the growth of the 
wheat to change in acidity of the soil must be considered, for it is now 
well established (p; that growing plants often cause a marked change in 
the hydrogen-ion concentration of the media in which they are growing. 
CONCLUSION 
As the results obtained by the writers in controlling this disease involve 
only one year of experimental work, it would be improper to make any 
definite recommendations at this time, but inasmuch as these experiments 
fully confirm numerous other observations made by the writers and by 
others, there seems to be sufficient ground for concluding that Ophiobolus 
cariceti confines its attack to weakened, plants. The discovery of this 
organism in such widely separated regions as New York, Oregon, Indiana, 
and Arkansas (5) suggests that it is present over a large part of the 
country, and that it has been overlooked because it is of little economic 
importance. 
SUMMARY 
Ophiobolus cariceti was discovered in two wheat fields in Arkansas and 
on the campus of the state university. Wheat, Bromus secalinus , 
Chaetochloa geniculata, Festuca 0 do flora, Festuca elatior , and Hordeum 
pusillum were found infected. 
Infection appears to be confined to weakened plants. Lack of proper 
nutrients and water-logged soils in particular were found to be conducive 
to attacks by this fungus. 
8 Under unfavorable conditions it is entirely conceivable that seedlings also become susceptible, and 
McKinney’s report 3 of a seedling blight in soil kept at temperatures near 22 ° and 24 0 C. would indicate 
that soil temperatures are important in the development of this disease. From Dickson's work (r) it is 
clear that wheat requires a rather low temperature for good growth. He writes (p. 840): “While spring 
wheat germinated more rapidly at soil temperatures of 24 0 to 28° C., the germination was more uniform and 
stronger plants resulted at the lower temperatures—about 8° to 16 °. The greatest development of roots 
as well as tops occurred at the lower soil temperatures. The earliest maturing, most stocky, and best filled 
plants resulted at soil temperatures of about 16V’ As far as winter wheat is concerned, he says: “The 
cardinal temperatures for the development of Turkey winter wheat were, in general, about 4 0 C. below 
those for spring wheat.” 
» McKinney, Harold H. take-all and foot-rot investigations. In U. S. Dept. Agr. Bur. Plant 
Indus. Cereal Courier, v. 14, p. 24-25. 1922 (mimeographed). 
