Feb. 16, 1924 
Flag Smut of Wheat 
485 
The present study has furnished data which may|be used as a basis 
for further field experimentation. Also the experimental results may be 
correlated in part with the present known distribution and seriousness 
of the disease in certain regions, and thus in conjunction with other 
data (distribution of wheat varieties, etc.), may serve to indicate the 
possibility of the disease becoming established j|in regions in which it 
does not at present occur. 
SUMMARY 
1. Flag smut of wheat, caused by Urocystis tritici Koern., was first 
found in Australia in 1868. It is now known to occur also in Japan, 
China, India, South Africa, southern Europe, and the United States. 
2. Flag smut is one of the most destructive diseases of wheat in Aus¬ 
tralia. It is becoming more widely distributed each year and annually 
destroys approximately 3 per cent of the total potential wheat crop. 
Losses up to 70 per cent have been observed in individual fields. 
3. The disease lesions may first appear on plants in any stage of growth 
up to heading. The earliest recorded lesions were observed on the fifth 
leaf of a wheat plant 29 days after inoculation. Other plants were 
observed in which the fourth leaf was first affected. The smut may 
cause considerable deformation of the host. All culms of a plant may 
not be affected. Under greenhouse conditions, the first formed culms of 
partially infected plants frequently were free from the disease. 
4. The “maturation’ ’ period of the spores can be considerably short¬ 
ened. Fresh spores did not germinate, although they did so after hav¬ 
ing been dried for 48 hours over concentrated sulphuric acid. Germi¬ 
nation tests were made in the manner previously described ( 36 ). 
5. Uninjured seedlings of nonsusceptible plants (field peas, beans, 
and rye) stimulated the germination of spores which had been pre¬ 
soaked in water. Such stimulation might be expected in the field 
when the environment causes a certain amount of anaerobic respiration 
of the plant roots. 
6. The expressed sap of wheat seedlings at a concentration of 1 part 
per 10,000 was most favorable for germination of presoaked spores. 
The germ tubes of Urocystis tritici were observed to grow to a length 
of 4 mm. in solid media. 
7. Surface films of benzaldehyde, salicylaldehyde, butyric acid, and 
acetone greatly stimulated the germination of presoaked spores. Other 
volatile substances were less effective. Benzaldehyde, 3 parts per 
2,000,000 parts of distilled water, and butyric acid, 1 part per 500,000 
parts water, were suitable concentrations for such stimulation. 
8. Presoaking the spores appeared to result in increased permeability 
of the spore enevlope and thus enabled more rapid ingress of the volatile 
stimulant. 
9. The stimulatory action recorded above was not correlated with 
any definite reduction of the surface tension of the medium as measured 
against air. 
10. It is suggested that the action of the stimulatory agents is mainly 
such as to cause a change in the physical condition of the protoplasmic 
spore contents, and thus increase the permeability of the latter. 
11. Preliminary tests indicate that films of some of the above- 
mentioned volatile materials also stimulate the germination of the 
teliospores of Puccinia graminis tritici and the spores of several other 
organisms. 
