Feb. 16,1924 
Physiological Studies on Flag Smut of Wheat 
445 
watering after maturity. Row 4 of this variety, which had not been cut, 
showed only 20 per cent of the plants infected at the time the culms 
became yellow and were maturing. By continuous watering, small 
secondary shoots were produced, which probably were comparable to 
those produced when the plants were cut back. There was a total 
infection of 93.3 per cent of the plants, or an increase of 73.3 per cent, 
that was the result of the appearance of smut sori in these small secondary 
shoots. In view of these facts it is possible that many apparently quite 
resistant varieties are not suitable for breeding for resistance to flag smut. 
However, varieties showing this tendency to develop smut only in second¬ 
ary shoots undoubtedly evidence a certain degree of resistance. Resist¬ 
ance was shown also by other varieties where the only infection on a 
whole plant consisted of a single very minute sorus. In one case a small 
lesion was found on a lower glume of a wheat head, thus indicating that 
the fungus had kept pace with the growth of the plant but was not able 
to sporulate extensively. In other instances there were only two or three 
minute sori on one leaf of an entire plant. This would indicate that the 
fungus was in the plant tissue even though the spores were not produced 
freely. As sporulation is the only superficial evidence of flag-smut infec¬ 
tion, cytological investigation might determine the presence or absence of 
mycelia in the leaves and culms of plants which apparently are free from 
the disease. It also might indicate whether or not the mycelia generally 
passed beyond the lower nodes of the culms. 
varietal RESISTANCE 
Experiments in varietal resistance were conducted during three 
winters, 1919, 1920, and 1921, in the greenhouse at Arlington Experi¬ 
ment Farm, Rosslyn, Va. In addition to the commercial winter wheats 
grown in Illinois, several other varieties of spring and winter wheats were 
included. Twenty-one varieties were tested for three years, while others 
were tested for one or two years. All inoculations were made by placing 
the seed and a sufficient quantity of dry ground leaves containing spore 
material in an envelope and shaking until the seed was covered with 
spores. The inoculated seeds were sown 2 inches apart, and about 2 
inches deep, in rows 6 inches apart in the greenhouse benches. In 1920 
and 1921 small quantities of spore material also were placed on each 
inoculated seed before covering with soil. The soil was moist and in good 
tilth, and the air tenperature was maintained approximately at 55°F. 
The data were obtained when the plants were beginning to head, or head¬ 
ing, except in cases of severe infection, which necessitated the removal of 
the plants before that time. Infection was noted for both culms and 
plants, except in 1922, when only the plant infections were recorded. 
The results for the three years are given in Table X. 
Of the 21 varieties which were tested for three years only Fulcaster, 
Poole, Red May, Red Rock, Early Defiance, and Galgalos were free from 
flag-smut infection during that time. Of 17 additional varieties tested 
for two years Illini Chief, Treadwell, Turkey, and Peliss were free from 
infection. The highest percentages of smutted plants recorded for the 
most susceptible varieties in any one year were 78.9 per cent for Fultz, 
93.1 for Harvest Queen, 86.7 for Jones Fife, 66.1 for Purplestraw, 72.9 
for Red Wave, 98.4 for Bobs, 93.3 for Comeback, 92.7 for Cowra No. 3, 
88.4 for Defiance, 98.2 for Hard Federation, and 100 per cent for Little 
Club and White Federation. 
