40 BULLETIN 1284, U. S. DEPARTMENT OF AGRICULTURE 
INOCULATION EXPERIMENTS WITH HEAD SMUT 
In view of the fact that head smut of sorghum, Sorosporium reilia- 
num (Ktihn) McAlpine, occurs regularly each year at the Amarillo 
Field Station, it was possible to observe the occurrence of this smut 
in the sorghum varieties planted in connection with the experiments 
with Sphacelotheca sorgJii. Potter (90), as a result of his studies, 
came to the conclusion that spores present in the soil, surviving from 
year to year, were largely responsible for this disease and that seed- 
borne spores were a very minor factor in the prevalence of head smut. 
His evidence indicates that the soil of the Amarillo Field Station is 
thoroughly infested with the spores of this smut. 
Table 9 presents the infection percentages recorded at Amarillo 
during three years, 1916, 1917, and 1919. Unfortunately, no distinc- 
tion between the head smut and covered kernel smut was made in 
the counts for 1918. Accordingly, the data on head smut for that 
year are not available. 
Table 9 shows that feterita and the milos, which are so markedly 
resistant to covered kernel smut, also were resistant to the head 
smut. None of the varieties of broomcorn showed any infection, 
although all are moderately susceptible to covered kernel smut. 
The writers are not aware of any record of the occurrence of Soro- 
sporium reilianum on broomcorn. Very little head smut was found 
among the kafirs and kaoliangs, and with two exceptions the durras 
proved very resistant, while the sorgos as a group were only slightly 
infected. 
The results show that only eight varieties of sorghum gave indica- 
tions of moderate susceptibility. Black Amber sorgo (S. P. I. No. 
32384) was grown three years, a total of 1,383 plants being obtained, 
of which 117 (8.5 per cent) were infected. Minnesota Amber 
(F. C. I. No. 01950) in one year gave 52 infected plants (10.5 per 
cent) out of a total of 494. Early Rose sorgo was grown one year, 
and 170 (10.2 per cent) out of 1,668 plants were infected. Red 
Amber sorgo (F. C. I. No. 1534) was grown three years and 1,512 
plants obtained, 341 (22.6 per cent) being infected. Red Amber 
sorgo (S. P. I. No. 17548) was grown three years, and 401 plants 
(22 per cent) out of a total of 1,820 were infected. Colman sorgo 
was grown one year, 292 (16.7 per cent) plants out of 1,745 being 
infected. Brown durra (S. P. I. No. 17537) was grown three years, 
a total of 893 plants being obtained, of which 173 (19.4 per cent) 
were infected. White durra (S. P. I. No. 17535) was grown two 
years, and 285 plants (20.2 per cent) out of a total of 1,414 were 
infected. Giant Schrock sorghum, grown one season, showed 37 
infected plants out of a total of 288, an infection of 12.8 per cent. 
All of these varieties are moderately susceptible to the kernel 
smut (Sphacelotheca sorghi). Table 10 presents a summary of the 
results ootained in infecting these varieties with the two smuts at 
Amarillo. Brown durra (F. C. I. No. 17537), Minnesota Amber 
sorgo (F. C. I. No. 01950), and Red Amber sorgo (S. P. I. Nos. 1534 
and 17548) appear to be more susceptible to the head smut (Soro- 
sporium reilianum). Schrock sorghum, Colman sorgo, and Early 
Rose sorgo appear to be more susceptible to Sphacelotheca sorghi. 
The other two varieties show no marked differences 
